Rhizobium sp. exopolysaccharide production,nodulation, and acetylene reduction activity (N2-fixation) in pigeon pea (Cajanus cajan L.)

Summary There was no correlation between the quantity of exopolysaccharide produced and acetylene reduction activity by Rhizobium spp. or by Bradyrhizobium spp. (Cajanus). The exopolysaccharide-defective mutants of Rhizobium sp. strain P 116 either failed to nodulate or showed a decrease in effectiveness. The deficiency in exopolysaccharide production was corrected by the addition of purified exopolysaccharide from the parent strain, or from Bradyrhizobium sp. strain P 149 or S24 isolated from pigeonpea (Cajanus cajan) and mungbean (Vigna radiata), respectively. However, the nodules so formed were not fully effective compared to those formed by the parent strain.