Abstract
The infection mechanism of bud scales with conidia of Japanese pear scab fungus was investigated. There was no clear difference in the number of conidia remained on bud scales of cv. Chojuro irrespective of the time of sampling or positions of bud scales on shoots. In cvs. Kosui and Chojuro, scab development on scales of an axillary bud was higher at under or left side of shoots. The outbreak of scab was higher at inside of axillary buds in three cultivars including cv. Hosui. No disease development was observed in axillary buds of cv. Chojuro when the buds inoculated with conidia were protected from rainfall under a plastic house. On the contrary, severe disease developed on axillary buds of cv. Chojuro inoculated outdoors. Results from scanning electron microscopic observation showed that conidia germinated at a high ratio and penetrated only into exposed and alive parts of axillary bud scales of cvs. Hosui, Kosui and Chojuro. The number of exposed and alive parts of scales of infection sites with pear scab fungus was clearly different among axillary, leaf and flower buds of cvs. Hosui, Kosui and Chojuro, and it was the greatest on axillary buds. These results coincided with the actual state of disease development of three cultivars in the orchards. It was indicated that the infection of bud scales occurred with conidia produced on leaf lesions and flowed down in rain water in autumn. Conidia on exposed and alive parts of scales germinated and penetrated into alive tissues of scales under wet condition for many hours.
