Effect of inoculum composition on infection of French bean leaves by conidia of Botrytis cinerea

Inoculation of leaves of French bean (Phaseolus vulgaris) with sprays or small drops of a suspension of conidia ofBotrytis cinerea gave rise to spreading lesions, lesions remaining restricted in size or to no visible necrosis. The type of reaction depended on the composition of the inoculum. In studies with drop inoculations with buffered inocula some of the factors involved were analyzed. The formation of spreading lesions depended on pH, type and molarity of the buffer, presence of glucose, and concentration of conidia in the inoculum. If the phosphate buffer used in most of the inocula was replaced by monobasic phosphate, similar results were obtained. The reactions were not influenced by the proportion of K⁺ or Na⁺ ions in the phosphate buffer. Inoculations with conidia suspended in a solution of 0.067 M phosphate buffer (pH 5.0) or monobasic phosphate and 0.11 M glucose always evoked a susceptible reaction, i. e. the formation of spreading lesions.