Population dynamics of the mycoparasite, sporidesmium sclerotivorum, and its host, sclerotinia minor, in soil

The infection and survival of sclerotia of Sclerotinia minor and the production ofmacroconidia of the mycoparasite, Sporidesmium sclerotivorum, were studied in vitro when each fungus was added to soil at various initial inoculum densities. The rate at which S. sclerotivorum invaded host sclerotia and caused their decay varied with the amount of the mycoparasite added to soil. The results suggest that approximately 5 macroconidia of the mycoparasite g^?1 of soil are needed to successfully infect sclerotia and bring about their decay, when soils are sampled and mixed every 2 weeks. The rate at which S. sclerotivorum infects sclerotia of S. minor and causes their decay is also dependent on the initial inoculum density of the host. Each infected sclerotium supports the production of about 15,000 new macroconidia in soil regardless of the initial inoculum density of the host. It is concluded that successful biological control by S. sclerotivorum is dependent on the soil population of both the host and the mycoparasite.