Abstract. confirmation of field diagnosis the assistance of skilled plant pathologists

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2 Abstract S u b r a h m a n y a m, P., W o n g k a e w, S., R e d d y, D.V.R., D e m s k i, J.W., McDonald, D., Sharma, S.B., a n d Smith. D.H Field diagnosis of groundnut d i s u s e s. Information Bulletin no (In En, Fr. S u m - maries in En, Fr, Es.) Patancheru, A.P , India: International Crops Research Institute for the Semi-Arid Tropics. 84 pp. ISBN Order code IBE 036. Diseases are major constraints to groundnut production throughout the world. This handbook is designed to assist agricultural research a n d extension workers, who may have little formal training in plant pathology, to make tentative diagnosis of diseases of groundnut caused by 31 fungi, 2 bacteria. 9 viruses, a mycoplasma-like organism, 4 nematodes, and a parasitic flowering plant. The most characteristic field symptoms of each disease are Illustrated and described. It is emphasized that for confirmation of field diagnosis the assistance of skilled plant pathologists will be required in most cases.

3 Field Diagnosis of Groundnut Diseases P. S u b r a h m a n y a m, S. Wongkaew, D.V.R. Reddy, J.W. Demski, D. M c D o n a l d, S.B. S h a r m a, and D.H. Smith I C R I S A T I n f o r m a t i o n Bulletin n o. 3 6 International C r o p s R e s e a r c h Institute for t h e S e m i - A r i d T r o p i c s P a t a n c h e r u, A n d h r a P r a d e s h , India 1992

4 Co-sponsors International Development Research Centre (IDRC) International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Peanut Collaborative Research Support Program (Peanut CRSP) The Peanut C R S P contribution to this publication w a s m a d e possible through support provided by the Office of Agriculture, Bureau of R e s e a r c h a n d Development. U.S. Agency for International Development, under Grant number. DAN G About the Authors P. S u b r a h m a n y a m : Principal Plant Pathologist, SADC/ICRISAT Groundnut Improvement Project, Malawi. S. Wongkaew: Virologist, Khon Kaen University, Khon Kaen, Thailand. D.V.R. Reddy: Principal Plant Virologist, Legumes Program, ICRISAT. J.W. Demski: Professor, Department of Plant Pathology, University of Georgia, Griffin, GA 30223, USA. D. McDonald: Director, Legumes Program, ICRISAT. S.B. Sharma: Nematologist, Legumes Program, ICRISAT. D.H. Smith: Principal Plant Pathologist, Legumes Program, ICRISAT.

5 Contents I n t r o d u c t i o n 1 D i s e a s e s C a u s e d b y F u n g i 2 F o l i a r D i s e a s e s Early Leaf S p o t L a t e L e a f S p o t R u s t W e b B l o t c h S c a b A l t e r n a r i a L e a f S p o t a n d V e i n a l N e c r o s i s P h y l l o s t i c t a L e a f S p o t P o w d e r y M i l d e w C e r c o s p o r a L e a f B l i g h t M y r o t h e c i u m Leaf B l i g h t Z o n a t e L e a f S p o t S c l e r o t i u m L e a f S p o t C h o a n e p h o r a W e t B l i g h t P e p p e r S p o t a n d L e a f S c o r c h A n t h r a c n o s e A l t e r n a r i a L e a f Blight P e s t a l o t i o p s i s L e a f Blight S e e d a n d S e e d l i n g D i s e a s e s P r e e m e r g e n c e S e e d a n d S e e d l i n g R o t s A s p e r g i l l u s C r o w n R o t Y e l l o w M o l d Diplodia Collar R o t R h i z o c t o n i a D a m p i n g - o f f S t e m, R o o t, a n d P o d D i s e a s e s S t e m rot S c l e r o t i n i a B l i g h t C y l i n d r o c l a d i u m B l a c k R o t Botrytis B l i g h t VerticiIlium W i l t

6 F u s a r i u m W i l t C h a r c o a l Rot B l a c k h u l l P o d R o t D i s e a s e s C a u s e d b y B a c t e r i a B a c t e r i a l W i l t B a c t e r i a l L e a f S p o t D i s e a s e s C a u s e d b y V i r u s e s a n d a M y c o p l a s m a - L i k e O r g a n i s m P e a n u t M o t t l e P e a n u t S t r i p e P e a n u t C l u m p B u d N e c r o s i s G r o u n d n u t R o s e t t e P e a n u t S t u n t G r o u n d n u t S t r e a k N e c r o s i s C o w p e a M i l d M o t t l e P e a n u t Y e l l o w S p o t W i t c h e s ' B r o o m D i s e a s e s C a u s e d b y N e m a t o d e s R o o t - k n o t R o o t - l e s i o n K a l a h a s t i M a l a d y P e a n u t C h l o r o s i s D i s e a s e C a u s e d b y a P a r a s i t i c F l o w e r i n g P l a n t W i t c h W e e d S u p p o r t i n g L i t e r a t u r e 7 6 P h o t o C r e d i t s 7 8

7 Introduction C u l t i v a t e d g r o u n d n u t ( p e a n u t ), Arachis hypogaea L., an a n n u a l l e g u m e n a t i v e t o S o u t h A m e r i c a, i s p r i m a r i l y c u l t i v a t e d i n a r e a s o f t h e w o r l d b o u n d e d b y l a t i t u d e s 4 0 ' N a n d 4 0 ' S. A p p r o x i m a t e l y 8 0 % o f t h e w o r l d g r o u n d n u t c r o p i s p r o d u c e d i n d e v e l o p i n g c o u n t r i e s w h e r e t h e y i e l d s a r e u s u a l l y v e r y l o w. D i s e a s e s a r e m a j o r c o n s t r a i n t s t o g r o u n d n u t p r o d u c t i o n t h r o u g h o u t t h e w o r l d. A l a r g e n u m b e r o f d i s e a s e s c a u s e d b y f u n g i, b a c t e r i a, v i r u s e s, m y c o p l a s m a, n e m a t o d e s, a n d p a r a - sitic f l o w e r i n g p l a n t s h a v e b e e n r e p o r t e d, a n d w i t h s o m e e x c e p t i o n s, t h e y a r e w i d e l y d i s t r i b u t e d. All p a r t s o f t h e g r o u n d n u t p l a n t a r e s u s c e p t i b l e t o d i s e a s e s. T h i s h a n d b o o k i s d e s i g n e d t o a s s i s t a g r i c u l t u r a l scie n t i s t s a n d e x t e n s i o n w o r k e r s i n t h e p r e l i m i n a r y f i e l d d i a g n o s i s o f c o m m o n d i s e a s e s o f g r o u n d n u t c a u s e d b y f u n g i, b a c t e r i a, v i r u s e s, m y c o p l a s m a, n e m a t o d e s, a n d a p a r a s i t i c f l o w e r i n g p l a n t. T h e m o s t c h a r a c t e r i s t i c f i e l d s y m p t o m s o f e a c h d i s e a s e a r e i l l u s t r a t e d a n d d e - s c r i b e d. It is i m p o r t a n t to. u n d e r s t a n d t h a t d i a g n o s i s of d i s e a s e s b a s e d o n t h e i r p a t t e r n o f o c c u r r e n c e a n d m a c r o s c o p i c s y m p t o m s c a n i n m o s t c a s e s b e o n l y t e n - tative, a n d that for a critical differentiation of d i s e a s e s w i t h n e a r l y s i m i l a r f i e l d s y m p t o m s, m i c r o s c o p i c e x a m - i n a t i o n o f t h e d i s e a s e d t i s s u e s a n d f r u i t i n g s t r u c t u r e s o f t h e p a t h o g e n is r e q u i r e d. A h a n d l e n s (x 15 to x 2 5 ) is n e c e s s a r y for f i e l d d i a g n o s i s o f s o m e d i s e a s e s. Identif i c a t i o n o f m o s t v i r u s d i s e a s e s r e q u i r e s l a b o r a t o r y t e s t s s u c h a s e n z y m e - l i n k e d i m m u n o s o r b e n t a s s a y ( E L I S A ), u s e o f d i a g n o s t i c t e s t p l a n t s, a n d e l e c t r o n m i c r o s c o p y. A s d i s e a s e s y m p t o m s c a n b e i n f l u e n c e d b y g e - n o t y p e a n d e n v i r o n m e n t, t h e u s e r s o f this h a n d b o o k a r e a d v i s e d t o h a v e t h e d i s e a s e d s p e c i m e n s / t i s s u e s f u r t h e r e x a m i n e d u n d e r t h e m i c r o s c o p e a n d l a b o r a t o r y t e s t s c o n d u c t e d b y c r o p p r o t e c t i o n s c i e n t i s t s t o c o n f i r m t h e f i e l d d i a g n o s e s. S e v e r a l p u b l i c a t i o n s t h a t s h o u l d p r o v e t o b e u s e f u l i n s u c h c o n f i r m a t o r y w o r k a r e listed o n p a g e s

8 Diseases C a u s e d by Fungi Foliar Diseases Early Leaf Spot Cercospora arachidicola Hori Distribution. W o r l d w i d e. S y m p t o m s. L e s i o n s a r e sub-circular, d a r k b r o w n o n the upper leaflet surface w h e r e m o s t sporulation occurs, a n d a lighter shade of brown on the lower leaflet surface [Fig. 1, three leaflets s h o w i n g upper surface, o n e leaflet (top right) t u r n e d to s h o w lower s u r f a c e ]. A chlorotic halo c o m m o n l y surrounds the lesion on the upper surface. Spores of C. arachidicola are p r o d u c e d mainly on the necrotic tissue of lesions on t h e u p p e r leaflet surface. Lesions are also p r o d u c e d on petioles, s t e m s, stipules, a n d p e g s ; t h e s e are oval to e l o n g a t e a n d h a v e m o r e distinct m a r g i n s t h a n leaflet l e s i o n s (Fig. 2). W h e n the disease attack is severe, affected leaflets b e c o m e chlorotic, then necrotic, a n d lesions often c o a l e s c e, resulting in p r e m a t u r e s e n e s c e n c e a n d s h e d d i n g of leaflets (Fig. 3). 2

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10 Late Leaf Spot Phaeoisariopsis personata (Berk. & M.A. Curtis) van Arx Cercosporidium personatum (Berk. & M.A. Curtis) Deighton D i s t r i b u t i o n. W o r l d w i d e. S y m p t o m s. W h e n t h e lower leaflet s u r f a c e i s v i e w e d, late leaf spots (Fig. 4, right) are nearly circular a n d darker t h a n early leaf spots (Fig. 4, left). On the lower leaflet s u r f a c e w h e r e m o s t o f t h e s p o r u l a t i o n o c c u r s t h e lesions are b l a c k a n d slightly r o u g h in a p p e a r a n c e ( F i g. 5, right, x 6). Circular rings of fruiting structures on t h e lesions of the lower leaflet surface c a n be s e e n with the aid of a h a n d lens. Late leaf spot lesions c a n be disting u i s h e d f r o m t h o s e of early leaf s p o t that are lighter in color a n d m a y be s u r r o u n d e d by a chlorotic h a l o (Fig. 5, left, x 6). W h e n d i s e a s e attack is s e v e r e, a f f e c t e d leaflets b e c o m e c h l o r o t i c, t h e n n e c r o t i c, a n d l e s i o n s often c o a l e s c e, r e s u l t i n g i n p r e m a t u r e s e n e s c e n c e a n d s h e d d i n g of the leaflets (Fig. 6). Oval to elongate lesions similar to t h o s e of early leaf spot (Fig. 2) are also f o r m e d o n p e t i o l e s, s t e m s, s t i p u l e s, a n d p e g s. Late leaf spot attack is u s u a l l y c o i n c i d e n t w i t h that of rust. 4

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12 Rust Puccinia arachidis Spegazzini D i s tribution. W o r l d w i d e. S y m p t o m s. O r a n g e - c o l o r e d p u s t u l e s (Fig. 7, x 7) appear on the lower surfaces of leaflets a n d rupture to release m a s s e s of reddish- brown spores. In susceptible (Fig. 8) cultivars the original pustules m a y be surr o u n d e d by c o l o n i e s of s e c o n d a r y p u s t u l e s. Pustules m a y a p p e a r later on t h e u p p e r s u r f a c e of the leaflets opposite t h o s e on the lower surface. Lesions c a n be formed on all aerial plant parts e x c e pt flowers. T h o s e on t h e s t e m s are e l o n g a t e (Fig. 9). In contrast to the rapid defoliation a s s o c i a t e d w i t h leaf s p o t s, l e a v e s infected with rust b e c o m e necrotic a n d dry up, but tend to remain attached to the plant (Fig. 10). Rust d i s e a s e usually occurs at the s a m e time as late leaf spot. 6

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14 Web Blotch Didymella arachidicola (Chock.) Taber, pettit & philley Distribution. A n g o l a, Argentina, Australia, Brazil, Canada, China, Commonwealth of Independent Sates, J a p a n, Lesotho, Malawi, Nigeria, South Africa, S w a z i l a n d, U S A, Z a m b i a, a n d Z i m b a b w e. S y m p t o m s. Lesions first a p p e a r on t h e upper surfaces of the lower leaves as scattered t a n - c o l o r e d s p e c k s or streaks that form a w e b b e d pattern (Fig. 11a, and b ). The discolored areas e x p a n d, forming large, nearly circular, purplish- brown to d a r k b r o w n blotches w i t h inc o n s p i c u o u s m a r g i n s ( F i g. 1 1 c ). B l o t c h e s o f t e n coalesce a n d cover the entire leaflet. Mature lesions are nearly black a n d have roughened surfaces (Fig. 11d). On the lower leaflet s u r f a c e, d i s e a s e s y m p t o m s b e c o m e visible only after the blotches on the upper s u r f a c e a r e w e l l d e v e l o p e d. P e t i o l e s, s t i p u l e s, a n d stems are also i n v a d e d by the fungus. Severe d i s e a s e attack l e a d s to p r e m a t u r e defoliation. U n d e r moist c o n - ditions fruiting bodies are f o r m e d on infected fallen leaves a n d may be detected by use of a hand lens. 8

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16 Scab Sphaceloma arachidis Bitancourt & Jenkins Distribution. Argentina, Brazil, J a p a n, a n d S w a z i l a n d (?). S y m p t o m s. N u m e r o u s r o u n d t o i r r e g u l a r l e s i o n s a p - p e a r o n b o t h s u r f a c e s o f leaflets a n d a r e e i t h e r unif o r m l y d i s t r i b u t e d o v e r t h e e n t i r e leaflet o r a r e c l u s t e r e d n e a r t h e m i d r i b. T h e l e s i o n s o n u p p e r leaflet s u r f a c e s a r e light t a n w i t h s u n k e n c e n t e r s a n d r a i s e d m a r g i n s. L e s i o n s a r e f r e q u e n t l y c o v e r e d w i t h c o n t i n u o u s v e l v e t - like l a y e r s o f g r e y i s h o l i v e - g r e e n f r u i t i n g b o d i e s. O n t h e s u r f a c e o f lower leaflets t h e l e s i o n s a r e d a r k e r a n d their m a r g i n s a r e not r a i s e d. O n p e t i o l e s a n d b r a n c h e s l e - s i o n s a r e n u m e r o u s, larger, a n d m o r e i r r e g u l a r i n a p - p e a r a n c e t h a n l e s i o n s o n l e a f l e t s. T h e l e s i o n s o n p e t i o l e s a n d b r a n c h e s m a y d e v e l o p into c a n k e r o u s s c a b s, g i v i n g t h e p l a n t s a b u r n t a p p e a r a n c e ( F i g. 12). L e s i o n s c o v e r n e a r l y all of t h e plant, i n c l u d i n g p e g s. In a d v a n c e d s t a g e s o f d i s e a s e d e v e l o p m e n t p l a n t s a r e s t u n t e d a n d s t e m s b e c o m e s i n u o u s ( F i g. 13). 10

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18 Alternaria Leaf Spot and Veinal Necrosis Alternaria alternata (Fries) Keissler D i s t r i b u t i o n. I n d i a, V i e t n a m, a n d T h a i l a n d. S y m p t o m s. S m a l l, chlorotic, w a t e r - s o a k e d l e s i o n s a p - p e a r r a n d o m l y o v e r both s u r f a c e s o f t h e leaflets. T h e y e n l a r g e, b e c o m e i r r e g u l a r i n s h a p e, a n d a r e b r o w n w i t h d a r k e r b r o w n m a r g i n s ( F i g. 1 4 ) ; t h e c e n t r a l p o r t i o n s later b e c o m e p a l e, d r y rapidly, a n d d i s i n t e g r a t e. Veins a n d veinlets adjacent to the lesions b e c o m e necrotic. Affected leaflets are chlorotic a n d in severe a t t a c k s t h e y p r e m a t u r e l y s e n e s c e. W h e n m a n y l e s i o n s are p r e s e n t they c o a l e s c e, g i v i n g t h e leaf a r a g g e d a n d b l i g h t e d a p p e a r a n c e. P r o f u s e s p o r u l a t i o n o c c u r s o n older l e s i o n s on t h e u p p e r s u r f a c e s of t h e leaflets. T h i s p a t h o g e n a l s o c a u s e s leaf blight. Phyllosticta Leaf Spot Phyllosticta arachidis-hypogaea Vasant Rao D i s t r i b u t i o n. B u r k i n a F a s o, India, M a l a w i, M o z a m b i - q u e, Niger, N i g e r i a, S w a z i l a n d, T h a i l a n d, a n d Z i m - b a b w e. S y m p t o m s. T h i s f u n g u s is a s e c o n d a r y p a t h o g e n. Infection starts i n d a m a g e d a n d n e c r o t i c t i s s u e a n d s u b - s e q u e n t l y s p r e a d s into t h e living g r e e n a r e a s o f t h e leaflets. Lesions are circular to irregular a n d are light t a n i n color s u r r o u n d e d b y a r e d d i s h - b r o w n b o r d e r ( F i g. 15). S h o t - h o l e s m a y a p p e a r later. L e s i o n s m a y c o - a l e s c e into i r r e g u l a r n e c r o t i c p a t c h e s. W h e n e x a m i n e d u s i n g a h a n d l e n s, n u m e r o u s s c a t t e r e d d a r k b r o w n fruiting b o d i e s c a n b e o b s e r v e d o n t h e l e s i o n s o n both leaflet s u r f a c e s. 12

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20 Powdery Mildew Oidium arachidis Chorin D i s t r i b u t i o n. India a n d Israel. S y m p t o m s. L a r g e s p o t s c o v e r t h e u p p e r s u r f a c e s o f l e a f l e t s. T h e s e s p o t s a r e c o v e r e d w i t h s u p e r f i c i a l s p o r u l a t i n g f u n g a l g r o w t h w h i c h g i v e s t h e m a p o w d e r y w h i t e a p p e a r a n c e (Fig. 16). T h e c e n t e r s o f t h e s p o t s later b e c o m e b r o w n a n d necrotic. Cercospora Leaf Blight Cercospora canescens EMS & Martin D i s t r i b u t i o n. T h a i l a n d. S y m p t o m s. S m a l l n e c r o t i c l e s i o n s a p p e a r o n leaflets, t h e s e l e s i o n s e n l a r g e a n d b e c o m e i r r e g u l a r o r a n g u l a r - s h a p e d light b r o w n s p o t s. W h e n long p e r i o d s o f leaf w e t n e s s o c c u r, t h e s p o t s c o a l e s c e l e a d i n g t o b l i g h t i n g a n d defoliation (Fig. 17). W h e n c l o s e l y e x a m i n e d, w h i t e m a s s e s o f s p o r e s a r e visible o n n e c r o t i c a r e a s o f b o t h leaf s u r f a c e s. 14

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22 Myrothecium Leaf Blight Myrothecium roridum Tode ex Fries Distribution. India a n d T h a i l a n d. S y m p t o m s. Lesions are round to irregular w i t h greybrown colored centers a n d b r o w n m a r g i n s s u r r o u n d e d by chlorotic halos. T h e y occur on both s u r f a c e s of leaflets. W h e n lesions coalesce leaves appear blighted. A b u n d a n t olive g r e e n to black fruiting b o d i e s, often arr a n g e d in concentric rings, are f o r m e d on the necrotic areas of both leaflet surfaces (Fig. 18). Zonate Leaf Spot Cristulariella moricola (Hino) Redhead Distribution: India, Thailand, a n d USA. S y m p t o m s : Necrotic spots r a n g i n g f r o m 2 to 12 mm in d i a m e t e r a p p e a r o n leaflets ( F i g. 19). S m a l l l e s i o n s have a light brown center surrounded by a brown ring of necrotic tissue, but larger lesions s h o w a zonate pattern on both leaflet surfaces. S p o r e s m a y be produced on necrotic tissues of both leaflet s u r f a c e s. 16

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24 Sclerotium Leaf Spot Sclerotium rolfsii Saccardo Distribution. India, Malawi, a n d Thailand. S y m p t o m s. A p p e a r on mature plants as grey necrotic ring spots w h i c h m a y d e v e l o p shot h o l e s (Fig. 2 0 ). During long periods of leaf w e t n e s s the spots c o a l e s c e leading to a severe blight. Minute sclerotia (about 0.5 to 0.8 mm in diameter) initially w h i t e, but later b r o w n i s h in color can be s e e n on both leaflet surfaces. This p a t h o g e n also c a u s e s s t e m, root, a n d p o d diseases which are more d a m a g i n g than the leaf spots. Choanephora Wet Blight Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. D i s tribution. Thailand a n d Philippines: S y m p t o m s. W a t e r - s o a k e d lesions first a p p e a r o n t h e tips of y o u n g unfolding leaves. Subsequently the les i o n s b e c o m e necrotic a n d a r e c o v e r e d w i t h a d a r k b r o w n s p o r e m a s s (Fig. 21). If leaves stay wet for long p e r i o d s, the f u n g u s c a n attack y o u n g s h o o t s a n d c a n kill the g r o w i n g tips. T h e s e s y m p t o m s c a n be m i s t a k e n for d a m a g e c a u s e d b y coreid b u g s. D e a d tissue d a m - a g e d by C. cucurbitarum c a n be d i s t i n g u i s h e d f r o m b u g - d a m a g e d t i s s u e b y t h e p r e s e n c e o f s p o r e s p r o - d u c e d by the wet blight p a t h o g e n. 18

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26 Pepper Spot and Leaf Scorch Leptosphaerulina crassiasca (sechet) jackson & Bell Distribution. A n g o l a, A r g e n t i n a, B u r k i n a F a s o, India, M a d a g a s c a r, M a u r i t i u s, M a l a w i, M o z a m b i q u e, Niger, Nigeria, S e n e g a l, S w a z i l a n d, T h a i l a n d, T a i w a n, U S A, V i e t n a m, Z a m b i a, a n d Z i m b a b w e. S y m p t o m s. T h e p e p p e r spot p h a s e o f the d i s e a s e i s r e c o g n i z e d by the a p p e a r a n c e of m i n u t e necrotic s p o t s on lower leaves (Fig. 2 2, above). The spots are numerous, dark brown to black, irregular to circular a n d o c c a s i o n a l l y d e p r e s s e d. D i s c r e t e l e s i o n s a p p e a r o n both s i d e s of the leaflet; but are m o r e often f o u n d on upper s u r f a c e s. W h e n a b u n d a n t, l e s i o n s c o a l e s c e giving the leaflet s u r f a c e a netted a p p e a r a n c e. Leaf s c o r c h, t h e m o s t c o m m o n s y m p t o m, frequently develops on the tips, a n d occasionally on the margins, of leaflets. T h e w e d g e - s h a p e d l e s i o n s h a v e a bright yellow z o n e a l o n g t h e p e r i p h e r y o f their a d v a n c i n g m a r - gins (Fig. 22, below). The necrotic tissue b e c o m e s dark brown a n d tends to fragment along the leaflet margins, so that t h e leaves look tattered. 20

27 22 21

28 Anthracnose Colletotrichum arachidis Sawada Colletotrichum dematium (Pers.) Grove Colletotrichum mangenoti chevaugeon D i s t r i b u t i o n. India, Niger, N i g e r i a, S u d a n, S e n e g a l, T a i w a n, T a n z a n i a, T h a i l a n d, U g a n d a, a n d U S A. S y m p t o m s. W e d g e - s h a p e d l e s i o n s w h i c h r e s e m b l e t h o s e c a u s e d by Leptosphaerulina crassiasca a p p e a r on the leaflet tips (Fig. 23). Lesions m a y also develop on the leaflet margins leading to marginal blight. T h e periphery of the advancing margins of t h e lesion is surr o u n d e d by a bright yellow z o n e. T h e necrotic tissue b e c o m e s dark brown and tends to fragment along the leaflet margins. T h e disease m a y also extend to stipules a n d s t e m s. Fruiting b o d i e s, visible t h r o u g h a h a n d lens, are a b u n d a n t on d i s e a s e d tissues. 22

29 23 23

30 Alternaria Leaf Blight Alternaria alternata (Fr.) Keissler Alternaria tenuissima (Kunze ex pers.) Wiltshire Alternaria arachidis Kulkarni Distribution. India, Nigeria, a n d Thailand. S y m p t o m s. Light to d a r k b r o w n irregular spots a p p e a r towards the tips or margins of the leaves. T h e s e rapidly enlarge a n d c o a l e s c e to form w e d g e - s h a p e d lesions. A distinct chlorotic zone c o m m o n l y develops along the edge of necrotic tissue (Fig. 24). In t h e later stages of d i s e a s e d e v e l o p m e n t, b l i g h t e d a r e a s b e c o m e d a r k brown a n d brittle a n d tend to fragment. Dark spore masses a p p e a r on necrotic tissues. Defoliation occurs w h e n the disease is severe. T h e s c o r c h s y m p t o m s r e s e m b l e t h o s e c a u s e d b y Leptosphaerulina crassiasca a n d Colletotrichum spp, a n d it is often difficult to distinguish b e t w e e n t h e s e diseases in the field. Alternaria alternata also c a u s e s leaf spots a n d veinal necrosis as described earlier. 24

31 24 25

32 Pestalotiopsis Leaf Blight Pestalotiopsis arachidis satya D i s t r i b u t i o n. India, N i g e r i a, a n d T h a i l a n d. S y m p t o m s. D a r k b r o w n circular l e s i o n s s u r r o u n d e d b y faint yellow haloes a p p e a r on infected leaves. Lesions e n l a r g e a n d c o a l e s c e l e a d i n g t o s e v e r e n e c r o s i s o f leaflets, especially on the m a r g i n s (Fig. 25). Very small b l a c k s p h e r i c a l fruiting b o d i e s visible t h r o u g h a h a n d lens c a n be f o u n d in t h e c e n t e r s of t h e l e s i o n s or in blighted a r e a s of leaflets. S y m p t o m s of this d i s e a s e r e s e m b l e t h o s e of altern a r i a leaf b l i g h t, e x c e p t t h a t t h e y e l l o w b o r d e r s u r - r o u n d i n g t h e b l i g h t e d a r e a s i s less c o n s p i c u o u s. 2 6

33 25 2 7

34 Seed and Seedling Diseases Preemergence Seed a n d Seedling Rots Aspergillus niger van Tieghem Aspergillus flavus Link ex Fries Macrophomina phaseolina (Tassi) Goidanich Sclerotium rolfsii Saccardo Rhizoctonia solani Kuhn Lasiodiplodia theobromae (Pat.) Griffon & Maubl. Rhizopus spp, Penicillium spp, Pythium spp, and Fusarium spp Distribution. W o r l d w i d e. S y m p t o m s. Infected s e e d a n d s e e d l i n g s are r e d u c e d to a d a r k b r o w n or black s p o n g y m a s s of rotted tissue c o v e r e d w i t h s p o r u l a t i n g m y c e l i u m w h i c h v a r i e s i n c o l o r d e p e n d i n g u p o n the s p e c i e s i n v o l v e d. Figure 2 6 s h o w s a seedling attacked by Pythium spp. D e c a y is most rapid w h e n infected s e e d s a r e s o w n b e c a u s e t h e s e e d - b o r n e f u n g i b e c o m e active as s o o n as t h e s e e d s absorb water. Bacteria are also involved in s e e d rotting but are normally s e c o n d a r y i n v a d e r s of s e e d a t t a c k e d by f u n g i. 28

35 26 29

36 Aspergillus Crown Rot Aspergillus niger van Tieghem D i s tribution. W o r l d w i d e. S y m p t o m s. In a moist soil e n v i r o n m e n t s e e d s m a y be attacked a n d killed l e a d i n g to a p r e e m e r g e n c e rotting. If s e e d s that did not e m e r g e are carefully r e m o v e d f r o m t h e soil they m a y be c o v e r e d w i t h m a s s e s of b l a c k c o n i d i a w h i c h g i v e t h e m a s o o t y a p p e a r a n c e. Poste m e r g e n c e infection often c u l m i n a t e s i n d e a t h a n d rapid d e c a y of s e e d l i n g s. T h e first s y m p t o m in e m e r g e d s e e d l i n g s is usually rapid d e s i c c a t i o n of t h e entire plant. A f f e c t e d tissue is c o v e r e d by the s p o r u l a t i n g f u n g u s at t h e soil s u r f a c e. As the infection p r o g r e s s e s, t h e entire collar region bec o m e s d a r k b r o w n a n d s h r e d d e d. S e e d l i n g infection c o m m o n l y occurs in the cotyledonary- hypocotyl region shortly after e m e r g e n c e. T h e infected a r e a s b e c o m e water- soaked a n d light b r o w n, and are soon covered with black fungal spores (Fig. 27). Mature plants are also a t t a c k e d. L e s i o n s d e v e l o p o n the stem just below the soil surface a n d then s p r e a d u p w a r d a l o n g the b r a n c h e s. B e c a u s e o f the w o o d i n e s s of mature plants, s y m p t o m s are generally not observed until either the b r a n c h e s wilt permanently, or wilting of t h e e n t i r e p l a n t i s a p p a r e n t. T h e d e a d a n d d r i e d branches are easily d e t a c h e d from the disintegrated collar r e g i o n. T h e f u n g u s s p o r u l a t e s on t h e s u r f a c e of mature p o d s resulting in p a t c h e s of b l a c k sooty s p o r e s (Fig. 28). 30

37

38 Yellow Mold Aspergillus flavus Link ex Fries D i s t r i b u t i o n. W o r l d w i d e. S y m p t o m s. S e e d s a n d n o n e m e r g e d s e e d l i n g s a t t a c k e d b y t h e f u n g u s a r e r a p i d l y r e d u c e d t o a s h r i v e l l e d, d r i e d b r o w n o r b l a c k m a s s c o v e r e d b y y e l l o w o r g r e e n i s h - y e l l o w s p o r e s. D e c a y i s m o s t r a p i d w h e n infected s e e d s a r e s o w n a n d t h e f u n g u s b e c o m e s a c - tive a s the s e e d s h y d r a t e. I n s o m e c a s e s t h e e m e r g i n g radicle a n d h y p o c o t y l b e c o m e i n f e c t e d a n d rapidly d e - c a y. After s e e d l i n g e m e r g e n c e t h e r e m i g h t not b e a n y n e w i n f e c t i o n, but p r e v i o u s l y i n f e c t e d c o t y l e d o n s h a v e necrotic l e s i o n s w i t h r e d d i s h - b r o w n m a r g i n s c o v e r e d b y y e l l o w o r g r e e n i s h - y e l l o w s p o r e s ( F i g. 2 9 ). T h i s p h a s e of t h e d i s e a s e is very s i m i l a r to t h e c r o w n rot c a u s e d by Aspergillus niger, a n d in s o m e d i s e a s e d p l a n t s b o t h f u n g i m a y be p r e s e n t. W h e n t h e s t r a i n of A. flavus c a u s i n g t h e s e e d l i n g d i s e a s e p r o d u c e s a f l a t o x i n, t h e plants m a y be severely stunted with chlorotic or pale g r e e n l e a v e s w i t h v e i n - c l e a r i n g o f l e a f l e t s, t h a t a r e s m a l l e r t h a n u s u a l a n d h a v e p o i n t e d tips ( F i g. 3 0 ). R o o t d e v e l o p m e n t i s r e d u c e d b y i n f e c t i o n. T h i s s y m p t o m i s k n o w n a s 'aflaroot'. 32

39

40 Diplodia Collar Rot Lasiodiplodia theobromae (Pat.) Griffon & Maubl. D i s t r i b u t i o n. A u s t r a l i a, I n d i a, I s r a e l S o u t h A f r i c a, T h a i l a n d, U S A, a n d V e n e z u e l a. S y m p t o m s. S e e d l i n g s o r m a t u r i n g p l a n t s a r e i n f e c t e d at or near the soil surface a n d the f u n g u s quickly inv a d e s t h e s t e m. W i l t i n g o f lateral b r a n c h e s o r t h e entire plant is the first field s y m p t o m. Infected plants usually die w i t h i n a f e w d a y s. T h e b a s e of t h e i n f e c t e d p l a n t s a n d t h e t a p root b e c o m e slate g r e y t o b l a c k a n d e a s i l y s h r e d ( F i g. 31). B l a c k p y c n i d i a d e v e l o p a s p i m p l e - l i k e d o t s o n t h e n e c r o t i c t i s s u e s. Rhizoctonia Damping-off Rhizoctonia solani Kuhn D i s t r i b u t i o n. W o r l d w i d e. S y m p t o m s. P r e - o r p o s t e m e r g e n c e i n v a s i o n b y s e e d - o r s o i l b o r n e i n o c u l u m r e s u l t s i n s e e d l i n g d e a t h. I n e m e r g e d s e e d l i n g s, l e s i o n s a r e m o s t f r e q u e n t l y o b - s e r v e d o n t h e h y p o c o t y l a s s u n k e n, e l o n g a t e, d a r k b r o w n a r e a s j u s t b e l o w t h e soil s u r f a c e ( F i g. 3 2 ). T h e l e s i o n s e n l a r g e, b e c o m e b l a c k, a n d g i r d l e t h e h y p o - cotyl l e a d i n g t o t y p i c a l ' d a m p i n g - o f f s y m p t o m s. S i m i l a r l e s i o n s d e v e l o p o n t a p r o o t s, a n d e x t e n d t o t h e entire root s y s t e m l e a d i n g t o d r y root rot, w h i c h s u b s e q u e n t l y kills t h e plant. T h e d e c a y e d a r e a s a r e often c o v e r e d b y a light b r o w n m y c e l i a l m a t. D a r k b r o w n, p i n h e a d - s i z e d sclerotia m a y d e v e l o p o n t h e d e a d t i s s u e s. 34

41

42 Stem, Root, and Pod Diseases Stem Rot Sclerotium rolfsii Saccardo D i s tribution. W o r l d w i d e. S y m p t o m s. The pathogen attacks all parts of the plant, but stem infection is the most c o m m o n a n d destructive. Yellowing and wilting of b r a n c h e s near the base of the plant is the first s y m p t o m. Sheaths of white mycelium develop at or near the soil line a r o u n d the affected a r e a s o f t h e s t e m w h i c h b e c o m e s h r e d d e d (Fig. 3 3 ). A b u n d a n t s c l e r o t i a, w h i t e initially a n d later t u r n i n g brown, develop on the infected areas. T h e entire plant c a n b e k i l l e d, but i n s o m e c a s e s only t w o o r t h r e e b r a n c h e s a r e a f f e c t e d. Infection o f p e g s, p o d s, a n d roots o c c u r s either i n d e p e n d e n t l y or together with s t e m infection. Lesions on the developing p e g s may retard p o d d e v e l o p m e n t. O r a n g e o r b r o w n c o l o r e d l e s i o n s may be found on the pods. Severely infected p o d s are c o m p l e t e l y c o v e r e d w i t h a w h i t e m y c e l i a l m a t, a n d eventually d e c a y. I n s o m e c a s e s t h e s e e d s f r o m t h e diseased p o d s s h o w a characteristic bluish- grey disc o l o r a t i o n o f t h e t e s t a k n o w n a s ' b l u e d a m a g e ' (Fig. 3 4 ). 3 6

43

44 Sclerotinia Blight Sclerotinia minor jagger Sclerotinia sclerotiorum (Lib.) de Bary D i s t r i b u t i o n. A r g e n t i n a, A u s t r a l i a, C h i n a, T a i w a n, U S A, a n d Z i m b a b w e. S y m p t o m s. First e v i d e n c e of infection is t h e s u d d e n wilting o f lateral b r a n c h e s, w h i c h a r e usually i n v a d e d a t t h e soil s u r f a c e. S m a l l, light g r e e n, w a t e r - s o a k e d les i o n s a p p e a r o n t h e s t e m s. T h e s e l a t e r b e c o m e sunken, elongated, a n d turn a light tan color. Older lesions are dark brown with a distinct border b e t w e e n infected a n d healthy tissues. T h e fungus c a n spread from the lateral b r a n c h e s t o infect t h e m a i n s t e m. T h e foliage o n infected b r a n c h e s b e c o m e s chlorotic, t u r n s dark b r o w n, a n d w i t h e r s, resulting in a b l i g h t e d a p p e a r - a n c e. W h i t e, fluffy m y c e l i u m d e v e l o p s o n d e a d t i s s u e s in wet w e a t h e r (Fig. 3 5 ). P e g s are usually i n v a d e d at the soil line. S h r e d d i n g of t h e b r a n c h a n d p e g t i s s u e s is characteristic of t h e d i s e a s e, a n d it results in severe p o d loss. Black, irregularly s h a p e d sclerotia are prod u c e d a b u n d a n t l y o n i n f e c t e d leaflets, b r a n c h e s, a n d p e g s. Sclerotia are a l s o p r o d u c e d o n p o d s (Fig. 3 6 ), a n d o n s e e d s i n s i d e t h e p o d s ( F i g. 3 7 ). 38

45

46 Cylindrocladium Black Rot Cylindrocladium crotalariae (Loos) Ben & sobers Distribution. Australia, India, J a p a n, a n d USA. S y m p t o m s. D i s e a s e d plants a p p e a r in t h e field in localized p a t c h e s (Fig. 38) w h i c h enlarge in s u b s e q u e n t years. Early s y m p t o m s are chlorosis a n d wilting of foliage on t h e m a i n s t e m. Lateral b r a n c h e s m a y not be affected, a n d occasionally plants m a y not wilt but app e a r chlorotic a n d s t u n t e d. R e d d i s h - o r a n g e fruiting b o d i e s a r e f o r m e d i n d e n s e c l u s t e r s o n i n f e c t e d b r a n c h e s at t h e soil line (Fig. 39). All s u b t e r r a n e a n plant parts c a n b e affected. L e s i o n s o n p e g s a n d p o d s m a y r e m a i n discrete (Fig. 40), or in severe c a s e s the disease may destroy pods a n d roots. 40

47

48 Botrytis Blight Botrytis cinerea pers. ex Fries D i s tribution. Australia, C o m m o n w e a l t h of I n d e p e n d e n t S t a t e s, J a p a n, M a l a w i, R o m a n i a, S o u t h A f r i c a, S w a z i l a n d, T a n z a n i a, U S A, V e n e z u e l a, V i e t n a m, a n d Z i m b a b w e. S y m p t o m s. F o l i a g e in c o n t a c t w i t h the soil surface is i n v a d e d a n d m a y d e c a y rapidly. Infected s t e m s a n d leaves are s p a r s e l y c o v e r e d w i t h grey s p o r u l a t i n g fungal growth (Fig. 41). T h e disease spreads to pegs and p o d s a n d t h e entire plant m a y b e killed. B l a c k sclerotia d e v e l o p o n t h e d i s e a s e d s t e m s a n d p o d s (Fig. 4 2 ). Verticillium Wilt Verticillium albo-atrum Reinke & Berthier Verticillium dahliae Kleb. D i s t r i b u t i o n. Argentina, Australia, Israel, a n d USA. S y m p t o m s. E a r l y s y m p t o m s u s u a l l y a p p e a r a t t h e f l o w e r i n g s t a g e. T h e y i n c l u d e ; m a r g i n a l c h l o r o s i s o f leaves (Fig. 43), loss of leaf turgidity, a n d leaf curling. Later s y m p t o m s a r e g e n e r a l y e l l o w i n g a n d leaflet n e c - rosis, followed by wilting a n d defoliation. During the early s t a g e s of d i s e a s e d e v e l o p m e n t, plants wilt d u r i n g the middle of s u n n y d a y s but usually recover turgidity d u r i n g t h e night. W i l t i n g e v e n t u a l l y b e c o m e s p e r m a - nent. W i l t s y m p t o m s a r e g e n e r a l l y m o r e s e v e r e o n younger plants t h a n on older ones. T h e roots of infected plants have a b r o w n discoloration of the vascular tissues. Occasionally plants die, a n d the roots of d e a d plants are severely rotted. 42

49

50 Fusarium Wilt Fusarium Oxysporum Schlechtend. emend Snyder & Hans. Distribution. W o r l d w i d e. S y m p t o m s. T h e d i s e a s e n o r m a l l y o c c u r s i n p l a n t s s u b j e c t e d to p r o l o n g e d d r o u g h t stress. Infected plants may wilt suddenly or gradually. W h e n plants wilt s u d - denly all their leaves turn greyish- green, a n d in dry w e a t h e r t h e entire plant b e c o m e s b l e a c h e d a n d dry. W h e n slow wilting o c c u r s t h e foliage b e c o m e s c h l o r o - tic, a n d leaflets are s h e d before t h e plant d i e s. T h e r e are no external s y m p t o m s on either the stem or roots, but if the roots are cut longitudinally, vascular discoloration is evident. This discoloration is a c o m m o n feature of other v a s c u l a r wilts c a u s e d by Verticillium s p p a n d Pseudomonas solanacearum. H e n c e, field diagnosis of f u s a r i u m wilt m u s t be c o n f i r m e d by laboratory tests. Pegs a n d p o d s m a y b e i n v a d e d b y t h e f u n g u s w h i c h c a u s e s a pink discoloration of the inner p o d surface (Fig. 4 4 ). 44

51 44 45

52 Charcoal Rot Macrophomina phaseolina (Tassi) Goidanich D i s t r i b u t i o n. W o r l d w i d e. S y m p t o m s. W a t e r - s o a k e d n e c r o t i c l e s i o n s d e v e l o p o n the hypocotyls of y o u n g plants near t h e soil surface. T h e l e s i o n s e n l a r g e, b e c o m e dull b r o w n, girdle t h e h y - pocotyl, a n d kill the plant. Older plants are infected near t h e soil surface. T h e infection s p r e a d s u p w a r d w i t h i n t h e s t e m s a n d b r a n c h e s, a n d d o w n w a r d into t h e root s y s t e m killing t h e p l a n t. S o m e t i m e s, t h e d i s e a s e i s r e s t r i c t e d t o t h e r o o t s. R o o t l e s i o n s a r e initially w a t e r - s o a k e d but later b e c o m e light b r o w n. T h e lateral roots b e c o m e r o t t e d a n d b l a c k e n e d, a n d t h e t a p root s h r e d s. W h e n p o d s a r e i n v a d e d t h e i r interior s u r f a c e s t u r n g r e y b e c a u s e o f t h e a b u n d a n t prod u c t i o n o f m i c r o s c l e r o t i a ( F i g. 4 5 ). W h e n t h e w e a t h e r i s w a r m a n d w e t a t h a r v e s t t i m e M. phaseolina and s o m e o t h e r f u n g i, e. g., Lasiodiplodia theobromae, Aspergillus niger, a n d Aspergillus flavus, i n v a d e t h e s e e d a n d p r o d u c e m a t s o f m y c e l i u m b e t - w e e n t h e inner s u r f a c e s o f t h e c o t y l e d o n s ( F i g. 4 6 ). W h e n this o c c u r s w i t h n o e x t e r n a l s y m p t o m s o f d i s e a s e o n t h e k e r n e l s i t i s k n o w n a s ' c o n c e a l e d d a m a g e '. Blackhull Thielaviopsis basicola (Berk. & Broome) Ferraris (syn. Chalara elegans Nag Raj & Kendrick) D i s t r i b u t i o n : A r g e n t i n a, Italy, S o u t h A f r i c a, a n d U S A. S y m p t o m s : N u m e r o u s b l a c k l e s i o n s d e v e l o p o n t h e p o d s u r f a c e ( F i g. 4 7 ). T h e l e s i o n s e n l a r g e a n d c o - a l e s c e p r o d u c i n g l a r g e m a s s e s o f s p o r e s w h i c h g i v e t h e p o d s u r f a c e a b l a c k e n e d a p p e a r a n c e. S e v e r e p e g i n f e c t i o n l e a d s t o e x t e n s i v e p o d l o s s e s a t lifting. 4 6

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54 Pod Rot Pythium myriotylum Dreschler Rhizoctonia solani Kuhn Fusarium solani (Mart.) Saccardo f. sp phaseoli (Burkholder) Snyder & Hans. Fusarium oxysporum Schlechtend. emend Snyder & Hans. Macrophomina phaseolina (Tassi) Goidanich D i s t r i b u t i o n. W o r l d w i d e. S y m p t o m s. P o d rots a r e c h a r a c t e r i z e d b y t h e p r e s - e n c e o f b r o w n i s h - b l a c k l e s i o n s o n t h e s h e l l ( F i g. 4 8 ). T h e l e s i o n s e n l a r g e a n d c o a l e s c e, a n d t h e entire p o d s u r f a c e b e c o m e s d i s c o l o r e d, a n d i n a d v a n c e d s t a g e s the shell tissues disintegrate a n d the kernels d e c a y. T h e texture a n d color o f t h e rotted t i s s u e s v a r y d e p e n d - ing o n the o r g a n i s m s i n v o l v e d a n d other e d a p h i c factors. P o d s rotted by s p e c i e s of Fusarium h a v e pink- or p u r p l e - s t a i n e d s h e l l s. Sclerotium rolfsii, Sclerotinia s p p, Verticillium s p p, a n d Botrytis cinerea c a u s e p o d rotting in a d d i t i o n to t h e other d a m a g e d e s c r i b e d earlier. Rhizoctonia solani in addition t o c a u s i n g p o d, root, a n d s t e m rots c a n a l s o invade lower leaves in contact with soil c a u s i n g a leaf blight (Fig. 4 9 ). 4 8

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56 Diseases C a u s e d by Bacteria Bacterial W i l t Pseudomonas solanacearum (smith) smith Distribution. A n g o l a, China, East Indies, Ethiopia, Fiji, India, Indonesia, Sri L a n k a, Libya, Madagascar, Malays i a, M a u r i t i u s, N i g e r i a, P a p u a N e w G u i n e a, P h i l i p - p i n e s, S o m a l i a, S o u t h A f r i c a, S w a z i l a n d, T a i w a n, T h a i l a n d, U g a n d a, U S A, V i e t n a m, Z a m b i a, a n d Z i m - b a b w e. S y m p t o m s. Infection of y o u n g plants c a n result in s u d - den wilting and death, but the leaves remain green (Fig. 50). Infection of mature plants results in loss of turgidity, and leaves b e c o m e light green, chlorotic, and curl at the tips. Eventually leaflets b e c o m e brown but remain attached to the plant. In s o m e instances only a single b r a n c h m a y wilt a n d d i e. T h e v a s c u l a r s y s t e m o f t h e t a p root b e c o m e s p l u g g e d a n d d i s c o l o r e d a n d this e x t e n d s into the main stem a n d lateral branches. M a s s e s of bacteria ooze from the cut e n d s of infected roots a n d stems w h e n these are placed in water (Fig. 51). 50

57

58 Bacterial Leaf Spot Unidentified bacterium Distribution. India a n d V i e t n a m. S y m p t o m s. S m a l l, light b r o w n, circular to irregular lesions appear on the lower leaves of y o u n g plants (Fig. 52). During the early s t a g e s of d i s e a s e d e v e l o p m e n t lesions are p r o m i n e n t on t h e u p p e r s u r f a c e s of leaflets. T h e lesions e n l a r g e, b e c o m e irregular i n s h a p e, a n d the tissues a r o u n d t h e m b e c o m e chlorotic. W h e n fully developed, the center of t h e lesion is colored a light brown a n d the margin is dark brown. In wet weather, the lesions coalesce and the leaves b e c o m e chlorotic a n d are s h e d. 52

59 52 53

60 D i s e a s e s C a u s e d b y V i r u s e s a n d a M y c o p l a s m a - l i k e O r g a n i s m Peanut Mottle Peanut mottle virus (PMV) D i s t r i b u t i o n. All g r o u n d n u t - p r o d u c i n g c o u n t r i e s in Africa, the A m e r i c a s, A s i a, a n d O c e a n i a. S y m p t o m s. A p p e a r o n y o u n g l e a v e s a s irregular d a r k g r e e n i s l a n d s. M o s a i c s y m p t o m s are not a p p a r e n t o n older l e a v e s, w h i c h s h o w m i l d mottle s y m p t o m s visible i n t r a n s m i t t e d light. P l a n t s a r e not s e v e r e l y s t u n t e d. S o m e g e n o t y p e s s h o w c h a r a c t e r i s t i c i n t e r v e i n a l d e - p r e s s i o n a n d u p w a r d rolling of leaflet m a r g i n s (Fig. 5 3 ). Infected plants produce only a few small p o d s. Peanut Stripe Peanut stripe virus (PStV) D i s t r i b u t i o n. M o s t g r o u n d n u t - p r o d u c i n g c o u n t r i e s i n S o u t h a n d S o u t h e a s t A s i a, a n d U S A. S y m p t o m s. I n earlier r e p o r t s f r o m s o m e c o u n t r i e s P S t V w a s m i s i d e n t i f i e d a s P M V but, unlike P M V, P S t V c a u s e s a w i d e r a n g e o f leaf s y m p t o m s. S y m p t o m s vary, d e p e n d i n g o n t h e virus isolate a n d g r o u n d n u t c u l - tivar. Necrotic a n d stripe isolates (Fig. 54) c a u s e severe yield reductions, w h e r e a s mild mottle a n d blotch isolates (Fig. 5 5 ) h a v e little or no effect on y i e l d. An " o a k leaf" s y m p t o m (Fig. 5 6 ) i s o c c a s i o n a l l y s e e n. 54

61

62 Peanut Clump Peanut clump virus (PCV) D i s tribution. India a n d West Africa. Probably several other countries in Asia. S y m p t o m s. This s o i l b o r n e d i s e a s e o c c u r s i n p a t c h e s in the field w h i c h recur in the s a m e p o s i t i o n s w h e n groundnuts are s o w n again in the s a m e field (Fig. 57). Young leaves s h o w mosaic, mottling, a n d chlorotic ring s y m p t o m s (Fig. 5 8 ). O l d e r leaflets a r e d a r k e r g r e e n with faint m o t t l i n g. Early- infected plants are c onspicuous in the field b e c a u s e they are severely stunted and dark g r e e n. 5 6

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64 Bud Necrosis Bud necrosis virus (BNV) T o m a t o s p o t t e d w i l t v i r u s ( T S W V ) D i s t r i b u t i o n. B N V w i d e s p r e a d i n A s i a ; T S W V i n A f r i c a, t h e A m e r i c a s, A u s t r a l i a, a n d E u r o p e. S y m p t o m s. T h e d i s e a s e i s c a u s e d b y t w o s e r o - logically distinct t o s p o v i r u s e s, B N V a n d T S W V, w h i c h p r o d u c e s i m i l a r s y m p t o m s i n g r o u n d n u t s. Initial s y m p t o m s a p p e a r o n y o u n g leaflets a s c h l o r o - tic s p o t s o r m o t t l i n g t h a t m a y d e v e l o p into c h l o r o t i c a n d n e c r o t i c r i n g s a n d s t r e a k s ( F i g. 5 9 ) until t h e w h o l e g r o u n d n u t p l a n t i s a f f e c t e d ( F i g. 6 0 ). T e r m i n a l b u d n e c - rosis o f t e n o c c u r s w h e n t e m p e r a t u r e s a r e r e l a t i v e l y h i g h. Early i n f e c t i o n r e s u l t s i n s t u n t i n g a n d s o m e t i m e s proliferation of axillary s h o o t s ( Fig. 61). Leaflets prod u c e d o n axillary s h o o t s s h o w a w i d e r a n g e o f s y m p - t o m s i n c l u d i n g r e d u c e d s i z e, d i s t o r t i o n o f t h e l a m i n a, m o s a i c, a n d g e n e r a l c h l o r o s i s. A n y s e e d s p r o d u c e d b y e a r l y - i n f e c t e d p l a n t s a r e s m a l l, s h r i v e l l e d, a n d m o t t l e d (Fig. 6 2 ). 5 8

65

66 Groundnut Rosette A complex of two viruses and satellite RNAs D i s t r i b u t i o n : R e s t r i c t e d t o A f r i c a s o u t h o f t h e S a h a r a. S y m p t o m s : T h e m o s t destructive g r o u n d n u t virus disease in Africa. Three types of rosette have been recorded: C h l o r o t i c r o s e t t e, w h i c h i s p r e v a l e n t t h r o u g h o u t A f r i c a, i s c h a r a c t e r i z e d b y s t u n t e d p l a n t s w i t h c h l o r o t i c, t w i s t e d, a n d d i s t o r t e d l e a f l e t s ( F i g. 6 3 ). Y i e l d f r o m e a r l y - i n f e c t e d p l a n t s i s s e v e r e l y r e d u c e d. M o s a i c rosette i s r e c o r d e d o n l y i n e a s t e r n, c e n t r a l, a n d s o u t h e r n A f r i c a. Y o u n g e r l e a f l e t s s h o w c o n s p i - c u o u s m o s a i c s y m p t o m s. G r e e n r o s e t t e c u r r e n t l y o c c u r s o n l y i n w e s t e r n A f r i c a. S y m p t o m s r e s e m b l e t h o s e o f p e a n u t c l u m p. Y o u n g l e a v e s s h o w m i l d m o t t l i n g. O l d e r l e a v e s a r e d a r k g r e e n, r e d u c e d i n s i z e, a n d s h o w d o w n w a r d rolling o f leaflet m a r g i n s. P l a n t s a r e s e v e r e l y s t u n t e d ( F i g. 6 4 ). 60

67

68 Peanut Stunt Peanut stunt virus (PSV) D i s t r i b u t i o n. N o r t h A m e r i c a a n d s o u t h e r n C h i n a. S y m p t o m s. T h e virus exists a s s e v e r a l distinct isolates; the o n e p r e v a l e n t in N o r t h A m e r i c a c a u s e s severe d w a r f i n g of either t h e entire plant or o n e or m o r e of its b r a n c h e s (Fig. 6 5 ). In C h i n a a different isolate of t h e virus d o e s not c a u s e severe stunting, but the leaflets on i n f e c t e d p l a n t s a r e m a l f o r m e d w i t h v a r i o u s c h l o r o t i c s y m p t o m s. Groundnut Streak Necrosis Sunflower yellow blotch virus (SYBV) D i s t r i b u t i o n. S o u t h e r n A f r i c a. S y m p t o m s. E a r l y s y m p t o m s are d i s c r e t e, bright y e l l o w p a t c h e s o n leaflets. R i n g s p o t s a n d line p a t t e r n s are c o m m o n. L e a f l e t s p r o d u c e d after i n f e c t i o n o c c u r s h a v e y e l l o w s t r e a k s a l o n g t h e v e i n s, a n d u l t i m a t e l y t h e s t r e a k s b e c o m e n e c r o t i c. T h e y o u n g e s t leaflets a r e dist o r t e d, p u c k e r e d, a n d s m a l l, w i t h i r r e g u l a r s t r e a k s o r m a r g i n a l n e c r o s i s ( F i g. 6 6 ). 62

69

70 Cowpea Mild Mottle C o w p e a mild mottle virus ( C M M V ) D i s t r i b u t i o n. Asia a n d Africa. S y m p t o m s. I n f e c t e d p l a n t s a r e c o n s p i c u o u s b y t h e outward rolling of their leaflet e d g e s ( Fig. 67) a n d sev e r e s t u n t i n g. Y o u n g e r leaflets o f t e n s h o w v e i n b a n d i n g a n d o l d e r leaflets m a y b e c o m e n e c r o t i c. T h e i n c i d e n c e o f C M M V i n g r o u n d n u t s c a n b e a s h i g h a s 3 0 % i f t h e y a r e s o w n a d j a c e n t to i n f e c t e d s o y b e a n (Glycine max) a n d / o r c o w p e a ( V i g n a unguiculata), t w o h i g h l y s u s c e p t - ible c r o p s. Peanut Yellow Spot P e a n u t y e l l o w s p o t v i r u s (PYSV) D i s t r i b u t i o n. T h a i l a n d a n d India. S y m p t o m s. C h l o r o t i c s p o t s first a p p e a r a l o n g t h e m i d - ribs o f y o u n g leaflets w h e r e t h e t h r i p s v e c t o r f e e d s. T h e s p o t s i n c r e a s e i n s i z e ( F i g. 68) a n d m a y c o a l e s c e a n d b e c o m e i r r e g u l a r i n s h a p e a s t h e l e a v e s a p p r o a c h m a - turity ( F i g. 6 9 ). A t t h i s s t a g e t h e c o l o r o f t h e s p o t s i s d i s t i n c t i v e l y y e l l o w. S i n c e t h e i n f e c t i o n i s l o c a l i z e d, s y m p t o m s a p p e a r o n l y o n i n f e c t e d leaflets. 6 4

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72 Witches' Broom Mycoplasma-like organism D i s t r i b u t i o n. B u r k i n a F a s o, C h i n a, I n d i a, I n d o n e s i a, J a p a n, N i g e r, T a i w a n, T h a i l a n d, a n d U S A. S y m p t o m s. T h e e x c e s s i v e p r o l i f e r a t i o n o f l e a f l e t s g i v e s i n f e c t e d p l a n t s a b r o o m - l i k e a p p e a r a n c e. L e a v e s a r e s m a l l a n d c h l o r o t i c a n d t h e p l a n t i s s t u n t e d ( F i g. 7 0 ). I f p e g s a r e f o r m e d, t h e y c u r l u p w a r d s a g a i n s t g r a v - ity ( F i g. 7 1 ). 6 6

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74 D i s e a s e s C a u s e d b y N e m a t o d e s Root-knot Meloidogyne arenaria (Neal) chitwood Meloidogyne hapla Chitwood D i s t r i b u t i o n. Meloidogyne arenaria; E g y p t, I n d i a, Israel, M a l a w i, S e n e g a l, T a i w a n, U S A, a n d Z i m b a b w e. Meloidogyne hapla; Australia, C h i n a, India, Israel, J a p a n, S o u t h A f r i c a, S o u t h K o r e a, U S A, a n d Z a m b i a. S y m p t o m s. G a l l s often f o r m o n r o o t s, p e g s, a n d p o d s o f i n f e c t e d p l a n t s. N e m a t o d e d a m a g e i s f r e q u e n t l y not s u s p e c t e d until r o o t s a n d p o d s a r e e x a m i n e d for t h e p r e s e n c e o f g a l l s, w h i c h m a y r e a c h a d i a m e t e r o f s e v - eral t i m e s t h e n o r m a l a d j a c e n t root. R o o t s y s t e m d e v e l - o p m e n t i s c o m m o n l y r e d u c e d. P o d s a l s o b e c o m e i n f e c t e d a n d d e v e l o p k n o t s, o r s m a l l w a r t s ( F i g. 7 2 ). P e g s a n d p o d s o c c a s i o n a l l y b e g i n t o d e t e r i o r a t e a t m a - turity. S e v e r e l y i n f e c t e d p l a n t s a r e s t u n t e d a n d h a v e c h l o r o t i c l e a v e s. S y m p t o m s o f r o o t - k n o t n e m a t o d e i n - f e c t i o n a r e s i m i l a r for all s p e c i e s ; h o w e v e r, t h e g a l l s p r o d u c e d by M. hapla a r e s m a l l e r t h a n t h o s e p r o d u c e d by M. arenaria. R o o t s infected with M. hapla t e n d to f o r m b r a n c h e s n e a r t h e p o i n t o f n e m a t o d e i n v a s i o n. T h i s f r e q u e n t l y p r o d u c e s a d e n s e, b u s h y root s y s t e m. 6 8

75 72 69

76 Root-lesion Pratylenchus brachyurus (Godfrey) Filipjev & Sch. Stekh. D i s t r i b u t i o n. A u s t r a l i a, B e n i n, E g y p t, G a m b i a, India, N i g e r i a, S e n e g a l, T h a i l a n d, U S A, a n d Z i m b a b w e. S y m p t o m s. R o o t - l e s i o n n e m a t o d e s a t t a c k r o o t s, p e g s, a n d p o d s a n d f e e d w i t h i n t h e p a r e n c h y m a t o u s t i s s u e s. Roots of infected plants are restricted in length a n d total v o l u m e, a n d t e n d t o b e d i s c o l o r e d. T h e p o d l e s i o n s b e g i n a s tiny, t a n - t o - b r o w n c o l o r e d, p i n - p o i n t a r e a s o n t h e shell s u r f a c e, a n d, a s t h e n e m a t o d e s f e e d a n d rep r o d u c e, t h e a f f e c t e d a r e a b e c o m e s larger a n d d a r k e r (Fig. 7 3 ). O l d e r l e s i o n s a r e c h a r a c t e r i z e d by a b l o t c h y a p p e a r a n c e a n d i n d i s t i n c t m a r g i n s. S e v e r e l y a t t a c k e d p l a n t s a r e s t u n t e d a n d c h l o r o t i c w i t h r e d u c e d root s y s - t e m s. O t h e r m i c r o o r g a n i s m s m a y c o l o n i z e t h e n e c r o t i c a r e a s a n d p e n e t r a t e t h e p o d c a u s i n g s e e d d a m a g e. Kalahasti Malady Tylenchorhynchus brevilineatus Williams D i s t r i b u t i o n. India. S y m p t o m s. Infected p l a n t s a p p e a r i n p a t c h e s i n t h e f i e l d, a n d a r e s t u n t e d w i t h g r e e n e r t h a n n o r m a l f o l i a g e. S m a l l b r o w n i s h - y e l l o w l e s i o n s a p p e a r o n t h e p e g s, a n d o n y o u n g d e v e l o p i n g p o d s. T h e m a r g i n s o f t h e l e s i o n s a r e slightly e l e v a t e d b e c a u s e o f t h e proliferation o f h o s t cells a r o u n d t h e l e s i o n s. P e g l e n g t h i s r e d u c e d a n d i n a d v a n c e d s t a g e s o f t h e d i s e a s e t h e entire p o d s u r f a c e b e c o m e s b l a c k e n e d ( F i g. 7 4 ). D i s c o l o r a t i o n c a n a l s o be o b s e r v e d on roots, but this is l e s s c o n s p i c u o u s t h a n p o d d i s c o l o r a t i o n. K e r n e l s f r o m d i s e a s e d p o d s a r e a p - p a r e n t l y h e a l t h y, a l t h o u g h c o m m o n l y s m a l l e r t h a n n o r m a l. 7 0

77

78 Peanut Chlorosis Aphasmatylenchus straturatus Germani D i s t r i b u t i o n. B u r k i n a F a s o. S y m p t o m s. I n f e c t e d p l a n t s a r e s e v e r e l y s t u n t e d a n d chlorotic, a n d a p p e a r i n l a r g e c i r c u l a r p a t c h e s i n t h e field. T h e s e p a t c h e s e n l a r g e y e a r after y e a r i f g r o u n d - nuts a r e r e p e a t e d l y g r o w n i n t h e s a m e f i e l d. C h l o r o s i s usually a p p e a r s 3 5 t o 4 5 d a y s after s o w i n g. L e a f l e t s are y e l l o w o r p a l e g r e e n but t h e p r i m a r y a n d s e c o n d a r y v e i n s r e m a i n g r e e n ( F i g. 7 5 ). L e a f s i z e i s n e a r l y n o r m a l. R o o t s are s e v e r e l y d i s t o r t e d a n d p o o r l y n o d u l a t e d. 72

79 75 73

80 D i s e a s e C a u s e d by a Parasitic F l o w e r i n g P l a n t Witch Weed Alectra vogelii Benth. D i s t r i b u t i o n. A n g o l a, B u r k i n a F a s o, M a l a w i, N i g e r i a, Z a m b i a, a n d Z i m b a b w e. S y m p t o m s. Alectra vogelii is a root p a r a s i t e of g r o u n d - nut a n d s e v e r a l o t h e r l e g u m i n o u s c r o p p l a n t s. M a t u r e plants of A. vogelii are 18 to 46 cm h i g h, with small l e m o n - y e l l o w f l o w e r s, a n d s t e m s t h a t b r a n c h out a t t h e b a s e o f t h e plant ( F i g. 7 6 ). T h e c o n n e c t i o n b e t w e e n A. vogelii a n d t h e g r o u n d n u t roots c a n be s e e n by c a r e - fully excavating the soil in the root z o n e ( Fig. 77). Parasitized p l a n t s are w e a k e n e d a n d r e d u c e d i n s i z e a n d yield. 7 4

81

82 Supporting Literature Feakin, S.D. (ed.) Pest control in groundnuts. PANS Manual 2, London, UK: Centre for Overseas Pest Research. 197 pp. Garren, K.H., and Jackson, C.R Peanut diseases. Pages in Peanuts - culture and uses. Yoakum, Texas, USA: American Peanut Research and Education Association, Inc. Jackson, C.R., and Bell, D.K Diseases of peanut (groundnut) caused by fungi. Research Bulletin no. 56. Athens, Georgia, USA: University of Georgia, College of Agriculture Experiment Stations. 137 pp. Kolte, S.J Diseases of annual oilseed crops. Peanut diseases, vol. 1. Boca Raton, Florida, USA: CRC Press, Inc. 143 pp. McDonald, D., and Raheja, A,K, Pests, diseases, resistance, and crop protection in groundnuts. Pages in Advances in legume science (Summerfield, R.J., and Bunting, A.H. eds.). Kew, Surrey, UK: Royal Botanic Gardens. McDonald, D., and S u b r a h m a n y a m, P Rust of groundnut. Pages in Plant diseases of international importance. Diseases of vegetables and oil seed crops vol. II. (Chaube. H.S., Kumar, J., Mukhopadhyay, A.N., and Singh, U.S., eds.). Englewood Cliffs, New Jersey 07632, USA: Prentice-Hall, Inc. McDonald, D., Subrahmanyam, P., Gibbons, R.W., and Smith, D.H Early and late leaf spots of groundnut. Information Bulletin no. 21. Patancheru, A.P , India. International Crops Research Institute for the Semi-Arid Tropics. 24 pp. Porter, D.M., Smith, D.H., and Rodriguez-Kabana, R Peanut plant diseases. Pages in Peanut science and technology (Pattee, H.E., and Young, C.T., eds.). Yoakum, Texas, USA: American Peanut Research and Education Society, Inc. 7 6

83 Porter, D.M., Smith, D.H., and Rodriguez-Kabana, R. (eds.) Compendium of peanut diseases. St. Paul, Minnesota, USA: American Phytopathological Society. 73 pp. Reddy, D.V.R Virus diseases. Pages in Groundnut (Reddy, P.S., ed.). New Delhi, India: Indian Council of Agricultural Research. 565 pp. Reddy, D.V.R Groundnut viruses and virus diseases: distribution, identification and control. CAB International, Review of Plant Pathology 70: Reddy, D.V.R., Wightman, J.A., Beshear, R.J., Highland, B., Black, M., Sreenivasulu, P., Dwivedi, S.L., Demski, J.W., McDonald, D., Smith Jr., J.W., and Smith, D.H Bud necrosis: a disease of groundnut caused by tomato spotted wilt virus. Information Bulletin no. 31, Patancheru, A.P , India. International Crops Research Institute for the Semi-Arid Tropics. 20 pp. Smith, D.H., Pauer, G.D.C., and Shokes, F.M Cercosporidium and Cercospora leaf spots of peanut (groundnut). Pages in Plant diseases of international importance. Diseases of vegetables and oil seed crops vol. II. (Chaube, H.S., Kumar, J., Mukhopadhyay, A.N., and Singh, U.S., eds.). Englewood Cliffs, New Jersey 07632, USA: Prentice-Hall, Inc. Subrahmanyam, P., and McDonald, D Rust disease of groundnut. Information Bulletin no. 13. Patancheru, A.P , India. International Crops Research Institute for the Semi-Arid Tropics. 20 pp. Subrahmanyam, P., and Ravindranath, V Fungal and nematode diseases. Pages in Groundnut (Reddy, P.S., ed.). New Delhi, India. Indian Council of Agricultural Research. 565 pp. Subrahmanyam, P., Reddy, D.V.R., Sharma, S.B., Mehan, V.K., and McDonald, D A world list of groundnut d i s e a s e s. Legumes Pathology Progress Report no. 12. Patancheru, A.P , India: Legumes Program, International Crops Research Institute for the Semi-Arid Tropics. 14 pp. (Limited distribution.) Wongkaew, S Compendium of groundnut diseases in Thailand. Bangkok, Thailand: Funny Publishing Co. 76 pp. 7 7

84 Photo Credits 1 D.H. Smith 2 P. Subrahmanyam 3 P. Subrahmanyam 4 P. Subrahmanyam 5 D.H. Smith, Compendium of Peanut Diseases, American Phytopathological Society 6 P. Subrahmanyam 7 P. Subrahmanyam, Plant Disease 69{9): D.H. Smith 9 P. Subrahmanyam. Plant Disease 69{9):813-S19 10 P. Subrahmanyam 11 D.H. Smith, Peanut Science and Technology. American Peanut Research a n d Education Society, Inc., p S.A. Moraes 13 D.H. Smith 14 P. Subrahmanyam 15 S. Wongkaew 16 Z.R.Frank 17 S. Wongkaew 18 P. Subrahmanyam, Compendium of Peanut Diseases, American Phytopathological Society 19 D,H. Smith, Compendium of Peanut Diseases, American Phytopathological Society 20 S. Wongkaew 21 S. Wongkaew 22 S. Wongkaew 23 S. Wongkaew 24 S. Wongkaew 25 S. Wongkaew 26 D.H. Smith 27 P. Subrahmanyam 28 D.H. Smith 29 D.H. Smith, Mycopathologia 100: D.H. Smith 31 ICRISAT 32 D.H. Smith 33 V.K. Mehan 34 S. Wongkaew 35 D.H. Smith 36 D.H. Smith 37 D.H. Smith 38 D.M. Porter 39 D.M. Porter 40 D.M. Porter 41 D.M. Porter 4 2 T.A. Lee 43 H.A. Melouk 44 D.H.Smith 45 P.M. Reddy 46 P. Subrahmanyam 47 D.H.Smith 48 D.H. Smith' 49 S. Wongkaew 50 D.G. Faris 51 S. Wongkaew 52 P. Subrahmanyam 53 D.H.Smith 54 S. Wongkaew 55 S. Wongkaew 56 D.V.R. Reddy 57 D.V.R. Reddy 58 D.V.R. Reddy 59 D.H. Smith 60 D.V.R. Reddy 61 D.V.R. Reddy 62 D.H.Smith 63 P. Subrahmanyam 64 D.V.R. Reddy 65 D.H. Smith 66 D.V.R. Reddy 67 D.V.R. Reddy 68 S. Wongkaew 69 S. Wongkaew 70 Ch. Ravinder Reddy 71 D.H.Smith 72 D.H.Smith 73 D.H. Smith, Peanut Science and Technology, American Peanut Research and Education Society, Inc., p P. Subrahmanyam 75 D.H. Smith 76 P. Subrahmanyam 77 D.H. Smith 7 8

85 Notes 7 9

86 The International Crops Research Institute for the Semi-Arid Tropics is a nonprofit, scientific, research and training institute receiving support from donors through the Consultative Group on International Agricultural Research. Donors to ICRISAT inc l u d e g o v e r n m e n t s a n d a g e n c i e s o f Australia. B e l g i u m, C a n a d a. C h i n a. Finland, F r a n c e. G e r m a n y. India. Italy. J a p a n. Korea, Mexico, Netherlands, Nigeria, Norw a y, S w e d e n, Switzerland, United K i n g d o m. United States of A m e r i c a, a n d the following international a n d private organizations: African Development B a n k, Agricultural University o f W a g e n i n g e n, A s i a n D e v e l o p m e n t B a n k, D e u t s c h e G e s - ellschaft fur T e c h n i s c h e Z u s a m m e n a r b e i t ( G T Z ), International B o a r d for Plant Genetic Resources. International Development Research Centre. International Fertilizer Development Canter, International Fund for Agricultural Development, International Fund for Agricultural Research. The European Economic Community. The Opec Fund for International Development. The Rockefeller Foundation. The World Bank. United Nations Development Programme. University of Arkansas, University of Georgia, University of H a m b u r g, a n d University of H o h e n h e i m. Information a n d conclusions in this publication do not necessarily reflect t h e position of the aforementioned governments, agencies, and international and private organizations. The opinions in this publication are those of the authors and not necessarily those of ICRISAT, The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of ICRISAT 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 t h e Institute. Copyright 1992 by t h e International C r o p s Research Institute for the Semi-Arid Tropics (ICRISAT). All rights reserved. Except for quotations of short p a s s a g e s for t h e purposes of criticism a n d review, no part of this publication m a y be reproduced, stored in retrieval systems, or transmitted, in any form or by any m e a n s, electronic, mechanical, photocopying, recording, or otherwise, without prior permission of ICRISAT. It is h o p e d that this Copyright declaration will not d i m i n i s h t h e b o n a fide use of Its research findings in agricultural research and development in or for the tropics.

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