Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: February 4, 2007
Publication Date: March 8, 2007
Citation: Kousik, C.S., Adkins, S.T. 2007. Preliminary Evaluation of USDA Watermelon Core Collection for Tolerance to SqVYV, 2006. Plant Disease Management Reports. 1:V011. Technical Abstract: Plants belonging to the USDA core collection of watermelon plant introductions (PI) were grown in 3.5-in pots filled with metromix in a greenhouse in Ft. Pierce FL. Four week old plants were mechanically inoculated with SqVYV, the causal agent of watermelon vine decline. Inoculum was prepared by grinding infected squash leaves in 20 mM sodium phosphate buffer (pH 7.0) containing 0.1% (wt/vol) sodium sulfite and 1% (wt/vol) celite. There were four single plant replications for each 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). Only 218 out of 253 PI in the core collection were evaluated because of low or no germination for some of the PI. Variability in reaction to SqVYV among plants within PI was observed. Overall, PI 500354 (C. lanatus var. citroides) and PI 392291 (C. lanatus var. lanatus) appeared to be tolerant to the virus in this screen. However, plants within these PI also succumbed to SqVYV. Further selections and evaluations need to be conducted in the field and greenhouse to confirm the reactions of these PI.