Infection of strawberry flowers by Botrytis cinerea and its relevance to grey mould development

SUMMARY Newly‐opened strawberry flowers of several cultivars were inoculated in the glasshouse, growth chamber and field with conidia of Botrytis cinerea from cultures of seven isolates. Infection in pistils, stamens, petals, sepals and receptacles was detected by u.v. microscopy after softening fixed tissues in 1 N sodium hydroxide and staining in 0–1% aniline blue. For all isolates, cultivars and environments, conidia germinated on the stigmas and their hyphae grew into the transmitting tissue of the styles, but so slowly that they sometimes took 4–6 wk to reach the style bases. Cv. Troubadour was the only cultivar in which hyphae grew from the style into the carpel, but growth there was limited and did not progress into the receptacle. The fungus produced conidiophores and conidia on the stigmas of 15 of the 23 cultivars tested in the field but did not do so in the growth chamber or glasshouse tests. It readily colonised the anthers and connective between the anther lobes and sporulated on anthers in the field; in some cultivars it grew to the base of a few stamen filaments and into the receptacle. In the glasshouse, conidia remained ungerminated on the petals and sepals for at least 6 days, but in a moist chamber they germinated and hyphae rapidly penetrated the epidermis and colonised internal tissues of these flower parts. Results indicated that stamens may be more important than styles as a source of latent infection.