Pleomorphism and conidiogenesis in Rhinocladiella atrovirens isolated from beetle galleries

Abstract

Three pleomorphic strains of Rhinocladiella atrovirens, a fungus identified as the normally blastic-sympodial anamorphic species, were examined. When freshly isolated from beetle galleries, an Exophiala synanamorph was dominant in cultures, but with repeated transfers it tended to become progressively less prominent, and a Rhinocladiella morph took over. The relative dominance was also influenced by culture media. Various intermediate or reduced forms of these two major synanamorphs appeared in culture. Apparently, interconversion of the Rhinocladiella-type and Exophiala-type proliferation in conidiogenous cells occurred. Transmission electron microscopy of the Exophiala morph revealed that its conidium development and secession differed from the typical enteroblastic-annellidic mode; annellationlike scars on generative pegs were very thin and fragile, and conidium secession was by the development of a separation line resembling a hilum in the nonlayered conidium-delimiting wall. The Phialophora morph reported previously was not encountered in the present study, but a morph resembling Chloridium occasionally occurred on Sabouraud dextrose agar.