Perithecial ontogeny in the fungal genus Epichloe: An examination of the clavicipitalean centrum

Abstract

The structure and development of perithecia in five collections of Epichloe from Europe and North America were studied. Perithecia in early stages of development are oblong to ovate in overall shape. Dichotomously branched paraphyses form on the bottom and sides of the inner walls of the perithecial primordium. As the ovate primordium expands, a mound of ascogenous mycelium develops in its base. As asci develop from the ascogenous mound, paraphyses proximal to asci evanesce and no paraphyses are observable within the cluster of asci. In E. amarillans and E. baconii paraphyses are converted into pseudoparenchyma-like tissues, while in E. typhina paraphyses remain filamentous until they evanesce. Ascospore development is seen to differ among all three species of Epichloe. The development and structure of the Epichloe centrum are compared to those of the Nectria and Xylaria types. It is apparent that a distinct type of centrum is present in Epichloe, and perhaps all of the Clavicipitaceae. It is proposed that the Epichloe type centrum may represent a key feature for distinguishing the Clavicipitaceae from the Hypocreaceae or other groups of pyrenomycetes.