Location: Vegetable Research
2016 Annual Report
Objectives
1. Identify and characterize host plant resistance genes and develop germplasm lines of sweetpotato and watermelon that are resistant or tolerant to economically important insect pests of important vegetable crops, and develop germplasm lines adapted to low input, sustainable production systems [NP304, Component 3, Problem Statement 3A2].
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 resistance genes and genotypes of sweetpotato with resistance to soil insect pests, elucidate mechanisms of pest resistance, and develop germplasm clones that are resistant to soil insect pests and have good horticultural characteristics.
1.C. Identify sweetpotato clones tolerant of weed interference and/or whitefly-transmitted viruses that are superior to conventional cultivars for organic and sustainable production.
2. Develop methods to improve control of insect pests, especially whiteflies, in vegetable production systems, and identify the effects of biotic and abiotic factors on populations of pests and their biological control agents, and on whitefly:host plant:virus interactions [NP304, Component 3, Problem Statement 3A1].
2.A. Determine the effect of biotic and abiotic factors on populations of biological control agents of whiteflies in vegetable production systems.
2.B. Determine the impact of factors associated with climate change on whitefly:host plant:virus interactions and whitefly endosymbionts.
2.C. Investigate sustainable management approaches for pests in vegetable crops, including detection of pest populations such as pickleworms.
Approach
Conduct laboratory, greenhouse and field experiments to identify sources of resistance and evaluate genetic populations to determine resistance against the sweetpotato whitefly in watermelon and against soil insect pests, weeds and whitefly-transmitted virus in sweetpotato. Assay chemical and physical mechanisms of resistance to pests using gas chromatography-mass spectrometry (GC-MS), portable “electronic nose,” Y-tube olfactometers, and other assays. Use PCR-markers and other genomic technologies, such as genotype by sequencing, to identify sequences linked to the studied characters and to locate controlling genes on linkage maps. Cross appropriate germplasm to facilitate the incorporation of resistance into advanced breeding lines or new cultivars. Assess the competitive advantage against weeds of sweetpotato genotypes with more vigorous growth habits in comparison to less competitive conventional cultivars, identify competitive genotypes with good horticultural quality, and evaluate them as a component in integrated management systems for conventional and organic growers. Use a recurrent mass selection breeding approach to generate sweetpotato clones with high levels of resistance and good horticultural characteristics. Continue ongoing searches for new resistances or tolerances among watermelon and sweetpotato accessions from the U.S. Plant Introduction System and other collections. Make improved germplasm available for use by the vegetable industry. Investigate the influence of climate and biotic factors on insect populations by using environmental chambers and field cages. Assess the behavior and ecology of pickleworms and other pests for their control by the development of new formulations and ratios of the pheromone components and testing them in flight tunnel and field environments. Study the epidemiology of whitefly-transmitted Sweet potato leaf curl virus in sweetpotato using biological assays and molecular detection techniques, including real-time (RT)-PCR and quantitative (q)PCR.
Progress Report
Progress was made on all objectives. Under Objective one, wild types of watermelon were assessed for resistance against whiteflies. An improved technique for evaluating whitefly response to plants was determined to be reliable, allowing us to assess differences in whitefly acceptance among different vegetable crops and in differences in their acceptance of different accessions of watermelon. Selected wild relatives of the cultivated watermelon were assayed in comparison to commercial watermelon cultivars for volatile leaf chemicals that may be associated with resistance to whiteflies.
As part of the on-going sweetpotato breeding program at the U.S. Vegetable Laboratory (Charleston, South Carolina), over 20,000 seeds from two breeding nurseries were collected, and 10,000 seeds were offered to collaborators. Sweetpotato DNA was isolated from the majority (737 of 760 accessions) of the Agricultural Research Service germplasm collection (located in Griffin, Georgia) to use in assessing respective genotypes of all accessions. Over 5,000 first year seedlings and over 150 second year, intermediate, advanced, and regional clones were evaluated in the field for response to insect pests and tolerance to weeds. Breeding plots were established and over 75 sweetpotato clones were maintained in the field. A statewide study was initiated to provide species-level identification of the click beetle complex that attacks sweetpotato. Factors affecting spatial distribution and damage to sweetpotato roots were further evaluated. Over 1,800 seedlings were evaluated and selections were made for plant habit that affects tolerance of weeds. Leaf samples were collected from over 2,500 seedlings and these were tested for Sweetpotato leaf curl virus to assess for possible seed transmission.
Under Objective 2, populations of the sweetpotato whitefly, as well as populations of the whitefly predator Delphastus catalinae, were established in different environments to assess their response to variable climate. Three single-nozzle operator-carried spray applicators were assessed for whitefly control on summer squash in collaboration with researchers in Egypt. The different applicators were evaluated with five biorational and conventional insecticides. The Economy Micro Ulva sprayer resulted in more whitefly mortality as compared with the Arimitsu sprayer and the CZP-3 sprayers, respectively. All insecticides suppressed the whiteflies; mortality ranged from 73% to 95% for a given insecticide and sprayer. A study with a neem-based biorational insecticide was conducted on whiteflies (B. tabaci) on collards. For plants sprayed with the insecticide, the adults were repelled, and egg laying and survival of the immatures were reduced. Yet, protection was partial; some whiteflies still fed, deposited eggs, and developed on the neem-sprayed plants. In a collaborative study (with an Egyptian researcher), several biorational insecticides suppressed whitefly populations in vegetable seedlings and delayed whitefly-transmitted viruses.
Field experiments were conducted on 200 plant introductions of cucumber for sources of resistance to the pickleworm. Additionally, field studies were established to isolate, identify, and characterize chemicals that affect the behavior of insect pests of sweetpotato (click beetles) and cucurbits (pickleworm). Colonies of click beetles and pickleworms were established from feral insects collected in Charleston, South Carolina; these insects are being used in studies to evaluate reproductive behavior in response to sources of resistance.
Accomplishments
1. Backpack sprayers assessed for whitefly management. The sweetpotato whitefly (Bemisia tabaci) is among the most destructive insect pests in the world because of direct damage to crops due to its feeding and also due to its transmission of plant viruses. Among three single-nozzle backpack spray applicators, the Economy Micro Ulva sprayer resulted in higher whitefly mortality as compared with the Arimitsu sprayer and the CZP-3 sprayer, respectively, for each of five biorational and conventional insecticides. The results provide pest management practitioners conducting small scale, limited-resource crop productions with performance assessment of the three backpack spray applicators for whitefly management with selected foliar insecticides.
None.
Review Publications
Abd-Rabou, S., Simmons, A.M. 2015. Infestation by Bemisia tabaci (Hemiptera: Aleyrodidae) and incidence of whitefly-transmitted viruses after the application of four biorational insecticides in some crops in Egypt. International Journal of Insect Science. 35:132-136.
Coffey, J.L., Simmons, A.M., Shepard, B.M., Levi, A. 2016. A vertical Y-tube is a valuable tool for assessing whitefly preference, yielding well-defined results among attractive versus poor host plants. Journal of Agricultural and Urban Entomology. 32(1):7-12. http://dx.doi.org/10.3954/1523-5475-32.1.7
Luan, J., Chen, W., Hasegawa, D.K., Simmons, A.M., Wintermantel, W.M., Ling, K., Fei, Z., Liu, S., Douglas, A.E. 2015. Metabolic coevolution in the bacterial symbiosis of whiteflies and related plant sap-feeding insects. Genome Biology and Evolution. 7(9):2635-2647. doi: 10.1093/gbe/evv170.
Pudjianto, Shepard, B.M., Shapiro, M., Jackson, D.M., Carner, G.R. 2016. Comparative infectivity of homologous and heterologous nucleopolyhedroviruses against beet armyworm larvae. Journal of Agricultural and Urban Entomology. 32:13-24.
Simmons, A.M., Abd-Rabou, S., Hindy, M. 2015. Comparison of three single-nozzle operator-carried spray applicators for whitefly (Bemisia tabaci) management on squash. Agricultural Sciences. 6:1381-1386.
Chen, W., Hasegawa, D., Arumuganathan, K., Simmons, A.M., Wintermantel, W.M., Fei, Z., Ling, K. 2015. Estimation of the whitefly Bemisia tabaci genome size based on k-mer and flow cytometry analyses. Insects. 6:704-715.
Trigiano, R.N., Windham, A.S., Windham, M.T., Wadl, P. 2016. ‘Appalachian Joy’ is a supernumery, white-bracted cultivar of cornus florida resistant to powdery mildew. HortScience. 51(5):592-594.
Deletre, E., Schatz, B., Bourguet, D., Chandre, F., Williams Iii, L.H., Ratnadass, A., Martin, T. 2016. Prospects for repellent in pest control: current developments and future challenges. Chemoecology. 26:1-16.
