Sorus Ontogeny and Sporogenesis in Some Smut Fungi

Abstract

Investigations of sorus ontogeny and sporogenesis in the type species of Ustilago and Sorosporium and in other species usually included in those genera have established criteria far defining Ustilago and Sorosporium. Ustilago is a genus to accommodate smuts that destroy host tissues and whose mycelium is converted entirely to spores after necrosis of host tissues. No columellae or peridia of fungal origin are formed. In Sorosporium species on Saponaria and several grasses, sporogenous hyphal coils are the progenitors of spore balls, this characteristic contrasting with the lack of such organization in Ustilago. Sorosporium saponariae has no well-defined sorus, the spore balls developing from hyphae that grow out of the plant tissues into the spaces between floral organs in buds. The graminicolous species of Sorosporium have sori with well-defined columellae and peridia of fungal origin developed from a soral meristem. It is suggested that smuts with sori developing in this way and having sporogenesis of the Sorosporium type should be grouped in a separate genus. The ontogeny of spore walls of several species of Ustilago and Sorosporium has been elucidated by electron micro- cope studies.