Competition between related strains of nodule bacteria and its influence on infection of the legume host

Abstract

T h e w o r k d e a ls w i t h t h e b e h a v io u r o f m ix e d s t r a i n s o f n o d u le b a c te r ia t o w a r d s e a c h o t h e r a n d to w a r d s t h e i r le g u m e h o s t.I t in t r o d u c e s t h e c o n c e p t o f d o m in a n c e in c o m p e t it io n b e tw e e n s tr a in s . T h is d o m in a n c e is i n d e p e n d e n t o f d e g re e o f e ff e c tiv e n e s s a s r e g a r d s n itr o g e n f i x a tio n .W h e r e tw o s t r a i n s o f n o d u le b a c t e r i a a r e b o t h p r e s e n t in t h e s u r r o u n d in g s o f t h e i r h o s t 's r o o t s y s te m , a c ti v e c o m p e t it io n b e tw e e n t h e m m a y c a u s e t h e s t r a i n h a v i n g t h e h ig h e r in i t i a l g r o w th r a t e a lm o s t c o m p le te ly t o c h e c k m u l t i p l i c a t i o n o f t h e o t h e r s t r a i n o u ts id e t h e p l a n t . T h is d o m i n a n t s t r a i n w ill t h e n b e r e s p o n s ib le f o r n e a r l y a ll t h e n o d u le s .I n p e a s a n d s o y b e a n s , w h e r e g r o w T h e r e a r e la r g e d iffe re n c e s in t h e r a t e s o f a p p e a r a n c e a n d fin a l n u m b e r s o f n o d u le s p r o d u c e d b y d if f e r e n t s t r a i n s s u p p lie d i n p u r e c u lt u r e , p a r t i c u la r ly w i t h c lo v e r . th o f t h e r o o t s y s te m is r a p i d a n d o f c o m p a r a t i v e l y s h o r t d u r a t i o n , t h e n o d u le -p r o d u c in g c a p a c i t y o f t h e p l a n t m a y b e p a r t i a l l y o r w h o lly s a tis f ie d b y t h e n o d u le s p r o d u c e d w ith i n t h e fir s t fe w w e e k s , so t h a t f u r t h e r in f e c tio n , w h e th e r b y t h e s a m e o r b y a d if fe re n t s t r a i n , is c h e c k e d o r inT h e r e l a t i v e n u m b e r s o f n o d u le s p r o d u c e d b y t h e tw o s t r a in s s im u l ta n e o u s l y a p p li e d t o t h e r o o t s is c o n d itio n e d b y t h e sp e c ific in f e c tiv ity p e c u li a r t o e a c h s t r a i n , u n le s s s o m e o t h e r f a c t o r , s u c h a s c o m p e t it io n o u ts id e t h e p l a n t , m a s k s t h i s e ffe c t.

Response of Groundnut (Arachis hypogaea L.) to inoculation withRhizobium strains isolated from wild arboreal legumes

“…This early infection then encourages the plant to develop immunity to further infection (Dunham & Baldwin 1931) and also the infection sites are covered with the nodules formed by them (Chen 1941). Poor competitive ability of the rhizobia also results in their failure to inoculate plants efficiently (Nicol & Thornton 1941). Hegde (1982), noticed that in India, the necessity to inoculate groundnut has neither been shown conclusively nor investigated thoroughly.…”

Isolation of competition-defective mutants of Rhizobium fredii

“…The mechanisms that confer saprophytic competence and competitiveness on a Rhizobium strain in such an environment are poorly understood (12,18,20,23,30). In this study we used a competition assay to isolate TnS-induced mutants of Rhizobium fredii whose sole known defect is reduced competitiveness.…”

Populations of Rhizobium japonicum in Iowa soils and inoculum level needed for nodulation of Glycine max (L.) Merrill

“…The percentage of soybean nodules formed by a given strain in a mixed inoculum was seldom the same as the percentage of the given strain in the inoculum (Nicol and Thornton, 1941;Means et al, 1961;Date, 1962;Damirgi, 1963;Johnson and Means, 1964;Ham, 1967). Two strains of R. j aponicum added as inoculum to soybeans in the ratio of 53 to 47 were reported by Means et al (1961) to form respectively 4 and 96% of the nodules.…”

“…Nicol and Thornton (1941) and Clark (1957) reported that different strains of R. japonicum varied in the number of nodules formed on a given soybean variety. Two strains of rhizobia produced 247 and 129 nodules per pot respectively on the same variety of soybean (Nicol and Thornton, 1941).…”

“…In the laboratory, strains of 110 effectively nodulated the Peking variety. Nicol and Thornton (1941) proposed that the differential ability of strains to compete for nodule sites was due to their ability to dominate the hosts rhizosphere bacterial population. They found that addition of related strains of rhizobia to the hosts rhizosphere in approximately equal numbers resulted in the strain that formed the majority of the nodules completely dominating the rhizosphere population ot bacteria.…”