Location: Vegetable Research2013 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:
Research continued in collaboration with a USDA, ARS researcher in Tallahassee, FL, to determine the attractant and repellant qualities of chemical odors to whiteflies and a predator of whiteflies. Laboratory and greenhouse assays of wild watermelon exhibiting whitefly resistance continued in collaboration with an ARS, research geneticist in Charleston, SC. Laboratory assays continued on sweetpotato leaf curl virus (SPLCV) transmission and whitefly population levels as they impact sweetpotato. Colonies of whiteflies from different origins were established and maintained in the laboratory. These include whiteflies from the field, greenhouse, and colonies originating from full siblings. Several cultural practices (mulching, time of planting, intercropping, and different irrigation methods) resulted in differences in whitefly populations and levels of whitefly-transmitted viruses. Whitefly infestation and virus infection were affected minimally by three irrigation methods (daily drip, weekly overhead sprinkler, and biweekly flood). Regardless of cultural practice, incidences of several whitefly-transmitted viruses were closely related to infestation levels of whiteflies. Studies to determine the potential impact of global warming on whiteflies and their natural enemies was done using laboratory and field experiments and these were primarily focused on the impact of elevated temperature and carbon dioxide, and on the ability of whiteflies to overwinter. As part of the on-going sweetpotato breeding program at the U. S. Vegetable Laboratory (USVL), over 400 established sweetpotato clones were planted in replicated field plots at the USVL. Roots from these plots will be harvested in October 2013. Two breeding blocks (seed nurseries) were planted in June 2013, and seed collection will begin in October 2013. Twenty sweetpotato clones were challenged with root knot nematodes and evaluated for disease resistance in a greenhouse experiment. The entire ARS sweetpotato plant introduction collection from Griffin, GA, was obtained as plantlets in tissue culture tubes. Plantlets were transferred to greenhouse pots and later planted in the field in replicated plots for phenotyping. Leaf color, leaf shape, root color (flesh and skin), root shape, dry weight, and other characteristics were recorded for over 250 genotypes in the past year.
1. Cultural control for whitefly and whitefly-transmitted plant viruses. Whiteflies (Bemisia tabaci) and the viruses they transmit are important pest problems in vegetable crops. Several cultural practices (especially mulching and intercropping) were demonstrated in the field to reduce population levels of whiteflies and reduce infection rates of some whitefly-transmitted viruses. Irrigation method and crop rotation had small impacts on the population of the whiteflies and incidence of whitefly-transmitted viruses. The results suggest that certain cultural practices may help growers manage whiteflies and whitefly-transmitted viruses in vegetable crops. These findings are of interest to vegetable producers seeking methods to reduce whitefly damage and to extension professionals advising them.