Antagonistic activity of Bacillus subtilis towards Rhizopus nigricans

Abstract

Antagonistic effect of seven isolates of Bacillus subtilis has been examined in dual culture tests against Rhizopus nigricans, the incitant of 'papaya' (Carica papaya L.) frult-rot. Isolate AF 1 which caused maximum inhibition (9.6 mm) was grown in potato dextrose broth for 96 h and cell-free culture filtrate was used to study the inhibition. The concentrated extract of culture filtrate of the antagonist was diluted to indicate 0-40 per cent in potato dextrose agar and Richard's solution. There was 93% inhibition at 40 per cent in both the media. Germinated spores formed clumps in Richard's solution at and above 20 per cent concentration of the antagonistic culture filtrate, but failed to produce sporangia. Concentrated extract induced formation of bulbous structures in hyphae. Biological control of papaya fruit-rot was achieved by dipping the fruits in cell suspension of B. subtilis or in the culture filtrate, 24 h before treatment with R. nigricans.