Abstract
In the present paper, the writers describe the results of the experiments on the varietal difference of the resistance of cucumber to the anthracnose disease. Cucurbita moschata and C. maxima were also used in comparison. 1. The inoculation experiments on mature leaves proved that all the varieties of cucumber used were invaded by the causal fungus. The squashes, however, were not affected by the present disease. Judging from the number of lesions in unit area of the inoculated lea-(_??__??__??__??_), Sekino No. 2(_??__??2??_), Sakata-Pickle, Taiwan-Kema(_??__??__??__??_)and wild cucumber were comparatively resistant, and Su-Yo(_??__??_), Kachu-Zairai(_??__??__??__??_), Nisshi-Aonaga(_??__??__??__??_), and San-To(_??__??_)were susceptible, showing 10-15 times more spots than the former. 2. The varietal difference in the susceptibility was recognized also by inoculating spores on cotyledons. In this case the significant difference was not deteced more clearly than in mature leaves. The cotyledons of Shirokikuza, a variety of C. moschata, was also affected. Mature leaves in this variety. however, were not attacked completely. 3. The degree of developing area of spots in leaves was hardly recognized between the cucumber varieties used. 4. In the expressed sap of cotyledons of every variety the conidia germination was accelerated, and the hyphae entered into the epidermal cells developed well in every variety. In these host tissues any different rea-ction accompaning the necrosis and discoloration of cells was not observed, only showed at first a water-soaked appearance of the spot. From these results, all the cells of the cucumber varieties used may be in a strongly susceptible condition to the anthracnose. 5. The conidia of the causal fungus germinated well in water drops gathered from the surface of cotyledons, showing no difference between the varieties. On the cotyledons of squash the germination and the appressoria formation of conidia were also recognized. 6. The degree of penetrating hypha formation from the appressoria, formed on cotyle-dons of cucumcer, differed significantly among the varieties. Between the degree of penetrating hypha formation and the number of spots per unit area there is a high correlation. This presumably accounts for the difference in the susceptibility of cucumber varieties, and the susceptibility may be attributed to the resistance to the invasion of epidermis.
