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

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... verer in the bloomless rootstock than in bloomy rootstock or scion root. The bloomless rootstock causes the reduc tion 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.