Development of Peronospora ducometi in buckwheat

Zimmer, R.C.¹, W.E. McKeen² and C.G. Campbell¹

¹ Research Station, Agriculture Canada, Morden, Manitoba, R0G 1J9, and ² (W.E.M) Department of Plant Sciences, The University of Western Ontario, London, Ontario N6A 5B7.

Zimmer, R.C., W.E. McKeen and C.G. Campbell. 1990. Development of Peronospora ducometi in buckwheat. Can. J. Plant Pathol. 12: 247-254.

Abstract: Buckwheat plants developing from seed infested with oospores of Peronospora ducometi were either symtomless or stunted. Two types of hyphae, designated A and B, occurred in the plants. Type A hyphae, found in stems, leaves, flowers, and seeds, but not in roots, were narrow (8.6µm diam), branched, and produced haustauria. This hyphal type was always associated with stunting, leaf mottling, and rugosity. Type B hyphae were wide (27µm diam.), unbranched, and did not form haustoria. They were common in the petioles and flowers of symptomless plants but were occasionally in stunted plants. Type B hyphae often followed the xylem vessels but were rarely found inside the vessel. This is the first known report of hyphal dimorphism in a fungus causing downey mildew. Sexual and asexual reproductive structures of P. ducometi originated from Type A hypae. Conidiogenesis generally occurred on the lower epidermis of cotyledons and true leaves. Hyphal knots, an early stage of conidiogenesis, developed in stomatal chambers. Typically, only one conidiophore developed per stomata; occasionally two were formed. Hyphal development in various plant parts is described and illustrated.

Key words: buckwheat, Pernospora ducometi, downy mildew