The influence of cultural medium composition on the proteolytic enzyme secretion of fungus <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

It was shown that change of medium growth composition of photopathogenic fungus Rhizoctonia solani Kühn, especially accessible sources of nutrition, leads to change of both quantity of produced proteinases and their action specificity. The mineral source of nitrogen suppressed the fungus proteinase secretion on cultivatiin medium containing potato thermostable proteins but an organic source of nitrogen accelerated mycelium growth and increased proteinase secretion. On the basis of an analysis of a fungus extracellular proteinase substrate-specificity, it is established that the presence of thermostable proteins of a potato in the cultural liquid induces the secretion of trypsin-like proteinases mainly, and the addition of yeast extract to this growth medium induces the secretion of subtilisin-like ones, thus suppressing the trypsin-like enzymes production. This fact can indicate that mycelium of fungus R. solani loses pathogenic properties and becomes saprophytes when the growth medium was enriched by an organic source of nitrogen.