Progress and future development of hybrid rapeseed in China

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1 Progress and future development of hybrid rapeseed in China Fu Tingdong,Zhou Yongming (Huazhong Agricultural University,Wuhan ,China) Abstract:The hybrid growth of rapeseed now has reached to hm 2,accounting for 70 % of total rapeseed growth area in China. Over the last 40 years,the researches and utilizations of hybrid rapeseed in China have significantly contributed to the development of rapeseed industry in China. The production of hybrid rapeseed mainly utilizes cytoplasmic male sterility(cms),combined at the same time with nuclear male sterility and other pollinating-control systems in China. The hybrid rapeseed studies in China are also characterized by the improvement of quality and oil content in hybrid breeding. Future studies to enhance the heterosis of rapeseed will be focused on several important issues,including the combination of heterosis and ideotype breeding,further increase of oil content in hybrids,utilization of sub-genomic heterosis and resistance improvement. The paper will discuss the following perspectives in hybrid rapeseed studies:relationships among heterosis,quality and disease traits,solutions for excessive source and pool in hybrids compared with open- pollinated cultivars,and the importance of increasing harvest index of hybrids to achieve a better yield in hybrids. Key words:oil crops;rapeseed;heterosis;plant breeding 1 Introduction Rapeseed production in China has increased significantly since 1950 s due to the following two major reasons. Firstly,cultivars with high yield and good quality have been developed and grown widely, although the overall cultivation level remains largely unchanged due to rapid migration of labor forces to cities from the countryside since 1990 s. Secondly, new cultivars offer higher yield and consequently a better income for farmers,which in return stimulate enlarged growth areas and rapid development of rapeseed industry. 2 Growing hybrid rapeseed promotes rapeseed production in China The discovery of Polima(Pol) cytoplasmic male sterility(cms)by Fu Tingdong at Huazhong Agricultural University in 1972 marked a milestone in rapeseed heterosis studies. Four years later,three lines of Pol CMS were developed at Hunan Academy of Agricultural Sciences,and Qinyou 2,the first commercial hybrid based on CMS three- line system was released by Shanxi Agricultural Centre in 1985,which enhanced the study and utilization of rapeseed heterosis in China [1,2]. With the development of hybrids and the increase of hybrid growth areas,the productive levels per unit increased gradually (Table 1). Since 1990 s, large numbers of farmers left for cities and at this stage the cultivation level did not change much. Therefore the increased productivity per unit was mainly contributed to new cultivars,especially hybrids. Furthermore,due to the improvement of both yield and quality,growing rapeseed became more profitable for farmers,which in return stimulated more nationwide rapeseed production. Compared with 1950 s,the growth area in China has now increased about 3 times and average unit yield increased about 4 times,which have resulted in more than 10 times of increase in total annual production (Table 1). It is worth to mention that ZY 821,a double highcultivar of Brassica napus,was a breakthrough Received 10 May 2013 Vol. 11 No.5,Oct

2 Year * Table 1 Production and cultivar development of rapeseed in China Annual growth area/ 10 6 hm Hybrid percentage/% 10~15 20~40 50~70 Yield per unit/ (kg hm -2 ) Annual production / 10 4 t Note: * is the peak years of the extension of high yield cultivar zhongyou 821(ZY 821) (double high) in high yield breeding in China. The cultivar was characterized by high yield and stability,tolerance to Sclerotinia sclerotiorum. The growth area of ZY 821 was as high as mu/a(1 mu m 2 ), which made ZY 821 the most popular cultivar in the 1980 s1990 s in China. After more than 20 years, the hybrid cultivars now normally have a 25 % more seed yield and about 3 % higher in oil content with double low quality (Table 2). 3 Characteristics of hybrid rapeseed research and development in China 3.1 Hybrid development promotes the wide growth of double low rapeseed Breeding for quality in rapeseed started in the middle of 1970 s with the introduction of Oro (low erucic acid) and Tower (low erucic and glucosinolate) Table 2 Comparison of yield and quality of double low hybrids with double high OP cultivars in Hubei Province Cultivar types ZY 821 Double lowhybrids Relative yield/% Note:OPopen pollination Glucosinolate/ (mol g -1 meal -1 ) ~28 Erucic/% 40~ Oleic/% 17 62~65 Linoleic/% Linolenic/% Oil content/% 39~41 41~45 from Canada in 1974 and 1976,respectively [3]. Conventional OP double low cultivars bred at early stage had low yield and thus faced to difficulty in large scale of extension. Such a situation remained unchanged until 2000 (Table 3),when double low hybrids had higher yield than double high variety ZY 821 (7 %),and the increase reached to 16 %~19 % in 2000 (Table 3);Huaza 4 was the hybrid with the largest growth area in China through ,replacing ZY 821 and Qinyou 2 as the major cultivar in China s main rapeseed production zones. The coverage of double low quality is 70 %~90 % now. Table 3 Yield advance of double low cultivars compared with double high control ZY 821 in Hubei Province Year Double low OP cultivars/% ~15 Double low hybrids/% ~19 20~25 > Combination of hybrid development with high oil content breeding The oil content of cultivars bred at the Yangtze River Valley fluctuated between 38 % ~42 % for a long time before 2005,due to high temperature during the seed filling stage (AprilMay),which had adverse effects on oil accumulation. Moreover,the analytic equipment at that time was limited. Based on a survey by the Quality Monitoring Centre for Oilseed Products,the Agriculture Ministry of China, the average oil content of 327 cultivars bred in winter rapeseed regions during was % (dry- based),while cultivars was % in spring type region. In last 10 years,the breeding for high oil content in China made great progress thanks to applications of the high- throughput analytic technology such as near infrared resonance (NIR) and/or nuclear magnetic resonance (NMR) and materials with 52 % ~ 58 % of oil content (dry-based) were developed. Among the cultivars bred in last 10 years,new cultivars bred during had high seed yield (14~16 kg/mu) and oil content (2 %) compared with the ones bred during Hybrids with > 45 % oil content now are in production (Table 4). 14 ENGINEERING SCIENCES

3 Table 4 Overview of the yield and quality of cultivars bred in China during Year Number Yield/ (kg mu -1 ) Erucic acid/% Glucosinolate /(mol g -1 ) Oil content/ % Note:The data were collected from the trials of national winter rapeseed reports 3.3 Hybrid production mainly uses CMS type with combination of multiple approaches The major pollination system for F1 hybrid production in China is CMS including Pol CMS and Shan 2A CMS,accounting for 70 % of total hybrids bred. There are some hybrids bred with ecotype system derived from Pol CMS,too. The other types of pollination systems include genetic male sterility (GMS) and gametocide hybrids (Table 5). Total % Table 5 Registered hybrids and their sources based on pollination systems in China during OP cultivars % CMS % GMS % Hybrid type Ecotype male sterility % Gametocides % Subtotal % 3.4 Progresses in GMS studies The major germplasms of GMS in China include recessive GMS S45A from Sichuan,117A from Guizhou and 9012A from Anhui as well as dominant GMS Yi 3A from Yibin City of Sichuan and 23A from Shanghai. We will briefly summarize the recent progresses on GMS study over the recent years. 1) Genetics of recessive male sterility and development of temporary- maintainer for production of 100 % sterile population. Genetic studies established that the male sterility in 7365A(9012A)is controlled by two loci. One is Ms3/ms3 and the other is locus including multiple alleles of Ms4/Rf/rf. The genetic effects of the alleles are Ms4>Rf>rf. This result thus corrected previous conclusion that attributed the genetic control in these materials to three- gene model. Then we would use the following to produce a full sterile line and F1 hybrids [4,5]. A schematic sketch for F1 hybrid production with recessive GMS 7365A and 9012 A is shown. ms3ms3 RfRf (sterile) Ms3ms3 RfRf (fertile) 50% fertile 50% sterile removal of fertile MS3mS3 RfRf ms3ms3 RfRf ms3ms3 rfrf (fertile) (temporary-maintainer) 100% sterile ms3ms3 Rfrf Ms3Ms3 RfRf (restorer) Ms3Ms3 rfrf (restorer) F1 hybrid As show,rfrf is the recessive inhibitory allele that inhibits sterile gene ms3 expression,resulting in fertile phenotype. 2) Genetics of dominant male sterility and development of temporary-maintainer for production of 100 % sterile population. Genetic studies established that the male sterility in 1046A(23A)is controlled by one locus. Then there are following genotypes,i.e. sterile MsMs,fertile MsMf,temporary- maintainer msms and restorer MfMf. This result modified previous conclusion that attributed the dominant control to two loci control. With the genetic model,we can have the following model to produce a full sterile line and F1 hybrids [6,7]. A schematic sketch for F1 hybrid production with dominant sterile materials 1046A(23A)is shown. Vol. 11 No.5,Oct

4 50 % sterile 50 % fertile MsMs rfrf MsMs Rfrf removal of fertile MsMs Rfrf sterile MsMs rfrf msms rfrf (temporary-maintainer) 100 % sterile Msms rfrf MsMs RfRf (restorers) msms RfRf(restorers) F1 hybrids As shown, Rf inbits sterile Ms expression. 3) Molecular cloning of genetic male sterile genes. Recently,researchers in Huazhong Agricultural University cloned the recessive Ms1 and Ms2 in S45A and the Ms3 in 7365 A [8,9]. They found that Ms1 mutation affects fertility proteins in S45A and the sterility is controlled in 7365A by a complex gene network including the down-regulation of TDF1,AMS and MYB103 genes. It was also proposed that BnMs3 plays a role in the development of anthers of rapeseed. 4 Views on current and future development of rapeseed hetorosis utilization 4.1 Combination of heterosis and ideotype breeding Heterosis and ideotype breeding have been shown to be effective in the enhancement of rapeseed yield. How does a rapeseed ideotype look like? The following criteria could be used for breeding selections to our opinions. Semi- dwarf and lodge- resistant,compact plant flowering branches with branch angle < 30 ;upward pods with pod density 1.3~1.5 cm -1 and a middle- long pod length. Recently,a rod- like rapeseed plant stature mutant was isolated. The mutant had very compact inflorescence with high pod density,which could be utilized in shortening flowering period and thus was highly desired for mechanization harvest. The mutant could also be used in breeding for further increase of the yield potential in hybrid development. 4.2 Sub-genome heterosis utilization Li Maoteng et al [10] proposed that sub-genome heterosis utilization could be an effective approach to raise further the yield potential in rapeseed hybrids. The genome of B. napus (designated as A n A n C n C n ) consists of B. oleracea( C o C o ) and B. rapa (A r A r ). Through interspecific hybridization between the two progenitor species,artificial synthesized B.napus will contain AA from B. rapa and CC from B. oleracea, which may introduce some novel variations from original AACC components in current B. napus. Similarly,interspecific hybridization between B.napus and B.rapa or B.oleracea can also substitute some genetic components in current AACC genomes. Using these novel B.napus as one of the parents for F1 hybrids could lead to stronger heterosis. A n A n C n C n A n A n C n C n (Hybrid from current B.napus) A n A n C o C o A n A n C n C n (Sub-genomic hybrid) A r A r C n C n A n A n C n C n (Sub-genomic hybrid) A r A r C o C o A n A n C n C n (Sub-genomic hybrid) Studies have showed that the F1 hybrids from sterile lines with subgenomic components exhibited stronger heterosis,three of which performed a 10 % increase of yield compared with the control group. 4.3 Quality traits and heterosis Previous studies on heterosis performance in rapeseed showed the following orders of the degree of heterosis ratios for agronomic traits:vegetative mass > seed yield trait > seed quality trait. Based on the calculations from the average heterosis ratios in 9 rapeseed varieties,it was found that vegetative traits had a heterosis of % ~30.15 %,plant yield 7.92 % and oil content 3.67 % [11]. Observations made in sorghum found that the average heterosis ration for 4 yield traits was 43.3 %,but % for 4 quality traits [12]. Possible reasons for weak heterosis in quality traits could be as follows. Firstly,formation of quality traits relates to not only the balance of each process of photosynthetic in source, flow and sink,but also substance transformation from one to another in sink. The physiological and biochemical processes are more complicated. Secondly,quality traits are beneficial for human demands,but may not for plant s survival and/or propagation. Thirdly,the direction of breeding selection and natural selection is often different,so it is very rare to have a desired 16 ENGINEERING SCIENCES

5 quality material in wild type. It has been demonstrated that many important quality traits are controlled by recessive major genes,for example two genes for erucic acid (e1e1e2e2),three genes for glucosinolate (g1g1g2g2g3g3) in rapeseed,and high lysine and high oil content as well as sweet kennels in maize. Therefore,to utilize heterosis for quality trait, both parents must have high quality. Normally,wild species have the dominant trait (AA) of poor quality, while a desirable quality trait controlled by aa gene is likely from artificial selection when AA mutated to Aa. It may be not easy to use the dominant effect of heterosis because the majority of quality traits are controlled by major recessive genes. 4.4 Disease resistance and heterosis On the contrast to quality traits,artificial selection and natural selection for disease resistance are in the same direction. This was demonstrated by the fact that disease resistant resources are often found in wild species. Furthermore,majority of disease resistant traits,if they are controlled by major genes,are controlled by dominant genes,for example,three genes for while rust resistance in B.napus (Table 6). Table 6 Crop Rapeseed Rapeseed Rice Sunflower Sunflower Sunflower Cotton Cotton Soybean Soybean Disease resistance traits and their genetic control in several major crops Traits (resistance to) White rust Blackleg at seedling stage Blast Downey mildew Rust Sclerosporiosis Angular leaf spot Wilt Frogeye leaf spot Downey mildew Genes 3 dominant genes 1 dominant gene 1~3 dominant genes The reasons for such a phenomenon could be as follows. Firstly,the resistance can only be kept when it is controlled by dominant genes (RR or Rr). Otherwise,the trait would be eliminated by natural selection before it becomes homozygous (if it is controlled by recessive gene (rr)). Secondly,the wild species populations due to natural selection usually contain highly resistant resources with a dominant nature. The evolution thus offers advantages to solve the problem in disease resistance by F1 hybrids. Apparently,we could make the following combinations: RR rr Rr (resistant to disease). Or even more, for more race specific resistance: R1R1r2r2 r1r1r2r2 R1r1R2r2 (resistant to 2 physiological races),or RRbb rrbb RrBb (resistant to 2 di-seases). We can also use both vertical (major genes) and horizontal resistance (polygenes) to obtain highly resistant and sustainable F1 hybrids,such as r1r1r2r2 (horizontal resistance) RR (vertical resistance) F1 (strong and stable resistance). 4.5 The relationships of source, sink and flow in hybrids Based on analysis of 46 hybrid varieties in 6 years,we found that the average heterosis percentage for vegetative biomass is 25 %~30 %,while for pods per plant,seeds per pod and seed weight are 73.3 %,17.5 % and 1.8 %,respectively. Leaves, pods and other above-ground green tissues are able to photosynthesize and are source organs, while seeds as the storage organs are sink for photosynthetic products. The fact that the seeds development is often not complete and seed weight has low heterosis ratio means that the sources are surplus while the sinks are not fully filled or utilized. This could be an indication that the flow is not so smooth,which results in lower heterosis in seed weight. This is also true in hybrid rice and triticale,which normally have a very flourish leaves and stems and large numbers of spikelet but are often not fully filled [13]. Therefore,to fully reach its potential in rapeseed heterosis,we should pay greater attention to solving inefficient transport,so that the photosynthetic products can be effectively transferred to reservoir. How to assay if the source, sink and flow are harmonized? We might consider that harvest index (HI) is used as a criterion. 5 Conclusions Rapeseed is the most important oil crop in China and the enhancement of rapeseed production through breeding high yield F1 hybrid cultivars plays a key role in promoting the further increase of seed yield and adaptability of cultivars. Currently Pol CMS is still the major type of pollination control system for F1 hybrid production in China. Great progresses are being made in researches on other pollination control systems,including recessive GMS. To reach the full potential of heterosis utilization in rapeseed,we need to better understand the genetic and physiological Vol. 11 No.5,Oct

6 mechanisms of heterosis and explore the novel approaches in breeding of F1 hybrids,as illustrated in this article. References [1] Cui Dexin,Deng Xixin. Studies and utilization of hybrid rapeseed (Brassica napus) [J]. Chinese Journal Oil Crops,1979(2): (in Chinese) [2] Fu Tingdong. Breeding and Utilization of Hybrid Rapeseed [M]. Wuhan:Hubei Press of Science and Technology,2000. (in Chinese) [3] McVetty P B E,Scarth R,Fernando W G D,et al. Brassica seed quality breeding at the University of Manitoba,sustainable development in cruciferous oilseed crops production [C]// Proceeding of the 12th International Rapeseed Congress. Wuhan,2007 (1): 2-4. [4] Ni Xiyuan,Xu Xiaodong,Ren Mengyang,et al. Fine mapping and candidate gene identification of a recessive genic male sterility gene (Bnms3) in rapeseed [C]// Proceedings of 13th International Rapeseed Congress. Prague,Czech,2011: [5] Xia Shengqian,Zu Feng,Zhu Yun,et al. Genetic analysis and improvement of a recessive genic male sterility in Brassica napus [C]//Proceedings of 13th International Rapeseed Congress. Prague,Czech,2011: [6] Song Laiqiang,Fu Tingdong,Tu Jinxing,et al. Molecular validation of multiple allele inheritance for dominant genic male sterility gene in Brassica napus L [J]. Theoretical and Applied Genetics,2006,113: [7] Hong Dengfeng,Liu Jun,Yang Guangsheng,et al. Development and characterization of SCAR markers associated with a dominant genic male sterility in rapeseed [J]. Plant Breeding,2008, 127: [8] Dun Xiaoling,Zhou Zhengfu,Xia Shengqian,et al. BnaC.Tic40,a plastid inner membrane translocon originating from Brassica oleracea,is essential for tapetal function and microspore development in Brassica napus [J]. Plant Journal,2011,68: [9] Yi Bin,Zeng Fangqin,Lei Shaolin,et al. Two duplicate CYP704B1 homologous genes BnMs1 and BnMs2 are required for pollen exine formation and tapetal development in Brassica napus[j]. Plant Journal,2010,63: [10] Li Maoteng,Qian Wei,Meng Jinling,et al. Construction of novel Brassica napus genotypes through chromosomal substitution and elimination using interploid species hybridization [J]. Chromosome Research,2004,12: [11] Zhang Shufen,Fu Tingdong,Song Wenguang. Heterosis research on yield and related agronomic traits of rapeseed cytoplasmic male sterility hybrids [J]. Act a Agriculturae Boreali- Sinica,1994,9: (in Chinese). [12] Zhang Wenyi. Heterosis analysis on Sorghum [J]. Liaoning Agricultural Sciences,1983(2):1-8. (in Chinese). [13] Li Zhebin,Xiao Xianghua,Zhu Yingguo. Studies and Practice of Hybrid Rice [M]. Shanghai:Shanghai Science and Technology Press,1982. (in Chinese) Author Fu Tingdong,male,born in 1938,graduated from Huazhong Agricultural University with a MS degree in He has been a full professor in plant genetics and breeding since His current research interests are the mechanism of heterosis and its utilization in rapeseed. He discovered the polima cytoplasmic male sterility cytoplasmic male sterility,the first rapeseed cytoplasmic mnle sterility type with practical values and widely utilized by rapeseed breeders worldwide. He bred thirteen rapeseed hybrid varieties,with a total accumulative area of over 7.0 million hectares. His group has cloned some important genic male sterility genes in rapeseed. He is an Academician of the Chinese Academy of Engineering and Academician of Third World Academy of Science (TWAS). He can be reached by futing@mail.hzau.edu.cn 18 ENGINEERING SCIENCES