Root-inhabiting Olpidium species: The O. radicale complex

Abstract

A light microscopic study of different stages in the life-cycle of the obligate plant parasitic fungus, Olpidium radicale Schwartz & Cook (Phycomycetes, Chytridiales) is presented. The most significant taxonomic characters are considered to be a resting sporangium with an apparent smooth outer wall and a honeycomb-like pattern on the endospore, and usually large elongated zoospores with a remarkably slow and steady way of swimming; the latter characteristic should be compared to the rapid and jerky swimming movement characteristic for zoospores of most Chytridiales. By the use of these characters, O. radicale is easily distinguished from O. brassicae , which has stellate resting sporangia. However, comparing O. radicale to other root-inhabiting olpidiaceous species described with smooth resting sporangia ( Pleotrachelus bornovanus Saht. and O. cucurbitacearum Barr), no significant differences may be found. On the basis of priority these species names are recognized as synonyms of O. radicale , for which a new description is given.