Location: Vegetable Research2012 Annual Report
1a. Objectives (from AD-416):
1. Identify and characterize host plant resistance and facilitate incorporation of resistance factors into advanced breeding lines of watermelon (for sweetpotato whitefly) and sweetpotato (for the complex of soil-borne insects including but not limited to wireworms, flea beetles, cucumber beetles, white grubs, and sweetpotato weevils): 1.A Characterize watermelon germplasm lines with resistance to the sweetpotato whitefly and incorporate resistance factors into advanced watermelon breeding lines; 1.B. Identify and characterize sweetpotato clones with resistance to soil insect pests and use a recurrent mass selection breeding approach to generate clones with high levels of resistance and good horticultural characteristics. 2. Assess the importance and utility of biological control agents for the management of insect pests of cucurbits to include sweetpotato whitefly using predators and parasitoids, and for pickleworms using nucleopolyhedroviruses (NPV). 2.A. Develop NPVs for management of pickleworms and other pests of cucurbits; 2.B. Assess the effect of mixed plantings of cucurbits with other vegetables and plant species on the population abundance and behavior of predators and parasitoids for the management of the sweetpotato whitefly. 3. Identify whitefly-host plant-virus relationships and develop methods for protection from the whitefly-vectored viruses of vegetables such as sweetpotato and watermelon.
1b. Approach (from AD-416):
Conduct greenhouse and field trials to identify sources of resistance and evaluate genetic populations to determine heritability of resistance against sweetpotato whiteflies in melon and watermelon, and against soil insect pests of sweetpotatoes; cross appropriate germplasm to facilitate incorporation of resistance into advanced sweetpotato breeding lines and new cultivars; evaluate chemical and physical mechanisms of resistance in sweetpotato to soil insect pests; investigate the influence of resource plants on predators and parasitoids of whiteflies in cage and field trials; assess the usefulness of baculoviruses for control of pickleworms and other cucurbit pests; study the epidemiology of sweet potato leaf curl virus in sweetpotato; and survey the presence and epidemiology of whitefly-transmitted viruses of cucurbits.
3. Progress Report:
Laboratory studies on transmission of sweet potato leaf curl virus by the sweetpotato whitefly are ongoing. Collaborative research between ARS researchers at Charleston, SC, and Beltsville, MD, was continued on the predation of whiteflies based on gut analyses of two predators (big eyed bug and minute pirate bug). Research was conducted on the attraction and repellency of a whitefly predator to different odors. In collaboration with ARS, Gainesville, FL, several biorational materials were studied for repellency against whiteflies in vegetable crops. Laboratory assays were conducted on whitefly resistance in wild watermelon. Collaborative grant research that is highly related to this project was initiated on the impact of global warming on whiteflies and their natural enemies. As part of the on-going sweetpotato breeding program at the U.S. Vegetable Laboratory (USVL), over 2,600 first-year sweetpotato seedlings (from true seed) were transferred directly to the field as single-plant plots, which will be harvested and analyzed in September, 2012. Also, over 400 established sweetpotato clones were planted in replicated field plots at the USVL. Roots from these plots will be harvested in October, 2012. Three breeding blocks (seed nurseries) were planted in June, 2012, and seed collection will begin in October, 2012. Two groups of 18 and 30 sweetpotato clones were challenged with root knot nematodes and evaluated for disease resistance in a greenhouse experiment.
1. Diet Effect on Predator of Whiteflies. Predators are important for controlling whiteflies and other pests. Delphastus catalinae is a lady beetle predator that is sold commercially to control whiteflies. Research by ARS scientists (Charleston, SC, and Tallahassee, FL) found that supplemental diets, such as a 10% honey-water solution or honeydew (a sugary substance that whiteflies and their plant-sucking relatives excrete onto leaves when they feed), help sustain the population of this predator. This predator can survive on these supplemental diets as well as they can on whitefly hosts, thus insuring their survival when whitefly infestations are low. Results from this research can help in the development of strategies to enhance the use of predators for the management of whiteflies and other plant-sucking insect pests.