Synergistic action of PGP agents and Rhizobium spp. for improved plant growth, nutrient mobilization and yields in different leguminous crops

The effect of Rhizobium inoculation alone and in conjunction with plant growth promoting (PGP) microbial inoculants was evaluated in three leguminous crops – chickpea, pea and lentil. Significant enhancement in soil polysaccharide content and plant dry weight was recorded over control, in all those treatments receiving microbial inoculation. Nitrogen fixation (measured as ARA, acetylene reducing activity) in the treatment involving Anabaena laxa (RPAN8) showed a two folds increase over both Rhizobium inoculation and control in lentil, and in Trichoderma–Rhizobium treatment in pea crop. An increase of two-four folds in leghaemoglobin content and a doubling of yields was recorded in the combined microbial inoculation treatments, as compared to both Rhizobium inoculation or control, particularly in chickpea crop. A significant positive correlation was observed between nitrogen fixation with plant biomass and yields in all the three crops. Among the treatments, the use of cyanobacterium Anabaena laxa (RPAN8) and Anabaena–Pseudomonas fluorescens biofilmed inoculant, were most promisimg, besides biofilmed inoculants of Trichoderma or Anabaena with Rhizobium being among the top ranking treatments. These investigations illustrate the promise of cyanobacterial inoculants in various leguminous crops. Future focus needs to be towards understanding signalling mechanisms between Rhizobium and cyanobacteria and their positive feedback on plant growth and yield of legumes.