Evaluation of Broccoli and Cauliflower Germplasm for Resistance to Race 2 of Peronospora parasitica

Abstract

Evaluations for resistance against race 2 of downy mildew, incited by Peronospora parasitica, were conducted on 240 U.S. Plant Introductions (PI) classified as Brassica oleracea var. botrytis (consists of both broccoli and cauliflower types). Plants were inoculated at the two-expanded leaf stage with 5.0 × 10 3 sporangia per ml. Inoculated plants were incubated in a dark 16C dew chamber for 24 hr and were then placed in a 22C growth chamber with a 12-hr photoperiod. On the 7th day after inoculation, plants were returned to the dew chamber for 30 hr and ratings for downy mildew reaction phenotypes were made at 9 days postinoculation on a 0-9 scale of increasing disease severity. A disease index (DI) was calculated for each entry. Based on the DI, no PI entries were highly resistant. PI entries 181860, 188562, 204765, 204768,204772,204773, 204775,204779,241612, 264656,291567,373906, and 462225 were moderately resistant. (DI of 3.1-5).