Comparative Studies on Infection Behavior of Four Isolates of Peronospora parasitica Differing in Pathogenicity to Cotyledons of Cruciferous Plants.

Abstract

Pathogenicities of four isolates of the downy mildew fungus of cruciferous plants, Peronospora parasitica, obtained from Japanese radish, oil seed, broccoli and shepherd's purse, were compared by observing infected cotyledons. These isolates eventually sporulated on host plant cotyledons (compatible combination), but formed only small necrotic lesions on non-host cotyledons (incompatible combina-tion). Sheath encasement of haustoria and host cell death frequently occurred in the incompatible combinations. Growth of intercellular hyphae stopped within 48hr after inoculation. The shepherd's