Submitted to: Plant Disease Management Reports
Publication Type: Research notes
Publication Acceptance Date: 2/4/2007
Publication Date: 3/9/2007
Citation: Kousik, C.S., Adkins, S.T., Roberts, P.D. 2007. Evaluation of Select USDA Watermelon Plant Introductions (PI) for Tolerance to Watermelon Vine Decline, 2006. Plant Disease Management Reports. 1:V012. Interpretive Summary:
Technical Abstract: Watermelon vine decline (WVD) caused by squash vein yellowing virus (SqVYV) is a new and emerging disease in southwest and west central Florida. Watermelon plant introductions (PI) selected on the basis of a greenhouse screening against SqVYV were evaluated for tolerance to watermelon vine decline in Immokalee, FL. The soil was Immokalee fine sand. Four week old plants grown in 50-cell Jiffy trays were transplanted onto raised beds covered with white plastic mulch on 12 Sep. The experimental design was randomized complete block with three replications. Plant to plant spacing was 24-inches, and each plot had 5 plants. Guidelines established by the University of Florida/IFAS were followed for land preparation, fertility, irrigation, and weed management. No chemicals were applied for whitefly management. A four week old squash plant inoculated with SqVYV was planted at the end of each plot after transplanting PI. Plants were monitored for symptom appearance on a regular basis. Plants were rated on a 1-9 scale with percent of plant effected and symptoms as indicated: 1=0% (no symptoms), 2=1-3% (very minor chlorosis/vein yellowing, no necrosis), 3= 4-10% (minor chlorosis/vein yellowing plus mild epinasty of youngest upper leaves), 4=11-25% (chlorosis/vein yellowing plus severe epinasty of youngest upper leaves, no necrosis), 5=26-35% (chlorosis of most basal leaves, necrotic streaks in petioles and/or tendrils), 6=36-50% (necrosis of most basal leaves, petiole collapse), 7=51-65% (necrosis of most leaves, total petiole collapse, main stem mostly green/yellow), 8=66-80% (necrosis of most leaves, stem necrosis and slight collapse, stem tip dead), 9=81-100% (plant dying or dead). Disease ratings were recorded on 31 Oct, 20 Nov and 4 Dec. The susceptible checks of Mickey Lee and Crimson Sweet were severely diseased at the first rating on 31 Oct. with most rated as 9. Overall, PI 500354 (C. lanatus var. citroides) and PI 386024 (Citrullus colocynthis) appeared to be tolerant to WVD in this screen and significantly slowed down disease development compared with Mickey Lee and Crimson Sweet. However, plants within these PI also succumbed to WVD. Most of the PI tested were dead by the time of the third rating on 4 Dec. However, fruit of PI 500354 did not exhibit any internal symptoms of watermelon vine decline. Further selections and evaluations need to be conducted in the field and greenhouse to confirm the reactions of these PI.