Abstract
Powdery mildew of wasabi (Eutrema wasabi Maxim.) has been found to occur in a green house in Toda city, Saitama Prefecture since 1990. The fungus was identified as an imperfect stage of Erysiphe cruciferarum Opiz ex Junell (Oidium sp.) on the basis of following obsevations, amphigenous, and thin mycelium covered the whole surface of diseased leaves. Formation of conidia was normally low, but occassionally abundant. Conidia were cylindric, 32.0-51.6×13.6-23.2μm, and contained no fibrosin body. Conidia were borne singly on straight erect conidiophores with cylindric foot-cells. Lobed appressoria were formed on short germ tubes at the end of conidia. No cleistothecium was observed. The mildew was pathogenic also on other species of Cruciferae.
