The effect of light intensity on nodulation and N2 fixation of winged bean Psophocarpus tetragonolobus Rhizobium strains

Abstract

AbstractTwo winged bean Rhizobium strains, RRIM 56 and NGR 258 were tested with different selections of winged bean Psophocarpus tetragonolobus and one selection of Psophocarpus palustris under high and low sunlight intensities and long and short day photoperiods in pot experiments.Nodulation and N2 fixation by the strain RRIM 56 was not affected by light intensity and photoperiod and it showed very effective nodulation and N2 fixation. It was found to be capable of showing a N‐gain of 140 kg per ha per 9 weeks and 750 kg per ha per year in winged bean selections. The strain NGR 258 was highly sensitive to light intensity and insensitive to photoperiod. High light intensity during the first two weeks after seedling emergence drastically inhibited nodulation. The light effect on this strain may relate to the reduction of tryptophan movement from shoot to root system. An experiment with tryptophan injection into the stem base indicates that the amount of tryptophan needed to produce indole – acetic acid in the root hairs plays an important role in controlling the infection and nodule initiation processes in winged bean.The conversion efficiency of tryptophan to the auxin indole‐acetic acid of this strain was also lower than that of strain RRIM 56. The former converts tryptophan mostly via tryptamine, while the latter follows the pathway via indole – pyruvic acid.