Competitive Ability and Efficiency in Nodule Formation of Strains of Bradyrhizobium japonicum

Abstract

In the American Midwest, superior N2-fixing inoculant strains of Bradyrhizobiumjaponicum consistently fail to produce the majority of nodules on the roots of field-grown soybean. Poor nodulation by inoculant strains is partly due to their inability to stay abreast of the expanding soybean root system in numbers sufficient for them to be competitive with indigenous bradyrhizobia. However, certain strains are noncompetitive even when numerical dominance is not a factor. In this study, we tested the hypothesis that the nodule occupancy achieved by strains is related to their nodule-forming efficiency. The nodulation characteristics and competitiveness of nine strains of B. japoniwum were compared at both 20 and 30°C. The root tip marking technique was used, with the nodule-forming efficiency of each strain estimated from the average position of the uppermost nodule and the number of nodules formed above the root tip mark. The competitiveness of the nine strains relative to B. japonicum USDA 110 was determined by using immunofluorescence to identify nodule occupants. The strains differed significantly in competitiveness with USDA 110 and in nodulation characteristics, strains that were poor competitors usually proving to be inferior in both the average position of the uppermost root nodule and the number of nodules formed above the root tip mark. Thus, competitiveness was correlated with both the average position of the uppermost nodule (r = 0.5; P = 0.036) and the number of nodules formed above the root tip mark (r = 0.64; P = 0.005), while the position of the uppermost nodule was also correlated to the percentage of plants nodulated above the root tip mark (r = 0.81; P < 0.001) and the percentage of plants nodulated on the taproot (r = 0.67; P = 0.002).

Host Variation in Traits Associated with Crown Nodule Senescence in Soybean

“…These were thinned to two seedlings per pot after emergence. Plants were grown in a greenhouse with a 16‐h photoperiod and 26 and 21°C day and night temperatures, respectively, and were watered alternately with sterile water and sterile low N plant nutrient solution (McDermott and Graham, 1990) In each experiment, except that on cultivar variation in nodule histology, three replicate plants per cultivar were harvested each week for 9 wk, beginning 10 DAE. This corresponded with the period from nodule initiation and development to nodule senescence.…”

Dual effect of Mesorhizobium loti T3SS functionality on the symbiotic process

“…Esmeralda. CI is defined as the number of singly occupied nodules formed by the mutant strain as a proportion of all nodules formed, divided by the proportional representation of viable cells of that strain in the inoculate mixture according to McDermott & Graham (1990); (c) competitiveness on Lo. japonicus MG-20.…”

Changes in electrophoretic profiles of lipopolysaccharides from competitive strains of Bradyrhizobium spp. induced by soybean roots

“…Only 29W nodule formation, or the infection process requires a smaller and Semia 587 produced profuse nodulation, occupying 90% number of cells and the sequence of the infection occurs with of the nodules formed. In contrast, strains Semia 566 and greater speed (McDermott and Graham 1990). From this CB1809 occupied only approximately 2% of the nodules premise, several authors have identified genes and phenotypes (Scotti et al 1982).…”

“…Effective nitrogen-fixing rhizobia-legume symbiosis occurs and Long 1992), exopolysaccharide (Leigh and Coplin 1992) Semia 566 (parental) were tested against 29W under aseptic conditions in Leonard jars (Somasegaren and Hoben 1985). and lipopolysaccharide (Carlson et al 1987). As in the Gramnegative bacteria, the outer membrane of rhizobia is the cell Soybean seedlings (Glycine max (L.) Merril cv.…”

“…Thus, cell surface LPS polysaccharides of rhizobia must play a primary role in the initial events of 1979), using antibodies produced against the parental strains (Semia 566 and 29W). recognition (Smit et al 1992) and root infection of herbaceous or arboreous legumes (Carlson et al 1987 ;López-Lara et al The other experiment was a field experiment. It was conducted from 1993-1994 at CPAC (Cerrado Center) located 1995).…”