Stimulative Effect of Potassium Phosphate on Infection of Cucumber Leaves by Conidia of Botrytis cinerea

Abstract

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.