spatial and temporal interactions of meloidogyne incognita and soybean

8/13/2019 Spatial and Temporal Interactions of Meloidogyne incognita and Soybean

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Suppl ement to Journal of Nematology 25 4S):738-745. 1993. Th e Society of Nematologist s 1993.

S p a t i a l a n d T e m p o r a l I n t e r a c t i o n s o f e l o i d o g y n ei n c o g n i t a a n d S o y b e a nG. L . WINDHAM AND K. R . BARKER2

Abstract: The spatial and tempo ral dynamics of Meloidogyne incognita relative to soybean shoot androot gro wth in field microplots, were dete rmine d at 11 sampling dates durin g a growing season. Thepopulation dynamics of M. incogni ta on soybean were dep end ent on initial populatio n Pi), soilmoisture, an d root spatial distribution. Final egg and juvenile population densities were greatest inplots with hi gher Pi. Th e populatio n densities of juveniles and eggs were highest fro m mid- tolate-season and were associated with increased soil moisture. Root spatial distributions and M. in -cognita num bers were closely related. Numb ers o f juveniles and eggs decreased with soil dep th anddistance from the center of the row. Greater numbers of uveniles and eggs were found in the u pper30 cm in the row center, and in the u ppe r 15 cm at 10 and 20 cm from the cen ter of the row. Therewere no consistent difference s in root weights between nematod e-infect ed and uninfe cted plants atany dept h or distance from the center of the row. The optimum time for determi ning the relation-ship between Pi and soybean shoot growth was from late mid-season September) to final harvest 14November). Th e relationship between Pi and seed yield for the final harvest was best described bya quadratic mode l: yield g) = 71.4 + 1,1 logt0[Pi + 1]) - 2.3 log]0[Pi + 1]) 2, R 2 = 0.99, P =0.03).Key words: Glycine m ax Meloido~ne incoffnita nematode, population dynamics, root-knot nema-tode, soybean, yield loss.

T h e s o u t h e r n r o o t - k n o t n e m a t o d e ,Meloidogyne incognita i s a s e r i o u s p e s t o ns o y b e a n , Glycine max i n t h e s o u t h e a s t e r nU n i t e d S t a t e s ( 1 2) . S o y b e a n y i e ld lo s s e s c a nb e s u b s ta n t ia l , d e p e n d i n g o n c u l t iv a r su s -c e p t i b i l i t y ( 1 4 , 1 8 ) a n d t h e a g g r e s s i v e n e s so f t h e M. incogrdta p o p u l a t i o n ( 1 8 ) . T h ep o t e n ti a l o f th is n e m a t o d e t o d a m a g e s oy -b e a n is a l so i n f l u e n c e d b y e n v i r o n m e n t a la n d e d a p h i c f a c t o r s s u c h a s s oil t e x t u r e( 1 7 , 1 9 ) , t e m p e r a t u r e ( 1 3 , 1 7 ) , a n d m o i s t u r e(2).P r o g r e s s h a s b e e n m a d e i n d e t e r m i n i n gt h e g e n e r a l r e l a t i o n s h i p s b e t w e e n i n it ia lp o p u l a t i o n (P i) d e n s i t ie s o f M. incogni tae g g s a n d s e c o n d - s t a g e j u v e n i l e s ( J 2) a n ds o y b e a n y i e ld ( I 1 ,1 4 ,1 9 ). T o i m p r o v e p r e -d i c ti v e c a p a b il it ie s a n d u n d e r s t a n d i n g o ft h e M . i n c o g n i t a - h o s t r e l a t i o n s h i p , m o r e

Received for publication 25 February 1993.1 This research was funded by USDA, CSRS Grant No.89-106 and the North Carolina Agriculture and Life SciencesExperiment Station. Use of trade names in this publicationdoes not imply endorsement of products named or criticismof similar ones not mentioned.Former graduate student and Professor, Department ofPlant Pathology, North Carolina State University, Raleigh,NC 27695. Present address of first author: USDA ARS, CropScience .Research Laboratory, Forage Research Unit, P.O.Box 5367, Mississippi State, MS 39762.We thank DeWitt Byrd and Donald Corben for technicalassistance and Kathleen Forrest for assistance with statisticalanalyses.7 3 8

d a t a a r e n e e d e d o n t h e t e m p o r a l a n d s p a -t i a l f l u c t u a t i o n s o f M. incogni ta p o p u l a -t io n s , a s w e l l a s o n t h e e f f e c t s o f t h e s en e m a t o d e s o n s o y b e a n s h o o t a n d r o o tg r o w t h t h r o u g h o u t a g r o w i n g s e a s o n .

T h e o b j e c ti v e s o f t h is s t u d y w e r e t o d e -t e r m i n e i ) t h e s p a t ia l a n d t e m p o r a l d i s tr i -b u t i o n o f M. incogni ta o n s o y b e a n d u r i n g ag r o w i n g s e a s o n a n d ii) t h e e f f e c t s o f M .incogni ta P i o n s o y b e a n s h o o t a n d r o o tg r o w t h p a t t e r n s .

MATERIALS AND METHODST h e e x p e r i m e n t w a s c o n d u c t e d i n 8 0 x1 0 0 c m f i b e r g l a s s m i c r o p l o t s i n s t a l l e d t o a

d e p t h o f 5 0 c m i n a F u q u a y s a n d a t C e n t ra lC r o p s R e s e a r c h S t a t i o n n e a r C l a y t o n ,N o r t h C a r o li n a. T h e F u q u a y s a n d w a s9 2 s a n d , 4 c la y , a n d 4 s il t a t 0 - 1 5 c m ;9 1 s a n d , 4 c la y , a n d 5 s il t a t 1 5 - 3 0c m ; a n d 8 8 s a n d , 5 d a y , a n d 7 s il t a t3 0 - 4 5 c m . T e n w e e k s b e f o r e p la n t in g a n di n f e s t a t i o n w i t h n e m a t o d e s , a l l p l o t s w e r ef u m i g a t e d w i th 9 8 g m e t h y l b r o m i d e / m r. AN o r t h C a r o l i n a i s ol a te o f M. incogni ta w a si n c r e a s e d o n t o m a t o , Lycopersicum esculen-t u m c v. M a n a p a l , i n t h e g r e e n h o u s e .N e m a t o d e i n o c u l u m w a s e x t r a c te d w i thN a O C 1 ( 1 0 ) f r o m i n f e c t e d r o o t s c u t i n t o2 . 5 - c m s e g m e n t s . P i w e r e 0 , 1 , 2 5 0 , 5 , 0 0 0 ,


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S p a ti al a n d T e m p o r a l I n t e r a c ti o n s o f M . incognita: Windham Barker 7 3 91 0 , 0 0 0 , a n d 2 0 , 0 0 0 e g g s / 5 0 0 c m s o f s o il.M i c r o p l o t s w e r e i n f e s t e d w i t h n e m a t o d ee g g s to a d e p t h o f 15 c m b y u n i f o r m l yp o u r i n g a w a t e r s u s p e n s i o n o n e a c h m i -c r o p l o t a n d t h o r o u g h l y m i x i n g t h e s o i lw i t h a s p a d e . T h i r t y - fi v e s e e d o f s o y b e a nc v . L e e 6 8 w e r e p l a n t e d i n a s i n g l e r o wt h r o u g h t h e m i d d l e o f e a c h m i c r o p l o t o n2 6 M a y 1 9 8 3. S o y b e a n s e e d w e r e c o a t e dw i t h a c o m m e r c i a l p r e p a r a t i o n o fBradyrhizobiumjaponicum ( N i t r ag i n , N i t r a -g i n C o . , M i l w a u k e e , W I ) a n d p l o t s w e r ei n f e s t e d w i t h 1 , 0 0 0 s p o r e s o f Glomus mac-rocarpus. A r e a s b e t w e e n m i c r o p l o t s w e r ep l a n t e d w i t h s o y b e a n to s i m u l a t e f i e l d c o n -d i t i o n s .P l a n t g r o w t h a n d n e m a t o d e r e p r o d u c -t io n w e r e d e t e r m i n e d b i w e e k ly f o r 18w e e k s a n d t h e n a t c a . 3 -w e e k i n te r v a ls f o rt h e l a st t w o s a m p l i n g d a t e s . P l a n t s f r o m 1 5m i c r o p l o t s ( t h r e e p e r P i t r e a t m e n t ) w e r ed e s t r u c t i v e l y s a m p l e d a t e a c h s a m p l i n gd a t e . A s u b s a m p l e o f f iv e sh o o t s p e r m i -c r o p l o t w a s a r b i t r a r i l y s e l e c t e d t o d e t e r -m i n e d r y w e i g h t s o f c o t y l e d o n s , l e a fl e ts ,p e t i o l e s , s t e m s , p o d s , a n d s e e d s . S o y b e a ns h o o t s f o r e a c h P i w e r e r a t e d f o r d e v e l o p -m e n t a l s t a g e b y t h e s c a le o f F e h r e t al. ( 6).R o o t a n d n e m a t o d e s a m p l e s w e r e c ol-l e c te d o n t h e s a m e s a m p l in g t i m e s w i th aG i d d i n g s ( F o r t C o l l i n s , C O ) h y d r a u l i c s o i lc o r i n g a n d s a m p l i n g m a c h i n e . P a i rs o f s oilc o r e s 5 .1 - c m - d w e r e t a k e n t o a d e p t h o f 45c m i n th e p l a n t r o w a n d a t 1 0 a n d 2 0 c mf r o m t h e c e n t e r o f t h e r o w . E a c h c o r e w ass p l it i n t o 1 5 - c m s e c ti o n s ( 0 - 1 5 , 1 5 - 3 0 , a n d3 0 - 4 5 c m s o il d e p t h s ) f o r n e m a t o d e a ss ay sa n d r o o t ex t ra c t i o n. N e m a t o d e s w e r e ex -t r a c t e d f r o m e a c h c o r e s e c t io n b y e l u tr i a -t io n a n d c e n t r i f u g a t i o n (3 ). R o o t s a m p l e sc o l le c t e d b y e lu t r i a t i o n w e r e d i v i d e d i nh a l f b y w e i g ht . H a l f o f t h e r o o t s a m p l e w a sd r i e d a n d w e i g h e d a n d M. incognita e g g sw e r e e x t r a c t e d f r o m t h e o t h e r h a l f w ithN a O C 1 ( 1 0 ) .A 5 . 1 - c m - d b y 4 5 c m s o i l c o r e w a s c o l -l e c t e d f r o m e a c h m i c r o p l o t a t e a c h h a r v e s td a t e f o r s o il n u t r i e n t a n a l y s e s f o r e a c hd e p t h . A c i d i ty , b a s e s a t u r a t i o n , c a t io n -e x c h a n g e c a p a c i ty , p e r c e n t a g e o r g a n icm a t t e r , p H , w e i g h t /v o l u m e , a n d l ev e ls o f

e x c h a n g e a b l e a n d e x t r a c t a b l e i o n s (c a l-c iu m , c o p p e r , m a g n e s i u m , m a n g a n e s e ,p h o s p h o r u s , p o t a s s i u m , a n d z i nc ) w e r e d e -t e r m i n e d b y th e A g r o n o m i c D i vis io n o f t h eN o r t h C a r o li n a D e p a r t m e n t o f A g r ic u l-t u r e .S o il t e m p e r a t u r e w a s m o n i t o r e d a t 1 5c m w i t h a C R 2 1 M i c r o lo g g e r ( C a m p b e l lS c i e n t i f i c , L o g a n , U T ) . G r a v i m e t r i c w a t e rc o n t e n t , [( w e t w e i g h t - o v e n d r y w e i g h t ) /o v e n d r y w e ig h t ] x 1 0 0 , w a s d e t e r m i n e d a te a c h s a m p l i n g d a t e . W a t e r c o n t e n t w a sc o n v e r t e d t o s o il w a t e r p o t e n t i a l ( b a r s )w i t h a s o il m o i s t u r e c h a r a c t e r i st i c c u r v ec o n s t r u c t e d f o r F u q u a y s a n d .

A r a n d o m i z e d c o m p l e t e b l o c k d e s i g nw i t h t h r e e r e p l ic a t io n s p e r tr e a t m e n t p e rs a m p l i n g d a t e w as u s e d . P a i re d n e m a t o d ea n d r o o t s a m p l e s w e r e p r o c e s s e d s e p a-r a t e l y f o r e a c h m i c r o p l o t . A n a l y s e s o f v a ri -a n c e w e r e p e r f o r m e d , w i th o r th o g o n a lc o n t ra s t s c o n s t r u c t e d t o c o m p a r e P i l ev e lsf o r n e m a t o d e r e p r o d u c t i o n a n d s h o o t a n dr o o t g r o w t h p a r a m e t e r s . D a t a w e r e s u b -j e c t e d t o r e g r e s s i o n a n a l y s e s t o d e t e r m i n et h e re l a t i o n s h i p s b e t w e e n P i a n d r o o tg r o w t h , s h o o t g r o w t h , a n d s e e d y ie ld . T h en u m b e r s o f n e m a t o d e s (X ) w e r e c o n v e r t e dt o l o g t 0 ( X + 1 ) t o s t ab i li z e t h e v a r i an c e i nthe s t a t i s t i ca l ana lyses .

R E S U L T S

Nematode populat ion dynamics: T h e t e m -p o r a l d i s t r i b u t i o n s o f M. incognita J 2 ( F i g .1 A ) a n d e g g s ( F ig . 1 B ) i n t h e u p p e r 1 5 c mo f t h e s o y b e a n r o w f o l l o w e d s im i la r t r e n d st h r o u g h m o s t o f t h e s o y b e a n g r o w i n g s e a-s o n . A f t e r a n i n c r e a s e i n so il m o i s t u r ef r o m 1 S e p t e m b e r t o 15 S e p t e m b e r (F ig .2 ) , t h e r e w a s a l a r g e i n c r e a s e i n t h e n u m -b e r o f J 2 . A s e c o n d p e a k i n J 2 n u m b e r so c c u r r e d o n t h e t e n t h s a m p l i n g d a t e ( 2 5O c t o b e r ). T h e h i g h e s t n u m b e r o f J 2 w a sr e c o v e r e d i n t h e 2 0 , 0 0 0 P i t r e a t m e n t a t t h et e n t h s a m p l i n g d a t e ( 2 5 O c t o b e r ) . N u m -b e r s o f J 2 w e r e g e n e r a l l y lo w e r o n t h e l as ts a m p l i ng d a t e ( 1 4 N o v e m b e r ) t h a n o n 2 5O c t o b e r .M eloidogyne incognita e g g s w e r e f i r s t r e -c o v e r e d o n 2 3 J u n e , 2 8 d a y s a ft e r p l a n t in g


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S a m p l i n g d a t e m o n t h / d a y )FzC. l. Nu mb er s of eloidogyne i ncogn i ta n t h eu p p e r i 5 c m i n t h e s o y b e a n r o w a s a f f e c t e d b y i n it ia l

p o p u l a t i o n (P i) d u r i n g a g r o w i n g s e a so n . Pi = e g g s /500 cm 3 soil. A)Ju ven ile s. B ) E g g s .

F i g . 1 B ) . T h e r e w a s a g r a d u a l i n c r e a s e i ne g g n u m b e r s i n t h e u p p e r 1 5 c m o f th es o y b e a n r o w t h r o u g h 1 S e p t e m b e r . A t t h en e x t s a m p l i n g d a t e 1 5 S e p t e m b e r ) , t h e

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11 s a m p l i n g d a t es f r o m J u n e 1983 to N o v e m b e r1983.

n u m b e r o f e g g s i n c r e a s e d d r a m a t i c a l l y a tt h e t w o h i g h e s t P i. A p e a k i n e g g n u m b e r sa l so o c c u r r e d o n t h e l as t s a m p l i n g d a t e 1 4N o v e m b e r ) .

N ematode spa t i a l d i st r i bu t i on : T h e s p a d a ld i s t r i b u t i o n p a t t e r n s o f M . i n cogn i ta J 2w e r e g r e a t l y i n f l u e n c e d b y d i s t a n c e f r o mr o w c e n t e r a n d d e p t h . S p a ti al p a t te r n s o fJ 2 w e r e s i m i l a r t h r o u g h o u t t h e g r o w i n gs e a s o n , a s s h o w n i n t w o e x a m p l e s h e r e i nF i g . 3 A , B ) . A s t h e d e p t h a n d d i s t a n c e

f r o m t h e c e n t e r o f t h e r o w i n c r e a s e d , t h en u m b e r s o f J 2 d e c r e a se d . T h e h i g h e s td e n s i ti e s o f M . i n cogn i ta w e r e i n t h e u p p e r3 0 c m o f s o i l i n t h e c e n t e r o f t h e r o w a n di n t h e u p p e r 1 5 c m a t 1 0 a n d 2 0 c m f r o mt h e r o w . A t t h e 3 0 - 4 5 c m l e v e l , h i g h e s td e n s i t i e s w e r e r e c o v e r e d m i d - t o l a te -s e a s o n .

S p a t i a l d i s t r i b u t i o n s o f M . i n cogn i t a e g g sw e r e s im i la r t o t h o s e f o r J 2 d u r i n g m o s t o ft h e g r o w i n g s e a so n . E g g n u m b e r s d e -c r e a s e d a s t h e d i s t a n c e f r o m t h e c e n t e r o f

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~-~ ~ ~1 0 2 0 0 1 0 2 0 0 1 0 2 0 0 1 0 2 0D i s t a n c e f r o m r o w ( m )1 , 2 ~ 0 5 , 0 0 0 1 0 , 0 0 0 2 0 , 0 0 0P i

F I G . 3 . S p a t i a l d i s t r i b u t i o n of e lo idogyne ncogni taj u v e n i l e s r e l a t i v e t o t h e c e n t e r of a s o y b e a n r o w a n di n i t i a l p o p u l a t i o n Pi). Pi = egg s/5 00 cm 3 soil. A) 21July. B) 14 N o v e m b e r .


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S p a ti a l a n d T e m p o r a l I n t e r a c t i o n s o f M. incogni ta: Windham Barker 7 4 1t h e r o w a n d d e p t h i n c r e a s e d ; h o w e v e r ,t h e r e w e r e e x c e p t i o n s F ig . 4 A ) . O n t h ef o u r t h s a m p l i n g d a t e 2 1 J u l y ) f o r t h e t w ol o w e s t M. incogni ta P i, m o r e e g g s w e r e e x -t r a c te d f r o m c o r e s 1 0 c m f r o m t h e ro wc e n t e r t h a n i n t h e r o w . E g g s p a t i a l d i s t r i -b u t i o n m o r e c lo s el y r e s e m b l e d J 2 s p at ia ld i s tr i b u t i o n , w i th e g g n u m b e r s d e c r e a s i n gw i t h i n c r e a si n g d i s t an c e a n d d e p t h f r o mr o w c e n t e r o n th e f in a l s a m p l i n g d a t e 1 4N o v e m b e r ) F ig . 4 B ) . S i g n i f i c a n t P =0 . 05 ) d i f f e r e n c e s i n e g g d e n s i t i e s a m o n g P iw e r e d e t e c t e d i n t h e u p p e r 1 5 c m o f so il a tt h e c e n t e r o f t h e r o w l a t e i n th e g r o w i n gs e as o n . R e p r o d u c t i o n d i f f e r e d i n t h e u p -p e r 1 5 c m o f th e p lo t s a t 1 S e p t e m b e r a n d3 O c t o b e r . A t t h e 1 5 - 3 0 c m d e p t h , d i f fe r -e n c e s P = 0 . 05 ) i n J 2 a n d e g g p o p u l a t i o nd e n s i t i e s w e r e d e t e c t e d i n t h e r o w c e n t e r a t3 O c t o b e r , a n d 1 0 c m f r o m t h e r o w a t 7J u ly . T h e l ow e s t J 2 a n d e g g n u m b e r s w e r ed e t e c t e d a t t h e 3 0 - 4 5 c m d e p t h a t a ll d is -t a n c e s f r o m t h e r o w .

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2 0 , 0 0 0

FzG. 4. Sp ati aldistribution of Meloidogyne ncognitaeggs relative to the cen ter of a soybean row a nd initialpopsulation Pi) at two samp ling dates. Pi = eggs/500cm soil . A) 21 July. B) 14 Novem ber.

P lan t grow th responses: M eloidogyne incog-nita s u p p r e s s e d s o y b e a n s h o o t d r y w e i g h tst h r o u g h m u c h o f t h e g r o w i n g s e a so n F ig .5 ). D i f f e r e n c e s P = 0 . 0 1 - 0 . 0 5 ) b e t w e e nt h e c o n t r o l a n d M . i nc ogn i t a - i n f e s t e d m i -c r o p l o t s w e r e o b s e r v e d a t e ig h t h a r v e s td a t e s , b e g i n n i n g w i t h t h e s e c o n d h a r v e s to n 2 3 J u n e a n d c o n t i n u i n g t h r o u g h t h ef in a l h a r v e s t o n 1 4 N o v e m b e r . S o y b e a ns h o o t d r y w e i g h t p e a k e d o n 3 O c t o b e r a n dd e c l i n e d t h e r e a f t e r a s t h e p l a n t s s e n e s c e d .R e g r e s s i o n m o d e l s d e s c r i b e d t h e r e l a t i o n -s h ip b e t w e e n P i a n d d r y s h o o t w e i g ht s f o rt h e la s t f o u r h a r v e s t d a t e s . L i n e a r m o d e l sb e s t d e s c r i b e d t h is r e l a t io n s h i p o n 1 5 S e p -t e m b e r Y = 1 7 2 . 4 - 1 8 .5 X , w h e r e X =l O g l 0 P i + 1 ), R 2 = 0 . 9 0 , P = 0 . 0 1 ) a n d o n3 O c t o b e r Y = 2 3 1 . 1 - 2 0 .5 X , w h e r e X =l o g l 0 P i + 1 ), R 2 = 0 . 9 5 , P = 0 . 0 1 ) . Q u a -d r a t i c m o d e l s a d e q u a t e l y d e s c r i b e d t h e r e -l a t i o n s h i p b e t w e e n P i a n d d r y s h o o tw e i g h t s o n 2 5 O c t o b e r Y - 1 1 9 . 6 + 3 8 . 8 X- 1 0 . 4 X 2 , w h e r e X = l o g l 0 P i + 1 ) , R =0 . 9 6, P = 0 . 0 2 ) a n d o n 1 4 N o v e m b e r Y =1 6 5 .2 + 2 . 2 X - 5 . 8 X 2, w h e r e X = l o g l 0 P i+ 1 ) , R 2 = 0 . 99 , P = 0 . 0 1 ) .D i f f e r e n c e s P = 0 . 0 1 - 0 . 0 5 ) w e r e a ls oo b s e r v e d i n d r y w e i g h ts o f s p e c if ic p l a n tp a r ts . L e a f l e t d r y w e i g h t s g e n e r a l l y p a r a l -l e le d i n d i v i d u a l p l a n t g r o w t h . L e a f l e tw e i g h ts f r o m n o n i n f e s t e d a n d i n f e s t e d m i -c r o p l o t s w e r e s i g n i f i c a n t l y d i f f e r e n t a t t h es e c o n d h a r v e s t 2 3 J u n e ) a n d l a t e r i n t h e

2 5 0

2 0 0 - o - 01,25o ? . > j \z 1 5 o - ~ 5 , 0 0 0 / ~ . . . . \ , /

1 o o o o;=~ >(o o o o o o

Sampling date month/day)FIc. 5. Soybean shoot growth dry weights of fiveplants pe r plot) as affected by initial popu lations Pi)o f Meloidogyne ncognitaove r a grow ing season. Pi =eggs/500 cms soil.


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742 Jou rna l o f Nema to logy Volume 25 Supplement to December 1993season from the seventh 1 September) tothe nin th harvest 3 October). Meloidogyneincogni ta had a more striking effect onstem and petiole development than onleaflet developme nt over the growing sea-son. Differences P = 0.01-0.05) in stemand petiole dry weights between nema-tode-infested and noninfested microplotswere observed at the second harvest 23June) and fr om the sixth 18 August) tothe final harvest 14 November), with theexception of the tenth harvest. Through-out much of the growing season, the rela-t ive suppression of stem and pet iolegro wth weights) incr eased with an in-crease in Pi; however, from early to mid-season, low numbers of nematodes stimu-lated stem and petiole development. Sup-pression of stem a nd petiole growth in M.i n c o g n i t a - i n f e s t e d plots increased withtime.Soybean pod and seed weights were alsoaffected negatively by Pi. Differences P =0.05) in pod weights between noninfestedand M. i n c o g n i t a - i n f e s t e d microplots wereobserved at the seventh sampling datefirst pod collection date, 1 September),and aga in at the nin th 3 October) and fi-nal 14 November) sampl ing dates datanot included). Th er e was a linear relation-ship between Pi and pod dry weight on 1Septe mber Y = 44.4 - 4.9X, where X =logl0 Pi + 1), R = 0.98, P = 0.01) and on14 Novemb er Y = 32.2 - 4.2X, where X= logl0 Pi + 1), R 2 = 0.97, P = 0.01).Seed yield was not significantly P = 0.01)affected until harvest at plant maturity 14November), although numerical differ-ences in seed weights were observed at thetwo previous sampling dates. Th e relation-ship between Pi and seed yield for the finalharvest was best described by a quadraticregre ssion model Y = 71.4 + 1.IX -2.3X 2, wher e X = logl0 Pi + 1), R 2 = 0.99,P = 0.03) Fig. 6).

Meloidogyne incogni ta had little effect onthe developmental stages of soybean. Dif-ferences P = 0.01) in soybean develop-ment were observed only at the four th har-vest date 21 July). Aver ag e vegetativegrowth stages for 0, 1,250, 5,000, 10,000,

8 0

~ 6 0

4 0 -

a 2 0

0 0 . 5 1 1 . 5 2 2 . 5 3 3 . 5 4L O g , o ( P i + 1 )FIG. 6. Relationshipbetween soybean yield dryweights [g] of seed from five plants per plot) and

initial population density Pi). x = log]0 x + 1) of Pi;quadratic regression equation: y = 71.4 + 1.1x -2.3x2, Re = 0.99, P = 0.03.

and 20,000 eggs per 500 cm 3 of soil were9.3, 9.0, 9.0, 8.3, and 7.6, respectively.These data signify a reducti on in the num-ber of nodes per soybean plant prior toflowering.Soybean root distribu tion followed simi-lar patterns throughout the growing sea-son, with root mass decreasing with depthand distance fro m the row center Fig.7A,B). No consistent significant differ-ences in root weights were detected be-tween nematode-infected and uninfectedplants at any depth or distance from therow. Or thogon al contrasts of root weightsfrom di ffer ent Pi were significant P =0.05) at two sampl ing dates 1 Septemberand 3 October).

DISCUSSIONThe population dynamics ofM. incogni ta

on soybean were dep end ent on Pi, time af-ter planting, environmental conditions,and root spatial distribution. Egg and J2densities throughout the soybean growingseason were closely related to Pi levels:generally, higher levels of eggs and J2were extracted from microplots infestedwith the higher Pi. J2 densities, regardlessof Pi were recovered at relatively low levelsearly in the season, as is typical for Meloi-dogyne spp. on annua l row crops 5) because


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S p a ti al a n d T e m p o r a l I n t e ra c t io n s o f M . incognita: W indham Barker 7 4 31 . 2. 8 - 10 . 6

2 0 . 4 -

0 . 2 -

0 , , , = ~ , m ' , = ~ - , , ~ = , , , ~ , = ~ ,0 1 0 ; 2 0 0 1 0 2 0 0 1 0 2 0 0 1 0 2 0D i s t a n c e r o m r o w ( c m )

D e p t h ( c r n )l 1 3 0 - 4 s 1 ~ 1 5 - 3 o [ Z ] O - 1 5

o0 1 , 2 5 0 5 , 0 0 0 1 0 , 0 0 0 2 0 , 0 0 0P i

D e p t h ( c m )B B 3 0 - 4 5 1 7 ~ 1 5 - 3 0 F ' ~ O - 1 5

~ 5. _m 4

1

0 1 0 2 0 0 1 0 2 0 0 1 0 2 0 0 1 0 2 0 G 1 0 2 0D i s t a n c e r o m r o w ( c r y )

0 1 , 2 5 0 5 , 0 0 0 1 0 , 0 0 0 2 0 , 0 0 0PJ

F~c.. 7. Inf lue nc e of Melo~dogyne ncognita nitialpopulations Pi) on spatial distribution of soybeanroots dry root weights) in relation to the center ofthe row at two sam pling dates. Pi = eggs/500cm3 soil.A) 21 July. B ) 15 Septem ber.m o s t J 2 h a v e p e n e t r a t e d p l a n t ro o t s a n da r e n o t r e c o v e r e d i n t h e e x t r a c t i o n p r o -c es s. E g g a n d j u v e n i l e n u m b e r s w e r e l o w e rt h r o u g h m o s t o f t h e s e as o n c o m p a r e d w i thl e v e l s o b s e r v e d a t t h i s l o c a t i o n i n p r e v i o u sy ea r s 1 9 ) .

S o il m o i s tu r e h a d a m a r k e d e f f e c t o n t h ep o p u l a t i o n d y n a m i c s o f M. incogni ta. Soi lm o i s t u r e le v el s w e r e lo w f r o m 2 1 J u l y- 8 . 3 b a r s) t o 1 S e p t e m b e r - 1 5 b a rs ).M eloidogyne incognita e g g h a t c h i s r e d u c e da t l o w s o il m o i s t u r e l e v e l s 9 ). E g g h a t c h i no u r e x p e r i m e n t w o u l d h a v e b e e n i n h i b i t e dd u r i n g t h e d r o u g h t p e r i o d f r o m 2 1 J u l yt h r o u g h 1 S e p t e m b e r , w h i ch w o u l d a c-c o u n t f o r t h e l o w J 2 p o p u l a t i o n d e n s i ti e sd u r i n g t hi s p e r i o d . T w o p e a k s i n J 2 p o p -u l a t i o n d e n s it ie s w e r e o b s e r v e d o n 1 5 S e p -t e m b e r a n d o n 2 5 O c t o b e r , o n w h ic h d a te ss oi l m o i s t u r e h a d i n c r e a se d f r o m t h e p r e -v i o u s s a m p l i n g d a t e s a n d a p p a r e n t l y s ti m -

u l a t e d e g g h a t c h . S o i l m o i s t u r e m a y h a v ea ls o h a d a n i n d i r e c t e f f e c t o n e g g p r o d u c -t i o n , w h i c h p e a k e d o n 1 5 S e p t e m b e r .S o il t e m p e r a t u r e e f f ec t s o n M. incogni tap o p u l a t io n d y n a m i c s w e r e u n c l e ar . T h es oil t e m p e r a t u r e r e m a i n e d w e ll a b o v e t h eJ 2 a c t iv i ty t h r e s h o l d 1 8 C ) 1 6 ) u n t i l t h et e n t h h a r v e s t d a t e 2 5 O c t o b e r ) , a n d t h e ns oil t e m p e r a t u r e s g r a d u a l ly d e c r e a s e d t o1 4 C o n t h e l as t h a r v e s t 1 4 N o v e m b e r ) .A l t h o u g h t h e r e w a s a m a r k e d d e c r e a s e i nJ 2 p o p u l a t i o n d e n s i t i e s a t t h e l a s t h a r v e s t ,e g g h a t c h s h o u l d n o t h a v e b e e n g r e a t ly in -f l u e n c e d b e c a u s e M. incogni ta e g g h a t c h i sn o t re s t r ic t e d u n t i l s oil t e m p e r a t u r e s d r o pb e l o w 1 2 C 9 ).V e r t i c a l d i s t r i b u t i o n s o f p la n t - p a r a s i t i cn e m a t o d e s a r e u s u a l l y c l o se l y r e l a t e d t or o o t d i s t r i b u t i o n 4 ), a n d t h is w a s t h e c a s ein o u r s t ud y . A s d e p t h a n d d i st a n ce f r o mt h e s o y b e a n r o w i n cr e a s ed , r o o t m a s s a n dn e m a t o d e n u m b e r s d e c r e a s e d . A l t h o u g ht h e h ig h e s t J 2 a n d e g g n u m b e r s w e r e i nt h e u p p e r 1 5 c m o f so il i n m i c r o p l o ts , h i g hn u m b e r s o f Meloidogyne s p p . w e r e f o u n dt h r o u g h o u t t h e u p p e r 4 5 c m in a s o y b e a nf ie ld i n a c o n c u r r e n t s t u d y W i n d h a m , u n -p u b l . ) . Meloidogyne s p p . h a v e a ls o b e e n r e -c o v e r e d a t g r e a t e r d e p t h s 8 ). M i c r o p lo t sin o u r s t u d y w e r e i n o c u l a te d t o a d e p t h o f15 c m . M o v e m e n t o f j u v e n i le s m a y h a v eb e e n le ss t h a n o b s e r v e d i n o t h e r s t u d i e s1 5), w i th t h e g r e a t e s t a m o u n t o f i n o c u l u mr e m a i n i n g in t h e u p p e r 3 0 c m o f so il. T h es p a t i a l d i s t r i b u t i o n o f M. incogni ta o n s o y -

b e a n c lo s el y r e s e m b l e s t h a t o f Heteroderaglycines o n s o y b e a n in f ie ld e x p e r i m e n t s1).E d a p h i c f a c t o r s a l so m a y h a v e h a d a ne f f e c t o n M. incogni ta s p a t i a l d i s t r i b u t i o n .B a s e s a t u ra t i o n , c a t i o n - e x c h a n g e c a p a c it y ,

p e r c e n t a g e o f o r g a n i c m a t t e r , p H , a n d l e v-e ls o f e x c h a n g e a b l e a n d e x t r a c t a b l e i o n sc a lc iu m , c o p p e r , m a g n e s i u m , m a n g a n e s e ,p h o s p h o r u s , a n d z in c) d i f f e r e d a m o n g s o ild e p t h s , w i t h le v e ls d e c r e a s i n g w i t h d e p t h .T h e e d a p h i c f a c to r s m a y h a v e i n f l u e n c e dJ 2 d i s t r i b u t i o n d i r e c tl y , o r i n d i r e c t ly b y a f -f e c t in g s o y b e a n r o o t p e n e t r a t i o n a t t h el o w e r d e p t h s .


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7 4 4 Jou rna l o f Nematology Volume 25 Supplement to December 1993Meloidogyne incognita h a d a n e g l i g ib l e e f-f e c t o n r o o t w e i g h t , a c c o u n t i n g f o r l e s st h a n 1 o f t h e v ar i a b il i ty i n t h e r o o t d a t a .S o y b e a n p l a n ts g r o w n i n lo w to m o d e r a t en e m a t o d e P i t e n d e d t o h a v e h i g h e r r o o t

w e i g h ts c o m p a r e d w i th t h o s e a t t h e h i g h e s tP i, a l t h o u g h t h e d i f f e r e n c e s w e r e n o t s ta -t i s t i c a l l y s i g n i f i c a n t . S o y b e a n r o o t s w e r en o t s e v e r e l y g a l l e d b y t h e M. incognita iso-l a t e u s e d i n t h i s e x p e r i m e n t c o m p a r e dw i t h t h e s e v e r e g a l l i n g r e p o r t e d i n a p r e -v io u s s t u d y a t~ th i s l o ca t i o n (1 9 ) . T h e e f -f e c t s o f M. incogni ta o n s o y b e a n r o o tg r o w t h a n d e f f ic i e n cy m a y h a v e b e e n m o r ea c c u r a t e ly d e s c r ib e d b y m e a s u r i n g r o o tl e n g t h s o r n u m b e r s o f r o o t t ip s ( 17). V a r i-a b i li ty o b s e r v e d i n r o o t w e i g h t s m a y b e a t -t r i b u t e d t o t h e s m a l l n u m b e r o f sa m p l e sp e r p l o t, a n d a l so t o t h e d i f f i c u l t y i n d i v id -i n g r o o t s i n c o r e s e c t i o n s . D e t e r m i n a t i o no f t h e g r o w t h o f w h o l e o r h a l f r o o t s y st em sf r o m t r e a t m e n t p l o t s , a s w a s d o n e f o r t h es h o o t s , m a y b e t h e i d e a l m e t h o d f o r o b -t a i n i n g t h e n e c e s s a r y m e a s u r e m e n t s f o rm o d e l i n g p u r p o s e s .

T h e m e t h o d s u s e d f o r d e t e r m i n i n g th ee f fe c ts o f M . incognita o n s h o o t g r o w t h a n dy ie ld w e r e m o r e t h a n a d e q u a t e . T h e o p ti -m u m t im e f o r d e t e r m i n i n g t h e r e la ti on -s h ip b e t w e e n p i a n d s o y b e a n s h o o t g r o w t hw a s f r o m m i d s e a s o n ( S e p t e m b e r ) t o h a r -v e s t ( h a rv e s t) f o r e a c h p a r a m e t e r . V a r i o u ss o y b e a n s h o o t c o m p o n e n t s r e f l e c t e d t h es e n s it iv i ty o f s o y b e a n t o M. incognita.T h e p r ec i s io n o f n e m a t o d e d a m a g ef u n c t i o n s c o n t a i n i n g o n l y p r e p l a n t n u m -b e r s o f n e m a t o d e s is l im i t ed . A n u m b e r o fe n v i r o n m e n t a l f a c t o r s a f f e c t t h e d a m a g ep o t e n t i a l o f M. incognita o n s o y b e a n ( 2 , 7 ,1 4 , 1 9 ) . S o y b e a n r e a c t i o n s t o M. incognitaa ls o v a r y w i t h c u lt i v a r (1 4) a n d d e p e n d o nt h e a g g r e s si v e ne s s o f t h e n e m a t o d e p o p u -l a t io n ( 18 ). M o r e p r e c i s e e s t i m a t e s o f so y -b e a n y i e ld lo s se s m a y b e o b t a i n e d b y m o d -e l i n g s o y b e a n g r o w t h a s a f f e c t e d b y c r o pm a n a g e m e n t p r ac ti ce s , e n v i r o n m e n t a l fa c-t o r s , p e s t s , a n d p a t h o g e n s . I n f o r m a t i o nc o l l e c te d in t hi s s t u d y m a y p r o v e u s e f u l int h e d e v e l o p m e n t o f a M . incognita l i fe cy c l es i m u l a t o r . T h e s e f i n d i n g s s h o u l d a l s o b e

h e l p f u l i n p l a n n i n g f u r t h e r r e s e a r c h f o rm o n i t o r i n g t h e e f f e c t s o f p l a n t - p a r a s i ti cn e m a t o d e s o n s o y be a n .L I T E R A T U R E C I T E D

1. Als ton , D. G. , an d D . P . Sch mi t t . 1987. P op ula -t i o n d e n s it y a n d s p a ti a l p a t te r n o f Heterodera glyc inesi n r e la t io n t o s o y b e a n p h e n o l o g y . J o u r n a l o f N e m a -t o l o g y 1 9 : 3 3 6 - 3 4 5 .2 . B a r k e r , K . R . 1 98 2. I n f l u e n c e o f s o il m o i s t u r e ,c u l ti v a r, a n d p o p u l a t i o n d e n s i ty o f M e l o i d o g y n e i n c o gn i t a o n s o y b e a n y i e l d i n m i c r o p lo t s . J o u r n a l o f N e m a -to log y 14:429 Abst r . ) .3 . B a r k e r , K . R . C h a i r m a n ) . 1 9 78 . D e t e r m i n i n gn e m a t o d e p o p u l a t i o n r e s p o n s e t o c o n t r o l a g e n t s. P p .1 1 4 - 1 2 7 i n E . I . Z e h r , e d . M e t h o d s f o r e v a l u a t i n gp l a n t fung i c i de s , ne ma t i c i de s , a nd ba c t e r i c i de s . S t .P a u l: 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 et y .4 . B a rk e r , K . R . , a nd J . L . Imbr i a n i . 1984 . Ne ma -t o d e a d v i s o r y p r o g r a m s - - - S ta t u s a n d p r o s p e c ts . P l a n tD i s e as e 6 8 : 7 3 5 - 7 4 1 .5 . B a r k e r , K . R . , C . J . N u s b a u m , a n d L . A . N e l s o n .1 9 69 . S e a s o n a l p o p u l a t i o n d y n a m i c s o f s e l e c t e dp l a n t - p a r a s i t i c n e m a t o d e s a s m e a s u r e d b y t h r e e e x -t r ac t io n p r o c e d u r e s . J o u r n a l o f N e m a t o l o g y 1 : 2 3 2 -239.6 . F e h r , W . R ., C . E . C a v in e s s, D . T . B u r m o o d ,a n d J . S . P e n n i n g t o n . 1 97 1. S t a g e o f d e v e l o p m e n t d e -sc r i p t i ons fo r soybe a ns , G l y c in e m a x L. ) Me r r i l l . C ropS c i e nc e 11 : 929-931 .7 . F e r r i s , H . 1981 . Dyna m i c a c t i on t h re sho l d s fo rd i s ea s e s i n d u c e d b y n e m a t o d e s . A n n u a l R e v i e w o fP h y t o p a t h o l o g y 1 9 : 4 2 7 - 4 3 6 .8 . F e r r i s , H . , a nd M. V. M c Ke n ry . 1974 . S e a sona lf l u c t u a t i o n s i n t h e s p a t i a l d i s t r i b u t i o n o f n e m a t o d ep o p u l a t i o n s i n a C a l i f o r n i a v in e y a r d . J o u r n a l o fN e m a t o l o g y 6 : 2 0 3 - 2 1 0 .9 . Go ode l l , P . B . , a nd H . F e r r i s . 1989 . In f l u e nc e o fe n v i r o n m e n t a l f a c t o r s o n t h e h a t c h a n d s u r v i v a l o fM elo idogyne incogn i ta . J o u r n a l o f N e m a t o lo g y 2 1 : 3 2 8 -334.10 . Husse y , R . S., a nd K. R . B a rke r . 1973 . A c om -

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Spa t ia l and Tem pora l I n te r ac t i ons o f M . i n co g n it a: W i n d h a m B a r k e r 745detection o f low population densities o f Meloidogyne.Nematologica 24:129-132.16. Roberts, P. A., S. D. Van Gundy, and H.E.McKinney. 1981. Effects of soil temperature andplanting date of wheat on M eloidogyne ncognita repro-duction, soil populations, and grain yield. Journal ofNematology 13:338-345.

17. Shane, W. W., and K. R. Barker. 1986. Effectsof temperature, plant age, soil texture, and Meloido-

gyne incognita on early growth of soybean. Journal ofNematology 18:320--327.18. Windham, G. L., and K. R. Barker. 1986. Rel-ative virulence of M eloidogyne incog nita host races onsoybean. Journal of NematoLogy 18:327-331.19. Windham, G. L., and K. R. Barker. 1986. Ef-fects of soil type on the damage potential of Meloi-dogyne incognita on soybean. Journal of Nematology18:331-338.

spatial and temporal interactions of meloidogyne incognita and soybean

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