TEMPORAL AND SPATIAL FACTORS AFFECTING GERMINATION OF MACROCONIDIA OFSPORIDESMIUM-SCLEROTIVORIUM

Macroconidia of Sporidesmium sclerotivorum are stimulated to germinate by sclerotia of Sclerotinia minor Substantial differences in germinat ion rate were demonstrated among ten isolates of Sporidesmium scleroti vorum. The rate of germination was usually related to the maximum perc ent germination, i.e. competence, of the strain; strains with a greate r proportion of competent macroconidia germinated more rapidly. Parame ters for stimulating macroconidia of a rapidly germinating strain of S poridesmium sclerotivorum were investigated in vitro and in soil. A si ngle sclerotium stimulated maximum germination of macroconidia in less than one week. Treatment with additional sclerotia increased the degr ee of early response, but had no effect on the final proportion of ger minated spores. As little as 5 minutes of incubation with a Single scl erotium could trigger germination of a substantial fraction of macroco nidia 48 hours after the stimulant was removed. Germination was stimul ated by a single sclerotium at maximum distances of 4 centimeters in v itro and 1 centimeter in soil. At that distance in soil, but not at 2 centimeters, the expanding germ tube of the mycoparasite was able to r each a sclerotium and infect it. These studies suggest that the mechan ism of germination plays a role in the survival of this fastidious myc oparasite, which is useful for biological control of Sclerotinia speci es.