Thermotolerant phosphate solubilizing microorganisms and their interaction with mung bean

Several phosphate solubilizing microorganisms (PSM) were tested for their efficiency at 35°, 40° and 45°C. There was a marked variation in their ability to solubilise tricalcium phosphate and the effect was more pronounced at 45°C. Two bacterial and one fungal strain were found to be thermotolerant as they solubilised a large amount of tricalcium phosphate at the three tested temperatures. These thermotolerant strains were identified as Bacillus subtilis (TT₀), Bacillus circulans (TT₈) and Aspergillus niger (TT₁₀). Seed inoculation of mung bean showed a better establishment of temperature tolerant strains as revealed by the rhizosphere population. The inoculation improved nodulation, the available P₂O₅ content of the alluvial soil, root and shoot biomass, straw and grain yield and phosphorus and nitrogen uptake of the crop. Among the bacterial strains, the best effect on yield was obtained with B. subtilis. However, statistically it was equivalent to streptomycin resistant mutant (M-20) and Pseudomonas striata (27). A. niger was less effective than bacteria. Though superphosphate was found to be a better source of phosphate fertiliser, the use of rock phosphate (RP₄₀), coupled with phosphate solubilising bacteria (PSB), gave results comparable to superphosphate (SP₂₀) + PSB inoculants.