STUDIES ON THE MICROBIOLOGY OF RECONTAMINATED STERILIZED SOIL IN RELATION TO ITS INFESTATION WITH OPHIOBOLUS GRAMINIS SACC.

Abstract

In these studies recontaminated steam-sterilized black soil, when infested with the take-all fungus, Ophiobolus graminis, gave, as a rule, less severe infection of wheat seedlings than similarly infested unsterilized soil. One explanation suggested is that the microflora that develops in sterilized soil following recontamination has a greater suppressive action on Ophiobolus graminis than that normally present in unsterilized soil. These two microfloras were found to differ both quantitatively and qualitatively. In general the number of microorganisms, as determined by the plate count method, was found to be much greater in sterilized recontaminated soil than in unsterilized soil. The fact that the fungus Trichoderma viride develops rapidly and becomes a dominant organism in sterilized recontaminated soil is considered to be of especial significance. The antagonism of this fungus toward Ophiobolus graminis probably plays an important role in suppressing the latter.