Effects of light, temperature, and moisture on release of ascospores byVenturia inaequalis(Cke.) Wint.

Abstract

Ascospores of Venturia inaequalis (Cke.) Wint. are not released from perithecia unless the perithecia are wetted. Greater numbers of ascospores are released when wetting occurs in light than when it occurs in darkness. Greater numbers are released when perithecia have been warm, or in a humid atmosphere, before they are wetted, than when they have been cold, or in a dry atmosphere before they are wetted. High numbers of ascospores in orchard air associated with daytime rains, compared with the low numbers associated with night rains or dew, are the result of the influence of light and of higher temperatures on ascospore release.