An electron microscope study of initiation of infection by conidia ofHarposporium oxycoracum, an endozoic nematophagous Hyphomycete

摘要

Infective conidia of an endozoic nematophagous hyphomycete,Harposporium oxycoracumDrechsler, were examined by means of electron microscopy. Each of the conidia is very narrow and has a sharply pointed distal and slightly swollen basal end. The swollen basal end was shown, in ultrathin sections stained with ruthenium reden bloc, to be an electron-dense mass of fibrils (ca. 2ndash;3ensp;mu;m in diameter). The fibrils, thought to be derived from the conidial cell wall, were densely aggregated and were surrounded by a network of more sparsely aggregated fibrils spreading from the fibrous mass of the conidial base. The spreading fibrils seemed to correspond to the mucous droplet observed under the light microscope. It was also found in the present study that the conidia of the fungus were swallowed by nematodes into their lower gut. On germination in the lower gut, a narrow germ tube 5ndash;6ensp;mu;m wide developed from the convex side of the conidium and produced a simple pore septum at the site of penetration to delimit the empty conidium.