Co-inoculation of phosphate solubilizing bacteria and rhizobia in the presence of L-tryptophan for the promotion of mash bean (Vigna mungo L.)

The development of symbiotic relationship between rhizobia and leguminous plants results in active nitrogen fixation and plays a marvelous role in agriculture systems. L-tryptophan (L-TRP) is an amino acid that acts as physiological precursor of auxins and is responsible for biosynthesis of auxins in the rhizosphere. Pot experiment was conducted at the Soil Bacteriology Section Faisalabad to assess the co-inoculation effect of N2-fixing (Rhizobium) and P-solubilizing (Bacillus sp) in the presence of L-TRP. Results revealed that co-inoculation improved the pod and straw yield considerably but the effect was more pronounced with L-TRP. Co-inoculation increased the root length, root mass, number of nodule and mass as compared to control with L-TRP. Co-inoculation with L-TRP produced 30.87 pod and 32.73 g pot-1 straw yield followed by 30.47 and 31.10 g pot-1 with rhizobial inoculation, respectively. Co-inoculation produced higher root mass (33.5 g), root length (36.0 cm), nodule number (34), nodule mass (0.131 g) and these values were further enhanced with L-TRP (40.5 g, 49 cm, 48 and 0.145 g). Co-inoculation enhanced the nutrient concentration in mash plant, grains and improved the nodulation as compared to the separate bacterial inoculations. Co-inoculation with L-TRP produced higher soil N and available P in post harvest soil samples as compared to control. Study demonstrated that co-inoculation of Rhizobium and Bacillus species influenced the yield components positively than their separate inoculation and this effect could be more assenting with L-TRP. However, the approach of precursor-inocula interaction should be studied more comprehensively in different ecological zones to sustain the crop yield.