The inheritance of resistance of some Brassica oleracea L. cultivars and lines to downy mildew - Peronospora parasitica [Pers.] ex Fr.

Resistance to downy mildew was tested on resistant cultivars: Brassica oleracea PI246077 and PI231210, a broccoli-cauliflower line from Polish selection, susceptible cauliflower lines and their F₁ and F₂ progenies. Infection degree of the inoculated plants was determined at the cotyledon and 4-5 leaf stages. To estimate score plant infection at the 4-5 leaf stage the Williams scale designed for plants inoculated at the cotyledon stage was modified. Resistance to the Polish fungus isolate proved to be a dominant character. At the cotyledon stage depending on the source of resistance, it was determined by four (in the broccoli-cauliflower line) or three (in PI USA) dominant complementary genes, while at the stage of 4-5 leaves - by a single dominant gene (in PI231210), two (in PI246077) or three (in the broccoli-cauliflower line) additive dominant genes.