Some observations on Erysiphe Polygoni DC.

Abstract

1. In field trials in 1913 no variety, out of seventy-seven varieties of Swedes, Turnips and Rape, was found to be immune to Erysiphe Polygoni DC. Swedes were attacked more severely than Turnips. 2. In inoculation experiments with cultivated varieties of Brassica campestris and B. oleracea , the form of Erysiphe Polygoni infecting these varieties was found to be a “biologic form” with this additional distinction that inoculations from B. campestris to B. oleracea invariably gave “subinfections” as the result. 3. “Biologic forms” on Polygonum aviculare, Trifolium Pratense and Pisum sativum were indicated. 4. “Subinfections” on varieties of B. oleracea were observed in the field and found to exist over the winter and in some cases grow into full infections. 5. Inoculations were undertaken in the laboratory and were successful both on uninjured leaves and on the internal tissues of stems; these latter were carried as far as the fourth generation. 6. Inoculationswithconidiafrom “subinfections” werecarried out and the conidia shown to be viable. 7. It is suggested that the most probable method of overwintering of the “biologic form” of Erysiphe Polygoni on the cultivated Brassicae is by means of “subinfections” on varieties of B. oleracea aided by persistent mycelium on varieties of B. campestris .