Abstract
Since 1953, a powdery mildew has been observed on the leaves of cabbage plants (Brassica oleracea var. capitata) and mustard (B. juncea) in the greenhouse and gardens at Fujisaki-cho, Aomori, and on rape (B. napus) in the greenhouse at Sapporo, Hokkaido. By inoculation experiments the conidia from cabbage proved to infect these two species of plants (cabbage, rape), but not cauliflower, Japanese radish, tobacco and peas. The mildew found on Japanese radish, rape and Cardamine flexuosa in Japan is reported by Homma (1933) as Erysiphe cichoracearum DC. The present fungus, though its perithecial stage is not yet observed, seems to be identified as E. polygoni DC. Measurements of size and shape of conidia produced on cabbage and the solitary formation of them on conidiophores agree well with Davis' descriptions concerning E. polygoni on Chinese cabbage in U.S.A (1928). The shape of germ tubes of conidia also belongs to the polygoni type (Hirata, 1942, '55).
