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Title: Potential sources of whitefly (Hemiptera: Aleyrodidae) resistance in desert watermelon (Citrullus colocynthis) germplasm

item Coffey, John
item Simmons, Alvin
item SHEPARD, B - Clemson University
item TADMOR, YAAKOV - Agricultural Research Organization Of Israel
item Levi, Amnon

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2014
Publication Date: 1/31/2015
Citation: Coffey, J.L., Simmons, A.M., Shepard, B.M., Tadmor, Y., Levi, A. 2015. Potential sources of whitefly (Hemiptera: Aleyrodidae) resistance in desert watermelon (Citrullus colocynthis) germplasm. HortScience. 50:13-17.

Interpretive Summary: Citrullus colocynthis is a wild relative of watermelon. For certain diseases or insect pest, it offers a source of pest resistance for the improvement of watermelon. The sweetpotato whitefly, also called silverleaf whitefly, is an important pest of watermelon. This insect pest is a problem because it feeds on the watermelon plant and because this whitefly can transmit destructive plant viruses to watermelon plants. A study was conducted to identify some C. colocynthis types that may be useful for improving commercial watermelon against whiteflies. Two of the C. colocynthis wild types (PI 346082 and PI 537277) in this study displayed good resistance against whiteflies. Information from this study may lead to the development of pest resistant watermelons which will benefit growers, consumers and the environment.

Technical Abstract: Selection for host plant resistance and incorporation of natural resistance into cultivars is a fundamental strategy to control insects and diseases in an environmentally-sensitive manner, and may help reduce reliance on synthetic pesticides. The sweetpotato whitefly, Bemisia tabaci (Gennadius), is an important pest of watermelon (Citrullus lanatus var. lanatus) and is among the most damaging pests in many agricultural systems worldwide. Citrullus colocynthis, a perennial melon species indigenous to arid regions of northern Africa, the Mediterranean, and southwestern Asia, is a viable source of resistance to insect pests and diseases of watermelon. Herein, 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 a horizontal two-choice Y-tube olfactometer in the laboratory. A selected subset of the genotypes was evaluated in a second experiment using a vertical olfactometer, in which whiteflies were allowed to feed and oviposit on leaves in the laboratory. A choice assay was also conducted on selected genotypes in cages in the greenhouse. This is the first study to report on the use of olfactometer bioassays to examine whitefly behavior on C. colocynthis genotypes. Of the genotypes evaluated, PI 346082 (collected in Afghanistan) exhibited the highest level of resistance against B. tabaci based on all three experiments. Additionally, PI 537277 (Collected in Pakistan) exhibited a notable level of whitefly resistance based on low adult presence, low whitefly survival, and a low ratio of nymphs to eggs. Sources of germplasm were identified in this study which may be useful for improving whitefly resistance in watermelon cultivars.