The Influence of Dew Duration, Relative Humidity, and Leaf Senescence on Conidial Formation and Infection of Onion byAlternaria porri

Formation of conidia by Alternaria porri was examined under variable dew duration and controlled relative humidity (RH). Viable conidia produced on lesions increased from 26% after 9 hr of dew to 72, 91, 93, 96, and 96% after 12, 15, 18, 21, and 38 hr of dew, respectively. Conidia formed during dew duration of 12 hr caused flecks when used to inoculate healthy plants, and those formed during dew duration of 16 hr caused typical lesions. Conidia were formed at all RHs tested (75-100%); numbers were very low at 75-85% RH but increased with increasing RH (...)