STUDIES ON THE EFFECT OF ASSOCIATED SOIL MICROFLORA ON FUSARIUM UDUM BUTL., THE FUNGUS CAUSING WILT OF PIGEON‐PEA (CAJANUS CAJAN (L.) MILLSP.), WITH SPECIAL REFERENCE TO ITS PATHOGENICITY

The interaction of certain soil saprophytes and Fusarium udum, the wilt organism of pigeon‐pea, with special reference to their effect on pathogenicity, has been studied. The filtrates of Aspergillus niger, Rhizopus nigricans and mixed filtrates of all the saprophytes inhibited the growth of Fusarium udum on solid medium. This inhibition of F. udum has been shown to be due to unfavourable reaction of the medium rather than to food exhaustion or the presence of toxic substances. The culture filtrates after passage through soil beds failed to affect adversely the growth of F. udum because of the change in pH. Inoculation experiments have indicated that only Rhizopus nigricans is effective in reducing the incidence of wilt because of its faster rate of growth. The mixed inocula of the organisms and mixed filtrates of all the saprophytes have also been observed to be effective in reducing wilt incidence. Aspergillus terreus appears to enhance the virulence of Fusarium udum.