GRAY LEAF SPOT OF RAPE IN MANITOBA

Abstract

A disease of rape characterized by black spots on stems and pods and gray to black spots on the leaves, caused considerable damage to crops in Manitoba in the wet years 1955 and 1956. Alternaria brassicae (Berk.) Sacc. was the only pathogen isolated from infected leaves, stems, pods and seed. Sporulation of the fungus was greatest on a 10% alfalfa seed decoction agar medium. The fungus was pathogenic to seedlings and adult plants. Penetration into leaves was indirect through stomata. Inoculations in greenhouse and field experiments resulted in a higher percentage of shrunken seed and seed infestation by the fungus, and in lower yield and percentage germination of seed compared with those from uninoculated plants.