Symbiotic specificity in nodulation and nitrogen fixation between winged bean and Rhizobium

Abstract

Four selections of winged bean (syn. Indies Goa bean, Psophocarpus tetragonolobus) and 1 selection of the closely related species P. palustris were tested with 3 Rhizobium strains, in a glasshouse with simulated tropical conditions, to study their symbiotic specificities in terms of nodulation and N 2 fixation. There were highly significant differences in nodulation factors such as nodule distribution within root-zone, nodule morphology and nodule mass, and in N 2 fixation factors such as nitrogenase activity and the amount of effective nodule tissues between the plant selections, Rhizobium strains and their interactions at sixth and ninth week after seedling emergence. The strain NGR 258 was highly effective on winged bean and highly ineffective on P. palustris in terms of nodulation and N 2 fixation. The strain SRI 1 was highly ineffective and could not be used in field practice, while strain MAR 655 showed a good symbiotic association with some of the winged bean genotypes, formed a good amount of effective nodule tissues equal to that of NGR 258, but performed poorly compared to NGR 258 in terms of total nodule mass and N 2 fixation. The winged bean selection LBNC 1 was the best genotype in terms of nodulation and N 2 fixation. The symbiotic specificities observed in the host and Rhizobium combination showed that winged bean selections LBNC 1 and TPT 2 with strain NGR 258 were excellent symbiotic systems while P. palustris and NGR 258 should not be used in field practice. P. palustris could be used in hybridization programs with winged bean without the nodulation and N 2 fixation, although care should be taken in selecting the strain of Rhizobium inoculum for such lines. P. palustris was equally good as winged bean selections as a potential mulch/cover crop in terms of N 2 fixation.