Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 1995
Publication Date: N/A
Interpretive Summary: Sclerotinia is a disease-causing fungus that results in severe economic loss of numerous crops throughout the world. This pathogen is difficult to control because it overwinters as sclerotia, hard seed- like structures that can persist in the soil for many years. Sporidesmium is a beneficial fungus with potential as a biological control agent because it parasitizes and destroys sclerotia of Sclerotinia. Spores of Sporidesmium do not germinate unless they detect the presence of sclerotia. This research demonstrates that strains of Sporidesmium require varying amounts of time to germinate in response to sclerotia. Experiments with a fast-germinating strain of Sporidesmium required less than one week for a response, and as little as five minutes of exposure to sclerotia to stimulate germination. In the laboratory sclerotia stimulated germination from a distance of four centimeters but in the soil the distance was as little as one centimeter. A germinating spore was able to grow up to one centimeter in order to infect the sclerotia. This data is useful for determining adaptive mechanisms of survival of Sporidesmium that correlate with rates of application of Sporidesmium for control of Sclerotinia diseases.
Macroconidia of Sporidesmium sclerotivorum are stimulated to germinate by sclerotia of Sclerotinia minor. Comparison of nine isolates of Sp. sclerotivorum demonstrated substantial differences in germination rate, which were usually related to the maximum level of germination, or competence, attained by the strain. When strains had a greater proportion of competent macroconidia, they germinated more quickly. Parameters for stimulating macroconidia of a rapidly germinating strains of Sp. sclerotivorum were investigated in vitro and in soil. Sclerotia stimulated maximum germination of macroconidia in less than one week. Treatment with multiple sclerotia increased the degree of early response, but had no effect on the final proportion of germinated spores. As little as 5 min incubation with a single sclerotium could trigger germination of a substantial fraction of macroconidia 48 h after the stimulant was removed. Germination was stimulated by a single sclerotium at maximum distances of 4 cm in vitro and 1 cm in soil. At that distance, but not at 2 cm, 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 spp.