Studies on the ecology and control of Corynespora target leaf spot of cucumber caused by Corynespora cassiicola
1993
Hasama, W. (Oita-ken. Agricultural Research Center, Usa (Japan))
Corynespora target leaf spot was first described in Europe in 1906 on cucumber; it also is present in Japan, where it was reported in Kanto district in 1913. During the summer of 1979, the disease was first noticed in Oita prefecture. These studies were conducted to clarify the ecology and epidemiology of the causal fungus Corynespora cassiicola for the establishment of control measures. An abstract of the results is as follows. 1. Symptoms, damage and geographical distribution. (1) Lesions at first appear as small light tan to white spots with a narrow olive brown margin. These necrotic spots are surrounded by a diffuse chlorotic zone. In the advanced stages the entire leaf becomes light yellow. Smaller elongate spot also occur on the petioles and stem. Very young fruits are infected through the blossom end, turn dark, and wither. Yellow ripened fruit also can become infected when wounded. (2) Rapid defoliation can result in reduced yield and early termination of harvesting. (3) Since rediscovery of the disease in Oita prefecture, subsequent investigation revealed that it had spread to almost major all cucumbe rproducing areas in Japan, including Okayama, Hiroshima, Yamaguchi, Ehime, Miyazaki, Kumamoto and Okinawa prefectures. 2. Identification of the pathogenic fungus Conidiophores averaged 220-570*5-10 micro m in dimension, were pale to light brown and erect, and formed singly or in groups. Each conidiophore had 1 to 5 septa and a pore at the end. No stroma was observed. The basal cells of conidiophores were swollen. Conidia of this fungus were hyaline to light brown, curved, and broad at the base, formed on conidiophores singly or in a chain, varied in morphology: i,e. obclavate to cylindrical,
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