Sources and Nature of Resistance to Downy Mildew and Turnip Mosaic in Chinese Cabbage

Forty-six Chinese cabbage [ Brassica campestris spp. pekinensis (Lour) Olsson] lines consisting of open-pollinated cultivars, inbreds, and F 1 hybrids from China were screened for seedling resistance to downy mildew ( Peronospora parasitica ) (Pers.) Ex. Fr. Thirty-seven lines of this collection were screened for turnip mosaic resistance. Five lines showed dual resistance to downy mildew and turnip mosaic. Resistance to downy mildew at the cotyledon stage, expressed as a reduction in the sporulation capacity of P. parasitica , was under dominant monogenic control. Turnip mosaic resistance was expressed as a hypersensitive reaction. Genetic analysis of a cross between turnip mosaic resistant and susceptible parents suggested that resistance was conditioned by 2 dominant genes.