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Abstract:
Rhizobium inoculation has successfully been used for improving growth and yield of legume crops in different parts of the world. L-Tryptophan (L-TRP) application may further improve its effectiveness due to substrate-dependent inoculum-derived auxins in the rhizosphere. Rhizobium phaseoli strains were isolated using dilution plate technique from the mung bean nodules. Auxin biosynthesis by these rhizobial isolates was determined in the absence and presence of L-TRP, a physiological precursor of auxins. Rhizobial isolates varied widely in auxins biosynthesis capabilities and A23, N12 and N42 being the highest auxin producer strains were further evaluated in the presence of different levels of L-TRP (10-3, 10-4 and 10-5 M) for improving the growth and yield of mung bean. Mung bean seeds were inoculated with peat-based inocula and sown following randomized complete block design with four replications. Fertilizers, NP were applied at 60-50-0 kg ha-1 as urea and single super phosphate (SSP) in all plots. Results revealed that L-TRP (at 10-4 and 10-5 M) and rhizobial inoculation when applied alone significantly increased the growth and yield of mung bean compared to untreated control. However, Rhizobium inoculation supplemented with L-TRP (10-4 and 10-5 M) gave the most promising results and significantly increased the plant height, number of nodules plant-1, nodular mass plant-1, number of grains pod-1, number of pods plant-1, total plant biomass, grain yield and 1000-grain weight up to 37, 80, 83, 46, 76, 62, 59 and 19%, respectively compared to uninoculated and untreated control. Similarly, N concentration in grain also increased significantly at this L-TRP level by the rhizobial inoculation. The results imply that supplementing rhizobial inoculation with L-TRP could be a useful approach for improving growth, nodulation and yield of mung bean.
Key words: Rhizobium, inoculation, L-tryptophan, yield, nodulation, mung bean