Abstract

Laboratory experiments were conducted to study the effects of five fungicides on the growth of Bradirhizobium japonicum and Phosphate solublizing bacteria (PSB) at different concentrations that is, (0, 0.1, 0.2, 0.3, 0.4 and 0.5%). Fungicide effects on bacteria were determined on the basis of their growth in respective medium. The population of B. japonicum declined significantly while PSB population showed non-significant growth reduction. Minimum (13.5 × 10⁴ CFU ml^-1) of B. japonicum were recorded at 0.5% concentration. However, reduction in PSB at 0.5% thiram was non-significant. The mean population of microorganisms declined significantly by carbendazim. Maximum reduction in B. japonicum and PSB population was recorded at 0.5 and 0.4% carbendazim concentration respectively. Vitavax exhibited maximum population reduction at 0.5% concentration where (6.5 × 10⁴ CFU ml^-1) of microorganisms were recorded. The mean population of microorganisms declined significantly with increasing carboxin concentration and 5.6 × 10⁴ CFU ml^-1 of B. japonicum was recorded at 0.5% concentration of carboxin. The effective mean population irrespective of the organisms showed significant decrease with increasing concentration of thiomethaxam. Among all the fungicides, minimum bacterial growth was observed at 0.5% thiomethaxam concentration. Experimental results revealed that, higher concentration of all the fungicides exerted toxic effect on beneficial soil microflora.

Key words:  Bradirhizobium japonicum, Phosphate solublizing soil bacteria (PSB), fungicides, growth.