International Crops Research Institute for the Semi-Arid Tropics

Transcription

1 International Crops Research Institute for the Semi-Arid Tropics

2 Citation: Pande, S., Liao Boshou, Nguyen X u a n Hong, Johansen, C., and G o w d a, C. L. L. (eds) G r o u n d n u t bacterial w i l t in Asia: proceedings of the Fourth W o r k i n g G r o u p Meeting, M a y 1998, V i e t n a m Agricultural Science Institute, Van D i e n, Thanh Tri, Hanoi, V i e t n a m. ( I n En. Summaries in En.) Patancheru , A n d h r a Pradesh, India: International Crops Research Institute for the S e m i - A r i d Tropics. 106 pp. I B S N Order code: CPE 120. Abstract T h e current status of research on bacterial w i l t of groundnut in Asia (specifically in China and V i e t n a m) is reviewed. Particular emphasis is given to the available disease management options, and t h e i r packaging and validation in on-farm participatory research at hot- spot locations in China and V i e t n a m. Recommendations are made for further collaborative research w i t h advanced institutes to provide training to scientists and technicians f r o m China and V i e t n a m in recent advances in serological and molecular techniques for identification and differentiation of races, biovars, and strains of the w i l t pathogen, Burkholderia solanacearum. Recommendations are also made for further collaborative research, and the need to interest potential donors in promoting the G r o u n d n u t Bacterial W i l t W o r k i n g Group's activities. The p u b l i c a t i o n includes papers describing the status of the disease in China and V i e t n a m. The opinions in this publication are those of the authors and not necessarily those of I C R I S A T. The designations employed and the presentation of the material in this publication do not i m p l y the expression of any opinion whatsoever on the part of I C R I S A T concerning the legal status of any country, territory, city, or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. Where trade names are used this does not constitute endorsement of or discrimination against any product by the Institute.

3 Groundnut Bacterial Wilt in Asia Proceedings of the Fourth Working Group Meeting May 1998 Vietnam Agricultural Science Institute (VASI), Van Dien, Thanh Tri, Hanoi, Vietnam Edited by S Pande, Liao Boshou, Nguyen Xuan Hong, C Johansen, and CLL Gowda ICRISAT International Crops Research Institute for the Semi-Arid Tropics Patancheru , Andhra Pradesh, India 1998

4 Co-sponsors V i e t n a m Agricultural Science Institute ( V A S I ) V a n D i e n, T h a n h T r i, H a n o i, V i e t n a m International Crops Research Institute for the Semi-Arid Tropics ( I C R I S A T ), Patancheru , Andhra Pradesh, India Organizing Committee S Pande, C Johansen, and C L L G o w d a - I C R I S A T, Patancheru, India Liao Boshou - O i l Crops Research Institute ( O C R I ), Chinese Academy of Agricultural Sciences ( C A A S ), W u h a n, C h i n a N g u y e n H u u N g h i a, N g u y e n X u a n H o n g, and N g u y e n V a n V i e t - V i e t n a m Agricultural Science Institute ( V A S I ), H a n o i, V i e t n a m

5 Contents Preface S Pande and C Johansen V Inaugural Session 1 W e l c o m e Address Nguyen Huu Nghia 3 W e l c o m e Address f r o m I C R I S A T S Pande 5 Objectives of the Fourth G r o u n d n u t Bacterial W i l t W o r k i n g G r o u p ( G B W W G ) M e e t i n g and an Overview of the Second International Bacterial W i l t Symposium Liao Boshou 8 Research o n Bacterial W i l t i n V i e t n a m Nguyen Xuan Hong 10 A Brief I n t r o d u c t i o n to Bacterial W i l t Research in C h i n a Duan Naixiong, Liao Boshou, He Li-Yuan, and Gao Guoquing 15 Groundnut Bacterial W i l t : Present Status Present Status of G r o u n d n u t Bacterial W i l t i n South C h i n a Liang Xuanqiang 23 Status o f Bacterial W i l t i n Central C h i n a Liao Boshou, Duan Naixiong, Tan Yujun, and Wu Yong 27 Status of G r o u n d n u t Bacterial W i l t in N o r t h e r n V i e t n a m Nguyen Xuan Hong, Nguyen Van Viet, and Nguyen Thi Yen 31 Bacterial W i l t o f G r o u n d n u t i n Southern V i e t n a m Nguyen Van Tung, V K Mehan, Phan Lieu, and Ngo Thi Lam Giang 37 iii

6 Technology Development for Disease Diagnosis and C o n t r o l Latent I n f e c t i o n of Burkholderia solanacearum in G r o u n d n u t and its Role in Resistance Enhancement Liao Boshou, Shan Zhihui, Li Dong, Lei Yong, and Tan Yujun 45 Pathological Aspects and C u l t u r a l and Biological C o n t r o l of G r o u n d n u t Bacterial W i l t i n V i e t n a m Nguyen Xuan Hong, Nguyen Thi Yen, and Vi Anh Tuan 53 Integrated Disease Management w i t h Special Reference to Bacterial W i l t o f G r o u n d n u t S Pande, C Johansen, and J Narayana Rao 58 Germplasm Screening and Breeding for Resistance to Bacterial W i l t i n C h i n a Liao Boshou, Duan Naixiong, Jiang Huifang, Liang Xuanqiang, and Gao Guoquing 75 Germplasm Evaluation and Breeding for G r o u n d n u t Bacterial W i l t Resistance i n V i e t n a m Nguyen Van Lieu, Tran Dinh Long, and Nguyen Xuan Hong 82 Recommendations 91 Participants 97 iv

7 Preface T h e fourth meeting of the G r o u n d n u t Bacterial W i l t W o r k i n g Group was held May, 1998 in V a n D i e n, T h a n h T r i, H a n o i, V i e t n a m. T h e meeting and field visits to bacterial w i l t h o t spot locations and experimental sites in V i e t n a m were co-sponsored by the V i e t n a m Agricultural Science Institute ( V A S I ) and International Crops Research Institute for S e m i - A r i d Tropics ( I C R I S A T ). Scientists from C h i n a (4), Vietnam (25) and I C R I S A T (1) participated in the meeting. T h e present status of bacterial w i l t management was discussed and accounts of current research on bacterial w i l t disease in different institutions, particularly in C h i n a and Vietnam, were presented. G o o d progress has been made, and prospects of c o n t i n u e d collaborative research i n t o the management of this disease are encouraging. W e sincerely believe that this volume w i l l provide a useful guide to the present status of groundnut bacterial w i l t i n Asia and w i l l further strengthen coordinated work on this economically important disease. S Pande Liao Boshou Nguyen X u a n H o n g C Johansen C L L Gowda v

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9 Inaugural Session

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11 Welcome Address Nguyen Huu Nghia 1 Distinguished guests and participants, first of a l l allow me on behalf of V i e t n a m A g r i c u l t u r a l Science Institute ( V A S I ) to warmly welcome all the guests and participants i n the Fourth G r o u n d n u t Bacterial W i l t W o r k i n g G r o u p Meeting, especially the participants from the International Crops Research Institute for the S e m i - A r i d Tropics ( I C R I S A T ) and C h i n a w h o have come to attend this meeting. T h i s is the Fourth M e e t i n g of the International W o r k i n g Group on G r o u n d n u t Bacterial W i l t, organized in the framework of the collaborative program of member countries of the Cereal and Legumes Asia N e t w o r k ( C L A N ). This w o r k i n g group was established in M a r c h, 1990 on the basis of suggestion of member countries of the N e t w o r k, w h o had great concern in research and control of groundnut bacterial w i l t. T h e previous meetings of this w o r k i n g group were organized in Malaysia (1990), Taiwan (1992), and C h i n a (1994). V A S I has great honor to host and co-sponsor this important meeting. Bacterial w i l t is one of the main constraints for groundnut production in many A s i a n countries. It has attracted a t t e n t i o n of various research and development agencies b o t h at national and international level. As you know, a lot of achievements in research and c o n t r o l of the disease have been obtained by Chinese research institutes in the last few years. Therefore, we are glad to see the presence of Chinese scientists w h o are specialized in research on g r o u n d n u t bacterial w i l t and have n o t only significantly contributed to the achievement of C h i n a but have also contributed to promoting research and control of the disease i n the region and C L A N member countries. In V i e t n a m, bacterial w i l t is a serious and damaging disease that is very difficult to c o n t r o l. Since 1990, after the establishment of the collaborative relationship between V i e t n a m and I C R I S A T, and w i t h the cooperation o f C L A N member countries, research on g r o u n d n u t bacterial w i l t has made significant progress. U n t i l now, several disease-resistant, high-yielding, high-quality groundnut varieties have been identified, tested in large-scale p r o d u c t i o n, and been accepted by Vietnamese farmers. Resistance sources, especially indigenous genetic sources, have been identified for utilization in varietal improvement programs. Research on the biology of the pathogen and c o n t r o l of the disease has also been started. 1. Vietnam Agricultural Science Institute ( VASI), Van Dien, Thanh Tri, Hanoi, Vietnam. 3

12 Collaboration in research and development in this field between national and i n t e r n a t i o n a l institutions has been strengthened. However, to overcome the problems caused by bacterial w i l t in groundnut production, there is a lot of work to be done in coming years. Achievements obtained by other countries in the region have strongly stimulated Vietnamese scientists in research and c o n t r o l of the disease. We hope that this meeting w i l l be a good opportunity for Vietnamese scientists to share their experiences in research and management of groundnut bacterial w i l t w i t h, international participants. We also hope that Vietnamese scientists w i l l learn from this meeting. On this occasion, allow me on behalf of V A S I to express our h i g h appreciation and grateful thanks t o I C R I S A T scientists and C L A N member countries for their enthusiastic and effective support and collaboration in research and development of groundnut in the past years. We sincerely hope that collaboration between V i e t n a m, I C R I S A T, and C L A N member countries w i l l be strongly developed. Finally, I w o u l d like to wish the meeting success. I wish all the guests and participants of the meeting good h e a l t h and happiness. T h a n k you for your attention. 4

13 Welcome Address from ICRISAT S Pande 1 Honorable Dr Nguyen H u u Nghia, Director General, V i e t n a m A g r i c u l t u r a l Science Institute ( V A S I ), Dr Phan Lieu, Director, O i l Plant Institute ( O P I ) Southern Vietnam, Dr Liao Boshou, Coordinator, G r o u n d n u t Bacterial W i l t W o r k i n g Group, Dr Nguyen X u a n H o n g, Cereals and Legumes Asia N e t w o r k ( C L A N ) Coordinator, and distinguished participants, ladies and gentlemen, o n behalf of I C R I S A T - C L A N and on my o w n behalf I welcome all of you to this 3-day W o r k i n g Group M e e t i n g on G r o u n d n u t Bacterial W i l t. It is my privilege to participate and represent I C R I S A T at this meeting being h e l d at one of the leading agricultural institutions i n Vietnam: V A S I, T h a n h T r i, H a n o i. T h e choice of T h a n h T r i and H a n o i, in northern Vietnam, for this meeting is most appropriate, especially considering the interest of W o r k i n g G r o u p members in interacting w i t h many Vietnamese scientists w h o have recently made notable c o n t r i b u t i o n s to collaborative research on the management of groundnut diseases, including groundnut bacterial w i l t. I am pleased to take this opportunity to spell out certain aspects of cooperation between I C R I S A T and V A S I. T h e first I C R I S A T mission i n V i e t n a m, headed by the t h e n Director General Dr L D Swindale was in 1989 and was followed by signing of the M e m o r a n d u m of Understanding ( M o U ) for cooperation between the M i n i s t r y of A g r i c u l t u r e and Food Industry ( M A F I ), V i e t n a m and I C R I S A T in India on 25 Sep Since then, Directors General, C L A N Coordinators, and I C R I S A T scientists have made countless visits to V i e t n a m. Some of the notable visits to strengthen groundnut research and integrated pest management research have been made by I C R I S A T breeders, agronomists, entomologists, and p l a n t pathologists. We have developed and implemented collaborative workplans w i t h V i e t n a m, the most recent being presented d u r i n g the C L A N Coordinators' Steering C o m m i t t e e M e e t i n g, N o v 1997 in Batu, Indonesia. M o r e t h a n 85 Vietnamese scientists and technicians have participated in various t r a i n i n g programs at I C R I S A T. Germplasm exchange has been a major activity. I C R I S A T has supplied V i e t n a m w i t h a t o t a l of 3825 germplasm accessions, breeding lines, and advanced generation lines o f groundnut. A l s o i n collaboration w i t h the N a t i o n a l Institute 1. International Crops Research Institute for the Semi-Arid Tropics ( ICRISAT), Patancheru , Andhra Pradesh, India. 5

14 of V i e t n a m I C R I S A T has collected 67 accessions of groundnut germplasm, and w i l l collect more i n the near future. Collaboration w i t h East and Southeast Asia on groundnut diseases caused by fungi, viruses, and bacteria has been encouraging, especially bacterial w i l t research, w h i c h was most rewarding, having generated w i l t basic and applied information on this disease. A n Information B u l l e t i n o n "Bacterial W i l t o f Groundnut"; a Technical M a n u a l on Techniques for Diagnosis of Pseudomonas solanacearum; a manual for resistance screening against groundnut bacterial w i l t ; and h i g h quality papers in the proceedings of the Bacterial W i l t W o r k i n g Group Meetings are a few classic examples of our collaborative efforts. We at I C R I S A T are n o t able to conduct research on bacterial w i l t of groundnut, and depend on the comparative advantage and expertise of groundnut scientists in C h i n a, Indonesia, V i e t n a m and other network member countries to collaborate in combating this disease. G r o u n d n u t bacterial w i l t, caused by Burkholderia solanacearum (E.E Smith) Yabuuchi et al. ( formerly P. solanacearum (E.E Smith) E.E Smith) has been a major constraint on crop production in the countries of South and Southeast Asia and the South Pacific. T h e disease has been a serious constraint to groundnut production in Indonesia and C h i n a for several decades. It is becoming potentially important in V i e t n a m, Malaysia, the Philippines, and T h a i l a n d. Bacterial w i l t is also a problem in some countries in Africa. It is a growing threat to groundnut production in several other parts of the world, particularly in warm, h u m i d areas. T h e destructiveness of the disease is compounded by the wide host range of the w i l t pathogen. Considerable research in Indonesia and C h i n a has provided an excellent understanding of the effects of cultural practices and environmental factors on g r o u n d n u t bacterial w i l t, and the results have been used to formulate recommendations to reduce w i l t incidence and severity. Research on genetic resistance has been g i v e n the highest p r i o r i t y since the early 1920s. T h e variety Schwarz 21 was released in Indonesia in 1927, the earliest record of a disease-resistant g r o u n d n u t being developed. M u c h progress has been made in Indonesia, C h i n a, and other countries in the development of various w i l t - resistant, high-yielding groundnut cultivars. However, there is a need for breeding wilt-resistant groundnut varieties w i t h h i g h yield potential and good agronomic characters, a n d to c o m b i n e resistance to other diseases and pests. Basic research on the w i l t pathogen B. solanacearum has been carried o u t in advanced laboratories in the developed countries as B. solanacearum attacks many other i m p o r t a n t food crops throughout the w o r l d. These studies have provided us w i t h such diagnostic tools as m o n o c l o n a l antisera and polymerase chain reaction techniques. It is 6

15 expected t h a t the results o f this research w i l l enhance our understanding i n the management of the pathogen and bacterial w i l t disease in groundnut. At I C R I S A T Patancheru, we the groundnut scientists have the responsibility of w o r k i n g j o i n t l y w i t h A s i a n national agricultural research system ( N A R S ) scientists to address constraints on groundnut p r o d u c t i o n in different agroecological systems in Asia. This function is facilitated by C L A N, w h i c h started in 1986 as the A s i a n G r a i n Legume N e t w o r k ( A G L N ), w i t h I C R I S A T providing a Coordinating U n i t. C L A N has successfully supported many collaborative activities concerning I C R I S A T' s mandate crops ( sorghum, pearl m i l l e t, chickpea, pigeonpea, and groundnut) and its mandate eco-region ( t h e semi-arid tropics). T h e " W o r k i n g Groups" concept to focus collaborative research on the challenging regional problems has been found useful and effective and has resulted in quick progress. O n e such effective W o r k i n g Group, on G r o u n d n u t Bacterial W i l t in Asia, is meeting here today. T h e foundation o f the Groundnut Bacterial W i l t W o r k i n g G r o u p ( G B W W G ) was laid in 1990 after a planning meeting held in Malaysia. This fourth meeting of the G B W W G is being held j o i n t l y under the auspices of V A S I and I C R I S A T G r o u n d n u t bacterial w i l t is an important problem in groundnut production systems in S o u t h and Southeast A s i a and in similar systems elsewhere. Because of the danger of its spreading to new areas where irrigation and multiple cropping are being introduced, we need to provide necessary support and funding to ensure that integrated disease management technology is soon available to farmers to minimize losses caused by this disease. We at I C R I S A T sincerely hope that the recommendations of this meeting w i l l further strengthen international collaborative research to f i n d and provide costeffective solutions to managing bacterial w i l t, the most i m p o r t a n t constraint on groundnut production in East and Southeast A s i a n countries. 7

16 Objectives of the Fourth Groundnut Bacterial Wilt Working Group (GBWWG) Meeting and an Overview of the Second International Bacterial Wilt Symposium Liao Boshou 1 G o o d m o r n i n g, respected Mr Chairman, ladies and gentlemen. First of all, I w o u l d like to express my w a r m welcome to all the participants to this meeting. I am also very pleased to have this chance, for the first time, to visit V i e t n a m w i t h several of my colleagues from C h i n a. As you know, groundnut has become a very important o i l crop and cash crop in C h i n a, Vietnam, and many other developing countries. W i t h the development of economy and society, groundnut w i l l be more and more important because of its h i g h n u t r i t i o n, wide adaptation to various ecological conditions, h i g h yield potential, and h i g h output or production efficiency. We take interest in n o t i c i n g that groundnut production in V i e t n a m has increased in recent years and that a considerable p o r t i o n has been exported, contributing significantly to the nation's economy. W h e n we try to increase groundnut production, we have to struggle against many diseases, and bacterial w i l t is one of them. Bacterial w i l t of groundnut, caused by Burkholderia solanacearum (E.F. Smith), Yabuuchi et al. is the most important bacterial disease of this crop throughout the world. In order to improve control of this disease and coordinate concerned research in various countries, a G r o u n d n u t Bacterial W i l t W o r k i n g Group ( G B W W G ) was established through the joint efforts of I C R I S A T and the Australian Centre for International Agricultural Research ( A C I A R ). In March, 1990, the first W o r k i n g Group ( W G ) meeting was held in Malaysia. T h e second WG meeting was held in November, 1992 at the A s i a n Vegetable Research and Development Center ( A V R D C ) in Taiwan. The third WG meeting was held in July 1994 at the O i l Crops Research Institute in China. We greatly appreciate the efforts of ICRISAT/Cereals and Legumes Asia Network ( C L A N ) in organizing this meeting. We are happy to see that this WG is considered one of the most successful organized by I C R I S A T. As most of you know, I C R I S A T has been subjected to reformation in recent years and as a result many scientists have left ICRISAT, including Dr V K Mehan, the former Technical Coordinator of this W G. In these circumstances, I was nominated Technical Coordinator of the W G during the C L A N Steering Committee Meeting in November 1997, in Malang, Indonesia. I happened to visit I C R I S A T during November and December, 1997 and had a chance to plan w i t h some of the 1. O i l Crops Research Institute ( O C R I ), Chinese Academy of Agricultural Sciences ( C A A S ), Wuhan , China. 8

17 I C R I S A T scientists, including Dr Pande, to hold the Fourth Working Group Meeting in Vietnam. Dr Gowda, the C L A N Coordinator, visited Vietnam in late February this year and decided to h o l d this meeting. I would like to express my thanks to the host institution, Vietnam Agricultural Science Institute ( V A S I ), and Dr Nguyen Xuan H o n g for hosting the meeting. I am also very glad to see that Dr Pande. a senior plant pathologist, is representing I C R I S A T here. T h e objectives of this meeting are as follows: Review research progress on groundnut bacterial w i l t, particular in C h i n a and V i e t n a m, since the T h i r d G B W W G meeting in Evaluate the status of, and exchange information on research on groundnut bacterial w i l t i n concerned countries. Discuss and recommend priorities for collaborative research at the n a t i o n a l and international levels. Determine the resources needed and to prepare j o i n t proposals for funding. I a m confident t h a t we w i l l have a good meeting here and that this meeting w i l l contribute significant knowledge to the members of this WG to combat bacterial w i l t. I would like to give you a brief introduction about the Second International Bacterial W i l t Symposium ( I B W S ) held in Guadeloupe, France, June W i t h support from the C h i n a Natural Science Foundation (CNSF) and C L A N, I was able to attend I B W S. T h e symposium was hosted by the Institut national de la recherche agronomique ( I N R A ) and attended by 120 participants representing 32 countries and organizations. T h e program of the symposium was divided i n t o eight sessions. These sessions included opening and welcoming remarks, pathogen diversity, disease diagnosis, pathogenicity, host resistance I, biological c o n t r o l and epidemiology, host resistance I I, and disease management. Forty-five papers were presented in the eight scientific sessions. In addition, 53 poster papers were also presented. There were 4 papers specifically on groundnut bacterial w i l t. T h e symposium revealed marked progress in investigating the molecular, ecological and phenotypical basis of the w i l t pathogen, diagnosis techniques, the molecular basis, and genetic enhancement of host resistance, and biological and cultural c o n t r o l. T h e proceedings of the symposium, entitled "Bacterial W i l t Disease: Molecular and Ecological Aspects", are being edited by P Prior (France) and C A l l e n ( U S A ) and w i l l be published by Springer Verlag in Germany in

18 Research on Bacterial Wilt in Vietnam Nguyen Xuan Hong 1 Abstract In recent years, research on bacterial wilt in Vietnam has been given high priority. Systematic surveys conducted in both northern and southern Vietnam have confirmed that bacterial wilt is a widespread and serious disease of groundnut. It is especially severe in hilly and upland areas, and in sandy soils along river banks, where it can cause considerable plant mortality (15-50%) and yield losses. Genetic resistance to bacterial wilt is a higjh-priority objective of several research institutions in Vietnam. The varieties Schwarz 21 and Matjan, reported to be resistant in Indonesia, also have shown stable resistance in northern Vietnam. The local variety Gie Nho Quan has been highly and stably resistant to bacterial wilt. All isolates of Burkholderia solanacearum from groundnut belong to biovars 3 and 4. Research on cultural and biological control of groundnut bacterial wilt is in progress. Introduction V i e t n a m has a tropical monsoon climate characterized by h i g h temperatures, h i g h humidities, and h i g h rainfall. Bacterial w i l t caused by Burkholderia solanacearum (E.F. Smith) Yabuuchi et al. has been k n o w n to cause serious problems on a number of economically important crops in V i e t n a m including groundnut, potato, tomato, sesame, tobacco, and eggplant. I n t r o d u c t i o n of susceptible new varieties of these crops has contributed to the increased incidence of bacterial w i l t. Therefore, in recent years research on bacterial w i l t in V i e t n a m has been given increasing attention. 1. Vietnam Agricultural Science Institute ( VASI), Van Dien, Thanh Tri, Hanoi, Vietnam. Nguyen Xuan Hong Research on bacterial wilt i n Vietnam. Pages in Groundnut bacterial wilt: proceedings of the Fourth W o r k i n g Group Meeting, May 1998, Vietnam Agricultural Science Institute, V a n Dien, T h a n h T r i, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C. L. L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi- Arid Tropics. 1 0

19 Current Research on Bacterial Wilt in Vietnam D u r i n g , systematic surveys j o i n t l y conducted by Vietnamese and I C R I S A T scientists have confirmed that bacterial w i l t is one of the most important biotic constraints to groundnut production in b o t h northern and southern V i e t n a m. In n o r t h e r n Vietnam, bacterial w i l t is more severe on spring (February to June) crops grown under rainfed conditions in h i l l y and upland areas, and in sandy soils along river banks. T h e disease is more serious in autumn (July to November) in some areas where the crop is g r o w n year after year. In southern provinces, bacterial w i l t occurs on groundnuts under b o t h irrigated ( winter- spring and summer crops) and rainfed (rainy-season crop) conditions. Considerable plant mortality and yield losses caused by bacterial w i l t ( %) have been observed i n various areas o f b o t h northern and southern provinces. In many groundnut-growing areas it was observed that the incidence of bacterial w i l t was low w h e n groundnut crops were first sown, but increased to h i g h levels in second and subsequent sowings, leading to the abandonment or discontinuation of the crop. It was also observed that continuous dry spells followed by rains could immediately induce severe w i l t under field conditions. R o t a t i o n of groundnut w i t h irrigated rice appears effective in containing disease incidence and severity. G r o w i n g wilt- resistant cultivars is considered the most effective and practical approach to controling bacterial w i l t. Genetic resistance to bacterial w i l t is a highpriority objective of several research institutions in Vietnam. T h e major research thrusts at the V i e t n a m Agricultural Science Institute ( V A S I ), H a n o i, are to identify wilt- resistant genotypes and to breed for resistance. A t o t a l of 715 germplasm a n d breeding lines were tested for reaction to bacterial w i l t at hotspots and in sickplots in V i e t n a m. A m o n g them, 4 lines were classified as highly resistant, and 25 lines as moderately resistant ( L i e u, 1997). T h e local variety G i e N h o Q u a n showed the highest level of resistance over seasons at disease h o t spots in n o r t h e r n Vietnam, w i t h disease incidence/plant mortality less than 2%. T h e varieties Schwarz 21 and M a t j a n, b o t h reported resistant in Indonesia, also have s h o w n stable resistance in V i e t n a m. These varieties gave markedly higher yields t h a n d i d the control cultivars Sen Nghe An ( i n northern Vietnam) and Se Dia Phuong ( i n central coastal areas). They are being rapidly multiplied and tested o n - farm for possible release in the near future. However, an accession of the variety Kidang ( I C G 11210), w h i c h was considered resistant in Indonesia, showed h i g h w i l t incidence i n northern Vietnam. I n southern Vietnam, research o n groundnut 1 1

20 bacterial w i l t w i t h emphasis on host-plant resistance has been intensified in recent years at the Institute of O i l Plants. Several groundnut lines supplied by I C R I S A T were resistant to bacterial w i l t. T h e line I C G 8666 (an accession of the variety Schwarz 21) showed the highest level of resistance, w i t h plant mortality less than 1% over 3 seasons in C u c h i (Duc C a m et al. 1995). Research on host- plant resistance to bacterial w i l t of potato also has been intensified in recent years. A p p r o x i m a t e l y 140 germplasm and breeding lines of potato available in northern V i e t n a m were screened over the past several years for resistance to bacterial w i l t. A total of 20 lines and varieties have shown h i g h levels of resistance to bacterial w i l t ; several varieties including K T 3, V T 2 also gave h i g h yields ( T h a n h, 1998). M o r e recently, research on host-plant resistance of tomato has been initiated at V A S I, H a n o i A g r i c u l t u r a l University, and the Institute of Vegetables and Fruits. A p p l i c a t i o n of molecular methods in studying B. solanacearum isolates have been initiated at the Institute of A g r i c u l t u r a l Genetics, H a n o i (Cuong, personal communication). U n t i l recently, research on bacterial w i l t of tobacco and eggplant was very limited, but the Department of Plant Pathology and Pesticides, H a n o i A g r i c u l t u r a l University has initiated research on the bacterial w i l t disease on these crops. Present Staffing and Resources Available for Research At V A S I, seven scientists including phytopathologists, agronomists, and breeders are now working on different aspects of bacterial wilt. A nationwide network of groundnut bacterial w i l t research has been established recently, on the initiatives of V A S I scientists. Several hotspot locations and sickplots also have been established and are regularly used for multilocational resistance screening of groundnut germplasm and breeding lines. Recently, V A S I scientists, in collaboration w i t h I C R I S A T scientists, have intensified local groundnut germplasm collection and characterization. M o r e local groundnut varieties resistant to bacterial w i l t are expected to be identified. T h e Department of Plant Pathology and Genetics at V A S I is currently responsible for carrying out a Ministry of Agricultural Research and Development ( M A R D ) research project on B. solanacearum and mechanisms of resistance to i t. Facilities and methodologies for pathogen isolation, biochemical tests, and artificial inoculation are also available at V A S I. Two researchers have completed their PhD work on identifying sources of resistance to bacterial w i l t on groundnut and potato. T w o scientists are engaged in research on soilborne diseases and bacterial w i l t w i t h emphasis on pathological aspects and control measures at the N a t i o n a l Plant Protection Institute ( N P P I ). T h e y also participated in surveys and research on the disease i n collaboration w i t h V A S I and I C R I S A T scientists. 1 2

21 In southern V i e t n a m, at the O i l Plants Institute ( O P I ), a team of scientists is actively involved in research on groundnut bacterial w i l t w i t h emphasis on hostp l a n t resistance and integrated disease management. T h e y have established close collaboration in research on bacterial w i l t. O n e group of researchers at the H a n o i Agricultural University is conducting extensive work on bacterial w i l t of major crops in H a n o i and surrounding areas. Two scientists have recently initiated research at the Institute of Agricultural Genetics on molecular aspects of B. solanacearum, in collaboration w i t h the A s i a n Vegetable Research and Development Center ( A V R D C ). However, funds for this research are still awaited. Future Plans In V i e t n a m, because of the economic importance of bacterial w i l t, we continue to give h i g h priority to research o n this disease. T h e following aspects w i l l receive attention in coming years. Further systematic research to identify biovars, races, pathotypes, host range, and conditions favouring the m u l t i p l i c a t i o n and spread of the pathogen. Rapid m u l t i p l i c a t i o n and introduction to large-scale production of promising bacterial w i l t resistant lines or varieties of groundnut. Breeding for bacterial w i l t resistance using local and introduced sources of resistance. Development of a farmers' participatory, community-based, integrated w i l t management program (using resistant cultivars, crop r o t a t i o n, crop husbandry, and certain cultural practices) to alleviate severe yield losses from bacterial w i l t and sustain groundnut cultivation and production. Investigation in upland areas of r o t a t i n g and/or intercropping groundnut w i t h maize, w h i c h is a non-host crop popularly grown in Vietnam's dryland crop systems. Increased emphasis on developing and strengthening collaborative research on bacterial w i l t between Vietnamese institutions and other C L A N member countries. References D u c C a m, L i e u, P. a n d D w i v e d i, S. L., I d e n t i f i c a t i o n o f sources o f resistance t o b a c t e r i a l w i l t i n g r o u n d n u t g e r m p l a s m u n d e r S o u t h e r n V i e t n a m e s e c o n d i t i o n s. I n t e r n a t i o n a l Arachis N e w s l e t t e r n o. 1 5 :

22 L i e u, N. V E v a l u a t i o n o f g r o u n d n u t g e r m p i a s m c o l l e c t i o n s f o r resistance t o b a c t e r i a l w i l t a n d i n i t i a l u t i l i z a t i o n o f resistance sources i n b r e e d i n g. P h D T h e s i s, H a n o i ( i n V i e t n a m e s e ). T h a n h, N. T R e s e a r c h o n i n i t i a l m a t e r i a l f o r b r e e d i n g p o t a t o f o r resistance t o b a c t e r i a l w i l t (Pseudomonas solanacearum Smith) i n n o r t h e r n V i e t n a m. P h D T h e s i s, H a n o i. 1 4

23 A Brief Introduction to Bacterial Wilt Research in China Duan Naixiong 1, Liao Boshou 1, He Li-Yuan 2, and Gao Guoqing 3 Abstract Bacterial wilt (BW) caused by Burkholderia solanacearum is an important bacterial disease for several crops of economic importance in China, including potato, tomato, tobacco, pepper, eggplant, ginger, and groundnut. The disease is generally serious in the tropical and subtropical regions of the country and less serious in the North, even though the pathogen has been observed to cause losses in some areas. The B. solanacearum isolates collected from various regions in China have been characterized and divided into five races and five biovars based on their host range and biochemical features. Extensive and intensive research on bacterial wilt on the major host crops has been conducted at several institutions, including the Plant Protection Research Institute (PPRI), the Oil Crops Research Institute (OCRI), and the Vegetable Research Institute (VRI) of the Chinese Academy of Agricultural Sciences ( C A A S ), and some provincial institutions. In recent years, the motility of some wild B. solanacearum strains and its role in infection have been studied. The molecular basis of pathogenicity has been investigated through international cooperation. Proteins related to BW resistance in potato were isolated, and the gene sequence was analyzed. Regenerates of potato from genetic transformation have been found with improved resistance to BW. Progress has been made in varietal improvement in tomato, tobacco, potato and groundnut. Cultural control practices, including rotation with paddy rice and other non-host crops, have been widely used. 1. O i l Crops Research Institute ( O C R I ), Chinese Academy of Agricultural Sciences ( C A A S ), Wuhan , China 2. Plant Protection Research Institute (PPRI), Chinese Academy of Agricultural Sciences ( C A A S ), Beijing , China 3. Industrial Crops Research Institute, Guangxi Academy of Agricultural Sciences ( G A A S ), Nanning , China. Duan Naixiong, Liao Boshou, He Li-Yuan, and Gao Guoqing A brief introduction to bacterial wilt research in China. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C, and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 1 5

24 Introduction Bacterial w i l t ( B W ) caused by Burkholderia solanacearum (E.F. Smith) Yebucchi et al. is considered one of the most important bacterial disease of plants worldwide. Even t h o u g h the pathogen was first described (as Pseudomonas solanacearum) and published by E r w i n E S m i t h in 1896, the disease had already existed for a long period in many tropical, subtropical, and temperate zones of the world. Plant species in more t h a n 50 families have been observed to be susceptible to the pathogen. Recently, 100 years after its discovery, the pathogen was re-named and classified as B. solanacearum. D u r i n g the past century, over 4000 papers have been published on various aspects of BW (Kelman 1998), reflecting active research on the disease. Host Range, Distribution and Economic Importance In C h i n a, BW caused by B. solanacearum is an important disease on many crops of economic importance ( H e 1986). T h e disease was first recorded in the country in the 1930s. I m p o r t a n t host plants include potato (Solatium tuberosum), tomato (Lycopersicum esculentum), tobacco (Nicotiana tabacum), groundnut (Arachis hypogaea), eggplant (Solanum melongena), pepper (Capsicum annum), ginger (Zingiber officinale), sesame (Sesamum indicum), sweet potato (Ipomoea batatas) mulberry (Morus alba) and eucalyptus (Eucalyptus spp). Bacterial w i l t is generally more serious in southern regions of C h i n a, where temperatures are generally h i g h year round and annual precipitation is also generally high. T h e disease is less important in the north, where low temperatures, especially during winter, do not favor the survival of the pathogen. However, the epidemiology of bacterial w i l t in different hosts is also closely related to soil type and other ecological factors. For example, sesame BW was observed in Jiangxi Province but n o t in H u b e i Province, where bacterial w i l t is serious in groundnut and tomato. Sweet potato BW has been observed to occur only sporadically. Currently, it is difficult to estimate the direct economic losses caused by bacterial w i l t in the m a i n host crops. Potato, groundnut, tobacco, and tomato are crops widely sown in the country, and yield losses from the disease in these crops are estimated to be very large. For groundnut, it is estimated that the area covered by infested fields has increased to over ha ( Liao et al. 1998) and that average yield loss is 7-10%, even when wilt-resistant cultivars are extensively sown. Concerned Research Institutions in China T h e r e are several institutions where research is currently conducted on BW in C h i n a. A b r i e f description of these institutions and the area of research on BW being conducted in them is as follows: 1 6

25 At PPRI, Beijing, BW has been an important research priority for over two decades. T h i s laboratory has well- equipped facilities for BW research. Research areas include c o l l e c t i o n of pathogen isolates, characterization of isolates based on virulence and pathogenicity, molecular mechanisms of resistance to B W, and biological control o f B W o f potato. A t the Tobacco Research Institute, C A A S, located i n Y i d u, Shandong Province, the m a i n activities are collection and evaluation of tobacco germplasm. T h i s I n s t i t u t e coordinates research on resistance screening and breeding for BW resistance throughout C h i n a. Research on screening and breeding for tomato, eggplant, and pepper for resistance to BW is coordinated by the Vegetables Research Institute ( V R I ), C A A S, Beijing. A t the S o u t h Potato Center, located i n Enshi, H u b e i Province, potato germplasm evaluation and breeding for BW is being conducted. Similarly in Fujian Academy of A g r i c u l t u r a l Sciences, Fuzhou, research on control of tobacco BW is being conducted. A d d i t i o n a l l y, work on breeding for resistance to BW of tomato is being undertaken at Jiangsu Academy of Agricultural Sciences, N a n j i n g. T h e molecular basis of pathogenicity of B. solanacearum is being studied at the G u a n g x i University, N a n n i n g. Several other institutions are conducting research on groundnut B W. T h e leading institution is O C R I, located in W u h a n. Research has been conducted at O C R I in various aspects, including germplasm screening, breeding, pathology, and integrated control. At the Crop Research Institute of Guangdong Academy of A g r i c u l t u r a l Sciences, Guangzhou, extensive research has been done on varietal improvement for host resistance and integrated c o n t r o l. Germplasm screening and breeding research is also being conducted in the Industrial Crops Research Institute of Guangxi Academy of Agricultural Sciences, located in Nanning, the Agricultural Research Institute of Nanchong C i t y in Sichuan Province, and Fujian Agricultural University located in Fuzhou. Significant Achievements Motility of wild B. solanacearum strains In PPRI, Beijing, 30 of 140 w i l d type strains of B. solanacearum were observed to have m o t i l i t y in semi-solid m o t i l i t y medium ( S M M ) w i t h agar after 48 hours incubation and in S M M medium w i t h o u t agar after 4 hours. M o t i l e w i l d type 1 7

26 strains could move dramatically toward and accumulate near root segments of host plants and some non-host plants. Some motile w i l d type strains could cause earlier and h i g h e r disease incidence in potato plants t h a n could others. It was speculated that m o t i l i t y was related to the infectivity of some B. solanacearum strains. Protein related to bacterial wilt resistance in potato In PPRI, Beijing, a k D protein ( A P I ) that could i n h i b i t B. solanacearum was purified from a BW-resistant potato variety. T h e biochemical characterization, antimicrobial spectrum, and ultrastructural localization of A P I were investigated. A P I m i g h t be a new k i n d of plant-specific constitutive disease resistant protein (Yuan and He 1998). Transgenic potato plants In the Biotechnology Research Center, C A A S, Beijing, transgenic potato plants w i t h improved resistance to BW have been obtained. This was the first case of improvement of resistance to B. solanacearum through genetic engineering (Jia 1996, personal communication). New resistant cultivars in some vegetables and groundnut In several institutes, new varieties of tomato and eggplant w i t h improved resistance to BW have been developed and released for p r o d u c t i o n. Several n e w groundnut cultivars w i t h desirable resistance have been developed. Further Research Needs Bacterial w i l t has attracted m u c h research effort in recent years in C h i n a. T h e disease is still important in terms of its wide distribution and host range, the considerable economic losses it causes, and the p o t e n t i a l for its further dissemination. Further research efforts w i l l be made to address the following: T h e molecular basis o f virulence or pathogenicity o f B. solanacearum w i l l be further investigated. Biotechnology approaches for resistance improvement w i l l be widely used, especially for those species in w h i c h no desirable resistance sources have been identified for conventional breeding. Varietal improvement w i l l be an important research priority i n various crops for b o t h resistance to BW and agronomic traits. Biological c o n t r o l of BW w i l l be further investigated especially in potato. 1 8

27 Cultural control approaches w i l l be investigated and applied for most host crops. Technology transfer to farmers w i l l be intensified. References H e, L. Y B a c t e r i a l w i l t i n t h e P e o p l e s R e p u b l i c o f C h i n a. Pages in B a c t e r i a l w i l t disease i n A s i a a n d t h e S o u t h Pacific: p r o c e e d i n g s o f t h e I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, O c t., 1985, P C A R R D, L o s, Banos, P h i l i p p i n e s (Persley, G.J., e d. ). A C I A R Proceedings N o. 13. C a n b e r r a, A u s t r a l i a : C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. K e l m a n, A O n e h u n d r e d a n d o n e years o f research o n b a c t e r i a l w i l t. Pages 1-5 in B a c t e r i a l w i l t disease: m o l e c u l a r a n d e c o l o g i c a l aspects: p r o c e e d i n g s o f t h e S e c o n d I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, June, , G o s i e r, G u a d e l o u p e. Paris, France: S p r i n g e r I N R A. L i a o, B. S., S h a n, Z. H., D u a n, N. X., T a n, Y. J., L e i, Y., L i, D., a n d M e h a n, V. K R e l a t i o n s h i p b e t w e e n l a t e n t i n f e c t i o n a n d g r o u n d n u t b a c t e r i a l w i l t resistance. Pages in B a c t e r i a l w i l t disease: m o l e c u l a r a n d e c o l o g i c a l aspects: p r o c e e d i n g s o f t h e S e c o n d I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, June, , Goiser, G u a d e l o u p e. Paris: France, S p r i n g e r I N R A. Y u a n, E H. a n d H e, L. Y A n a n t i - B u r k h o l d e r i a solanacearum p r o t e i n f r o m p o t a t o a n d its i m m u n o g o l d l o c a l i z a t i o n i n v i v o. Pages in B a c t e r i a l w i l t disease: m o l e c u l a r a n d e c o l o g i c a l aspects: p r o c e e d i n g s o f t h e S e c o n d I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, June, , Goiser, G u a d e l o u p e. Paris, F r a n c e : S p r i n g e r I N R A. 1 9

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29 Groundnut Bacterial Wilt : Present Status

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31 Present Status of Groundnut Bacterial Wilt in South China Liang Xuanqiang 1 Abstract Bacterid wilt caused by B u r k h o l d e r i a solanacearum is an important production constraint in over 70% of the groundnut ( A r a c h i s h y p o g e a ) crops in southern China, Scientists in Guandong Province have been conducting research on bacterial wilt since the 1950s, developing integrated management measures. Crop rotation and field management are effective ways to control the disease, but the most useful strategy is employment of host-plant resistance. Several highyielding varieties resistant to bacterial wilt have been developed and now cover more than 70% of the diseased fields. Through intensive breeding, wilt resistance and high yield have been combined with resistance to rust and root rot, in some varieties. Disease Distribution a n d Economic Importance Groundnut is an important o i l and industrial crop in South C h i n a (including Guangdong, Guangxi, Jianxi, Fujiang, and H a i n a n provinces), where it is cultivated on about ha. Bacterial w i l t ( B W ) caused by Burkholderia solanacearum (E.E Smith) Yabuuchi et al. is a major constraint to groundnut production on over 70% of southern China's production area. Yield losses of 15-25% are common. T h e annual loss in pod yield caused by BW is estimated at over 35 x 10 6 kg. W i l t intensity varies w i t h season, soil type, and cultural practices. In general, BW is more severe in spring t h a n in autumn. W i l t incidence in rice fields w i t h r i c h clay soil on high tablelands is less t h a n on nonirrigated uplands, poor, sandy soils, or low tablelands. G o o d cultural practices and resistant cultivars help to reduce BW incidence. 1. Crops Research Institute, Guangdong Academy of Agricultural Sciences ( G A A S ), Wushan, , Guangzhou, China. Liang Xuanqiang Present status of groundnut bacterial wilt in South China. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C, and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 2 3

32 Scientists in Guangdong have been conducting research on BW since the 1950s and have developed integrated BW management measures. A d d i t i o n a l l y, they have released several cultivars w i t h resistance to BW. Improved management practices and cultivars have been widely adopted. As a result, mean yield in South C h i n a has increased from 1.53 t ha -1 in the 1980s to 2.0 t ha -1 in Some BW management measures are described here. Crop Rotation C r o p r o t a t i o n has many advantages. It can m a i n t a i n and increase soil fertility and reduce soilborne insect pests and diseases, i n c l u d i n g soilborne propagules of B W. To minimize BW incidence and severity, crop rotation has been widely used in South C h i n a since In South C h i n a, groundnut is cultivated in t w o cropr o t a t i o n systems: 1. rotation w i t h paddy rice in lowlands, usually w i t h a cycle of 2 to 3 years (the longer the rotation cycle, the more effective the control), and 2. r o t a t i o n w i t h sweet potato, jute, maize, sugarcane, soybean, black bean, mung bean or other non-bw-host crops in upland areas, always w i t h a rotation cycle of 2 to 3 years. In South C h i n a, 6 0 % of the groundnut crop is in upland areas. R o t a t i o n w i t h BW host-crops for example tobacco, tomato, eggplant, and pepper - is discouraged. Field Management Such suitable cultural practices as flooding can effectively c o n t r o l BW. In the 1995 spring season in Guangzhou, flooding a field w i t h a w i l t incidence of 4 2 % for days before sowing of groundnut lowered w i l t incidence to 5%, an approximately ninefold reduction. Improved field drainage also helps reduce BW incidence and severity if followed before the groundnut crop starts flowering. Experiments conducted on the management of soil moisture showed t h a t 6 0 % soil moisture is an i m p o r t a n t threshold: if soil moisture is above 6 0%, the BW pathogen can easily reproduce. Some field observations and greenhouse tests showed that soil w i t h ph is favorable for pathogen g r o w t h. In general, alkaline soils suppress BW pathogen g r o w t h. In X i x i n county, groundnut is rotated repeatedly w i t h tobacco (a host crop of B W ) in purple soil w i t h ph 8-9, but the incidence of w i l t is always low ( < 5 % ). Field sanitation practices such as burning crop residues and removing weeds especially Agerratum conyzoides also h e l p reduce BW incidence. O t h e r agronomic practices, including soil application of organic manure seem to reduce BW incidence. Chemicals, including fertilizers and nutrients, have n o t been found t o c o n t r o l B W. 2 4

33 Host-Plant Resistance Genetic resistance to BW is recognized as the most effective disease management strategy. In the past three decades, great emphasis has been placed on managing BW through host plant resistance. A b o u t 60 genotypes, including local landraces (led by Taishan Sanlirou, Taishan Zhenzhou, and Xiekangqing), exotic varieties from I C R I S A T (led by Gajah, S c h w a r z 21, I C G 1703, PI , and CS 30), and w i l d Arachis species have been identified as sources of high, stable resistance to BW in artificial inoculation tests and multilocational sick-plot tests. Several high- yielding BW resistant varieties e.g., Yue You 589, Yue You 92, Yue You 256, Wu You 4, Guiyou 28, and Yue You 200 have been developed through the modified pedigree method and released for general cultivation in South China. These cultivars are g r o w n on more than 70% of the diseased fields, playing an important role in controlling the disease, and significantly increasing groundnut production in South China. Breeding for Multiple Resistance to BW, Rust, and Root Rot Yue You 256 and Yue You 200 have a h i g h level of resistance to BW, as well as moderate resistance to rust and h i g h susceptiblity to root rot caused by Fusarium spp. These t w o widely distributed fungal diseases cause substantial y i e l d losses in South C h i n a. Since 1988, incorporation of resistance to B W, rust, and root rot i n t o high-yielding cultivars has received h i g h priority. From screening of about 2000 germplasm accessions, Yinduhuapi, a runner type groundnut from I C R I S A T, I n d i a, was identified as possessing h i g h levels resistance to a l l three diseases. T h r o u g h large-scale hybridization, a potential breeding line Yue You 39 w i t h h i g h yield and h i g h resistance to B W, rust, and root rot was developed. But Yue You 39 has some agronomically unacceptable characters such as late maturity, l o w shelling percentage, and too many aerial pegs. T h o u g h backcrossing w i t h high-yielding, early-maturing cultivars, t w o varieties, Yue You and Yue You 79, w i t h higher y i e l d, resistance to B W, rust, and root rot, and wide adaptation were developed and released in Guangdong province. These t w o varieties are gradually replacing Yue You 92 and Yue You 256 in that region. Yue You was developed f r o m the cross Yue You x Yue You 116, and was released by Guangdong C r o p Varieties A p p r o v a l C o m m i t t e e in D u r i n g , in advanced groundnut varieties trials, the average yield of Yue You was 3.87 t ha -1 over 13 locations, a net 23.4% gain over Yue You 116, the control. T h e groundnut cultivar Yue You is of medium duration, taking 120 days to mature. It has an erect g r o w t h habit and dark green leaves. T h e seeds c o n t a i n 54.3% o i l and 26% protein. T h e reactions of Yue You to B W, rust, and root rot are excellent (Table 1). 2 5

34 T a b l e 1. P e r f o r m a n c e of some g r o u n d n u t varieties resistant to bacterial w i l t released i n S o u t h C h i n a 1 Yield BW Rust Root rot Resistance Year of Cultivars (t ha -1 ) incidence (%) (score) incidence (%) source used 2 release Yue You Taishan 1970 Sanlirou Yue You Taishan 1983 Sanlirou Yue You A H G u i You Taishan 1986 Sanlirou W u You PI Yue You Taishan 1992 Sanlirou Yue You Yinduhuapi 1996 Yue You Yinduhuapi Results from South China Groundnut Varieties Tests and Provincial Groundnut Varieties Tests. 2. Resistance sources used in breeding these varieties 3. Free from root rot disease incidence Yue You 79 was derived from a cross i n v o l v i n g Yue You x Yue You 116, and released by Guangdong C r o p Varieties A p p r o v a l C o m m i t t e e in D u r i n g 1996/97, in Guangdong Groundnut Varieties Trials, its average yield was 4.09 t ha -1 over 10 locations, a net increase over Yue You It matures in 120 days in the spring season and 115 days in the summer season. It has an erect g r o w t h habit a n d dark green leaves. Disease scores of B W, rust; and root rot of Yue You 79 are similar to those of Yue You (Table 1). Yue You and Yue You 79 have good stability and adaptability for pod yield w h e n sown in either rice-paddy or upland conditions. 2 6

35 Status of Groundnut Bacterial Wilt in Central China Liao Boshou 1, Duan Naixiong 1, Tan Yujun 1, and Wu Yong 2 Abstract Bacterial wilt (BW) caused by Burkholderia solanacearum in groundnut was first reported in central China in the 1950s. The disease has been a constraint to groundnut cultivation in several provinces in central China, including Sichuan, Chongqing, Hubei, Henan, Anhui, Jiangxi, Hunan, and Guizhou (Liao and Zeyong 1997). The total infested groundnut area is estimated at over hectares in the central provinces. The disease is becoming more widespread because of expansion of groundnut and its continuous cultivation. The disease generally causes yield losses of 10 to 30% in central China if susceptible groundnut cultivars are grown, but wilt incidence in the traditional problem areas has been significantly reduced by sowing improved resistant cultivars. Therefore, as in most other diseased regions, the most important control approach for BW in the central provinces is to grow resistant cultivars, including E Hua 5, Zhong Hua 2, Lu Hua 3, Yue You 200, and Other practical control approaches include rotation with paddy rice or with such non-host upland crops as wheat and rapeseed. The Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences has been the leading research agency addressing the problem in this region. In the future, genetic enhancement for resistance and other traits will continue to be the most important control strategy in this region. 1. O i l Crops Research Institute, Chinese Academy of Agricultural Sciences ( C A A S ), Wuhan , China. 2. Agricutural Bureau of Hong An County, Hubei Province , China. Liao Boshou, Duan Naixiong, Tan Yugun and Wu Yong Status of groundnut bacterial wilt in central China. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 2 7

36 Introduction Bacterial w i l t caused by Burkholderia solanacearum (E.F. Smith) Yabuuchi et al. has been an important disease of groundnut (Arachis hypogaea L.) for several decades in central C h i n a. In the eastern part of H u b e i Province, the disease was first recorded in Huangzhong A g r i c u l t u r a l College in the 1950s, but the local farmers were w e l l acquainted w i t h the w i l t problem earlier t h a n this. G r o u n d n u t bacterial w i l t became more serious in the 1960s and was reported from all other groundnutgrowing provinces of central C h i n a. Progress in disease control has been made in the past two decades using integrated control approaches. Distribution and Severity Currently, bacterial w i l t of groundnut is a serious constraint to groundnut production in several provinces in central C h i n a, including Sichuan, Chongqing, H u b e i, H e n a n, A n h u i, Jiangxi, H u n a n, and Guizhou. T h e disease has also been reported in Zhejiang and Jiangsu Provinces on the east coast, b u t economic losses were low there (Liao and Zeyong 1997). T h e total area infested w i t h BW in central C h i n a is over ha. T h e disease is becoming more widespread w i t h the expansion of groundnut cultivation in most of the provinces i n central C h i n a. However, w i l t incidence i n traditionally endemic areas has significantly decreased because resistant cultivars are being g r o w n ( Z h o u and W e i 1996). T h e disease generally causes yield losses of 10 to 3 0 % in susceptible groundnut cultivars. At present, BW incidence in central C h i n a ranges between 2 and 12% wherever resistant cultivars are grown. Disease Control As in many other regions, the most important control approach for groundnut BW is to grow resistant cultivars. Currently, the following resistant cultivars are being g r o w n in the central provinces. E H u a 5 is highly resistant to B W. It has small seeds, matures early, and has desirable uniformity of pod shape. T h i s cultivar was developed at the O i l Crops Research Institute ( O C R I ) and released in 1985 and is used in Hubei, Henan, and Jiangxi Provinces. T h e yield of E Hua 5 is only moderate, but it has desirable tolerance to shallow soil and poor fertility, so that it can be grown in upland fields. Zhong H u a 2 is h i g h l y resistant to BW, w i t h medium-sized seed and h i g h seed protein content. It was developed at O C R I, released in 1990, and is extensively cultivated in the central provinces. However, the cultivar has poor seed dormancy, so preharvest germination usually causes up to 10% loss. 2 8

37 Lu H u a 3 is moderately resistant to B W, w i t h medium- sized seed. It was developed at Shandong Peanut Research Institute (SPRI). Since 1986 it has been cultivated in some regions of Sichuan and H e n a n Provinces in central C h i n a. Yue You 200 is a h i g h l y resistant c u l t i v a r w i t h i m p r o v e d yield p o t e n t i a l and d r o u g h t tolerance. It was developed at the Crops Research I n s t i t u t e of G u a n g d o n g A c a d e m y of A g r i c u l t u r a l Sciences and released in Sichuan Province in 1997 as T i a n f u ( Z H 212). A h i g h l y resistant breeding l i n e w i t h i m p r o v e d y i e l d p o t e n t i a l and tolerance to acid soil was also developed a t O C R I. O t h e r practical control approaches include rotation w i t h paddy rice and w i t h some non-host upland crops such as wheat or rapeseed. However, the area that can be rotated w i t h paddy rice in central C h i n a is very small. Long-term rotation w i t h non-host crops has also become less feasible in this region because of l i m i t e d arable land and expanded groundnut cultivation. Research Organizations I n central C h i n a, the O C R I o f the Chinese Academy o f A g r i c u l t u r a l Sciences ( C A A S ), located in W u h a n, is the leading research organization addressing groundnut BW. T h e scientists at O C R I are responsible for coordinating groundnut BW research; conducting groundnut germplasm c o l l e c t i o n and evaluation for resistance to B W ; c o n v e n t i o n a l breeding; and resistance i m p r o v e m e n t through biotechnology. N a n c h o n g A g r i c u l t u r a l Research Institute in Sichuan Province is also engaged in breeding for resistance to BW. In central C h i n a, there is a network of eight sites for evaluation for resistance t o B W i n groundnut varietal trials. Problems and Further Research Needs Incidence of w i l t diseases other t h a n BW (probably caused by soilborne fungi) has significantly increased in recent years. These soilborne fungal diseases have obviously complicated the further increase of groundnut p r o d u c t i v i t y in regions where BW is a problem. T h e sizes of pathogen populations in infested fields after long-term c u l t i v a t i o n of resistant cultivars is u n k n o w n. It w o u l d be interesting to investigate the dynamics of population pathogenicity in soil. Farmers w o u ld take an interest in k n o w i n g whether susceptible groundnut cultivars w i t h higher yield could be grown in diseased fields after c u l t i v a t i o n of resistant ones for several years. 2 9

38 T h e yield potential of most cultivars resistant to BW is often lower t h a n that of susceptible ones. Further breeding efforts should be made to c o m b i n e resistance and h i g h yield. Despite a l l o f our efforts, there are areas where B W incidence is still very h i g h because of continuous c u l t i v a t i o n of susceptible groundnut cultivars. Therefore, efforts w i l l be made to extend BW-resistant cultivars to farmers i n such areas. References L i a o B o s h o u a n d X u Z e y o n g R e p o r t o f c o l l a b o r a t i v e research o n g r o u n d n u t v i r u s a n d b a c t e r i a l w i l t diseases w i t h I C R I S A T f o r Paper p r e s e n t e d a t C h i n a - C L A N / I C R I S A T R e v i e w a n d W o r k p l a n M e e t i n g, J u l y , B e i j i n g C h i n a. ( L i m i t e d d i s t r i b u t i o n ) Z h o u Z h a n g l a i a n d W e i X i u p i n g A g r o u n d n u t n e w c u l t i v a r W a n h u a 2. O i l C r o p s o f C h i n a. 1 8 ( 3 ) :

39 Status of Groundnut Bacterial Wilt in Northern Vietnam Nguyen Xuan Hong, Nguyen Van Viet, and Nguyen Thi Yen 1 Abstract Groundnut bacterial wilt (BW) is a widespread disease in the major groundnut-producing areas of northern Vietnam. The disease is increasingly serious in many parts of Nghe A n, Ha Tinh, Thanh Hoa, and other provinces. Bacterial wilt is severe not only in traditional groundnut-growing areas but also in newly cultivated areas. Wilt incidence in groundnut-producing areas has increased substantially in the past few years. It is highest in dryland cropping systems, especially in upland areas of hilly regions in light sandy soil along river banks and in fields where groundnuts are intercropped with dryland crops. Rotation of groundnut with rice is effective in reducing wilt incidence. The disease is more serious in the autumn crop. Most local varieties are susceptible to disease. Research on identification of wilt-resistant genotypes, development of improved, varieties, and integrated management of BW is needed. Introduction In n o r t h e r n V i e t n a m, groundnut is cultivated mainly in the spring season (February to June). It is the most important food legume crop of T h a n h Hoa, Nghe A n, Ha T i n h, and other provinces. T h e area under groundnut increased from ha in 1992 to ha in A l t h o u g h soil and environment conditions are favorable for groundnut production, average yields are still low (1.09 t ha -1 ). Bacterial w i l t ( B W ) caused by Burkholderia solanacearum (E.F. Smith) Yebuuchi et al. is widespread in major groundnut-producing areas and has become one of major constraints to groundnut production. This report summarizes the results of surveys on status of groundnut bacterial w i l t conducted by scientists of V i e t n a m A g r i c u l t u r a l Science Institute ( V A S I ) during the last year. 1. Vietnam Agricultural Science Institute ( VASI), Van Dien, Thanh Tri, Hanoi, Vietnam. Nguyen Xuan Hong, Nguyen Van Viet, and Nguyen T h i Yen Status of groundnut bacterial wilt in northern Vietnam. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 3 1

40 Distribution and Severity of Disease in Different Production Systems I n n o r t h e r n V i e t n a m, groundnut i s concentrated mostly i n Nghe A n, H a T i n h, T h a n h H o a, and Bac G i a n g provinces, and some areas of other provinces. G r o u n d n u t is cultivated mainly under rainfed conditions in h i l l y and upland areas, and along river banks in dryland cropping systems. G r o u n d n u t is also grown in rotation w i t h rice in the spring season. T h e area of groundnut has significantly increased in the last 3 years (Table 1). Bacterial w i l t has undoubtedly been present on groundnut in n o r t h e r n V i e t n a m for many years, although it was first documented in detail in 1991 ( M e h a n et al. T a b l e 1. S o w n area a n d y i e l d o f g r o u n d n u t i n n o r t h e r n V i e t n a m S o w n area (ha x 10 3 ) Yield (t ha - 1 ) Region N o r t h N o r t h M o u n t a i n and m i d l a n d Red River delta N o r t h C e n t r a l coast Province Bac T h a i H o a B i n h Q u a n g N i n h V i n h P h u H a Bac H a n o i H a Tay H a i H u n g N a m H a N i n h B i n h T h a n h H o a N g h e A n H a T i n h Q u a n g B i n h

41 1991, H o n g et al. 1994). It is widely distributed in all areas of groundnut production. Some regions are heavily infected, while in other areas the disease is sporadic. It is most severe in Nghe A n, Ha T i n h, T h a n h Hoa, Ha Tay, Bac Giang, and T h a i N g u y e n provinces. In general the average w i l t incidence ranges from %, b u t in the most heavily infected fields it reaches %. T h e disease is severe n o t o n l y in the traditional groundnut-producing areas ( N a m D a m and N g h i a D a n districts o f Nghe A n province, H a Trung, Hoang Hoa, T i n h G i a districts of T h a n h H o a province, Lang G i a n g and Viet Yen districts of Bac G i a n g province) but also in newly cultivated areas in Ha Tay, Bac N i n h, T h a i Nguyen, and H o a B i n h provinces. W i l t incidence i n traditional groundnut-producing areas has increased very fast. In fields where groundnut has been g r o w n year after year, especially in upland areas and i n the soils along the river banks, w i l t incidence has significantly increased. C r o p rotation and host resistance have been considered important to manage BW in these areas. W i l t incidence varies greatly from place to place, depending on cropping patterns and soil conditions. T h e disease is most severe in h i l l y and riverbed areas where w i l t incidence ranges from % (Table 2). T a b l e 2. B a c t e r i a l w i l t o f g r o u n d n u t i n d i f f e r e n t ecological conditions o f n o r t h e r n V i e t n a m, W i l t incidence (%) N u m b e r o f A r e a locations surveyed Range Average H i l l y River beds U p l a n d Rice-groundnut r o t a t i o n I n upland areas o f h i l l y regions, w i l t incidence is highest i n fields where groundnut is grown twice a year. In these fields w i l t incidence was 10-60%. T h e disease was also found ( % ) in sandy soils along river banks where o n l y d r y l a n d crops such as groundnut, maize, tomato, and other vegetables were g r o w n. W i l t was also present ( % ) in fields where groundnut was intercropped w i t h vegetables, maize, or m u n g bean. In irrigated rice-based, groundnut-growing areas, w i l t incidence was lowest ( 0-5 % ) (Table 3 ). Thus, rotation of groundnut w i t h 3 3

42 irrigated rice is the most effective way to control bacterial w i l t. Similar results have also been reported in C h i n a (Tan et al. 1994). T a b l e 3. W i l t incidence ( % ) o f g r o u n d n u t i n different p r o d u c t i o n systems i n V i e t n a m, H i l l y w i t h H i l l y w i t h D r y l a n d Rice- M a i n 1 crop of 2 crops of River crop groundnut L o c a t i o n cultivar groundnut groundnut banks systems r o t a t i o n H a T i n h Sen N A N g h e A n T h a n h H o a N i n h B i n h Cuc N A C h u m N A Sen L a i Bac G i a n g D o B G T h a i N g u y e n Chay H B V i n h Phuc H a n o i Su tuyen Sen N A H a Tay Tram X u y e n T a b l e 4. I n f l u e n c e o f cropping season o n the incidence o f g r o u n d n u t bacterial w i l t ( % ) a t six locations i n V i e t n a m, Spring crop (Feb-Jun) A u t u m n crop ( J u l - N o v ) L o c a t i o n C u l t i v a r Average Highest Average Highest H a T i n h C h u m N g h e A n H a T i n h Cue N g h e A n Bac G i a n g Do Bac G i a n g Bac G i a n g Su Tuyen H a Tay Sen L a i N i n h B i n h Bacterial w i l t is widespread i n a l l groundnut-producing areas year-round. However, it is more serious in a u t u m n ( J u l - N o v ) in areas where the crop is g r o w n year after year. Spring crop incidence reached a m a x i m u m of % in a 1995 survey; m a x i m u m incidence in the a u t u m n season was even higher, reaching % (Table 4 ). 3 4

43 T h e majority of currently grown groundnut varieties are highly susceptible to B W. O n l y t w o genotypes, Tram Xuyen and 4329, have shown moderate levels of susceptibility to w i l t under h i g h disease pressure (Table 5). In recent years, germplasm accessions have been extensively evaluated for resistance to bacterial w i l t ( H o n g et al. 1994) but more research on identification of wilt-resistant groundnut genotypes is needed. T a b l e 5. B a c t e r i a l w i l t r e a c t i o n o f m a j o r g r o u n d n u t varieties p o p u l a r l y g r o w n i n n o r t h e r n V i e t n a m ( / 9 5 ) W i l t incidence i n Varieties h o t - s p o t locations (%) Disease reaction 1 Sen N g h e A n Sen L a i Do Bac G i a n g Su Tuyen T r a m X u y e n C h u m N g h e A n V S S s s M S s s M S 1. S = susceptible, MS = moderately susceptible Conclusion and Suggestions Bacterial w i l t is one of the most important constraints to groundnut p r o d u c t i o n in n o r t h e r n V i e t n a m. In recent years, yield losses caused by the disease in farmers' field have significantly increased. M a j o r groundnut varieties popularly g r o w n in n o r t h e r n V i e t n a m are susceptible to the disease. Further genetic evaluation to identify sources of resistance to BW is needed. Research on development of improved varieties w i t h m u l t i p l e disease resistance to BW and other major diseases should be given h i g h priority. M o r e systematic research needs to be undertaken on integrated management of groundnut BW, using host p l a n t resistance and cultural practices, particularly crop rotation, in order to alleviate losses caused by the disease in major g r o u n d n u t - g r o w i n g areas of n o r t h e r n V i e t n a m. 3 5

44 References M e h a n, V. K., H o n g, N. X., a n d Ly, N. T O n t h e i d e n t i f i c a t i o n o f p a t h o g e n s c a u s i n g t h e so-called g r o u n d n u t w i l t disease i n N o r t h e r n V i e t n a m. Pages in I m p r o v e d c u l t i v a t i o n t e c h n i q u e s f o r g r o u n d n u t a n d o t h e r f o o d legumes i n V i e t n a m. H a n o i, V i e t n a m : A g r i c u l t u r a l P u b l i s h i n g H o u s e ( i n V i e t n a m e s e ). H o n g, N. X., M e h a n, V. K., L y, N. T., a n d V i n h, M. T S t a t u s o f g r o u n d n u t b a c t e r i a l w i l t research i n V i e t n a m. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. T a n, Y. J., D u a n, N. X., L i a o, B. S., X u, Z. Y., H e, L. Y., a n d X h e n g, G. R S t a t u s o f g r o u n d n u t b a c t e r i a l w i l t research i n C h i n a. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. 3 6

45 Bacterial Wilt of Groundnut in Southern Vietnam Nguyen Van Tung 1, V K Mehan 2, Phan Lieu 1, and Ngo Thi Lam Giang 1 Abstract Bacterial wilt (BW) caused by Burkholderia solanacearum is becoming increasingly prevalent and severe in the groundnut (Arachis hypogaea L.) crop of southern Vietnam. Scientists at the Oil Plant Institute in Hanoi have carried out a detailed survey of BW in southeastern Vietnam. Incidence and severity was low in fields under groundnut-rice-rice cropping systems and moderate to severe (up to 40% wilting) under groundnut-groundnut-rice systems. The disease was more serious in the summer-autumn season because of high soil temperature and moisture. Nine resistant ICRISAT breeding lines had good wilt reactions over 2 years, but their shelling percentage was lower than that of local varieties. Integrated disease management systems are needed to control fungal diseases and BW. I n t r o d u c t i o n Bacterial w i l t ( B W ) is a serious constraint to groundnut production in many regions of V i e t n a m. Depending upon the agroecological c o n d i t i o n and crop rotations, the severity of BW varies across a region. I n collaboration w i t h I C R I S A T, the O i l Plant Institute ( O P I ) i n H a n o i has carried out a detailed survey to determine the status of this disease in some groundnut-growing districts in the southeast region of Vietnam. A l s o during these surveys, disease was m o n i t o r e d on bacterial wilt- resistant groundnut lines sent from I C R I S A T. T h e results of this survey are presented in this paper. 1. O i l Plants Institute (OPI), , Ham Nghi St., 1st District, Ho C h i M i n h City, Vietnam. 2. International Crops Research Institute for the Semi-Arid Tropics ( ICRISAT), Patancheru , Andhra Pradesh, India. Nguyen Van Thang, Mehan, V.K., Phan Lieu, and Ngo T h i Lam Giang Bacterial wilt of groundnut in southern Vietnam. Pages in Groundnut hacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, G, and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 3 7

46 Survey of Bacterial Wilt Incidence D u r i n g the winter-spring season of 1995/96, an expert from I C R I S A T ( D r V K M e h a n ) directly collaborated w i t h us in carrying out the survey in four districts. In each district, 5 to 6 villages and 5 to 50 g r o u n d n u t fields were surveyed. D a t a collection included cropping system, crop growth stage, BW incidence, and crop cultivars g r o w n in each district (Table 1). Trang Bang district In this district, BW incidence was 0-2 8% (mostly 16-18% on day-old crops) in Loc H u n g Village, and 0-9 % in G i a Loc village where farmers follow a groundnut-groundnut-rice ( G - G - R ) cropping system. Incidence was % in fields w i t h a groundnut-fallow-vegetable ( G - F - V ) cropping system. L o w incidence ( 0-3 % ) of BW was recorded in day-old crops in fields w i t h a G - G - R cropping system i n A n T i n h and D o n T h u a n villages. I n fields i n Loc H u n g and D o n T h u a n villages where a groundnut-rice-rice ( G - R - R ) rotation was followed, BW occurred at low incidence ( 0-4 % ). It was seen in a few fields (incidence < 1 % i n day-old crops) i n A n T i n h village. Go Dau district In Go D a u district, BW was very severe in Phuoc D o n g village. It was prevalent in almost all fields w i t h a G - G - R cropping system, w i t h incidence of 11-43% (mostly % ) in day-old crops, and 2-8 % in day-old crops. Some apparently healthy plants also showed latent bacterial infection in their roots. Incidence c o m m o n l y reached % in the winter-spring season, and % in the summer-autumn season. Because of the increasing severity of BW in this village, many farmers are now switching to maize and vegetables in the summera u t u m n season. Bacterial w i l t was observed in all fields w i t h G - G - R cropping systems surveyed in H i e p T h a n h village, w i t h incidence of %. T h e disease occurred in most fields in Phuoc T h a n h village (incidence % in dayo l d crops, and 0-5 % in day-old crops). In T h a n h Phuoc and Bau D o n villages, bacterial w i l t was present at l o w incidence in day-old crops, in fields w i t h G - R - R ( 0-2 % ) and G - G - R ( 2-5 % ). It occurred at moderate incidence ( % ) in 70 day-old crops w i t h a groundnut-groundnut-vegetable ( G - G - V ) rotation i n T h a n h Phuoc village. Cu Chi district Bacterial w i l t was observed at 1-4% in day-old crops in G - G - R, and 2-8 % 38

47 T a b l e 1. B a c t e r i a l w i l t o n g r o u n d n u t i n s o u t h e r n V i e t n a m, w i n t e r - s p r i n g / 9 6, season Cropping Crop age No of fields B W incidence District Village system 1 (days) surveyed (%) Trang Bang Loc Hung G - G - R G - R - R Gia Loc G - G - R G - F - V D o n T h u a n G - G - R G - R - R A n T i n h G - G - R G - R - R G o Dau Phuoc Dong G - G - R G - G - R Hiep T h a n h G - G - R Phuoc T h a n h G - G - R G - G - R T h a n h Phuoc G - G - R G - R - R G - G - V Bau D o n G - R - R G - G - R C u C h i Trung Lap Ha G - R - R G - R - R G - G - R Phuoc T h a n h G - G - R G - R - R Phuoc Hiep G - R - R Duc Hoa Hoa Khanh Dong G - G - R G - R - R G - F - G / R Duc Lap Thuong G - G - R Due Hoa Thuong G - G - R G - R - R Duc Lap Ha G - G - R G - R - G / R G = groundnut, R = rice, V = vegetable, F = fallow 3 9

48 i n fields i n G - R - R cropping systems i n T h i n g Lap H a village o f C u C h i district. I n the latter cropping system, a number of plants in some fields showed i n i t i a l disease symptoms. T h e disease was not visible in day-old crops. In Phuoc T h a n h village, bacterial w i l t incidence was 2-4 % in G - G - R cropping systems, and 0-2 % in day-old crops in G-R-R cropping systems. Due Hoa district Bacterial w i l t incidence was 0-6 % in fields w i t h G - G - R cropping system surveyed in Duc Lap T h u o n g and Duc H o a T h u o n g, and 0-8 % in Duc Lap Ha village. It was n o t observed in day-old crops in black soil fields in Duc H o a T h o u n g village. In H o a K h a n h D o n g village, BW incidence was low in day-old crops in fields w i t h G - G - R ( 1-3 % ) and G - R - R ( 0-2 % ) cropping systems. Bacterial w i l t occurred at moderate incidence in day-old crops w i t h a G- F-G r o t a t i o n in Due Lap Ha ( 4-8 % ) and H o a K h a n h Dong ( 7-8 % ) villages. BW Incidence and Yield of ICRISAT Groundnut Lines From the several groundnut lines that were identified by I C R I S A T as sources of resistance to BW, O P I selected nine lines and evaluated them for agronomic and other characteristics, including BW reaction, in t w o seasons. M e a n duration of these varieties (90 days) was at par w i t h a local variety (Table 2). A m o n g these lines, I C G V 8666 had the highest resistance ( B W incidence=0.1%). In other characteristics, such as shelling and o i l content, it also corresponded to a local variety (Table 2). In the winter-spring season of , we carried out trials at five locations to compare the performance of I C G 8666 and I C M 8645 w i t h that of a local variety (Table 3 ). These t w o resistant genotypes were liked by the farmers. Conclusions Bacterial w i l t is b e c o m i n g increasingly prevalent and severe, as a result of continuous cropping and irrigation practices. Incidence and severity was low in G-R-R cropping system, and moderate to severe ( % ) in fields w i t h a G - G - R cropping system. Incidence and severity were higher in the summer- autumn season, m a i n l y due to h i g h soil temperature and moisture content. Farmers approved of the resistance, duration, pod yield, and other traits of I C G 8666, 8645, However, there is a need to i m p r o v e the shelling percentage of these varieties. 4 0

49 T a b l e 2. B a c t e r i a l w i l t incidence a n d yield o f some selected g r o u n d n u t varieties, s u m m e r - a u t u m n a n d w i n t e r - s p r i n g / 9 6, i n T r a n g B a n g district, V i e t n a m BW inci- Shelling Strong 100-seed O i l content Pod yield (kg ha -1 ) Varieties dence (%) (%) seed (%) mass (g) (%) S- Autumn W-Spring I C G 8625 I C G I C G 8632 I C G 8645 I C G I C G 8662 I C G 8666 I C G Local control C V (%) L S D (0.05) T a b l e 3. Y i e l d o f g r o u n d n u t varieties I C G a n d I C G i n w i n t e r - s p r i n g / 9 8 (means of five locations) Sound 100-seed Pod yield Varieties Shelling (%) kernels (%) mass (g) (kg ha - 1 ) I C G 8666 ( V D - 9 ) I C G 8645 ( V D ) Local c o n t r o l C V (%) S E ( ± )

50 Suggestions Diseases such as pod rot and damping-off, in addition to B W, play very important roles in groundnut production in southern V i e t n a m. Therefore, integrated disease management ( I D M ) systems must be established. In order to f i n d valuable components for building I D M systems, support from I C R I S A T and other organizations w i l l be needed. 4 2

51 Technology Development for Disease Diagnosis and Control

52

53 Latent Infection of Burkholderia solanacearum in Groundnut and its Role in Resistance Enhancement Liao Boshou, Shan Zhihui, Li Dong, Lei Yong, and Tan Yujun 1 Abstract Bacterid wilt (BW) caused by B u r k h o l d e r i a solanacearum is an important disease of groundnut ( A r a c h i s hypogaea L.) in China, Indonesia, Vietnam, and some other countries. Sowing resistant groundnut cultivars is the most efficient and practical way to control the disease. Generally, success of breeding for resistance to BW of groundnut and other crops was judged by the percentage of surviving plants of newly bred lines relative to that of the susceptible line under inoculation and infection pressure. However, latent colonization of B. solanacearum without obvious uniting symptoms has recently become common in some resistant cultivars. Latent colonization could reduce root proliferation, tolerance to drought, and ultimately, pod yield of infected plants. Specific experiments involving artificial inoculation and enzyme-linked immunosorbent assays (ELISA) were conducted to investigate the characteristics of reaction to latent colonization and their variation among resistant groundnut genotypes. Frequencies of latent colonization varied among genotypes. Low latent colonization was detected in only a few resistant lines; these lines also possessed stable resistance to BW across seasons and locations. Genotypes with high latent colonization frequencies were more sensitive to drought stress in late growth stages, even when wilt incidence was low. Hypocotyl tissues supported the highest bacterial colonization frequency. Improved techniques to detect latent colonization and evaluate resistance have been developed. Latent infection is a new trait to be addressed in breeding for BW resistance. Introduction Bacterial w i l t ( B W ) caused by Burkholderia solanacearum (E.F. Smith) Yabuuchi et al. in groundnut (Arachis hypogaea L.) has been an important constraint to groundnut 1. O i l Crops Research Institute, Chinese Academy of Agricultural Sciences ( C A A S ), Wuhan , China. Liao Boshou, Shan Zhihui, Li Dong, Lei Yong, and Tan Yujun Latent infection of Burkholderia solanacearum in groundnut and its role in resistance enhancement. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C. L. L, eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 4 5

54 production in C h i n a, Indonesia, and V i e t n a m for decades and is becoming increasingly widespread in several other countries ( M e h a n et al. 1990, M e h a n and Liao 1994, Liao et al. 1994). In C h i n a, it is believed that in recent years, groundnut fields infected w i t h B. solanacearum have increased to over ha. T h e spread of BW has been caused by expansion in area of groundnut cultivation; use of susceptible cultivars in the new growing regions, and lack of rotation w i t h non-host crops (Liao et al. 1994). It has been w e l l proven that genetic improvement for host resistance is the most important component of any integrated control program for groundnut BW. T h e use of resistant cultivars is the most practical and feasible control method for farmers in many regions ( M e h a n and L i a o 1994). Thus, germplasm screening and breeding for resistance have been the research priorities for alleviating the disease in the past few decades. Even though w i l t incidence has been significantly reduced by sowing resistant cultivars, groundnut production and productivity i n diseased areas are still relatively low. Generally, resistant cultivars have l o w yield potentials and undesirable reactions to drought and other stresses. Latent infection of B. solanacearum w i t h o u t obvious w i l t i n g symptoms in resistant groundnut cultivars can reduce root proliferation, symbiotic nitrogen fixation, tolerance to drought, and yield (Liao et al. 1994). These effects appeared to be associated w i t h low p r o d u c t i v i t y of the crop in diseased areas. Several solanaceous species, such as tobacco, potato ( C i a m p i and Sequeria 1980, C i a m p i et al. 1980), and tomato (Prior et al. 1990), are also k n o w n to be latently infected by the pathogen w i t h o u t symptoms. However, in previous breeding programs, latent infection and its effects were seldom considered. Obviously, further breeding efforts should be made to overcome the latent i n f e c t i o n problem. In this paper, latent infection related to breeding for resistance to B. solanacearum in g r o u n d n u t is described, based on the available research results. Traditional Criteria for Testing Resistance to Bacterial Wilt T h e major objective of plant breeders has been to combine favorable agronomic characteristics w i t h acceptable resistance to abiotic and biotic stresses. Traditionally, w h e n evaluating resistance to BW in several crops infected by B. solanacearum, the p r o p o r t i o n of w i l t e d to n o n - w i l t e d plants has been the selection c r i t e r i o n, and all components of the interaction between plant, pathogen, and the e n v i r o n m e n t have been taken i n t o account (Prior et al. 1994). In previous breeding programs in C h i n a and other countries, resistance to BW in groundnut was defined o n l y as h i g h plant survival percentage under specified infection pressure ( M e h a n et al. 1990, Liao et al. 1994). W h e n the 4 6

55 survival percentage is over 80%, the genotype is said to be resistant; over 90%, it is h i g h l y resistant ( L i and T a n 1984, M e h a n et al 1990). T h i s d e f i n i t i o n appeared to be simple and practical in conventional breeding. T h e resistant cultivars were once considered pathogen-free based on the lack of visual occurrence o f w i l t. In terms of the interaction of plant and pathogen, resistance is defined as any measurable mechanism able to overcome completely or to l i m i t the development of a pathogen or its effects (Prior et al. 1994). This definition emphasized the positive c o n t r o l of a pathogen by plant metabolism. Tolerance is defined as the overall ability of a plant to withstand the development of a pathogen w i t h o u t major losses in yield (Prior et al. 1994). Accordingly, where infection or colonization of B. solanacearum in groundnut genotypes w i t h o u t w i l t i n g symptoms is concerned, the genotypes may be classified as resistant to, or tolerant of the disease. But if the yield losses or other undesirable influences on the symptomless plants are considered, the above definitions for resistance or tolerance must be modified. Visual occurrence of w i l t symptoms is n o t enough for evaluating resistance to BW. Influence of Latent Infection of B. solanacearum on Groundnut E v e n t h o u g h g r o u n d n u t plants w i t h h i g h s u r v i v a l percentage i n n a t u r a l l y diseased fields or a r t i f i c i a l i n o c u l a t i o n t r a d i t i o n a l l y were t h o u g h t to be free f r o m B. solanacearum, l a t e n t i n f e c t i o n by the p a t h o g e n has been f o u n d in some of these genotypes. L a t e n t infections of B. solanacearum are also k n o w n t o occur i n c u l t i v a r s o f potato ( C i a m p i a n d Sequeria 1980, B o w m a n a n d Sequeria 1982), t o m a t o ( P r i o r et a l. 1990), eggplant, and pepper ( P r i o r et a l. 1994) i n c l u d i n g some resistant genotypes. L a t e n t i n f e c t i o n was t h o u g h t to be a generalized a n d c o m m o n t r a i t of B. solanacearum pathogenesis ( P r i o r et a l. 1994). In repeated artificial inoculation experiments (Liao et al. 1997, unpublished data), groundnut seed emergence was reduced by % by soaking the seeds in a bacterial suspension. It was assumed t h a t the invasion of B. solanacearum i n t o groundnut seeds m i g h t encourage the infection of other bacteria or fungi in soil, even i f the w i l t pathogen could n o t k i l l the seeds directly. Liao et al. (1997) found reduced dry root mass, root volume, number of nodules, pod number plant - 1, and yield plant - 1 in resistant groundnut cultivars artificially inoculated w i t h bacteria, compared to noninoculated plants of the same cultivars grown under the same conditions. It is interesting to note that there is v a r i a t i o n among groundnut genotypes in their reaction to latent infection (Table 1). 4 7

56 T a b l e 1. Percentage reduction in root mass, r o o t v o l u m e, nodules, a n d yield per plant in g r o u n d n u t lines artificially inoculated by B. solanacearum a n d tested in C h i n a Genotype Root mass Root volume Nodules plant - 1 Pods plant - 1 Yield plant - 1 Xiekangqing Zao Taishan Zhenzhu Z H 212 Z H 112 Yueyou Luhua Yueyou 92 Taishan Sanlirou G u i y o u 28 E H u a 4 Gouliaozhong Jiangtainzhong Zhonghua Zhonghua In naturally diseased field plots, w i l t was noticed in resistant plants at the late g r o w t h stages, w h e n the plants were stressed by drought. In these w i l t e d plants, vascular bundles were discolored or destroyed due to infection and colonization by B. solanacearum. T h e latent infection in resistant cultivars was thought to reduce the absorption ability and drought tolerance in later g r o w t h stages. It was noteworthy that some of the released resistant cultivars yielded w e l l in fields free from B. solanacearum b u t yielded relatively poorly in infested fields even t h o u g h w i l t incidence was n o t h i g h. Latent infection m i g h t be a reason, along w i t h the poor soil fertility of the diseased fields. Latent infection should be considered in further efforts to breed for BW resistance. 4 8

57 Techniques for Detecting Latent Infection T o enumerate culturable populations o r t o t a l populations o f bacteria i n p l a n t tissues, new methods were developed. Counts of culturable bacteria were obtained after growing t h e m on a suitable medium. Additionally, serological methods were developed, p r o v i d i n g means for rapid detection and identification of bacteria. Research in this field has mainly been conducted to obtain race- or biovar-specific antibodies for use in the detection of B. solancearum f r o m soil or plant tissues, particularly i n detecting latent infection. In order to investigate latent colonization by B. solanacearum and its variation among different groundnut genotypes, a special project was started, supported by the Chinese N a t u r a l Science Foundation. Experiments consisting of artificial inoculation and enzyme-linked immunosorbent assays ( E L I S A ) were conducted to detect latent colonization in resistant groundnut genotypes. Polycolonal antibodies were produced by immunizing a female rabbit w i t h an isolate of B. soalancearum collected from the natural disease nursery in H o n g An ( Shan et al. 1997). Seeds of 30 resistant genotypes were artificially inoculated by soaking t h e m in a bacterial suspension for 30 minutes and then sowing them in sandy soil. At 50 to 60 days after sowing, inoculated plants of each genotype were sampled and cut i n t o root, hypocotyl, base stem, and midstem portions. These samples were t h e n tested by E L I S A. Frequencies of latent colonization varied among different resistant genotypes. A h i g h l y resistant line, , w h i c h had survival percentage of 100% for several seasons, showed a latent colonization frequency less t h a n 20%, while those in other resistant and susceptible genotypes ranged from 3 0 % to 8 0%. T h e resistant germplasm accessions Xiekangqing and Taishan Sanlirou, extensively used as breeding parents in C h i n a, possessed colonization frequencies of 35% and 46%, respectively, in this experiment. It was noteworthy that n o t a l l inoculated seeds were infected or colonized, even in susceptible lines. T h i s phenomenon needs further investigation. T h e tap-root tissues of tomato plants were highly colonized by B. solanacearum ( Prior et al. 1994), but in groundnut, tissues from the h y p o c o t y l had highest colonization frequency in seed inoculation tests. Infection of roots occurred in naturally diseased fields o n l y after emergence. T h e base stem of groundnut was colonized by the bacteria, but colonization of the midstem was detected in only a few samples. These results were similar to the results obtained after inoculation of different plant parts of tomato. However, in tomato, the proportion of invaded midstems w i t h o u t w i l t symptoms varied according to the degree of resistance, i.e., lines w i t h more resistance had lower levels of stem invasion (Prior et al. 1994). 4 9

58 Implication of Latent Infection in Groundnut Breeding Breeding for BW resistance and its application in managing the disease are l i k e l y to r e m a i n the major components of c o n t r o l strategies. In general, groundnut breeding for resistance to BW has progressed very slowly, especially w h e n attempts have been made to combine resistance w i t h h i g h yield p o t e n t i a l and resistance or tolerance to o t h e r stresses. T h i s slow progress m i g h t be related to lack of awareness in earlier breeding programs about the role of latent infection. Therefore, there is a need to modify germplasm evaluation methods and selection criteria in breeding for w i l t resistance to overcome the effects of latent infection. Disease incidence based o n visual w i l t i n g symptoms w i l l remain the basic c r i t e r i o n for evaluating resistance, particularly under field conditions. Plants colonized at low levels could be selected w i t h i n a p o p u l a t i o n of symptomless plants to o b t a i n more resistant cultivars. A c o m b i n a t i o n of w i l t incidence and colonization values could optimize breeding programs and result in selection of wider resistance w i t h greater adaptation to different environments (Prior et al. 1994). In groundnut, more t h a n 90 accessions belonging to different botanical types have been identified as resistant to BW worldwide (Liao et al. 1994). Resistance has also been found in w i l d species of Arachis (Yeh 1990) and interspecific hybrid derivatives (Zhang 1996, personal communication). Compared to several solanaceous crops such as potato, t o m a t o, and tobacco, sources of resistance to BW in g r o u n d n u t are m u c h more diverse. However, there is a need to screen these diverse sources of resistance to groundnut BW for latent infection by B. solanacearum isolates. In this direction, improved techniques for detecting latent colonization in groundnut tissues by E L I S A appear to be useful in BW resistance breeding programs. In preliminary investigations, groundnut genotypes w i t h h i g h latent colonization frequencies were more sensitive to terminal drought stress, even w h e n w i l t incidence was low. Hypocotyl tissue had the highest bacterial colonization frequency, and should be used for evaluating reaction of latent colonization in groundnut lines used in breeding for BW resistance. Acknowledgments T h i s research on latent infection of B. solanacearum in groundnut was supported by the C h i n a Natural Science Foundation ( N o ) and the International Crops Research Institute for the S e m i - A r i d Tropics ( I C R I S A T ). T h e above organizations are sincerely acknowledged. 5 0

59 References B o w m a n, J. E., a n d Sequeria, L Resistance t o Pseudomonas solanacearum i n p o t a t o : i n f e c t i v i t y t i t r t i o n s i n r e l a t i o n t o m u l t i p l i c a t i o n a n d spread o f t h e p a t h o g e n. A m e r i c a n P o t a t o J o u r n a l 5 9 : C i a m p i, L., a n d Sequeria, L M u l t i p l i c a t i o n o f Pseudomonas solanacearum i n resistant p o t a t o p l a n t s a n d t h e e s t a b l i s h m e n t o f l a t e n t i n f e c t i o n s. A m e r i c a n P o t a t o J o u r n a l 5 7 : C i a m p i, L., Sequeria, L., a n d F r e n c h, E. R L a t e n t i n f e c t i o n o f p o t a t o tubers by Pseudomonas solanacearum. A m e r i c a n P o t a t o J o u r n a l 57: L i, W. R., T a n, Y. J I n o c u l a t i o n t e c h n i q u e s f o r g r o u n d n u t b a c t e r i a l w i l t. O i l C r o p s o f C h i n a 2 : L i a o, B. S., D u a n, N. X., W a n g, Y. Y., S u n, D. R., a n d M e h a n, V. K H o s t - p l a n t r e s i s t a n c e t o g r o u n d n u t b a c t e r i a l w i l t : g e n e t i c d i v e r s i t y a n d e n h a n c e m e n t. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a P r a d e s h, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. L i a o, B. S., L i, D., S h a n, Z. H., T a n, Y. J., D u a n, N. X., a n d T a n g, G. Y I n f l u e n c e o f l a t e n t i n f e c t i o n o f Ralstonia solanacearum o n g r o u n d n u t. O i l C r o p s o f C h i n a 1 9 ( 4 ) : M e h a n, V. K., a n d L i a o, B. S G r o u n d n u t b a c t e r i a l w i l t : past, present, a n d f u t u r e. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g 4-5 J u l , O i l C r o p s Research I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s Research I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. M e h a n, V. K., N i g a m, S. N., and M c D o n a l d, D., M a n a g e m e n t o f b a c t e r i a l w i l t o f g r o u n d n u t u s i n g g e n e t i c resistance a n d c u l t u r a l practices. Pages in B a c t e r i a l w i l t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e Research P l a n n i n g M e e t i n g, M a r 1990, G e n t i n g H i g h l a n d s, M a l a y s i a. ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.) A C I A R Proceedings n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t e r f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. P r i o r, P., B e r a m i s, M., C h i l l e t, M., a n d S c h m i t, J P r e l i m i n a r y studies f o r t o m a t o b a c t e r i a l w i l t (Pseudomonas solanacearum E.F. Smith) resistance m e c h a n i s m s. S y m b i o s i s 9 :

60 P r i o r, P., G r i m a u l t, V., a n d S c h m i t. J Resistance t o b a c t e r i a l w i l t (Pseudomonas solanacearum) in t o m a t o : present status a n d prospects. Pages in B a c t e r i a l w i l t : t h e disease a n d its c a u s a t i v e agent, Pseudomonas solanacearum ( H a y w a r d, A. C., a n d H a r t m a n, G. L. eds.). W a l l i n g f o r d, U K : O x o n, C A B I n t e r n a t i o n a l. S h a n, Z. H., L i a o, B. S., T a n, Y. J., L i, D., L e i, Y., a n d S h e n, M. Z D e t e c t i o n t e c h n i q u e f o r l a t e n t i n f e c t i o n o f g r o u n d n u t b a c t e r i a l w i l t. O i l C r o p s o f C h i n a 1 9 ( 2 ) : Y e h, W. L., A r e v i e w o f b a c t e r i a l w i l t o n g r o u n d n u t i n G u a n g d o n g P r o v i n c e, People's R e p u b l i c o f C h i n a. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, M a r c h G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.). A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. 5 2

61 Pathological Aspects and Cultural and Biological Control of Groundnut Bacterial Wilt in Vietnam Nguyen Xuan Hong, Nguyen Thi Yen, and Vi Anh Tuan 1 Abstract In recent years, extensive research at the Vietnam Agricultural Sciences Institute has explained much about pathogenicity of Burkholderia solanacearum, which causes bacterial wilt (BW) of groundnut, and how to control the disease. Vietnamese isolates of B. solanacearum vary greatly in their ability to cause wilt, and groundnut genotypes also vary in their reaction to the pathogen. Rotation of groundnut with rice or sugarcane significandy reduces disease severity, but this type of rotation is not always feasible. Some Pseudomonas species and Bacillus subtilis have shown potential as biological control agents in seed treatment. More research on biological control is needed. Introduction G r o u n d n u t bacterial w i l t caused by Burkholderia solanacearum (E.F. Smith) Yabuuchi et al. is widespread in the major groundnut-production areas of V i e t n a m. T h e disease has become increasingly serious since it was first d o c u m e n t e d in 1991 ( M e h a n et al. 1991). In recent years, major research efforts in V i e t n a m have been focused on systematic surveys to assess economic importance, distribution, and severity of the disease in major groundnut growing areas and identification of sources of resistance among local and introduced germplasm breeding lines, and varieties. Several groundnut cultivars resistant to bacterial w i l t have been identified and widely tested for their possible release in near future. However, research on the pathogen and o t h e r management measures has made l i m i t e d progress. 1. Vietnam Agricultural Science Institute (VAS1), Van Dien, Thanh Tri, Hanoi, Vietnam. Nguyen Xuan Hong, Nguyen T h i Yen, and Vi Anh Tuan Pathological aspects and cultural and biological control of groundnut bacterial wilt in Vietnam. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 5 3

62 T h i s paper reports the preliminary results of research on pathology and cultural and biological c o n t r o l of groundnut BW conducted recently at V i e t n a m A g r i c u l t u r a l Science Institute ( V A S I ), H a n o i. R a c e s, B i o v a r s, a n d Pathogenecity of Burkholderia solanacearum In V i e t n a m, isolates of B. solanacearum from groundnut belong to biovars 3 and 4. A m o n g 25 isolates collected from different ecological areas of n o r t h e r n and central V i e t n a m, 14 belonged to biovar 3 and 11 belonged to biovar 4. Isolates of b o t h biovars were found in the same endemic region (Table 1). T a b l e 1. Races a n d biovars of selected Burkholderia solanacearum isolates i n V i e t n a m 1 Isolate Source Dulcitol Mannitol Sorbitol Maltosa Lactosa Cellobiosa Biovar Race H T - 1 H a T i n h + H T - 2 H a T i n h + H T - 3 H a T i n h + H L - 3 N g h e A n _ H L - 7 N g h e A n + X H - 3 Nghe A n + X H - 5 N g h e A n + H T R - 4 T h a n h H o a + Q O - 1 H a Tay + VY 10 Bac G i a n g + H B - 1 Bac G i a n g + A K H a Tay + B D - 1 B i n h D i n h B D - 2 B i n h D i n h + B D - 3 B i n h D i n h + B D - 4 B i n h D i n h = positive reaction; - = negative reaction Isolates of B. solanacearum from groundnut are h i g h l y v i r u l e n t on eggplant, potato, tomato, and sesame but less v i r u l e n t on tobacco (Table 2). A l l isolates grow w e l l on SPA m e d i u m at C and release b r o w n pigment in this m e d i u m. U n d e r greenhouse conditions at temperatures of C, they cause a hypersensitive reaction on tobacco leaves 18 to 24 after i n o c u l a t i o n by 5 4

63 i n j e c t i o n. I n j e c t i o n of leaf axils of young, susceptible groundnut plants w i t h a pathogen suspension (108 C F U m L - 1 / m L ) 3 weeks after sowing caused w i l t symptoms in 3 to 4 days. T a b l e 2. Reactions of six crop species to g r o u n d n u t isolates of Burkholderia solanacearum in V i e t n a m C r o p species Eggplant (Solarium melongena) Potato (Solanum tuberosum) Tomato (Lycopersicum esculentum) Sesame (Sesamum indicum) Tobacco (Nicotianna tabacum) Sweet potato (Ipomea batatas) Period of incubation (days) W i l t intensity (%) = Data not available Isolates of B. solanacearum from different areas of Vietnam vary widely in their pathogenicity. Isolates from hot spot locations, such as Ha Tinh and X u a n M a i are more virulent t h a n those from other provinces (Table 3). T a b l e 3. P a t h o g e n i c i t y of 6 isolates of Burkholderia solanacearum on selected g r o u n d n u t genotypes f o l l o w i n g seed inoculations, V i e t n a m A g r i c u l t u r a l Science I n s t i t u t e, W i l t intensity (%) 1 Genotype D A X M H T B D Q N T T H I C G V I C G I C G I C G G i e N h o Q u a n DA = Dong A n h (Hanoi), BD = Binh Dinh, XM = Xuan Mai (Ha Tay), QN = Quang N i n h, HT = Ha Tinh, T T H = Thua T h i e n (Hue) Some groundnut varieties, such as I C G 8666 (Schwarz 21) and G i e N h o Q u a n showed stable resistance to a l l isolates of B. solanacearum tested, whereas the 5 5

64 variety I C G V gave differential reactions to different isolates. On the same g r o u n d n u t variety and under the same conditions, one isolate of the pathogen can be more v i r u l e n t and cause higher w i l t intensity t h a n others. Research on the possible pathotypes of the B. solanacearum in V i e t n a m is in progress. Preliminary research conducted at V A S I has indicated that highly-virulent isolates of B. solanacearum f r o m g r o u n d n u t are more tolerant and can survive under stress conditions longer t h a n less-virulent isolates. Different methods of inoculation significantly affect w i l t severity in groundnut genotypes. In comparison to seed inoculation, stem inoculation caused m u c h more severe w i l t on the genotype I C G 5273 but less intense w i l t on I C G These data showed that different mechanisms of resistance to groundnut BW exist among test genotypes (Table 4). T a b l e 4. R e a c t i o n ( % w i l t e d plants) o f selected g r o u n d n u t cultivars t o stem a n d seed i n o c u l a t i o n w i t h a h i g h l y v i r u l e n t isolate ( H T ) o f Burkholderia solanacearum G r o u n d n u t cultivar I C G 8666 (Schwarz 21) I C G 5273 ( M a t j a n ) I C G 3704 Stem inoculation Seed inoculation Cultural Control Measures R o t a t i o n of groundnut w i t h rice has proved most effective in reducing the i n o c u l u m in soil and w i l t incidence ( H o n g et al. 1997). However, in upland and riverbed areas, groundnut is grown as a dryland crop. In these areas, groundnut cannot be rotated w i t h rice. Therefore, rotation of groundnut w i t h alternate nonhost crops w o u l d be an important means to contain the disease. Intercropping groundnut and nonhost crops also reduces w i l t incidence. In n o r t h e r n V i e t n a m, surveys in different dryland cropping systems on upland ( h i l l y ) and riverbed areas indicated that rotating or intercropping groundnut w i t h maize significantly reduced w i l t incidence. Sugarcane also was a good crop for r o t a t i o n w i t h groundnut. In some areas that are heavily infested w i t h the pathogen, r o t a t i o n of groundnut w i t h sugarcane for 3 years significantly reduced B W incidence. 5 6

65 Biological Control In recent years, scientists at V A S I have i n i t i a t e d experiments using antagonistic bacteria to c o n t r o l BW. O n e strain of Pseudomonas fluorescens ( N o. 4) and another strain of Pseudomonas sp. are h i g h l y effective in suppressing B W. These possible b i o c o n t r o l agents were used for seed treatment (Table 5). M o r e recently, preliminary research conducted in H a n o i Agricultural University ( H A U ) indicated that P. fluorescens and B. subtilis could significantly suppress B. solanacearum. Further research o n biological control o f B W w i l l be conducted at V A S I and H A U. T a b l e 5. Effect of seed t r e a t m e n t w i t h antagonistic bacteria on w i l t intensity o f g r o u n d n u t variety I C G , i n sick plots a t V i e t n a m A g r i c u l t u r a l Science I n s t i t u t e, Treatment N o seed treatment Seed treatment w i t h Pseudomonas fluorescens Seed treatment w i t h Pseudomonas sp (P. aeruginosa?) W i l t intensity (%) References H o n g, N. X., L i e u, N. V. a n d Y e n, N. T D i s t r i b u t i o n, s e v e r i t y o f g r o u n d n u t b a c t e r i a l w i l t a n d i d e n t i f i c a t i o n o f race a n d b i o v a r b e l o n g i n g o f Pseudomonas solanacearum isolates i n N o r t h e r n V i e t n a m. J o u r n a l o f P l a n t P r o t e c t i o n, N o. 6 ( i n V i e t n a m e s e w i t h s u m m a r y i n E n g l i s h ). M e h a n, V. K., H o n g, N. X., a n d L y, N. T O n t h e i d e n t i f i c a t i o n o f p a t h o g e n s c a u s i n g t h e s o c a l l e d g r o u n d n u t w i l t disease i n N o r t h V i e t n a m. I n I m p r o v e d c u l t i v a t i o n t e c h n o l o g i e s f o r g r o u n d n u t a n d o t h e r f o o d legumes i n V i e t n a m. M i n i s t r y o f A g r i c u l t u r e a n d F o o d I n d u s t r y V i e t n a m : H a n o i, V i e t n a m, A g r i c u l t u r a l P u b l i s h i n g H o u s e. ( i n V i e t n a m e s e w i t h s u m m a r y i n E n g l i s h ). 5 7

66 Integrated Disease Management with Special Reference to Bacterial Wilt of Groundnut S Pande, C Johansen, and J Narayana Rao 1 Abstract Groundnut is one of the most important oilseed crops in Asia, Africa, and the Americas. Because of the tremendous diversity of its uses, and of environments in which groundnut is cultivated, it is infected by over 100 plant pathogens. Bacterial wilt (BW), caused by B u r k h o l d e r i a s o l a n a c e a r u m, is a major constraint to groundnut production in China, Indonesia, Vietnam, Malaysia, and Uganda. Much progress has been made in understanding the epidemiology of races and biovars of B. s o l a n a c e a r u m that attack groundnut. Effective greenhouse and field screening techniques have been developed, resistance sources identified, and resistant cultivars developed. Integrated BW management in groundnut involves wilt-resistant cultivars, rotation with nonhost crops, and crop sanitation, but these practices are not yet sufficiently refined to be used by resource-poor farmers in South and Southeast Asia. Therefore, more on-farm participatory research by farmers is needed to devise appropriate packages of these strategies for BW endemic areas. Introduction T h e cultivated groundnut (Arachis hypogaea L.) is a self-pollinating annual herbaceous legume. It is a unique plant because it flowers above ground and produces pods containing one to five edible kernels below ground. It is g r o w n on over ha throughout the w o r l d. India, C h i n a, U S A, Sudan, Senegal, 1. International Crops Research Institute for the Semi-Arid Tropics ( ICRISAT), Patancheru , Andhra Pradesh, India. I C R I S A T Conference Paper no. CP Pande, S., Johansen, C., and Narayana Rao, J Integrated disease management w i t h special reference to bacterial wilt of groundnut. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, T h a n h T r i, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 5 8

67 Nigeria, and Indonesia are the seven largest producers of groundnut (Porter et al. 1984). It is a valuable source of protein for h u m a n and animal n u t r i t i o n, and provides a high-quality cooking o i l. T h e crop is important to the economies of farmers in several developing countries. Vietnam is one country where the crop is gaining importance and has become an essential component of cropping systems and the farm economy. C r o p management practices for groundnut vary f r o m labor-intensive practices w i t h few or no other inputs in some developing countries of A frica and Asia to almost total mechanization in the U S A. Accordingly, disease management practices vary widely. There may be m i n i m a l disease management, some use of chemicals, or total reliance on host plant resistance ( H P R ). M a d d e n (1987) defined integrated pest management as "a holistic, multidisciplinary management system t h a t integrates c o n t r o l methods on the basis of ecological and economic principles for pests t h a t coexist in an agroecosystem". T h i s n o t i o n certainly describes disease management w i t h i n groundnut production systems worldwide. C u l t u r a l practices, host p l a n t resistance, and fungicide usage are generally integrated i n t o management plans designed to minimize i n i t i a l levels of disease a n d obstruct disease progress. In this paper, specific examples of integrated management of BW are discussed. Emphasis has been placed on g r o u n d n u t p r o d u c t i o n systems in A s i a and current strategies for disease management in the principal groundnut countries in South and Southeast Asia. In addition, future needs are considered at the conclusion of the paper. Economic Losses Bacterial w i l t caused by Burkholderia solanacearum (E.F. Smith) Yabuuchi et al. is a major constraint to groundnut production over large areas of C h i n a, Indonesia, and V i e t n a m (Table 1). Yield losses are usually in the range of 10-40%, but losses can reach 100% w h e n h i g h l y susceptible cultivars are g r o w n in heavily infested fields. In C h i n a, it is estimated that the annual loss of groundnut pods from w i l t exceeds t. Severe losses are also reported i n parts o f Malaysia, Fiji, Papua N e w Guinea, and Uganda ( O p i o and Busolo-Bulafu 1990, M e h a n et al. 1994). Geographical Distribution T h e global d i s t r i b u t i o n o f groundnut B W i s given i n Table 2. I n C h i n a, the disease occurs in 16 groundnut-growing provinces, ranging from 1 9 N to 3 9 N. It is most severe in the southern and central provinces, where it is estimated that over ha of groundnut fields are infested w i t h the w i l t pathogen ( M e h a n e t a l 1994). 5 9

68 T a b l e 1. E s t i m a t e d a n n u a l g r o u n d n u t yield losses caused by bacterial w i l t i n A s i a 1 C o u n t r y C h i n a Indonesia Malaysia Philippines T h a i l a n d V i e t n a m Yield loss (%) ~30 > Reference Tan et al M a c h m u d and Rais 1994 L u m and H a m i d a h 1994 N a t u r a l 1994 Butranu et al H o n g et al Based on surveys of farmers' fields and research station data. I n Indonesia, the incidence and severity o f B W vary depending o n locations and seasons; the disease is most severe in West Java, South Sulawesi, and South Sumarta. It is also economically i m p o r t a n t in central and eastern Java, B a l i, and N o r t h Sulawesi. In V i e t n a m, the disease can be severe in at least six major groundnut-growing provinces. In Malaysia, BW is severe in Serdang and Kelantan areas and less severe in the Kedah area. Bacterial w i l t has been reported in Thailand, Sri Lanka, Papua N e w Guinea, and I n d i a (Hayward 1990) and in several A f r i c a n countries (Ethiopia, Libya, Madagascar, Mauritius, Somalia, South Africa, Uganda, and Zimbabwe), as well as in Australia, Taiwan, and Japan, (Table 2, M e h a n et al. 1986); however, i n f o r m a t i o n is sparse, and the present status of the disease in many of these countries is n o t k n o w n. T h e disease has been reported in the U S A (Gitaitis and H a m m o n s 1984), and it is an important constraint to groundnut production in central and northwestern regions of Uganda ( O p i o and Busolo-Bulafu 1990). Etiology and Biology T h e taxonomy, characteristics, natural and inoculated host range, and geographical distribution of the causal agent of B W, Burkholderia solanacearum, are reviewed by Bradbury (1986). Burkholderia solanacearum is an aerobic, n o n - fluorescent, non- spore- forming, rod-shaped, gram-negative bacterium, approximately 0.5 W 1.5 5m ( K e l m a n 1954, Hayward 1964). Key diagnostic features are its cultural characteristics on tetrazolium agar medium, where v i r u l e n t isolates, that are mainly non-flagellate and non-motile, f o r m irregularly round, fluidal, creamy w h i t e colonies w i t h l i g h t p i n k centers ( K e l m a n 1954). Extracellular slime formation is a c o m m o n attribute of all v i r u l e n t isolates of B. 6 0

69 T a b l e 2. G l o b a l d i s t r i b u t i o n a n d i m p o r t a n c e o f g r o u n d n u t bacterial w i l t 1 C o u n t r y Province/ Region Importance C h i n a 2 Indonesia V i e t n a m Malaysia India Liaoning, Shandong, Hubei, Jiangsu, A n h u i, H e n a n, Zhejiang, H u n a n, Sichuan, G u i z h o u H u b e i, Jiangxi, Fujiang, G u a n g x i, Guangdong, H a i n a n I r i a n Jaya, K a l i m a n t a n Java, Sumatra, Sulawasi, L o m b o k, Bali N o r t h e r n V i e t n a m : V i n h Phu Northern Vietnam: Bac Thai, Ha Bac, Ha Tinh, Thanh Hao, Nghe An (Nghe Tinh) Southern Vietnam: Long A n, Tay Ninh Kedah, I p o h K e l a n t a n, Terengganu, Selangor A n d h r a Pradesh, Meghalaya, T a m i l N a d u, Karnataka G r o w i n g importance: disease incidence < 2 0 % observed Important; disease incidence > 3 0 % observed Important; disease incidence % observed Very important; disease incidence > 3 0 % observed G r o w i n g importance; disease incidence < 1 0 % observed Important; disease incidence > 3 0 % observed G r o w i n g importance; disease incidence < 1 0 % observed Important; disease incidence > 3 0 % observed N o t considered important; but disease observed or reported 1. Groundnut bacterial wilt has also been reported in the Philippines, Thailand, Sri Lanka, and Papua New Guinea (Hayward, 1990). It has also been reported from Mauritius, Madagascar, Libya, Somalia, Ethiopia, Zimbabwe, South Africa, Swaziland, Taiwan, Japan and Australia (Mehan et al. 1986), and from Georgia and N o r t h Carolina in U S A (Gitaitis and Hammons 1984). It is an economically important disease in Uganda (Opio and Busolo-Bulafu 1990). 2. Based on information from provincial surveys. solanacearum. A v i r u l e n t isolates usually bear one to four polar flagella a n d are h i g h l y m o t i l e. T h e bacterium produces a b r o w n diffusible pigment on some media, including tyrosine. A c i d production from carbohydrates varies greatly between biovars and strains. O p t i m u m temperature for growth varies between 25 and 35 C. Further i n f o r m a t i o n is available in a recent review ( M e h a n et al. 1994). 6 1

70 Burkholderia solanacearum has a very wide natural host range w h i c h includes many crop plants and weeds that are found in groundnut production systems (Bradbury 1986). Susceptible legumes include phaseolus bean, lupins, pea, soyabean, faba bean, cowpea, Trifolium spp. and Styfosanthes spp. T h e species is h i g h l y heterogenous (Bradbury 1986). Isolates are classified i n t o five races based on host range (Buddenhagen and Kelman 1964, He et al. 1983), and into five biovars based on biochemical characteristics ( Hayward 1964, He et al. 1983). Races and biovars are informal groupings at the intraspecific level. A l t h o u g h the t w o systems of classification are largely independent, each system has contributed considerably to understanding the complex pathogenicity of B. solanacearum ( M e h a n et al. 1994). Race 1 isolates cause w i l t in groundnuts and in many other leguminous and solanaceous plants. Biovar 1 isolates cause w i l t of groundnut in the U S A ; biovar 3 and, to a lesser extent, biovar 4 isolates cause w i l t of groundnut in Asia and Africa (Hayward 1991). Biovars 2 and 5 have not been reported from groundnut. Serological techniques based on b o t h polyclonal and monoclonal antibodies have been developed for detection and identification of B. solanacearum (Alvarez et al. 1993, R o b i n s o n 1993). Molecular techniques are also being developed to enhance d e t e c t i o n of the bacterium and to better understand its considerable genetic diversity ( C o o k et al. 1989, Seal 1994). Burkholderia solanacearum-specific D N A sequences have been identified and oligonucleotide primers constructed for those regions that helped in detecting single cells of the bacterium in hosts by the polymerase chain reaction (PCR) (Seal 1994). A rapid identification test was also developed for distinguishing biovars 3, 4, and 5 based on restriction fragment length polymorphism D N A probes. Further work is focusing on development of an immunocapture PCR test for B. solanacearum. Bacterial w i l t is most important on groundnut in the warm, humid, and subhumid tropics, especially in South and Southeast Asia (Hayward 1991, M e h a n and Liao 1994). It has also caused sporadic damage in wetter areas of the semi-arid tropics. In general, isolates of B. solanacearum from groundnut are reported to be more virulent on groundnut than are isolates from other hosts (Mehan and Liao 1994); however, strains from groundnut differ gready in their pathogenicity on the host ( Tan et al. 1992). Further information is needed on the geographic distribution of races that infect groundnut before specific linkages w i t h environmental conditions can be made to explain why w i l t is severe in some zones but not in others. Symptoms and Disease Diagnosis W i l t symptoms can be observed 2 to 3 weeks after sowing. Very young seedlings may w i l t, but it is more c o m m o n for w i l t i n g to commence at flowering ( M e h a n et 6 2

71 al. 1994). Burkholderia solanacearum invades groundnut t h r o u g h wounds or t h r o u g h natural openings in roots. T h e bacteria enter the water- conducting tissues, multiply, and block the vessels to cause w i l t i n g of the plant. Infection of young plants results in rapid w i l t i n g of stems and foliage, but leaves remain green u n t i l final r o t t i n g occurs. W h e n older plants or cultivars that are n o t highly susceptible are infected, w i l t i n g proceeds more gradually, usually starting w i t h the lateral branches. Infected plants have discolored and rotted roots and sometimes r o t t e d pods. T h e diagnostic characteristics of this disease are dark b r o w n discoloration in the xylem and p i t h, and streaming of bacterial ooze from the cut ends of infected stems and roots w h e n these are immersed in water. Epidemiology T h e disease is soilborne, and its long- term survival is favored by continuous cropping of groundnut and other host plants and the presence of weed hosts ( M e h a n and Liao 1994). T h e bacterium is mainly disseminated through water and infested soil. Soil temperatures above 25 C together w i t h h i g h soil moisture favor the development of w i l t (Wang et al. 1983). W i l t peaks w h e n the soil temperature is over 3 0 C for 10 days (Tan and Liao 1990). Under continuously wet conditions, w i l t develops and spreads, but severe w i l t symptoms may not appear for some time. Infected plants w i l t rapidly if they are subjected to a dry period. A clear relationship between soil type and groundnut w i l t has n o t been established. In Indonesia, w i l t is predominantly a problem of heavy clay or loam soils ( M a c h m u d 1986), whereas in C h i n a w i l t is more c o m m o n in sandy soils ( H e 1990). W i l t is less prevalent in soils w i t h h i g h organic matter, and preliminary information suggests t h a t alkaline soils are wilt-suppressive ( Yeh 1990). M a c h m u d and M i d d l e t o n ( 1990) found seed transmission of 5 to 8% in freshly harvested seed, but this was greatly reduced by drying. Seed transmission is of obvious quarantine significance, and more research is needed to determine the extent of transmission ( M e h a n and Liao 1994). Disease Management T h e best approach to management of w i l t is to combine appropriate cultural c o n t r o l practices w i t h the sowing of resistant varieties. C r o p sanitation measures such as burning crop residues, removing weeds, and cleaning implements after c u l t i v a t i o n also help to reduce carry-over and spread of the disease. Adjustment of sowing date to avoid periods of h i g h temperature and soil moisture has had l i m i t e d success (Kelman 1953). Rotation w i t h immune or highly resistant crops, including 6 3

72 rice, maize, sugarcane, soyabean, and sorghum, is useful ( W a n g and H o u 1982, He 1990). C h e m i c a l control is n o t economically feasible. Varieties w i t h h i g h levels of resistance and good agronomic qualities have been bred in C h i n a and Indonesia (Liao et al. 1990, Yeh 1990, M a c h m u d 1993) and M e h a n et al. (1994) list 54 resistant genotypes. A d d i t i o n a l l y, several w i l d Arachis spp. are h i g h l y resistant ( Y e h 1990). Considerable progress has been made in the management of the BW o f groundnut. Agronomic and Cultural Management Crop rotation As groundnut BW is mainly soilborne, rotation of groundnut w i t h crops that are immune or highly resistant to B. solanacearum and w i t h nonhost crops such as rice, maize, soybean, and sugarcane, are effective measures. R o t a t i o n of groundnut w i t h rice or sugarcane for 2 to 3 years can greatly reduce w i l t incidence and severity ( W a n g and H o u 1982, He 1990, Tan and Liao 1990, M a c h m u d 1993). Groundnutrice rotation systems are successfully used in several regions of C h i n a (He 1990). Rotation w i t h wheat, sorghum, and cotton is also effective in reducing w i l t incidence. In rainfed uplands, r o t a t i o n of groundnut w i t h maize and sorghum or intercropping groundnut w i t h maize are useful ways to contain the disease. A l t h o u g h crop rotations for shorter periods w i t h immune crops have proved effective in c o n t a i n i n g the disease, leaving a gap of at least 3 to 4 years between groundnut crops is more effective, especially in soils that are heavily infested w i t h the pathogen. L o n g gaps are n o t practical where groundnut is important major crop (e.g., in V i e t n a m ). L i t t l e is k n o w n about h o w various cropping systems affect soil microorganisms in general or the survival of the w i l t pathogen in particular. Continuous c u l t i v a t i o n of highly resistant groundnut cultivars could either reduce or m a i n t a i n the B. solanacearum population, or it could select for more v i r u l e n t strains. Flooding a n d fallowing Flooding groundnut fields for 15 to 30 days before sowing also reduces w i l t incidence ( L i et al. 1981, He 1990). In areas where groundnut is g r o w n under irrigation in the dry season, it should be possible to control or greatly reduce disease levels by dry season fallowing, because the bacterium is h i g h l y susceptible to desiccation. T h e effects of fallowing can be enhanced by c u l t i v a t i o n to improve soil drying and reduce weed growth. Improved soil drainage helps in reducing w i l t incidence and severity. 6 4

73 Sowing date Depending upon the length of the growing season and cultivars grown, the sowing date can be adjusted to a v o i d periods of h i g h temperature or ample soil moisture conditions that favour bacterial infection and disease development. A few attempts have been made to m i n i m i z e crop losses by altering sowing dates, but these have had l i m i t e d success ( K e l m a n 1953). In the H u b e i Province of C h i n a, early sowing in m i d - A p r i l results in m u c h lower incidence and severity of BW t h a n does sowing in June ( M e h a n et al. 1994). Crop sanitation C r o p sanitation (e.g., burning crop residues, removing weeds, and cleaning farm tools after operations in infested fields) should h e l p reduce disease levels. Experimental evidence on the effects of crop sanitation is n o t available. Soil amendments by fertilizers and manures Soil application of urea, mineral ash, and organic manure can be useful in reducing w i l t incidence (Chang and Hsu 1988, Yeh 1990). These fertilizers are likely to stimulate soil microbial activity against the w i l t pathogen, and some of their components may enhance host resistance. M o r e research is required to elucidate the mechanisms by w h i c h soil amendments control w i l t, specifically from other groundnut-producing countries of South and Southeast Asia. Chemical soil treatment Soil treatment w i t h sulfur, lime, and other chemicals, including fungicides and antibiotics, has n o t proved useful in controlling groundnut BW A p p l y i n g 300 kg ha" 1 of chloropicrin 10 days before sowing can effectively control the disease ( W a n g and H o u 1982), but this treatment is expensive. S e e d T r a n s m i s s i o n a n d P l a n t Q u a r a n t i n e T h e bacterium, B. solanacearum is transmitted through infected groundnut seed ( M a c h m u d and M i d d l e t o n 1990). Seed transmission is reported to be at the rate of 58%, particularly in freshly harvested seed. Thus, infected seed is l i k e l y to provide a primary source of i n o c u l u m, particularly for disease-free areas. There is rapid loss of viability of the bacterium as groundnut seeds dry out to a moisture content below 9% ( Zhang et al. 1993). Seed transmission is of obvious quarantine significance, and more research is needed to determine the degree to w h i c h B. solanacearum can be seed-transmitted in groundnut. 6 5

74 Management Using Biological Agents Biological control of B. solanacearum has been extensively investigated and found p r o m i s i n g under laboratory and greenhouse conditions. However, most biological c o n t r o l agents used to control B W, including several antagonistic Pseudomonas (P. cepacia, P. fluroresoens, P. glumae, and Bacillus spp.), have n o t proved h i g h l y effective against B. solanacearum in the field ( Trigalet et al. 1994). Of considerable interest is the more recent work i n v o l v i n g some genetically engineered hrp a v i r u l e n t mutants of B. solanacearum ( Trigalet and Trigalet- Demery 1990). It w o u l d be useful to develop such biocontrol agents into effective commercial products for seed treatment. However, it may take a l o n g t i m e before approaches to biological control reach the stage of commercial application. Host-Plant Resistance S o w i n g disease resistant cultivars is the cheapest and most effective m e t h o d by w h i c h to combat BW of groundnut. M u c h progress has been made in developing screening techniques, identifying stable sources of resistance and breeding resistant cultivars ( M e h a n et al. 1994). W o r l d w i d e, some 90 germplasm accessions and improved cultivars of groundnut have been reported resistant to B W. M o s t of these resistant genotypes are f r o m C h i n a and Indonesia ( M e h a n et al. 1994). Resistant lines have also originated in or been collected from Argentina, Brazil, India, Israel, Peru, Uganda, and U S A ( M a c h m u d 1993). Most of the screening efforts have been made in C h i n a and Indonesia, where more t h a n 6000 germplasm accessions have been tested. A m o n g the available resistant genotypes, 31 belong to the Spanish type ( var vulgaris) including more t h a n 20 improved cultivars bred in C h i n a and Indonesia. A few Valencia (var. fastigiata) lines resistant to foliar diseases have also been found resistant to BW in C h i n a and Indonesia (Yeh 1990, M e h a n and Liao 1994). Resistance to BW in these genotypes (e.g., N C A c and PI ) m i g h t be less stable t h a n t h a t in the resistant Spanish lines. Recently, these Valencia lines showed varying levels of resistance at different locations in C h i n a. O n l y three resistant genotypes belong to the Virginia type (var hypogaea), and they are important in breeding programs ( D u a n et al. 1993). In recent years, 50 "Chinese dragon" type genotypes have been identified as resistant to BW ( D u a n et al. 1993). A l l of the resistant dragon lines were collected f r o m heavily infested locations i n southern C h i n a. N o resistant material o f this type has been obtained from the n o r t h e r n provinces. T h e dragon lines are landraces that have long been cultivated in C h i n a (Sun et al. 1963); 66

75 arachaeological evidence indicates that they had been c u l t i v a t e d for at least 500 years before the Virginia type groundnuts were introduced toward the end of the 19 th Century. As resistant genotypes are far more c o m m o n in the dragon type than in the other three botanical types, there may have been selection for resistance d o w n through the centuries in w h i c h BW has been a serious problem in southern C h i n a. T h e characterization of some 200 dragon genotypes indicates considerable variation in many characters. Genetic diversity for resistance among dragon lines merits further investigation. Screening on a l i m i t e d scale has led to the identification of some resistant accessions of w i l d Arachis species. Resistance has also been found in some interspecific h y b r i d derivatives t h a t also have resistance to foliar fungal diseases ( M e h a n and Liao 1994). Efforts to breed groundnuts w i t h resistance to BW have been concentrated mainly in Indonesia and China. In Indonesia, Schwarz 21 and its derivatives (Gajah and Kidang) have been extensively used as resistance donors in breeding programs since the early 1950s. In China, two wilt-resistant lines w i t h good general combining ability, Xiekangqing and Taishan Sanlirou, have been used as resistance donors (Liao et al. 1990). As most resistance donors used in breeding programs belong to ssp. fastigiata, the genetic base of w i l t resistance is narrow. In Indonesia, t w o wilt-resistant cultivars, Schwarz 2 1, released in 1925, and G a j a h released in 1952, are widely g r o w n in Java where BW previously caused heavy y i e l d losses in susceptible cultivars. In the 1950s, three wilt- resistant cultivars (Kidang, Banteng, and Macan) were developed from crosses between Schwarz 21 and some introductions from Japan, Israel, and U S A. Wilt-resistant cultivars such as A n o a, Rusa, Pelanduk, Tupai, and Tapir, released in 1982/83, were developed from crosses between Gajah or Kidang and introductions from Honduras and U S A. Some of these cultivars (e.g., Pelanduk and Tupai) are n o w grown by farmers in Indonesia ( M a c h m u d 1993). In C h i n a, breeding efforts in the 1960s led to the release of t w o moderately resistant cultivars, Yue You 589 and Sueitien. Later, an exotic resistance source was crossed w i t h a local cultivar, and two important resistant and high-yielding cultivars, Yue You 92 and Yue You 256, were bred in Guangdong (Liao et al. 1990). In the last decade, several high-yielding, wilt-resistant cultivars were released to farmers. These include Jinyou , G u i y o u 28, Lutlua 3, El hua 5, and Z h o n g H u a 2 (Liao et al. 1990). El H u a 5 is currently grown on some ha in most of the wilt-affected areas in central C h i n a. Zhong H u a 2, an early maturing, wilt-resistant cultivar w i t h wide adaptation, is becoming popular w i t h farmers in 6 7

76 central C h i n a. A new wilt-resistant breeding line, Yue You 200, w i t h h i g h yield potential, is n o w at the demonstration stage and w i l l be released soon i n Guangdong Province, C h i n a (Zhang et al. 1994). Some recently bred cultivars that have multiple resistances to w i l t and rust have also been developed in C h i n a. M o r e t h a n half of the global groundnut germplasm collection has still to be screened for resistance to B W, and new sources of resistance could s t i l l be identified. Special emphasis should be placed on c o m b i n i n g w i l t resistance w i t h h i g h yield potential and resistance to foliar fungal diseases. Integrated Disease Management In general an integrated approach to BW control should involve wilt-resistant groundnut cultivars, rotation w i t h non-host crops, and crop sanitation. R o t a t i o n of groundnut w i t h rice in lowland areas or in upland areas equipped w i t h an irrigation system, or rotation w i t h a non-host coupled w i t h the use of resistant groundnut cultivars and the use of herbicides in irrigated areas, are important and effective means of reducing disease incidence in infested soils. It is n o t possible to adopt crop rotations in u p l a n d and marginal lands where groundnuts are g r o w n under rainfed conditions. In such areas, use of resistant cultivars and seed f r o m disease-free areas is advocated. However, more on-farm research is needed to devise appropriate packages of these strategies for BW-endemic areas. Future Research Needs A l t h o u g h BW has been extensively studied worldwide for several decades, efficient a n d complete c o n t r o l measures are n o t yet available to resource-poor farmers in A s i a or elsewhere. Substantial progress has been made in the development and release of resistant cultivars, b u t resistant varieties alone have n o t solved the problem completely. It is expected that highly resistant and h i g h - yielding cultivars endowed w i t h other desirable characteristics w i l l be made available to farmers in the near future, specifically in regions where the disease is a major constraint to crop production. H i g h priority should be given to participatory on-farm validation of the components of disease management and their integration. Extension programs that include supplying seed of newly developed resistant cultivars to farmers should be mandatory for any research and development program. To enhance a n d diversify genetic resistance to B W, it is imperative to assemble various germplasm accessions a n d varieties w i t h putative resistance in countries where the disease is endemic. Sources of resistance f r o m different b o t a n i c a l accessions w i l l be useful i n increasing the diversity and stability o f resistance. 6 8

77 There is a need to establish an International G r o u n d n u t Bacterial W i l t Nursery ( I G B W N ) to determine the stability of w i l t resistance through multilocational testing. Concerted efforts are also needed to foster the exchange of wilt-resistant germplasm and breeding lines. Priority should also be given to testing resistant lines, i n c l u d i n g possible differentials, for their reaction to various groundnut-adapted strains of pathotypes of the w i l t pathogen from different regions of the world. C r o p rotations w i t h non- host crops are often n o t acceptable to farmers, especially if such rotations are prolonged, and this highlights the need for complementary c o n t r o l measures. Therefore more research is needed to devise appropriate integrated packages i n v o l v i n g H P R, crop rotation, sanitation, and agronomical soil amendments specifically for local disease-endemic areas. It is likely that control methods i n v o l v i n g biological agents w i l l need local adaptations in the future. T h i s prospect offers a new research avenue. T h e r e is a need to increase and strengthen the collaboration in research on bacterial w i l t through the G r o u n d n u t Bacterial W i l t W o r k i n g Group. It is expected that this collaboration w i l l provide solutions to l o c a t i o n- and regionspecific problems and w i l l contribute to improved disease control. References A l v a r e z, A. M., Berestecky, J., Stiles, J. I., F e r r e i r a, S. A., a n d B e n e d i c t, A. A S e r o l o g i c a l a n d m o l e c u l a r approaches t o i d e n t i f i c a t i o n o f Pseudomonas solanacearum strains f r o m Helicona. Pages in B a c t e r i a l w i l t : p r o c e e d i n g s o f a n I n t e r n a t i o n a l C o n f e r e n c e, O c t , K a o h s i u n g, T a i w a n ( H a r t m a n, G. L. a n d H a y w a r d, A. C., eds.). A C I A R Proceedings n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. B r a d b u r y, J. F G u i d e t o p l a n t p a t h o g e n i c b a c t e r i a. K e w, U K : C A B I n t e r n a t i o n a l M y c o l o g i c a l I n s t i t u t e p p. B u d d e n h a g e n, I. W a n d K e l m a n, A B i o l o g i c a l a n d p h y s i o l o g i c a l aspects o f b a c t e r i a l w i l t caused b y Pseudomonas solanacearum. A n n u a l R e v i e w o f P h y t o p a t h o l o g y 2 : B u t r a n u, W., Y i n a s a w a p u n, S., a n d S r i t h o n g c h a i, W Status o f g r o u n d n u t b a c t e r i a l w i l t research i n T h a i l a n d. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. 6 9

78 C h a n g, M. L., a n d H s u, S. T S u p p r e s s i o n o f b a c t e r i a l w i l t o f t o m a t o b y s o i l a m e n d m e n t s. P l a n t P r o t e c t i o n B u l l e t i n 3 0 : C o o k, D., B a r l o w, E., a n d Sequeira, L G e n e t i c d i v e r s i t y o f Pseudomonas solanacearum: d e t e c t i o n o f r e s t r i c t i o n f r a g m e n t l e n g t h p o l y m o r p h i s m w i t h D N A probes t h a t specify v i r u l e n c e a n d t h e h y p e r s e n s i t i v e response. M o l e c u l a r P l a n t - M i c r o b e I n t e r a c t i o n s 2 : D u a n, N., T a n, Y., Jiang, H., a n d H u D u a n h o n g S c r e e n i n g g r o u n d n u t g e r m p l a s m f o r resistance t o b a c t e r i a l w i l t. O i l C r o p s o f C h i n a 1 : G i t a i t i s, R. D., a n d H a m m o n s, R. O B a c t e r i a l w i l t. Pages in C o m p e n d i u m o f p e a n u t diseases (Porter, D. M., S m i t h, D. H., a n d R o d r i g u e z - K a b a n a, R., eds.). St. Paul, M i n n e s o t a, U S A : A m e r i c a n P h y t o p a t h o l o g i c a l Society. H a y w a r d, A. C C h a r a c t e r i s t i c s o f Pseudomonas solanacearum. J o u r n a l o f A p p l i e d B a c t e r i o l o g y 2 7 : H a y w a r d, A. C D i a g n o s i s, d i s t r i b u t i o n a n d status o f g r o u n d n u t b a c t e r i a l w i l t. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : Proceedings o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, M a r c h , G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C, eds.). A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. H a y w a r d, A. C B i o l o g y a n d e p i d e m i o l o g y o f b a c t e r i a l w i l t caused b y Pseudomonas solanacearum. A n n u a l R e v i e w o f P h y t o p a t h o l o g y 2 9 : H e, L. Y., S e q u e i r a, L., a n d K e l m a n, A C h a r a c t e r i s t i c s o f strains o f Pseudomonas solanacearum f r o m C h i n a. P l a n t Disease 6 7 : H e, L. Y C o n t r o l o f b a c t e r i a l w i l t o f g r o u n d n u t i n C h i n a w i t h e m p h a s i s o n c u l t u r a l a n d b i o l o g i c a l m e t h o d s. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : P r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g M a r c h G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C, eds.). A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. H o n g, N. X., M e h a n, V. K., L y, N. T., a n d V i n h, M. T S t a t u s o f g r o u n d n u t b a c t e r i a l w i l t research i n V i e t n a m. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l y , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.) P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. 7 0

79 K e l m a n, A T h e b a c t e r i a l w i l t caused b y Pseudomonas solanacearum. T e c h n i c a l B u l l e t i n N o N o r t h C a r o l i n a, U S A : N o r t h C a r o l i n a A g r i c u l t u r a l E x p e r i m e n t a l S t a t i o n. K e l m a n, A T h e r e l a t i o n s h i p o f p a t h o g e n i c i t y i n Pseudomonas solanacearum t o c o l o n y appearance o n a t e t r a z o l i u m m e d i u m. P h y t o p a t h o l o g y 4 4 : L i, W. R., C h e n, C. R., a n d X u, Z. Y Studies o n b a c t e r i a l w i l t o f p e a n u t. I I. I n v e s t i g a t i o n o f disease e p i d e m i o l o g y i n east H u b e i. O i l C r o p s o f C h i n a 1 : L i a o, B. S., W a n g, Y. Y., X i a, X. M., T a n g, G. Y., T a n, Y. J., and S u n, D. R G e n e t i c a n d b r e e d i n g aspects o f resistance t o b a c t e r i a l w i l t i n g r o u n d n u t. Pages i n B a c t e r i a l w i l t o f g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, M a r G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.). A C I A R Proceedings n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e for I n t e r n a t i o n a l A g r i c u l t u r a l Research. L u m, K. Y., and H a m i d a h, S Status o f g r o u n d n u t bacterial w i l t research i n M a l a y s i a. Pages in G r o u n d n u t bacterial w i l t i n A s i a : proceedings o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 July 1994, O i l C r o p s Research I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.) Patancheru , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s Research I n s t i t u t e for t h e S e m i - A r i d Tropics. M a c h m u d, M B a c t e r i a l w i l t i n I n d o n e s i a. Pages in B a c t e r i a l w i l t disease i n A s i a a n d t h e S o u t h Pacific: p r o c e e d i n g s o f t h e I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, P C A R R D, Los Banos, P h i l i p p i n e s, O c t , (Persley, G.J., ed.) A C I A R Proceedings n o. 13. C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e for I n t e r n a t i o n a l A g r i c u l t u r a l Research. M a c h m u d, M Present status o f g r o u n d n u t b a c t r i a l w i l t research i n I n d o n e s i a. Pages in G r o u n d n u t b a c t e r i a l w i l t : p r o c e e d i n g s o f t h e S e c o n d W o r k i n g G r o u p M e e t i n g, 2 N o v e m b e r , A s i a n V e g e t a b l e R e s e a r c h a n d D e v e l o p m e n t C e n t r e, ( A V R D C ), T a i n a n, T a i w a n ( M e h a n, V. K., a n d H a y w a r d, A. C., eds.). T a i n a n, T a i w a n : A V R D C a n d P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. M a c h m u d, M., a n d M i d d l e t o n, K. J Seed i n f e c t i o n a n d t r a n s m i s s i o n o f Pseudomonas solanacearum on g r o u n d n u t. Page 57 in B a c t e r i a l w i l t of g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g M a r G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.). A C I A R Proceedings n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. 7 1

80 M a c h m u d, M., a n d R a i s, S. A Status o f g r o u n d n u t b a c t e r i a l w i l t research i n I n d o n e s i a. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : proceedings o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l 1994, O i l C r o p s Research I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s Research I n s t i t u t e for t h e S e m i - A r i d T r o p i c s. M a d d e n, L. V Pests a s p a r t o f t h e ecosystem. Pages 3-4 i n Pesticides: m i n i m i z i n g t h e risks (Ragsdale, N a n c y N. a n d K u h r, R.J., eds.). O h i o, U S A : A m e r i c a n C h e m i c a l S o c i e t y S y m p o s i u m Series M e h a n, V. K., a n d L i a o, B. S G r o u n d n u t b a c t e r i a l w i l t : past, p r e s e n t a n d f u t u r e. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. M e h a n, V. K., M c D o n a l d, D., a n d S u b r a h m a n y a m, P B a c t e r i a l w i l t o f g r o u n d n u t. C o n t r o l w i t h emphasis o n h o s t - p l a n t resistance. Pages i n B a c t e r i a l w i l t diseases i n A s i a a n d t h e S o u t h Pacific: p r o c e e d i n g s o f t h e I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, P C A R R D, L o s Banos, P h i l i p p i n e s, O c t 1985 (Persley, G.J., e d. ). A C I A R P r o c e e d i n g s n o. 13. C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l R e s e a r c h. M e h a n, V. K., L i a o, B. S., T a n, Y. J., R o b i n s o n - S m i t h, A., M c D o n a l d, D., a n d H a y w a r d, A. C B a c t e r i a l w i l t o f g r o u n d n u t. I n f o r m a t i o n B u l l e t i n N o P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. 2 8 pages. N a t u r a l, M. P Status o f g r o u n d n u t b a c t e r i a l w i l t research i n t h e P h i l i p p i n e s. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : proceedings o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l 1994, O i l C r o p s Research I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.) P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s Research I n s t i t u t e for t h e S e m i - A r i d T r o p i c s. O p i o, A. F., a n d B u s o l o - B u l a f u, C. M Status o f b a c t e r i a l w i l t o n g r o u n d n u t i n U g a n d a. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, M a r , G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C. eds.) A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l R e s e a r c h. P o r t e r, D. M., S m i t h, D. H., a n d R o d r i g u e z - K a b a n a, R. (eds.) C o m p e n d i u m o f p e a n u t diseases. S t. P a u l, M i n n e s o t a, U S A : A m e r i c a n P h y t o p a t h o l o g i c a l S o c i e t y. 73 pages. 7 2

81 R o b i n s o n - S m i t h, A S e r o l o g i c a l d e t e c t i o n o f Pseudomonas solanacearum b y E L I S A. Pages in B a c t e r i a l w i l t : p r o c e e d i n g s o f a n I n t e r n a t i o n a l C o n f e r e n c e, O c t o b e r , K a o h s i u n g, T a i w a n ( H a r t m a n, G. L., a n d H a y w a r d, A. C., eds.) A C I A R Proceedings n o C a n b e r r a, A u s t r a l i a, A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. Seal, S D N A - b a s e d d i a g n o s t i c t e c h n i q u e f o r Pseudomonas solanacearum w i t h e m p h a s i s o n b i o v a r s 3 a n d 4. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. S u n, D. R., W a n g, Y. Y., L i u, Y. Q., W a n, W. Z., a n d Z h a n g, C. X C l a s s i f i c a t i o n o f c u l t i v a t e d g r o u n d n u t s i n C h i n a. A n n u a l R e s e a r c h R e p o r t, W u h a n, C h i n a : O i l C r o p s Research I n s t i t u t e. T a n, Y. L., and L i a o, B. S G e n e r a l aspects o f g r o u n d n u t bacterial w i l t i n C h i n a. Pages in Bacterial w i l t o f g r o u n d n u t : proceedings o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e Research P l a n n i n g M e e t i n g, M a r 1990, G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K.J., a n d H a y w a r d, A. C., eds.). A C I A R Proceedings N o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e for I n t e r n a t i o n a l A g r i c u l t u r a l Research. T a n, Y. L., D u a n, L. X., L i a o, B. S., L i, W. R., a n d X u, Z. Y R e s e a r c h o n g r o u n d n u t b a c t e r i a l w i l t. Page i n G r o u n d n u t a g l o b a l p e r s p e c t i v e : p r o c e e d i n g s o f a n I n t e r n a t i o n a l W o r k s h o p, N o v , I C R I S A T ( N i g a m, S. N. e d. ). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. T a n, Y. L., D u a n, N. X., L i a o, B. S., X u, Z. Y., H e, L. Y., a n d Z h e n g, G. R Status o f g r o u n d n u t b a c t e r i a l w i l t research i n C h i n a. Pages in G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. T r i g a l e t, A., a n d T r i g a l e t - D e m e r y, D U s e o f a v i r u l e n t m u t a n t s o f Pseudomonas solanacearum f o r b i o l o g i c a l c o n t r o l o f b a c t e r i a l w i l t o f t o m a t o p l a n t s. P h y s i o l o g i c a l a n d M o e l c u l a r P l a n t P a t h o l o g y 3 6 : T r i g a l e t, A., F r e y, P., a n d T r i g a l e t - D e m e r y, D B i o l o g i c a l c o n t r o l o f b a c t e r i a l w i l t caused b y Pseudomonas solanacearum: state o f t h e a r t a n d u n d e r s t a n d i n g. Pages in B a c t e r i a l w i l t : t h e disease a n d its causative a g e n t 7 3

82 Pseudomonas solanacearum ( H a y w a r d, A. C., a n d H a r t m a n, G. L., eds.) W a i l i n g f o r d, O x o n, U K : C A B I n t e r n a t i o n a l. W a n g, J.S., a n d H o u, X. Y A s t u d y o n c o n t r o l o f b a c t e r i a l w i l t o f p e a n u t. A g r i c u l t u r a l S c i e n c e a n d T e c h n o l o g y i n L i n g y i. 1 : W a n g, J.S., H o u, X. Y., a n d H u, B. J S t u d i e s o n t h e c o n t r o l o f b a c t e r i a l w i l t o f p e a n u t. A c t a P h y t o p h y l a c t i c a S i n i c a 1 0 : Y e h, W. L A r e v i e w o f b a c t e r i a l w i l t o n g r o u n d n u t i n G u a n g d o n g P r o v i n c e, Peoples' R e p u b l i c o f C h i n a. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, M a r , G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.). A C I A R Proceedings n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. Z h a n g, Y. X., H u a, J. Y., a n d H e, L. Y Effect o f i n f e c t e d g r o u n d n u t seeds o n t r a n s m i s s i o n o f Pseudomonas solanacearum. B a c t e r i a l W i l t N e w s l e t t e r 9 : Z h a n g, G. R., L i, X. Y., Y e h, W. L., L i a n g, X. Q., a n d L i, Y. H R e s e a r c h o n g r o u n d n u t b a c t e r i a l w i l t i n G u a n g d o n g P r o v i n c e, C h i n a. Page 103 i n G r o u n d n u t b a c t e r i a l w i l t i n A s i a : p r o c e e d i n g s o f t h e T h i r d W o r k i n g G r o u p M e e t i n g, 4-5 J u l , O i l C r o p s R e s e a r c h I n s t i t u t e, W u h a n, C h i n a ( M e h a n, V. K., a n d M c D o n a l d, D., eds.). P a t a n c h e r u , A n d h r a Pradesh, I n d i a : I n t e r n a t i o n a l C r o p s R e s e a r c h I n s t i t u t e f o r t h e S e m i - A r i d T r o p i c s. 7 4

83 Germplasm Screening and Breeding for Resistance to Bacterial Wilt in China Liao Boshou 1, Duan Naixiong, Jiang Huifang 1, Liang Xuanqiang 2, and Gao Guoqing 3 Abstract Bacterial wilt (BW) caused by Burkholderia solanacearum is an important constraint on groundnut production on > ha in China. This is about 8% of the total groundnut area sown each year. Wilt incidence and yield loss are estimated to be 10-30% in susceptible groundnut cultivars. It is well known that genetic resistance is the most important component of integrated management of groundnut BW. Therefore, between 1974 and 1978, about 1700 germplasm accessions were screened at hot spot locations in China. Two lines, Xiekangqing and Taishan Sanlirou, were identified as highly resistant to BW. Since then, these lines have been extensively used in breeding for BW resistance. In addition to these lines, during , over 3000 germplasm accessions were also screened and over 50 dragon type lines and 3 Virginia lines were identified as resistant. Furthermore, of the 1100 local groundnut germplasm screened during , 13 lines were identified as resistant. These resistant genotypes ( ~ 70 including checks) were tested across locations in China, and resistance in most of these genotypes was stable. Seventy-eight wild A r a c h i s accessions were also evaluated under natural infection conditions, and 24 showed good levels of resistance to BW. Twelve resistant genotypes were also identified from the lines received from I C R I S A T d u r i n g Fifteen resistant lines were transferred from China to I C R I S A T in Several new breeding lines, including Yue You 200, Yue You 79, and , have been developed. A few resistant lines were also selected from an interspecific hybrid (Baisha x W A r a c h i s chacoense) at Henan Academy of Agricultural Sciences. Efforts to enhance resistance by genetic transformation are in progress. Further research efforts will be made for enhancing yield potential, resistance to other wilt pathogens, and drought tolerance of BW-resistant groundnut cultivars. 1. O i l Crops Research Institute, Chinese Academy of Agricultural Sciences ( C A A S ), Wuhan , China. 2. Crops Research Institute, Guangdong Academy of Agricultural Sciences ( G A A S ), Guangzhou , China. 3. Industrial Crops Research Institute, Guangxi Academy of Agricultural Sciences ( G A A S ), Nanning , China. Liao Boshou, Duan Naixiong, Jiang Huifang, Liang Xuanqiang, and Gao Guoqing Germplasm screening and breeding for resistance to bacterial wilt in China. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 7 5

84 Introduction G r o u n d n u t is an important o i l and cash crop in C h i n a. In the mid-1990s, groundnut was annually harvested from an area of about 3.8 m i l l i o n ha, w i t h production of around 9 to 10 m i l l i o n tons. Bacterial w i l t caused by Burkholderia solanacearum (E.F. Smith) Yabuuchi et al. has been an i m p o r t a n t constraint to groundnut production in C h i n a for decades. In recent years, the disease has spread to more t h a n ha, nearly 8% of the annually sown area of groundnut in the country. Incidence is about % in susceptible cultivars and less t h a n 10% in resistant cultivars currently grown in the major groundnut-growing regions of C h i n a. In the past three decades, extensive research has been done to identify the components of integrated c o n t r o l approaches for bacterial w i l t. Despite this effort, no effective chemical means to minimize BW are yet available. Long-term rotation is the o n l y effective cultural control practice, but is seldom feasible because of the limitations of arable land. However, use of BW-resistant groundnut cultivars is the most effective and practical m e t h o d for control in farmers' fields. Hence, g r o u n d n u t germplasm screening and resistance enhancement have been emphasized in recent years. In this paper, progress made in genetic i m p r o v e m e n t of host resistance to BW in C h i n a since 1994 is reviewed. Germplasm Screening Screening methods In large-scale germplasm screening for resistance to B W, g r o u n d n u t lines are usually evaluated in single-row plots w i t h o u t replication, under natural disease pressure at hot- spot locations. Genotypes t h a t show h i g h survival percentage are selected and further tested under natural disease pressure in three to four replications w i t h a susceptible control sown at regular intervals. In C h i n a, disease nurseries have been established at such hot- spot locations as H o n g A n, H u b e i Province by the O i l Crops Research Institute ( O C R I ), Chinese Academy of A g r i c u l t u r a l Sciences ( C A A S ), and in Guangzhou, Guangdong Province. In the H o n g An nursery, groundnut has been continuously grown for over 30 years, and w i l t incidence in susceptible groundnut genotypes is consistently over 90%, indicating a desirable disease pressure for meaningful evaluation of groundnut genotypes. A r t i f i c i a l inoculation is routinely followed to enhance infection and confirm resistance. Infection pressure in artificial inoculation is kept similar to that available under natural conditions. Soaking seeds in bacterial suspension for 30 minutes before sowing has been the most effective m e t h o d of inoculation. However, the seed 7 6

85 inoculation method also reduced seed emergence. W h e n sample size was small, stem and root inoculation techniques were also used to evaluate and confirm BW resistance. Multilocational tests were generally needed to verify the stability of resistance. Field resistance can also be evaluated at hot-spot locations in Sichuan, Guangxi, Jiangxi, and other provinces (Tan and Liao 1990). Germplasm screening before 1994 D u r i n g , about 1700 groundnut germplasm accessions collected in C h i n a were systematically tested in H o n g A n, Hubei Province. T h i s was the first largescale screening for resistance. Two groundnut accessions - Xiekangqing and Taishan S a n l i r o u - were identified as resistant and have been extensively used in breeding in C h i n a. D u r i n g , over 3000 groundnut germplasm accessions were screened, and over 50 dragon type lines and 3 Virginia lines were identified as resistant. A t o t a l of 70 lines were resistant, and t h e i r resistance was generally stable across locations and seasons in C h i n a ( D u a n et al. 1993). Germplasm screening, 1994 to date A b o u t 1100 accessions of groundnut germplasm were screened for their reaction to bacterial w i l t between 1994 and M o s t of these accessions were breeding lines developed by various research institutes in C h i n a. From these screenings, 13 resistant lines were identified. Seventy-eight w i l d accessions were evaluated under natural disease pressure, and 24 showed reasonable levels of resistance. However, the resistance in w i l d Arachis spp. needs further evaluation and confirmation. T w e l v e resistant genotypes were repeatedly identified among germplasm lines introduced from I C R I S A T during T h e resistance of this material was desirable (Table 1), but most of t h e m were small-seeded w i t h lower yield potential t h a n the local resistant germplasm. In 1995, 15 groundnut accessions w i t h desirable resistance to bacterial w i l t developed or identified in C h i n a (Table 2) were sent to the I C R I S A T genebank. These lines are available to interested researchers. Breeding for Resistance Breeding methodology C o n v e n t i o n a l hybridization has been applied effectively in breeding for resistance to BW groundnut. Resistance to BW in groundnut is simply inherited and could be easily transferred to different cultivars. Selection for resistance has been conducted in the F 2 through F 6 generations. An effective disease-screening nursery 7 7

86 T a b l e 1. R e a c t i o n o f g r o u n d n u t g e r m p l a s m lines f r o m I C R I S A T t o bacterial w i l t i n C h i n a, Resistance (%) L i n e M e a n Reaction I C G 1608 I C G 1610 I C G 3121 I C G 5313 I C G 6417 I C G 7919 I C G 8684 I C G 8701 I C G 8704 I C G 8706 I C G 8707 I C G R R R H R H R H R H R H R R H R R H R 1. R = resistant, HR = highly resistant. Table 2. R e a c t i o n o f local g r o u n d n u t lines t o bacterial w i l t i n C h i n a, Lines Xiekangqing Taishan Zhengzhu E H u a 5 Z h o n g H u a 2 Yue You 92 G u i You 28 Yue You 200 Jiangtianzhong Gouliaozhong Luhua 3 Kangqing ( Z H 112) ( Z H 212) Zao 18 Reaction R R R R R R R M R M R M R R R R R R H S Sources Local variety Local variety Improved cultivar Improved cultivar Improved cultivar Improved cultivar Breeding line Local variety Local variety Improved cultivar Breeding line Breeding line Breeding line Breeding line Breeding line Breeding line 1. R = resistant, MR = Moderately resistant, HS = highly susceptible. 7 8

87 is available for resistance selection, and artificial i n o c u l a t i o n is used as and w h e n needed. Survival percentage is currently used as the resistance selection criterion. M u l t i l o c a t i o n a l tests are conducted to determine stability, yield, and adaptation of selected lines ( C h e n and H o n g 1995). Resistance donors In C h i n a, several resistant germplasm accessions have been used in breeding. Xiekangqing and Taishan Sanlirou have been most extensively used as resistance donors. Improved resistant cultivars, including E H u a 5, Lu H u a 3, and Yue You 92, were bred from Xiekangqing, w h i l e Zhong H u a 2 and Zhong H u a 4 were bred from Taishan Sanlirou. Induhuapi has been effectively used as a resistant parent in Guangdong Province. It is interesting to note that o n l y germplasm lines belonging to ssp. fastigiata in the cultivated Arachis have been successfully used as resistance donors in breeding programs. Apparently, early maturity and tolerance to acid soil and poor soil fertility in Spanish or Valencia types are most desirable in different agro-ecological conditions and wilt-prone areas in China. Generally, the resistant genotypes identified from spp. hypogaea are thought to be promising in increasing yield levels of BW resistant lines; however, some of their characters may i n h i b i t integration of w i l t resistance w i t h desirable agronomic traits necessary for adaptation in the disease-prone areas. Large pods are usually important for h i g h yield potential, but in most cases this trait is associated w i t h a sensitive reaction to calcium deficit in acid soils, a c o n d i t i o n predominating i n most regions where B. solanacearum causes serious w i l t i n groundnut. Therefore, direct use of large-podded genotypes in breeding seems difficult. Efforts are currently in progress to use some of the resistant h i g h- y i e l d i n g genotypes of ssp. hypogaea in BW resistance breeding programs in C h i n a and elsewhere (Liao and Xu 1997, Liao et al. 1990). Status of resistant cultivars and breeding lines Since 1994, several improved groundnut cultivars or promising breeding lines have been developed or released in C h i n a. Yue You 200, a breeding l i n e developed at Guangdong Academy of A g r i c u l t u r a l Sciences ( G A A S ), promising b o t h for resistance to BW and h i g h yield in central C h i n a, was released as Tianfu 11 in Sichuan Province. Yue You also was developed at G A A S and released in Guangdong Province in 1997 (Liang et al. 1997). It is resistant to b o t h bacterial w i l t and rust (Puccinia arachidis), w i t h a relative h i g h o i l content ( % ). A promising breeding line, Yue You 79, w i t h desirable resistance to b o t h BW and rust, has been developed at G A A S. 7 9

88 At O C R I, two resistant lines have been developed. L i n e is highly resistant, w i t h tolerance to acid soil. A n o t h e r resistant line, 93-76, w i t h desirable pod shape and uniformity, as well as drought tolerance, has been identified ( C u i 1998, personal communication). M a n y advanced breeding lines are in the pipeline under further selection. W a n H u a 2 was released in A n h u i Province in I t. was described as resistant to BW. In Fujian Province, Q u a n H u a 10, w i t h moderate resistance to B W, was released in 1995 ( Z h o u and W e i 1996). Resistant lines developed from interspecific hybridization An advanced breeding line, 9102, was developed at H e n a n Academy of A g r i c u l t u r a l Sciences ( H A A S ) located in Zhengzhou (Zhang X i n g y o u 1997, personal c o m m u n i c a t i o n ). It was developed from a cross between Baisha 1016, a Spanish-type cultivar, and A. chacoense. T h e groundnut line 9102 is resistant to BW in G u a n g x i and H u b e i Provinces. It matures early, has h i g h seed o i l content ( 5 6 % ), and produces h i g h yields. Biotechnology for resistance enhancement Even t h o u g h resistance to BW in groundnut has n o t been found negatively correlated w i t h agronomic traits, integrating B W resistance w i t h h i g h yield potential has progressed relatively slowly. In order to enhance yield potential, stability of resistance to B W, an anti-bacterial gene and transformation system like those employed successfully in potato for resistance to B. solanacearum are being used in transforming groundnut at O C R I. Further Research Needs Genetic enhancement for resistance w i l l be the most important research area i n further addressing the BW problem in C h i n a. T h e f o l l o w i n g are possible subjects for future research efforts: Screening more desirable resistant resources Investigating genetic diversity of w i l t resistance in groundnut Enhancing yield potential of wilt-resistant groundnut cultivars Enhancing resistance to other w i l t pathogens and drought tolerance of B W - resistant cultivars Enhancing quality of BW-resistant cultivars 8 0

89 References C h e n Y., a n d H o n g, D B r e e d i n g o f a h i g h y i e l d i n g g r o u n d n u t c u l t i v a r w i t h resistance t o b a c t e r i a l w i l t Q u a n h u a 10. O i l C r o p s o f C h i n a 17(4): D u a n N., T a n, Y., Jiang, H., a n d H u, D S c r e e n i n g g r o u n d n u t g e r m p l a s m f o r resistance t o b a c t e r i a l w i l t. O i l C r o p s o f C h i n a. 1 5 ( 1 ) : L i a n g, X., L i, S., L i, Y., Z h e n g, G., L i, X., a n d Y e, M A n e w g r o u n d n u t c u l t i v a r Y u e y o u O i l C r o p s o f C h i n a 1 9 ( 3 ) : 7 2. L i a o, B., a n d X u, Z R e p o r t o f c o l l a b o r a t i v e research o n g r o u n d n u t v i r u s a n d b a c t e r i a l w i l t diseases w i t h I C R I S A T f o r Paper p r e s e n t e d at C h i n a - C L A N / I C R I S A T R e v i e w a n d W o r k p l a n M e e t i n g, July , B e i j i n g. ( L i m i t e d d i s t r i b u t i o n ) L i a o, B., W a n g, Y., X i a, X., T a n g, G., T a n, Y., a n d S u n, D G e n e t i c a n d b r e e d i n g aspects o f resistance t o b a c t e r i a l w i l t i n g r o u n d n u t. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, M a r , G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.). A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l R e s e a r c h. T a n, Y., a n d L i a o, B G e n e r a l aspects o f g r o u n d n u t b a c t e r i a l w i l t i n C h i n a. Pages in B a c t e r i a l w i l t o f g r o u n d n u t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g M a r G e n t i n g H i g h l a n d s, M a l a y s i a ( M i d d l e t o n, K. J., a n d H a y w a r d, A. C., eds.). A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l R e s e a r c h. Z h o u Z h a n g l a i a n d W e i X i u p i n g A g r o u n d n u t n e w c u l t i v a r W a n H u a 2. O i l C r o p s o f C h i n a 1 8 ( 3 ) :

90 Germplasm Evaluation and Breeding for Groundnut Bacterial Wilt Resistance in Vietnam Nguyen Van Lieu, Tran Dinh Long, and Nguyen Xuan Hong 1 Abstract Bacterid wilt caused by B u r k h o l d e r i a s o l a n a c e a r u m is one of the most serious diseases of groundnut in Southeast Asia, particularly in Vietnam. Before 1991, evaluation of groundnut germplasm for bacterial wilt (BW) resistance had never been done in Vietnam. The first systematic screening for BW resistance was done in , when a total of 715 groundnut accessions were screened in sick plots at hot-spot locations in northern Vietnam. Only 4.1% of the screened lines were resistant to BW. Of those, only 0.6% were highly resistant. Most available accessions were susceptible to the disease. Groundnut line Gie Nho Quan possessed the highest resistance to BW, with a survival rating of 97%. This variety also had good agronomic characters, and therefore is a good candidate to be cultivated in infested areas, and to be used as a BW resistance gene donor in breeding for BW resistance in Vietnam. Several other genotypes, such as Schwarz 21 (KPS 13), Matjan (KPS 18), and I C G V are promising resistant cultivars. The pod yield of these cultivars is substantially higher than that of the local control, Do Bac Giang. Breeding for BW resistance has been initiated and some progress made. Introduction Bacterial w i l t of g r o u n d n u t caused by Burkholderia solanacearum (RE Smith) Yabuuchi et al. is the o n l y economically i m p o r t a n t bacterial disease of groundnuts 1. Vietnam Agricultural Science Institute ( V A S I ), Van Dien, Thanh T r i, Hanoi, Vietnam. Nguyen Van Lieu, Tran Dinh Long, and Nguyen Xuang Hong Germplasm evaluation and breeding for groundnut bacterial wilt resistance i n Vietnam. Pages in Groundnut bacterial wilt: proceedings of the Fourth Working Group Meeting, May 1998, Vietnam Agricultural Science Institute, Van Dien, Thanh Tri, Hanoi, Vietnam (Pande, S., Liao Boshou, Nguyen Xuan Hong, Johansen, C., and Gowda, C.L.L., eds.). Patancheru , Andhra Pradesh, India: International Crops Research Institute for the Semi-Arid Tropics. 8 2

91 ( H o n g and M e h a n 1993). It develops favorably in warm, h u m i d regions of the w o r l d where groundnuts are grown. Southeast A s i a is the most favorable region for B W. C h i n a and Indonesia are t w o other countries w i t h large groundnutg r o w i n g areas infected by B W. These t w o countries have paid m u c h a t t e n t i o n to B W research. T h e most remarkable achievement i n B W research was the development of groundnut variety Schwarz 2 1, w h i c h was bred in Indonesia in 1925 ( M e h a n et al. 1986). Soon after this discovery, several h i g h l y resistant varieties were bred in Indonesia, C h i n a, and other countries and have contributed to reducing yield losses in groundnut. U n t i l 1994, it was estimated that more t h a n 6000 groundnut accessions had been evaluated for BW resistance in C h i n a a n d Indonesia alone, a n d about 140 accessions were resistant to B W. From those genetic resources, many h i g h l y BW resistant varieties w i t h good agronomic characteristics have been released for direct p r o d u c t i o n or to be used i n B W resistance breeding programes. Bacterial w i l t of groundnut has been found in V i e t n a m since 1962 ( U n g D i n h 1962, Dang 1968). Scientists w h o carried out preliminary experiments to find BW resistant genotypes among local varieties d i d n o t have any success. F r o m 1970 to 1990, research on BW was negligible. A comprehensive research program, i n c l u d i n g germplasm evaluation and breeding for BW resistance, has been conducted since 1991 ( H o n g and M e h a n 1993). Materials and Methods Germplasm evaluation Sick plots were sown at hot-spot locations to identify BW resistance. In these sick plots, densities of bacteria exceeded 10 6 C F U 100 g - 1 soil. Sowings for resistance screening were carried o u t t w i c e a year. In the spring season, sowings usually started 10 M a r c h, and in the a u t u m n season, sowing time was around 20 July. Seeds of tested entries were soaked in a bacterial suspension (6 x 10 8 C F U 1 m L - 1 ) for 20 minutes before sowing. Experiments were laid out in an augmented design w i t h o u t replication. A susceptible c o n t r o l ( I C G 3704) and one local c o n t r o l ( D o Bac G i a n g or Sen Nghe A n ) were sown after every 10 test entries. Each test entry was sown in a 1-m 2 plot area w i t h 60 to 80 plants n r 2. These experiments were repeated for at least three seasons. From 1992 through 1995, a total of 715 groundnut accessions (including 596 e x o t i c lines) were screened for BW resistance in sick plots. Seventy days after sowing, the percentage o f w i l t e d plants was counted to assess B W incidence. Test lines were categorized as, 1. highly resistant ( < 1 0 % wilted plants), 2. resistant 8 3

92 ( % ), 3. moderately susceptible ( % ), 4. susceptible ( % ), and 5. highly susceptible ( > 9 1 % ). Breeding for bacterial wilt resistance Bacterial wilt-resistant lines were evaluated for agronomic characteristics. Germplasm lines or bred varieties w i t h such desirable agronomic characteristics as high pod yield or good potential to resist drought and/or some m a i n foliar diseases, were further selected evaluation for stability of yield in multilocational trials. Remaining lines and varieties were kept in the gene bank for future use. In multiiocational trials, these lines were sown in randomized complete block designs and scored for pod yield and seed characteristics. Results and Discussion Germplasm evaluation O u t of 715 lines, o n l y a few (~ 4 % ) were found to be resistant to BW in the germplasm evaluation (Table 1). Most of the resistant accessions belonged to the Spanish type; few were Virginia or Valencia types. Frequency of occurrence of resistance in short-duration lines was lower t h a n in medium- and long-duration lines. T a b l e 1. G e r m p l a s m e v a l u a t i o n f o r bacterial w i l t resistance, , V i e t n a m Disease category N u m b e r Percentage M o s t promising lines in category 1. H i g h l y resistant 2. Resistant Moderately susceptible Susceptible H i g h l y susceptible G i e N h o Q u a n, N c A c 17127, PI Schwarz 2 1, I C G V M a t j a n S e K o n t u m, d o Lao C a i, N c A c Sen N g h e A n, D o Bac G i a n g, T r a m X u y e n N o 2, I C G 3704, U P L - P N 2 T o t a l

93 T a b l e 2. B a c t e r i a l w i l t resistant p e r f o r m a n c e o f G i e N h o Q u a n g r o u n d n u t v a r i e t y u n d e r artificial i n o c u l a t i o n 1 Burkholderia solanacearum w i t h d i f f e r e n t isolates o f Plants surviving 21 days after treatment (%) Genotype Q O 2 HT 1 H T r 4 H B G i e N h o Q u a n Sen N g h e A n I C G Inoculation method: seed treatment + root cutting 2. Q0, H T 1, Htr 4, H B : Isolates of B. solanacearum T a b l e 3. B a c t e r i a l w i l t resistant p e r f o r m a n c e o f G i e N h o Q u a n g r o u n d n u t v a r i e t y i n n a t u r a l sick plots a t f o u r locations i n V i e t n a m d u r i n g spring season, Plants surviving at 70 days after sowing (%) Thach Binh Thanh Liem Agr. U n i. N 3 Xuan Mai Genotype ( N i n h Binh) (Ha Ham) (Thai Nguyen) (Ha Tay) Gie N h o Quan Schwarz 21 (KPS 13) Matjan (KPS 18) Sen Nghe An V ICG T h e significant finding of our resistance screening was the identification of a highly resistant landrace, Gie N h o Quan. This landrace, when inoculated w i t h different isolates of B. solanacearum, was h i g h l y resistant in comparison to other genotypes (Table 2). It was evaluated along w i t h other available BW-resistant sources in sick plots at hot-spot locations (Table 3). T h e data presented in Tables 2 and 3 clearly indicate that G i e N h o Q u a n was the most resistant groundnut genotype. Its resistance was more stable over locations, t h a n that of other varieties. Its resistance level was higher t h a n those of the t w o traditional sources of BW 8 5

94 resistance, Schwarz 21 and Matjan. Gie N h o Q u a n is considered to be the best source of resistance to BW of groundnut in Vietnam. T h e characteristic features of G i e N h o Q u a n are Spanish type, dark-green leaf color, cm stem height, small seeds and pods, pink-white testa color, h i g h shelling percentage (77.8%), short duration, moderate foliar disease resistance, and drought tolerance. Pod yield of this variety was not high, but could be acceptable when grown in BW infested areas. Breeding for bacterial wilt resistance T h e selected resistant groundnut lines were evaluated in multilocational trials for pod yield and other important characters, such as 100-pod mass, 100-seed mass, shelling percentage, testa colour, and duration. After three years of multilocational testing, we identified four good varieties (Table 4). A l l four were of m e d i u m duration w i t h exportable testa colour. A l l o f t h e m except G i e N h o Q u a n had higher yields t h a n the local control. These varieties w i l l be further tested i n farmers' fields for BW resistance. Several crosses have been made since genotypes is in progress. 1996, and selection for resistant T a b l e 4. M a i n characteristics o f some promising resistant g r o u n d n u t varieties w i t h good y i e l d p o t e n t i a l i n V i e t n a m Duration Mature looseed Shelling Pod yield Variety (days) pods plant -1 mass (g) percentage mean (kg ha -1 ) Schwarz 21 ( KPS 13) M a t j a n I C G V G i e N h o Q u a n Do Bac G i a n g Local c o n t r o l C V ( % ) L S D Conclusions M o s t of evaluated groundnut accessions were susceptible to BW in N o r t h V i e t n a m. T h e resistance potential of Spanish types was higher t h a n the potential of Virginia and Valencia types. 8 6

95 Short-duration accessions were more susceptible to BW t h a n were mediumand long-duration accessions. G i e N h o Quan, a local landrace, is potentially one of the most valuable source of resistance in V i e t n a m. It can be used for growing in BW infested areas and making crosses to create resistant varieties. Schwarz 2 1, M a t j a n, and some other BW resistant varieties gave good yields and therefore were selected for on-farm testing in BW infested areas. References D a n g T h a i T h u a n ( A b o u t bacterial w i l t o f g r o u n d n u t s i n N g h e A n ) A g r i c u l t u r a l Science a n d T e c h n o l o g y B u l l e t i n ( H a n o i ) 7 8 : ( I n V i e t n a m e s e ) H o n g, N. X. a n d M e h a n, V. K R e s e a r c h o n b a c t e r i a l w i l t o f g r o u n d n u t i n V i e t n a m. Pages in B a c t e r i a l w i l t : p r o c e e d i n g s o f a n A C I A R / I C R I S A T C o l l a b o r a t i v e R e s e a r c h P l a n n i n g M e e t i n g, O c t , K a o h s u i n g, T a i w a n ( H a r t m a n, G. L., a n d H a y w a r d, A. C., eds.). A C I A R P r o c e e d i n g s n o C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l R e s e a r c h. M e h a n, V. K., M c D o n a l d, D., a n d S u b r a h m a n y a m, P B a c t e r i a l w i l t o f g r o u n d n u t. C o n t r o l w i t h emphasis o n h o s t - p l a n t resistance. Pages i n B a c t e r i a l w i l t diseases i n A s i a a n d t h e S o u t h Pacific: p r o c e e d i n g s o f t h e I n t e r n a t i o n a l B a c t e r i a l W i l t S y m p o s i u m, P C A R R D, L o s Banos, P h i l i p p i n e s, O c t , (Persley, G.J., e d. ). A C I A R Proceedings n o. 13. C a n b e r r a, A u s t r a l i a : A u s t r a l i a n C e n t r e f o r I n t e r n a t i o n a l A g r i c u l t u r a l Research. U n g D i n h ( I n t e n s i v e t e c h n i q u e s for i m p r o v i n g g r o u n d n u t y i e l d. ) H a n o i : R u r a l P u b l i s h i n g H o u s e p p. ( I n V i e t n a m e s e ) 87

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97 Recommendations

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99 Recommendations D u r i n g the Fourth G r o u n d n u t Bacterial W i l t W o r k i n g G r o u p ( G B W W G ) M e e t i n g, further research priorities and related workplans were intensively discussed among the participants. It was believed that most of the recommendations formed i n the T h i r d G B W W G Meeting held i n W u h a n, C h i n a in July 1994 still stand. Following are the revised recommendations based on the discussions. Disease Monitoring Systematic surveys have been conducted in the past in all member countries, and substantial information is available on the disease distribution across different regions and cropping systems. However, high-yielding varieties, w h i c h may or may n o t be resistant to bacterial w i l t, have been extensively used or distributed recently, especially in the non-traditional groundnut-growing areas of C h i n a and V i e t n a m. It is therefore agreed that annual surveys should continue in all countries, and i n f o r m a t i o n should be gathered on the changing scenario of BW w i t h the change in varieties. A l s o, it was suggested to conduct targeted surveys of disease-endemic areas using Geographical Positioning System ( G P S) and Geographical Information Systems ( G I S ). Basic Research on Burkholderia solanacearum Basic research on B. solanacearum strains affecting groundnut is h i g h l y desired. Research activities for disease diagnosis, pathogen detection, and determination of pathogenicity at h o t spots i n C h i n a and Vietnam w i l l be conducted and strengthened t h r o u g h collaboration w i t h advanced laboratories i n developed and developing countries. Wherever possible, use of both molecular and conventional approaches w i l l be followed. Efforts should be made to develop more sensitive and specific m o n o c l o n a l antibodies to detect the i n d i v i d u a l biovars and pathotypes of B. solanacearum in different plant parts (seed, plant tissues, and soil). Strains highly v i r u l e n t on groundnut, reported from C h i n a and Vietnam, should be sent to an advanced research laboratory (such as Rothamsted Experimental Station in U K ) for maintenance, characterization, and documentation. Priority in this effort should be given to strains collected from member countries. 9 1

100 Germplasm and Information Exchange Among Member Countries A W o r k i n g G r o u p news sheet w i l l be edited by the Technical Coordinator ( T C ) and circulated among members o f the W o r k i n g Group. Two to three issues w i l l be produced annually. G r o u n d n u t genotypes w i l l be exchanged among member countries. T h e exchange w i l l be carried out bilaterally or through I C R I S A T. Genetic Enhancement for Host-Plant Resistance H o s t - p l a n t resistance is an important component of disease management. M o r e coordinated research is needed to evaluate w i l t resistant landraces, especially those collected f r o m h u m i d areas of C h i n a and V i e t n a m. These landraces should be assembled at I C R I S A T and screened at disease h o t spots in C h i n a and V i e t n a m. T h e r e is a concerted need to collect promising germplasm f r o m disease-endemic areas, and conserve it at I C R I S A T. Sources of stable resistance to BW are available in member countries, and most of these sources are available at the I C R I S A T gene bank. Researchers are encouraged to test these sources systematically at h o t spots in their countries. T h i s was suggested as an alternative to an International G r o u n d n u t Bacterial W i l t Nursery ( I G B W N ). Results of screening should be reported i n G B W W G meetings. T h e G r o u p strongly felt the need to give h i g h priority to breeding high-yielding cultivars c o m b i n i n g resistances to BW and major fungal foliar diseases, specifically late leaf spot and rust. Members also wanted to m o n i t o r the incidence and severity of web b l o t c h, w h i c h has been recently found to be a disease of increasing potential in southern C h i n a and northern V i e t n a m (specifically on newly developed BW- resistant cultivars). These foliar diseases are serious constraints to groundnut production i n warm, h u m i d environments. T h e G r o u p also felt the need to emphasize understanding of the mechanism of resistance (such as the role of incubation period and latent infection) and its use in breeding for disease resistance. Further screening of groundnut germplasm lines to identify additional and diverse sources o f resistances to B W w i l l be continued i n China, Indonesia, and Vietnam. Breeding for BW resistance combined w i t h multiple resistance to fungal foliar diseases (late leaf spots and rust) and other w i l t diseases, w i t h drought tolerance and improved quality w i l l be highly emphasized. Further investigation w i l l be made o f t h e genetics and mechanisms o f resistance t o B W i n groundnut. Priority w i l l be given to improving methods for resistance evaluation, including techniques for artificial inoculation and for detecting latent infection. 9 2

101 Interaction between pathogens B. solanacearum and other soilborne T h e Group strongly felt the need to start systematic studies on the interaction of the groundnut w i l t pathogen w i t h such soilborne fungi as Fusarium spp. Aspergillus flavus, and Sclerotium rolfsii. T h i s relationship is quite c o m m o n l y observed, and it is felt that bacteria and fungi together are causing enormous damage, especially in droughts and other r a i n- free periods in upland areas. T h e Group also felt a need to develop and/or assemble a package of practices available to combat soilborne diseases and include t h e m in on-farm studies on groundnut BW management. Integrated Disease Management and Transfer of Technology Cultural control w i l l be further studied in terms of mechanisms of crop rotation influencing the pathogen population and pathogenicity. R o t a t i o n and field management practices are still recommended to farmers wherever feasible. It was felt that substantial information is available on host-plant resistance and cultural practices that reduce disease incidence, but these combinations are n o t yet sufficiently verified and validated in on-farm research so that these practices can be used by farmers. Therefore, concerted efforts are needed to initiate farmers' participatory research to devise appropriate location-specific packages of these strategies. More research efforts w i l l be made for biological control by using avirulent strains of B. solanacearum strains. Seed transmission w i l l be further monitored. Workshop and Training Activities In-country workshops were recommended for C h i n a and V i e t n a m. These i n - country workshops w i l l be held for more extensive information exchange and technology transfer. T h e activity w i l l be supported mainly by individual member countries w i t h l i m i t e d support from C L A N. A n in-country workshop i s tentatively planned for 1999 or 2000 in southern Vietnam. Funding Proposal Development It was agreed that a l l n a t i o n a l programs of the member countries should support research on g r o u n d n u t BW wherever this disease is a constraint to crop production. At present, national programs are the m a i n sources of research funding. International project and fundings are important for BW research, especially for international cooperation. Proposals w r i t t e n by member countries w i l l be prepared and submitted to donors for potential funding. 9 3

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103 Participants

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105 Participants China Duan Naixiong Groundnut Breeder O i l Crops Research Institute (OCRI) Chinese Academy of Agricultural Sciences ( C A A S ) Wuhan Gao Guoqing Groundnut Breeder Industrial Crops Research Institute Guangxi Academy of Agricultural Sciences Nanning Liang Xuanqiang Director and Groundnut Breeder Crops Research Institute Guangdong Academy of Agricultural Sciences ( G A A S ) Wushan , Guangzhou Liao Boshou, Technical Coordinator Groundnut Bacterial W i l t Working Group O i l Crops Research Institute (OCRI) Chinese Academy of Agricultural Sciences ( C A A S ) Wuhan Vietnam Doan T h i Thanh Potato Breeder Vietnam Agricultural Science Institute ( VASI) Van Dien, Thanh Tri Hanoi Do Tan Dung Agronomist National Center for Varietal Evaluation and Seeds Certification No. 6 Nguyen Cong Tru Hanoi Agricultural University Hanoi Do T h i Dung Information Center Ministry of Agriculture and Rural Development ( M A R D ) 2, Ngoc Ha, Ba D i n h Hanoi Hoang Minh Tam Head of Technology Department Legumes Research and Development Center Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Le Luong Te Plant Pathologist Biological Association Hanoi Le Quoc Doanh Head Department of Science Planning and International Cooperation Vietnam Agricultural Science Institute ( V A S I ) Van Dien, Thanh Tri Hanoi Le Van Thuyet Director National Institute of Plant Protection Ministry of Agriculture and Rural Development Chem Tuliem Hanoi Ngo The Dan Vice Minister, Ministry of Agriculture and Rural Development Cereals and Legumes Asia Network ( C L A N ) Country Coordinator 2 Ngoc Ha, Ba D i n h Hanoi Nguyen Van Tung Plant Pathologist O i l Plants Institute (OPI) Han Nghi St., 1st District H o C h i M i n h City Ngo T h i Lam Giang Groundnut Breeder O i l Plants Institute (OPI) Han Nghi St., 1st District H o C h i M i n h City Nguyen Van Tuat Deputy Director National Institute of Plant Protection Ministry of Agriculture and Rural Development Chem Tuliem Hanoi 9 7

106 Nguyen T h i Ly Plant Pathologist National Institute of Plant Protection Ministry of Agriculture and Rural Development Chem Tuliem Hanoi Nguyen H u u Nghia Director General Vietnam Agricultural Science Institute ( V A S I) Van Dien, Thanh Tri Hanoi Nguyen Van Viet Plant Pathologist Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Nguyen T h i Yen Plant Pathologist Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Nguyen Ngoe Quyen Microbiologist Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Nguyen T h i Chinh Agronomist Legumes Research and Development Center Vietnam Agricultural Science Institute ( V A S I) Van Dien, Thanh Tri Hanoi Nguyen Van Thang Groundnut Breeder and Head Legume Breeding Department Legumes Research and Development Center Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Nguyen Xuan Hong Head of Department of Plant Pathology and Immunology Vietnam Agricultural Science Institute ( V A S I) Van Dien, Thanh Tri Hanoi Nguyen Van Lieu Groundnut Breeder Department of Science Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Nguyen T h i H a u Technical College Bac Giang Province Phan Lieu Director O i l Plants Institute (OPI) , Ham Nghi St., 1st District H o - C h i - M i n h City Tran Nghia Groundnut Breeder Legumes Research and Development Center Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Tran Dinh Long Grain Legume Breeder Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi Vi A n h Tuan Microbiologist Vietnam Agricultural Science Institute (VASI) Van Dien, Thanh Tri Hanoi India Suresh Pande Senior Scientist Natural Resource Management Program International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Patancheru , Andhra Pradesh, India 9 8

107 About ICRISAT The semi-arid tropics (SAT) encompasses parts of 48 developing countries including most of India, parts of southeast Asia, a swathe across sub-saharan Africa, much of southern and eastern Africa, and parts of Latin America. Many of these countries are among the poorest in the world. Approximately one-sixth of the world's population lives in the SAT, which is typified by unpredictable weather, limited and erratic rainfall, and nutrient-poor soils. ICRISAT' s mandate crops are sorghum, pearl millet, finger millet, chickpea, pigeonpea, and groundnut; these six crops are vital to life for the ever-increasing populations of the semi-arid tropics. ICRISAT' s mission is to conduct research w h i c h can lead to enhanced sustainable production of these crops and to improved management of the limited natural resources of the SAT I C R I S A T communicates information on technologies as they are developed through workshops, networks, training, library services, and publishing. I C R I S A T was established in It is one of 16 nonprofit, research and training centers funded through the Consultative Group on International Agricultural Research ( C G I A R ). The C G I A R is an informal association of approximately 50 public and private sector donors; it is co-sponsored by the Food and Agriculture Organization of the U n i t e d Nations ( FAO), the United Nations Development Programme ( U N D P ), the United Nations Environment Programme ( U N E P ), and the W o r l d Bank.

108 ICRISAT International Crops Research Institute for t h e Semi- Arid Tropics Patancheru , Andhra Pradesh, India Consultative Group on Inernational Agricultural Research ISBN Order code CPE