Temporal and spatial factors affecting germination of macroconidia of Sporidesmium sclerotivorum

Abstract

Macroconidia of Sporidesmium sclerotivorum are stimulated to germinate by sclerotia of Sclerotinia minor. Substantial differences in germination rate were demonstrated among ten isolates of Sporidesmium sclerotivorum. The rate of germination was usually related to the maximum percent germination, i.e. competence, of the strain; strains with a greater proportion of competent macroconidia germinated more rapidly. Parameters for stimulating macroconidia of a rapidly germinating strain of Sporidesmium sclerotivorum were investigated in vitro and in soil. A single Sclerotium stimulated maximum germination of macroconidia in less than one week. Treatment with additional sclerotia increased the degree of early response, but had no effect on the final proportion of germinated spores. As little as 5 minutes of incubation with a single Sclerotium could trigger germination of a substantial fraction of macroconidia 48 hours after the stimulant was removed. Germination was stimulated by a single Sclerotium at maximum distances of 4 centimeters in vitro 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 reach a Sclerotium and infect it. These studies suggest that the mechanism of germination plays a role in the survival of this fastidious mycoparasite, which is useful for biological control of Sclerotinia species.

Key Words:

• biocontrol
• host-parasite
• mycoparasite
• Sclerotinia
• Sporidesmium