Effect of rj1rj1 (non-nodulating) soybeans on nodulation of near isogenic Rj1Rj1 plants in nutrient culture.

An earlier proposal (Can. J. Microbiol. 7: 851; 1961) that rj1rj1 (non-nodulating) soybeans (Glycine max (L.) Merr.) excrete a substance that inhibits nodulation of Rj1 Rj1 (nodulating) plants was tested. Using near isogenic lines (isolines) of "Clark" and "Harosoy" soybeans, we consistently found nonsignificant reduction in nodule number and acetylene reduction per Rj1Rj1 plant grown in association with their rj1rj1 counterparts: these results suggest that a nodulation inhibitor is not associated with the rj1 gene. Reducing the number of plants grown in each pot produced significant (P = 0.05) reductions in nodule number per Rj1Rj1 plant, and resembled the observations of the earlier report. On this basis, we suggest that the reported inhibition of nodulation was due to a failure to detoxify or remove an inhibitor (possibly nitrate) already present in the nutrient solution. Both Clark isolines removed nitrate from their nutrient solutions at similar rates. Harosoy rj1rj1 plants removed nitrate at a significantly (P - 0.05) slower rate than Harosoy Rj1Rj1 plants, but the differences were not correlated (P = 0.05) with the small observed decreases in nodulation. These differences in nitrate uptake were highly correlated (P = 0.01) with reduced dry weight per Harosoy rj1rj1 plant.