Interactions between Sclerotinia sclerotiorum (Lib.) de Bary, Bradysia coprophila Lintner (dark-winged fungus gnat) and mycoparasitic fungi

Sclerotinia sclerotiorum is a pathogen of crops grown in the muck soil regions of Quebec. Soil baiting tests indicated that the sclerotia of S. sclerotiorum are attacked and destroyed by the larvae of Bradysia coprophila and mycoparasites. Sclerotia with rinds partially damaged by the larvae were found to be more susceptible to mycoparasitism by Trichoderma viride. Increasing the organic matter content and porosity of soils resulted in increased damage to sclerotia when larvae were present. Studies conducted to determine if larvae could be reared on diets of various fungi and plant tissue showed that mycelia and sclerotia of S. sclerotiorum were the most successful food sources, followed by mycelia and sclerotia of Botrytis porri and Rhizoctonia solani. Adults produced on mycelia and sclerotia of Sclerotinia minor, Fusarium solani f. sp. pisi, and Botrytis cinerea seldom were fertile. Larvae generally failed to survive when reared on cultures of Trichoderma viride. Larval development occurred on all plants inoculated with the above pathogens but failed to occur on noninoculated healthy plants. Salivary gland secretions of the larvae were found to inhibit the germination of sclerotia. Analyses of the secretion determined that it contains 4.3% protein and had chitinase activity. Mechanically damaged and undamaged sclerotia exhibited an increase in eruptive mycelial germination when treated with 1.5 $ mu$g ml$ sp{-1}$ chitinase but germination decreased at 50, 100 and 150 $ mu$g ml$ sp{-1}$ chitinase concentrations. Noneruptive mycelial germination and carpogenic germination occurred when sclerotia were treated with acetate buffer and distilled water.