CELLULOSE DECOMPOSITION BY PYTHIUM AND ITS RELEVANCE TO SUBSTRATE-GROUPS OF FUNGI

When assessed by strength-loss of cellulose film or weight-loss of filter paper, the following Pythium spp. were cellulolytic: P. debaryanum, P. graminicola, P. intermedium, P. irregulare, P. mamillatum, P. scleroteichum, P. sylvaticum and 1 (atypical) isolate of P. acanthicum. By contrast, P. anandrum, P. aphanidermatum, P. butleri, P. heterothallicum, P. spinosum, P. splendens, P. ultimum and P. vexans were weakly or non-cellulolytic. Isolates within each species behaved similarly in cellulolysis and, for the pythia as a whole, there was a positive correlation (P = 0.001) between degradation of cellulose film and that of filter paper. P. graminicola was the most active decomposer of cellulose film, on which it formed swollen, appressorium-like bodies and rooting branches. Using these for identification, P. graminicola made limited growth on cellulose film in soil. THe cellulolytic activity of some Pythium spp. removes them from the substrate-group, sugar fungi. An index linking cellulolysis to growth on sugars may be more satisfactory for defining the substrate-relationships of pythia; this concept is discussed in relation to saprophytic activities of fungi in general.