In this study, changes of the development of the target leaf spot on cucumber plants (Cucumis sativus) were investigated with three different culture methods; i.e, (1) scion cv. ‘Shinhokusei-ichigo’ grafted on cv. ‘Shintosa-ichigo’ (Cucurbita maxima/C. moschata) as a bloomy rootstock, (2) grafted on cv. ‘Super-Unryu’ (C. moschata/C. pepo//C. moschata) as a representative bloomless rootstock, and (3) cv. ‘Shinhokusei-ichigo’ as a non-grafting culture. The disease development in the field is severer in the bloomless rootstock than in bloomy rootstock or scion root. The bloomless rootstock causes the reduction of resistance to Corynespora target leaf spot caused by Corynespora melonis. Inoculation tests indicated that the bloomless rootstock was inferior to bloomy rootstock and scion root in preventing penetration and spread of the lesion. The leaf-analysis showed that no difference was observed in essential and major elements among three culture methods, but silica was conspicuously less in the cucumber grafted on bloomless rootstock. Development of the disease increased in non-silicate fertilizer culture. These results strongly suggest that the low-absorption of silica in the cucumber grafted on the bloomless rootstock may cause the decrease of disease resistance to Corynespora target leaf spot.

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When the lower leaves of Nicotiana glutinosa were inoculated with an ordinary strain of tobacco mosaic virus (TMV), β-1, 3-glucan hydrolase activity increased in the upper leaves of the same plant. The increase in enzyme activity was first detected 4 days after inoculation of the lower leaves, reaching a maximum of 6 times higher than the mock-inoculated control plants 10 days after the inoculation. The enzyme activities of the intercellular fluid (ICF) and of the rest of the tissue homogenates of both the inoculated lower leaves and the uninfected upper leaves of the plant increased with the progress of infection. The enzyme activity of ICF in the inoculated lower leaves was 6-10% of the total activity and in the upper leaves 7-11%. Acquired systemic resistance in the upper leaves to TMV appeared 4 days after inoculation of the lower leaves with TMV. Ten days after inoculation the size of local lesions in the upper, virus-challenged leaves decreased to 50% of the control. However, when the inoculated lower leaves were cut off the 2nd day after inoculation, no increase of the enzyme activity in the upper leaves was detected and no acquired resistance to TMV was observed. The relationship between β-1, 3-glucan hydrolase activity and the acquired resistance to TMV-infection is discussed.

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[in Japanese]

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When apparently healthy leaves of mulberry were irradiated with ultraviolet light (UV) for 3-5 min and kept in a moisture box, brownish gray-color and orbicular-shaped spots often appeared on the leaves after 3-4 days. Then a lot of acervuli, conidiospores and setae were formed on the spots. The shape of the conidiospores was cymbi-form or falcate-form, and the fungus was identified as being Colletotrichum morifolium Hara, the pathogen of anthracnose disease of mulberry. Thus, it was shown that the UV-induced spots appeared at the sites where the pathogen had infected latently. The number of latent infection sites can be estimated by UV-irradition.

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