Study of Nutritional and Environmental Factors Affecting the Fruiting Competence of Rhizoctonia solani AG‐1

The study of nutritional, physiological and physical factors affecting basidiospore development in Rhizoctonia solani evidenced the critical influence of the physiological state of the mycelium subjected to a nutritional stress for fruiting induction. Comparison of four preculture media allowed identification of the optimal nutrient status provided by glucose, yeast extract and bacto‐peptone, for subsequent basidial differentiation on a starved water agar medium. While variations of glucose and yeast extract concentrations are not determinant for basidial differentiation, the breakdown observed with a low bactopeptone concentration underscores a major role for the nitrogen content which however should be considered in a balance with the carbon source. The basidial differentiation was shown: (i) to increase as the age of the preculture used to inoculate water agar increases; (ii) to be stimulated by a dark/light regime, and (iii) to be induced and increased by a cold temperature shock (8 o C) when the mycelium was derived from young precultures. The effect of the cold temperature shock indicates that the preculture conditions can induce long‐term physiological modifications in the myccelia. While the fruiting response to nutritional factors is similar whatever the strain used the response to environmental factors depends mainly on the genotype of the strains.