EFFECT OF MICROCLIMATE AND NUTRIENTS ON DEVELOPMENT OF CUCUMBER GRAY MOLD (BOTRYTIS-CINEREA)

Infection of young parthenocarpic cucumber fruits by Botrytis cinerea begins in the petals. Removing petals or washing nutrients from the flower significantly reduced infection. Germination of conidia occurred at relative humidity (r.h.) above 92%, but when water deposition on artificial surfaces was prevented, germination did not occur even at 98% r.h. Germination of conidia on petals is promoted by deposition of an aqueous film not visible on the petal surface by the bare eye (but demonstrable by CoCl2). Provided there is a film of water on the surface of the host, germination and the infection process occur at a wide range of temperatures up to 25-degrees-C. Pre-exposure of cucumber plants at temperatures as high as 30-degrees-C or as low as 8-degrees-C, prior to their infection and incubation under conditions conducive to gray mold, resulted in greater severity of the disease on young fruits or leaves as compared with plants previously incubated at 10-25-degrees-C. The relevance of these results to cultural control of gray mold is discussed.