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POSTERS: Host resistance screening

Screening commercial cucumber cultivars for resistance to anthracnose using image analysis
Robert Schlub - University of Guam. Meghan Borja- University of Guam, Brian Marx- Louisiana State University, Mingyan Cong- Louisiana State University, Victoria Santos- University of Guam

Anthracnose was first reported on Guam in 1979. Colletotrichum orbiculare was identified as the causal agent in 2017. Four replications of 22 commercial cultivars were grown in pots, at the fourth leaf stage, they were spray inoculated to point of runoff with a 1x104 conidia/ml suspension, then afterwards placed under a plastic tent at 100% RH for 24 hrs. On the fifth day, the third leaf was removed and pressed between sheets of paper towel. This flattened the leaf and arrested further disease development. Leaves were scanned and images were evaluated using Adobe Photoshop and Imagej software. Statistical analyses consisted of one independent variable (cultivars) and four dependent variables: VR (Thompson and Jenkins 1985 Visual Rating scale), TL (Total Leaf area), PerDis (Percent Diseased area within a 5 cm diameter ascribed circle), and LesionsC (Lesions per cm2, in the ascribed circle). Tukey’s studentized range (HSD) Test was <0.001 for all dependent variables. Contrast testing of Resistance Vs Susceptible revealed the following significant pairs: 26 among 231 for VR, 7 among 231 for PerDis, and 19 among 231 for Lesions. Following visual inspection of cultivar groupings of t-test (LSD) results across VR, PerDis, and LesionsC, it was determined that Summer Top, Olympia (trd), Olympia, Blessing, Poinsett76, Soarer, and TI-09E were the most resistance cultivars, while those identified as the most susceptible included Early Triumph, Tasty King, and Turbo.