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Claude E. Thomas and E.L. Jourdain

Evaluations for resistance against race 2 of downy mildew, incited by Peronosporu parasitica Pers. ex Fr., were conducted on 325 U.S. Plant Introductions (PI) classified as Brassicu oleracea var. capitata L. (cabbage). A disease index (DI) was calculated for each entry. In 77 of the tested PIs, from 2% to 100% of the plants had reaction phenotypes ≥ 3. The DIs for 24 PIs were significantly lower than the DI for the most resistant cabbage control, `Headstart' (DI = 5.9). Eight of these PIs were highly resistant, because all plants had a reaction phenotype ≥ 3. However, most of these eight are apparently misclassified as B. oleracea var. capitata.

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Claude E. Thomas and E.L. Jourdain

Field evaluations for resistance against downy mildew, incited by Pseudoperonospora cubensis [(Berk. and Cart.) Rostow], were conducted on 942 U.S. Plant Introductions (PI) of Cucumis melo L. (melon). A disease index (DI) was calculated for each entry. Based on DI, PI 124112 was highly resistant (DI = 3.7), and PIs 124111, 122847, 124210, 145594, and 165525 were resistant (DI = 3.0, 2.8, 2.6, 2.7, and 2.5, respectively). PIs 124111 and 124112 had one or more plants that exhibited a highly resistant reaction type (RT 4). Resistant (RT 3) plants were identified in 31 accessions, and 49 accessions bad moderately resistant (RT 2) plants.

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Claude E. Thomas and E.L. Jourdain

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 × 103 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).