THE TRIPARTITE RELATIONSHIP IN GILL-KNOT DISEASE OF THE OYSTER MUSHROOM, PLEUROTUS-OSTREATUS (JACQ, FR) KUMMER

A disease that causes knots on the gills of the oyster mushroom, Pleur otus ostreatus, has been reported from western Japan. Nematodes Inhabi t and lay many eggs inside the gill knots. It is surprising that the n ematodes causing this disease live in the fruiting body of this fungus , which is known to be nematophagous. In the present study, the fungus gnat Rhymosia domestica (Mycetophilidae, Diptera) was confirmed to be the Vector of the nematodes inside the gill knots. This nematode has different adult stages, i.e., a mycetophagous adult female, an adult f emale infective to the fungus gnat, an adult male, and a mature entomo phagous adult female. The occurrence of gill-knot disease was investig ated in the field. Laboratory experiments determined that the fungus g nat could not itself form gill knots, because formation of knots was n ot observed on the gills of fruiting bodies incubated with nematode-fr ee gnats. Observation by means of microscopy and the spore patterns of diseased fruiting bodies confirmed that the knots consist of dediffer entiated hyphal tissues, which do not form spores.