Zoospore ultrastructure of Olpidium cucurbitacearum (Chytridiales)

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Abstract
Zoospore ultrastructure of Olpidium cucurbitacearum Barr & Dias is described. Isolates from Ontario and Japan are alike. The elliptical zoospore has an anterior nucleus partially surrounded by lobed and branched mitochondria. In the central part an interconnecting network consisting ofsmooth and rough endoplasmic reticulum, a Golgi complex, microbodies, and multivesicular bodies predominates. Vacuoles are abundant in the posterior. Ribosomes occur throughout the cytoplasm. The flagellar apparatus consists of the following: a short fibrillar rhizoplast connecting both kinetosome and nonfunctional centriole to an electron-opaque bar on the nuclear envelope; an elongated transition zone; and a 9 + 2 flagellum axoneme running much of the length of the zoospore through to the posterior end. Props do not connect the kinetosome to the plasmalemma; however, prop parts connect to the kinetosome, and prop parts connect to the plasmalemma at the posterior end of the zoospore. The taxonomic relationship to other chytrids is discussed; the zoospore is similar to that of O. brassicae (Woronin) Dang, and Rhizophlyctis rosea (deBary &Woronin) Fischer, and somewhat similar to that of Rozella allomycis Foust.