Coffey, J.L., 66 George Street, Charleston, SC, United States, U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC, United States
Simmons, A.M., U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC, United States
Merle Shepard, B., Clemson University, Coastal Research and Education Center, 2700 Savannah Highway, Charleston, SC, United States
Tadmor, Y., Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Levi, A., U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC, United States

Selection for and incorporation of host plant resistance into cultivars is a fundamental strategy to control insects and diseases and may help reduce reliance on synthetic pesticides. The sweetpotato whitefly, Bemisia tabaci (Gennadius), is an important pest of watermelon [Citrullus lanatus (Thunberg) Matsum. and Nakai var. lanatus] and is among the most damaging pests in many agricultural systems worldwide. Citrullus colocynthis L., a perennial melon species indigenous to arid regions of northern Africa, the Mediterranean region, and southwestern Asia, is a valuable source of resistance to insect pests and diseases of watermelon. Laboratory and greenhouse experiments were conducted to evaluate selected C. colocynthis genotypes for sources of resistance to B. tabaci. Thirty genotypes of C. colocynthis, collected in different geographic regions, were evaluated against the heirloom cultivar Calhoun Gray using first a horizontal Y-tube olfactometer in the laboratory. A selected subset of the genotypes was evaluated in a second experiment in the laboratory using a vertical monitoring assay. In this assay, whiteflies could freely move upward to feed and oviposit on leaves placed in the upper portion of a Y-tube. In a third experiment, a choice assay was conducted on selected genotypes in cages in the greenhouse. Of the 30 C. colocynthis genotypes evaluated, PI 346082 (collected in Afghanistan) exhibited the highest level of resistance against B. tabaci based on all three experiments. PI 537277 (collected in Pakistan) exhibited a significantly high level of whitefly resistance based on low survival of adult whiteflies and a low ratio of nymphs to eggs. PI 346082 and PI 537277 should be a useful source for breeding projects aiming to improve whitefly resistance in watermelon cultivars. © 2015, American Society for Horticultural Science. All rights reserved.