Fungal Assciations: II. Cultural Studies on Rhizoctonia solani Kuhn, Fusariutn solani Snyder and Hansen, and Other Fungi, and Their Interactions

Several types of interaction between Rhizoctonia solani, Fusariumsolani, and Phoma foveata were found when these fungi were grownon potato-dextrose agar. After being used by Rhizoctonia a potatomash medium gave better growth of Rizoctonia and Fusarium thanit did when the medium was initially used by Fusarium; and thiswas so whether the reaction of the spent medium was readjustedor not. It is suggested that potato mash medium used by Fusariumcontains a thermostable factor(s) affecting the subsequent growthof Rhizoctonia or Fusarium. The range of pH values suitable for Rhizoctonia growth was narrowerthan that for Fusarium, optimum values being approximately 5•9for the former and 7•8 for the latter. In mixed culturesof the two fungi on potato-dextrose agar adjusted to differentpH values, the fungus for which the reaction of the medium wasmore suitable usually became visually predominant after sometime. A study of various carbon sources showed that poor growth ofRhizoctonia was obtained when pectin was used as the sole sourceof carbon. On a pectin-agar medium, the rate of growth of aRhizoctonia colony increased on the sector which lay towardsan adjacent Fusarium colony; also, after the two fungi camein contact, there was more rapid growth of Rhizoctonia roundthe Fusarium colony than elsewhere. On a synthetic liquid mediumwith pectin as the carbon source better Rhizoctonia growth wasobtained when Fusarium-spent medium was added to it than whenRMzoctoma-spent medium was added. Rhizoctonia showed partial deficiencies in thiamine, biotin,and inositol. Both the extract of Fusarium mycelium, grown onvitamin-free medium, and the Fusarium-spent medium, stimulatedthe growth of Rhizoctonia on vitamin-free medium.