Studies on black leaf blight of Welsh onion, Allium fistulosum I. Conditions of disease occurrence and certain biological characteristics of the causal fungus.

摘要

Aetiological and biological studies were carried out on the causal fungus of black leaf blight of Welsh onion which is grown continuously using home-grown seeds. The disease was observed in the fields of Shimonita-cho, Gunma prefecture, Japan, as well as in the northern part of the Kanto District including Shimonita-cho, the Tohoku District and Hokkaido. However, it is scarcely observed in the southern part of Kanto District and western Japan. Symptoms appearing on Welsh onion inoculated with a mycelial mat of Mycosphaerella or with naturally matured ascospores were similar to those developed in natural infections. On all diseased lesions originating from both natural infection and artificial inoculation, only the perfect state was observed. The optimum temperature for growth of the fungus on PDA was about 20deg C, and 20-25deg C for the maturation of asci and germination of ascospores. The pH range for fungal growth was from 4 to 9, with the optimum from 6 to 9.