EFFECT OF PHOSPHATE-SOLUBILIZING STRAINS OF AZOTOBACTER CHROOCOCCUM ON YIELD TRAITS AND THEIR SURVIVAL IN THE RHIZOSPHERE OF WHEAT GENOTYPES UNDER FIELD CONDITIONS
A field experiment was carried out to investigate the establishment of phosphate-dissolving strains of Azotobacter chroococcum, including soil isolates (wild type) and their mutants, in the rhizosphere and their effect on the growth attributes and root biomass of three genetically divergent wheat cultivars (Triticum aestivum L.). Four fertilizer doses were applied: 90 kg N ha—1, 90 kg N + 60 kg P2O5ha—1, 120 kg N ha—1and 120 kg N + 60 kg P2O5ha—1, besides a control plot without fertilizers or bioinoculants. Phosphate-solubilizing and phytohormone-producing parent soil isolates and mutant strains of A. chroococcum were isolated and selected following the enrichment method. On an overall basis the mutant strains performed better than the soil isolates for in vitro phosphate solubilization (11–14%) and growth hormone production (11.35%). Seed inoculation of wheat varieties with phosphate-solubilizing and phytohormone-producing A. chroococcum showed a better response over the control. Mutant strains of A. chroococcum showed a higher increase in grain (15.30%) and straw (15.10%) yield over the control and better survival (12–14%) in the rhizosphere as compared to their parent soil isolate (P4). Mutant strain M15 performed better in all three varieties in terms of increase in grain yield (20.8%) and root biomass (20.6%) over the control.