Fine structure of the walls of the conidia of various fungi and of the conidiophore of Fomes annosus

Abstract

Light and phase contrast microscopy were used to investigate the structure and mode of formation of the conidia of various fungi. Conidial walls were examined with the electron microscope before and after chemical treatment of the walls to remove surface electron-opaque material. Two sorts of microfibrillar arrangement occurred: (i) a circular arrangement about an electron-opaque papilla at one pole which gives way to a more disperse arrangement at the opposite pole (Fomes annosus); (ii) a disperse arrangement (Pithomyces chartarum, Hormodendron resinae, Aschochyta pisi, Colleto- trichum lindemuthianurn). Conidial wall texture did not appear to be related to conidial ontogeny. Type (ii) conidia had perforate end walls. The occurrence of such walls is discussed in relation to spore formation and germination. The possibility that conidium formation involves the sequence: arrestment of growth →altered chemical composition and/or microfibrillar wall texture → swelling → conidium formation - is discussed on the basis of the microfibril arrangements in the conidiophore of Fomes annosus.