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Submitted to: Plant Disease Management Reports
Publication Type: Research Notes Publication Acceptance Date: 7/10/2014 Publication Date: 8/12/2014 Citation: Kousik, C.S., Ikerd, J.L. 2014. Evaluation of commercial melon varieties for tolerance to downy mildew, 2010. Plant Disease Management Reports. 8:V310. Interpretive Summary: N/A Technical Abstract: In recent years, changes in the downy mildew pathogen have been detected particularly on cucumbers where previously resistant varieties have become susceptible. This study was undertaken to determine the performance of commercial melon varieties with resistance to downy mildew. This experiment was conducted at the U.S. Vegetable Laboratory farm in Charleston, SC. The experimental design was a randomized complete block with three replications for each variety. Commercial melon varieties were seeded in 50-cell jiffy trays on 30 Jul. Seedlings were transplanted on 30 Aug onto raised beds with 40-in centers. Beds were spaced 21 ft apart and covered with white plastic mulch. Each variety plot was a single row of 5 plants spaced 18-inches apart with 9-ft spacing between plots. Vines of the melon plants were regularly turned every week so as to keep the plants from growing into the neighboring plots. Plants of downy mildew susceptible cultivars Iran H and Ananas were used as controls. A USDA line MR-1 was used as the resistant control. After bedding but before planting, the row middles were sprayed with Roundup Pro (1 pt/A) and Strategy (2 pt/A) for weed management. Weeds between beds were controlled during the season with spot application of Roundup. Plant foliage for each variety was rated for downy mildew on 15, 29 Sep, and 4, 12 Oct, using a 0-10 rating scale of increasing disease severity (0=no visible symptoms of disease observed, 1=trace <1-2% on foliage, and 10= plants dying or dead). The rating included both chlorosis and necrosis of the plant foliage. The downy mildew ratings collected for each melon variety over time were analyzed as repeated measures data using the nonparametric analysis as described by Shah and Madden (2004, Phytopathology 94:33-43). Pair wise comparison tests on the ranks for the individual rootstocks over time were done using descriptions provided by Arkitas and Brunner (1997, J. Stat. Plan. Infer. 61:249-277), using a macro written for SAS. Means for the final downy mildew ratings taken on 12 Oct were separated using LSD (a=0.05). A significant difference (P=0.0001) in the response of the melon varieties to downy mildew over time was observed. The appearance of downy mildew on these varieties was confirmed by the presence of sporangia of the pathogen on the abaxial surface of the leaves. Significant disease development was observed on the susceptible cultivar Iran H and by end of the season most of the plants were severely defoliated and dying or dead. MR-1 was the most resistant line in the trial followed by the commercial melon varieties. |
