Some biological observations on pale fruit,a viroid-incited disease of cucumber

A viroid-incited disease characterized by pale fruits, crumpled flowers, and rugosity and chlorosis on the leaves of cucumber, occurs occasionally in cucumber crops grown in glasshouses in the Netherlands. The disease is found primarily in crops planted in spring, rarely in those planted in summer but not in those planted in late summer. The pathogen can be transmitted with sap, during pruning, by grafting and with dodder to cucumber and a number of other cucurbitaceous species, but not withM. persicae. There is no evidence for seed or nematode transmission. The incubation period is 21 days at high temperatures (30°C) but shorter after inoculation by razorbalade slashing. The number of glasshouses with the disease has increased since 1965, but the number of diseased plants is usually low. The initial distribution of diseased plants in the glasshouses suggests that the pathogen is introduced by an insect.