Location of Oospores in buckwheat seed and probable roles of oospore and conidia of Peronospora ducometi in the disease cycle on buckwheat.

R.C. Zimmer¹, W.E. McKeen² and C.G. Campbell¹.

¹ Research Station, Agriculture Canada, Morden, Manitoba, Canada; ² Department of Plant Sciences, The University of Western Ontario, London, Ontario, Canada.

R.C. Zimmer , W.E. McKeen and C.G. Campbell. 1992. Location of Oospores in buckwheat seed and probable roles of oospore and conidia of Peronospora ducometi in the disease cycle on buckwheat. J. Phytopathology 135: 217-223.

Abstract: Oospores of Peronospora ducometi, the causal agent of downy mildew of buckwheat (Fagopyrum esculentum), were found in the calyx remnant attached to the seed, on the inside of the seed coat and in the spermoderm layer between the seedcoat and the endosperm. This constitutes the first report documenting the location of oospores in buckwheat seed. Conidial germination was greater at 14°C than at 25°C. Systemic infection also incurred as the result of infection of leaves. It is proposed that primary infection of buckwheat occurs by the germination of seed-borne oospores resulting in systematic invasion of the seedlings by the germtubes, and followed by conidial formation on the cotyledons. Secondary infection occurs initially from conidia produced on the cotyledons as a result of systemic infection from seed and subsequently as the result of repeated infections by conidia produced on leaf lesions as the disease progresses up the plant.

Key words: buckwheat, Fagopyrum esculentum, downy mildew, Pernospora ducometi, oospores