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, Pleurotus ostreatus, has been reported from western Japan. Nematodes inhabit and lay many eggs inside the gill knots. It is surprising that the nematodes 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 female infective to the fungus gnat, an adult male, and a mature entomophagous adult female. The occurrence of gill-knot disease was investigated in the field. Laboratory experiments determined that the fungus gnat could not itself form gill knots, because formation of knots was not observed on the gills of fruiting bodies incubated with nematode-free gnats. Observation by means of microscopy and the spore patterns of diseased fruiting bodies confirmed that...