Fruit rot of Chinese white pear (
Pyrus ussuriensis Maximowicz var.
sinensis Kikuchi) and Japanese pear (
P. serotina Rehder var.
cuta Rehder) recently occurred in Okayama Prefecture. Two types of fruit rot, namely, blossom end rot and core rot were observed. The former is found on fruits of Chinese white pear ‘Lai Yang Ci Li’ of which calix end is separate from core, and the symptoms are same with that already reported on European pear. The latter is found on fruits of Japanese pear ‘Atago’ and ‘Kosui’ of which calix end is connected with core. Thus, difference of the symptom of pear fruit rot is dependent on difference of shape of calix end part of fruit.
Phomopsis sp. was isolated at very high frequency from diseased lesions of affected fruits. All isolates of
Phomopsis sp. obtained show pathogenicity on fruits and twigs of several cultivars of pear, and their degree of pathogenicity is as high as that of causal agent of Japanese pear canker,
P. fukushii. These isolates of
Phomopsis sp. are divided into two types according to their characteristics of mycelial mat grown on potato-sucrose-agar media under a light condition. One formed a plenty of aerial mycelia and induced the medium to turn red purple in color, while the other formed little amount of aerial mycelia and induced the medium to turn grey or blownish green in color. These two groups of
Phomopsis sp., however, have same size of α and β conidia, and their morphology are identical with that of
P. fukushii described by Tanaka and Endo, and
Phomopsis sp. which is causal agent of blossom end rot of European pear described by Ikata. From these results mentioned above, it is considered that the causal agent of two types of fruit rot of pear found in Okayama Prefecture is identified to
P. fukushii and fruit rot is one of the symptoms of pear canker.
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