1987 Volume 53 Issue 2 Pages 175-181
Spreading lesions were formed on cucumber leaves (cv. Sagami-Hanjiro) when inoculated with conidia of Botrytis cinerea in the presence of KH2PO4 in the droplet of conidial suspension containing glucose. In the KH2PO4 solution, development of the lesion was earlier than the development in inosine solution containing glucose. Light microscopy of infection processes of the fungal conidia indicated that it penetrated the epidermis both from the primary and the secondary appressoria without significant defense reactions of the host cells in the presence of KH2PO4 in the inoculum. On cucumber leaves pre-treated with KH2PO4 solution, formation of spreading lesions was not found even in glucose solution. The light microscopy revealed that penetration from the primary appressoria was arrested by defense reactions of the epidermal cells, e.g. deposition of well-developed papillae and hypersensitive cell death. Also, formation of the secondary appressoria was not observed. From these results, it was suggested that KH2PO4 acts to enhance the penetration activity of B. cinerea, but not to suppress of resistance reaction in cucumber leaves.