Growth, nodulation and yield of mash bean (Vigna mungo L.) as affected by Rhizobium inoculation and soil applied L-tryptophan

Most of the grain legumes in Pakistan are poorly nodulated either because of low indigenous rhizobial population or due to inefficient strains of native rhizobia. However, improvement in nodulation could be achieved through inoculation with effective rhizobial strains. A pot trial was conducted to evaluate the effect of Rhizobium inoculation along with L-tryptophan (L-TRP), a precursor of indole acetic acid (IAA) on growth, yield and nodulation of mash been. The results indicated that Rhizobium inoculation along with L-tryptophan application (6 mg kg^-1 soil) significantly improved plant height (44.6%) as compared to control. Different improvements in root length (72.4%), oven dry root weight (Five fold), no. of pods plant^-1 (86.4%), no. of grains per pod (42.8%), 100- grain weight (18.9%) and nitrogen concentration in grains (two fold), was noted as compared with the control where L-TRP was applied @ 2 mg kg^-1 soil. There was a significant increase in number of nodules plant^-1 (one fold), nodule fresh weight plant^-1 (two fold) and nodule dry weight plant^-1 (four fold) with Rhizobium inoculation along with L-TRP application @ 2 mg kg^-1 soil as compared to Rhizobium inoculation alone. The study showed that Rhizobium inoculation along with L-TRP application could be a better approach for sustainable legume production.