Location: Vegetable Research
2022 Annual Report
Objectives
1. Develop and enhance germplasm for host plant resistance of sweetpotato and watermelon that are resistant or tolerant to economically important pests, including whiteflies and soil dwelling pests.
1.A. Develop and characterize watermelon germplasm with resistance to whiteflies and incorporate the resistance into advanced breeding lines.
1.B. Develop sweetpotato germplasm clones that are resistant to soil dwelling pests and have desirable horticultural traits.
2. Assess whitefly-virus-host plant interactions and effects of biotic and abiotic factors on vegetable pests and their biological control agents.
2.A. Determine the effect of biotic and abiotic factors on populations of whiteflies and biological control agents of whiteflies in vegetable production systems.
2.B. Assess the impact of biotic and abiotic factors on whitefly:host-plant:virus interactions and whitefly endosymbionts.
3. Develop new or improved methods for the management of insect pests (including whiteflies and soil dwelling pests) and whitefly-transmitted viruses in vegetable crop production systems.
3.A. Identify and characterize genomics factors and develop novel genomics-based biotechnologies that would impede virus acquisition and transmission from whiteflies to plants.
3.B. Characterize genetic diversity and population structure of the sweetpotato weevil within the U.S.
3.C. Characterize infochemicals and plant-based chemicals affecting vegetable pests (e.g., click beetles, sweetpotato weevil and whiteflies) for use in detection, monitoring, and biologically-based management.
3.D. Identify and characterize sources of pickleworm resistance in cucumbers.
4. Develop sweetpotato germplasm lines adapted to low input, sustainable production systems, especially lines that are productive under weed competition.
4.A. Identify and characterize sweetpotato germplasm that is tolerant/competitive with weed pressure within sustainable production systems.
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, against soil insect pests, weeds and whitefly-transmitted viruses in sweetpotato, and resistance against pickleworms in cucurbits. Assay chemical and physical mechanisms of resistance to pests using tools including gas chromatography-mass spectrometry (GC-MS), and Y-tube olfactometers. 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. Investigate the influence of climate and biotic factors on insect populations and secondary endosymbionts and virus transmission by using field and controlled environments. Study the epidemiology of whitefly-transmitted viruses using biological assays and molecular techniques. Infochemicals used by vegetable pests in mate- and host-finding will be assessed using chemical, electrophysiological and behavioral studies for pests such as click beetles. Make improved plant germplasm available for use by the vegetable industry.
Progress Report
Research addressing Objective 1 was conducted in which ARS researchers in Charleston, South Carolina, conducted assays on whitefly acquisition and transmission of Cucurbit leaf crumple virus (CuLCrV; a plant virus) infectious clones that can be used in watermelon breeding for whitefly and whitefly-transmitted virus resistance. Having plants that are resistant or tolerant to whitefly-transmitted viruses and whiteflies is needed for watermelon production. New quantitative techniques for CuLCrV detection using digital PCR were developed for measuring the quantity of viruses in whiteflies and in plant materials. Assays were conducted on the response of whiteflies to selected watermelon lines based on phytochemicals and plant volatiles. Clonal watermelon plants were developed and established in soilless media for bioassays against whiteflies under controlled environment. Collaborative research between ARS and researchers at Auburn University, Claflin University, and University of Georgia was conducted on host plant resistance in snap bean (Phaseolus vulagris) against either whiteflies or whitefly-transmitted viruses. This research included assessing commercial cultivars and plant introduction lines. ARS collaborated with the University of Georgia on the use of molecular markers to detect whitefly-transmitted viruses and investigated the role of planting date and temperature on the disease incidence and severity of whitefly-transmitted viruses; the newly identified cucurbit chlorotic yellows virus (CCYV), cucurbit yellow stunting disorder virus (CYSDV) and cucurbit leaf crumple virus (CuLCrV) were not detected in the spring cantaloupe and watermelon, which suggests that these viruses may overwinter on non-cucurbitaceous crops or weed hosts. Collaborative studies between ARS and University of Georgia were continued on the evaluation of Cucurbita lines to identify sources of resistance to whiteflies and whitefly-transmitted viruses-complexes. In collaborative research, over 15,000 seeds from breeding nurseries were harvested by ARS researchers and 3,000 seeds each were sent to Mississippi State University and North Carolina State University per collaborative agreements. Sweetpotato germplasm (~ 400 samples) was genotyped with a 5K SNP (single nucleotide polymorphisms) array developed in collaboration with Breeding Insight at Cornell University. The Fieldbook app was implemented into the sweetpotato breeding program to allow seamless data collection from the field to the database curated and maintained by Breeding Insight. Selection of improved sweetpotato germplasm was continued with over 7,500 1st year seedlings and over 100 advanced clones evaluated in replicated field plots. A single breeding nursery was established to develop new germplasm with insect and nematode resistance. Research addressing Objective 2 was conducted in which an isoline colonies of whiteflies were established from a single whitefly (isoline) and later maintained at different temperatures, and representative whiteflies from each temperature treatment are regularly sampled. The isoline colony was determined to be the MEAM1 whitefly stain and it was found to harbor two secondary endosymbionts (Hamiltonella and Rickettsia) as well as the primary endosymbiont Portiera aleyrodidae. Digital PCR is being used to quantify the baseline endosymbiont compositions and evaluate changes in whitefly endosymbionts after temperature and field treatments. Sweet potato leaf curl virus (SPLCV) transmission by whiteflies is being detected using digital and conventional PCR. New sensitive and specific primers were designed for detection of SPLCV from whiteflies and plant materials. An evaluation of shifts in endosymbiont communities in response to temperature is underway. Whiteflies were regularly collected from each of four temperatures (16°C, 21°C, 28°C, and 35°C) when the populations could support sampling. DNA was extracted from individual males and females and groups of male or female whiteflies for 14 temperature-time point collections, and digital PCR evaluations of Portiera, Hamiltonella, and Rickettsia are in progress. Colonies of MEAM1 whiteflies have been established on collards, sweetpotato, and tomato from the original isoline established in the previous year. Cultures of tomato yellow leaf curl virus (TYLCV) and SPLCV are being maintained in preparation for examining host adaptation and host switching effects on virus transmission efficiency. Research was conducted on assessing the performance of the isoline populations of the MEAM1 whitefly in field cages during the fall, winter, and spring seasons in consideration to climate impact. Related research on climate impact on whitefly populations in vegetable crops was conducted by ARS in collaboration with researchers at Abraham Baldwin Agricultural College, San Diego State University, and Agricultural Research Center in Egypt. Moreover, research between ARS and University of Georgia is being conducted on the population of whiteflies and whitefly predators at different seasons in the agricultural landscape. The role of several types of predators of whiteflies in the agricultural landscape are being assessed. Research addressing Objective 3 was conducted in which the effects of virus acquisition on whitefly endosymbiont communities are being determined. Studies on the endosymbiont compositions of whiteflies feeding on infected versus healthy plants are in progress. The mitochondrial genomes of sweetpotato weevils collected from South Carolina, Georgia, Texas, and Hawaii were assembled, and a phylogenetic analysis was conducted. Sweetpotato weevil samples were obtained from locations in Georgia, Mississippi, South Carolina, Jamaica, and Vietnam. Genome sequencing data from 40 sweetpotato weevils from Georgia, Hawaii, South Carolina, and Texas was used to create KASP markers for genetic characterization. Efforts continued for the development of optimized trapping, preservation, and automated DNA isolation for sweetpotato weevil. Field studies were conducted in Virginia, North Carolina, and South Carolina on the reproductive biology of click beetles. One study addressed improving trapping technology of click beetles, which are important pests of sweetpotato. Using a sex pheromone previously discovered at ARS Charleston, South Carolina, researchers evaluated trap design, lure longevity, and killing/preservative agents. In related studies, pheromone traps were used to characterize the region-wide phenology of click beetles, to determine if pheromone trap captures can be used to time insecticide applications for click beetles in sweetpotato, and to determine the relationship between beetle captures in pheromone traps and wireworm (immature click beetle) densities in nearby soil samples. In other field trials, sex attractants for two species of click beetles were identified. A field study evaluated the use of sex pheromone lures of multiple species together in the same trap to improve cost efficiency. Cucumber germplasm (67 plant introductions and 9 commercial pickling cultivars) was screened for resistance to natural infestations of pickleworm in replicated field trials. Thirty-one plant introductions had less than 10% damage and a single plant introduction had no damaged cucumbers. Several biopesticides were assessed for their impacts on whiteflies and a whitefly predator (a lady beetle called Delphastus catalinae). Some of the biopesticides killed more of the insects than the other biopesticides. ARS researchers collaborated with University of Georgia researchers on the evaluations of the role of insecticides and potential insecticide resistance in management of whiteflies and whitefly-transmitted viruses. A new insecticide, Senstar, was proven efficacious and was incorporated into recommendations for growers by the University of Georgia. Field trials evaluating potential use of insecticides for suppression of whitefly-transmitted viruses showed poor results regardless of level of the pest and virus pressure. However, that research demonstrated increased yield with the control of whiteflies in sweetpotato. Additional collaborative research between ARS and Fort Valley State University and University of Georgia was continued on the assessment of entomopathogenic nematodes (EPN) against whiteflies on vegetable crops, and the role of ultraviolet radiation from the sun on the survival of the nematodes. Research addressing Objective 4 was conducted in which a total of 39 first year seedlings (FYS) that had combined suitable storage root traits and upright vigorous plant habit were selected from 7,500 FYS and 21 of these selections are being evaluated in replicated field trials in 2022, and the remaining will be evaluated in 2023. An open pollinated breeding nursery was established to create new germplasm resistant to soil dwelling pests with modified plant architecture to be competitive with weed pressure.
Accomplishments
1. Understanding the role of insecticides in adaptation by whiteflies. Whiteflies are global problems in numerous vegetable crops as well as other crops because this pest has adapted to many environments. ARS researchers in Charleston, South Carolina, collaborated with University of Georgia researchers on defining the role of chemical insecticides on the population buildup of whiteflies. The researchers described interactions between plant chemicals and insecticides that are commonly used to control whiteflies; this led to the ability of the whitefly to adapt and build up its populations. This work provides a framework for the biological processes of chemical response and population selection that can impact insecticide resistance management for this important pest. This information is useful to scientists and pest management practitioners.
2. Evaluation of resistance to underground insect pests in sweetpotato for organic production. There has been a recent increase in interest in organically produced sweetpotato because of the potential economic benefits and production of this crop using plastic mulches to reduce weed and pest issues. Therefore, ARS researchers in Charleston, South Carolina, along with Clemson University collaborators, evaluated sweetpotato cultivars and insect resistant breeding lines for performance under conventional and organic production systems. Overall, this study demonstrates that black plastic mulch (BPM) is a viable production system for sweetpotato in South Carolina as well as other southern states in the U.S. Although the use of BPM did not always lead to increases in marketable yield in this study, BPM may deter underground insect pests. Although more research is needed, it appears that plastic mulch may deter insects that damage sweetpotato roots while simultaneously decreasing weed pressure during the critical weed free period which will benefit both organic and conventional growers.
3. Screening for whitefly resistance in snap bean. The sweetpotato whitefly is a major insect pest on vegetable crops worldwide. The evaluation of commercially available snap bean cultivars for differences in susceptibility to the sweetpotato whitefly is critical to providing growers with alternative control strategies against this pest. Whitefly infestation and snap bean performance were studied by ARS researchers in Charleston, South Carolina, in collaboration with Fort Valley State University researchers. Among 24 commercially available cultivars of snap bean, cultivars ‘Gold Mine’, ‘Golden Rod’, ‘Long Tendergreen’, and ‘Royal Burgundy’ supported lower numbers of whiteflies, although the cultivars with the highest yield were ‘Affirmed’, ‘Momentum’, ‘PV-857’, ‘Sybaris’, and ‘Tema’. These results provide useful information for growers when they consider types of snap bean to plant each season
4. Identifying and ranking predators of whiteflies. Natural enemies are important in and around agricultural fields for reducing populations of pests like whiteflies. A collaborative study between researchers at the University of Georgia and ARS researchers in Charleston, South Carolina, was conducted to identify and rank the most importance whitefly predators in the agricultural landscape. Results from this study supports that some DNA methods are more effective than others in identifying what predators have eaten. Several predators, including those who feed by sucking (such as minute pirate bugs and big-eyed bugs) or chewing (such as fire ants and lady beetles), and spiders, were identified as being highly ranked for feeding on whiteflies in the field. These findings will help pest management practitioners in developing a successful biological control program for whiteflies and other pests in field settings.
Review Publications
Li, M., Xia, S., Zhang, T., Williams III, L.H., Xiao, H., Lu, Y. 2022. Volatiles from cotton plants infested by Agrotis segetum (Lep.: Noctuidae) attract the larval parasitoid Microplitis mediator (Hym.: Braconidae). Plants. 11(7):863. https://doi.org/10.3390/plants11070863.
Andreason, S.A., Lahey, Z., Ayala-Ortiz, C., Simmons, A.M. 2022. Genome sequences of novel iflaviruses in the gray lawn leafhopper, an experimental vector of corn stunt spiroplasma. Microbiology Resource Announcements. https://doi.org/10.1128/mra.00446-22.
Li, Y., Mbata, G., Simmons, A.M., Punnuri, S. 2022. Susceptibility of snap bean cultivars to the sweetpotato whitefly, Bemisia tabaci, in the Southern United States. Crop Protection. 159:106022. https://doi.org/10.1016/j.cropro.2022.106022.
Millar, J.G., Williams Iii, L., Serrano, J.M., Halloran, S., Grommes, A.C., Huseth, A.S., Kuhar, T.P., Hanks, L. 2022. A symmetrical diester as the sex attractant pheromone of the North American click beetle Parallelostethus attenuates (Say) (Coleoptera: Elateridae). Journal of Chemical Ecology. 48;598-608. https://doi.org/10.1007/s10886-022-01360-8.
Pellegrino, A.M., Dorman, S.J., Williams III, L.H., Millar, J.G., Huseth, A.S. 2021. Evaluation of 13-tetradecenyl acetate pheromone for Melanotus communis (Coleoptera: Elateridae) detection in North Carolina row crop agroecosystems. Environmental Entomology. 50(5):1248-1254. https://doi.org/10.1093/ee/nvab075.
Perier, J.D., Riley, D.G., Champange, D.E., Simmons, A.M. 2022. Whiteflies at the intersection of polyphagy and insecticide resistance. Insects. https://doi.org/10.1093/aesa/saac008.
Simmons, A.M., Chong, J., Pitts Singer, T. 2021. Retrospective of a virtual experience: ESA 2020 Annual Meeting. American Entomologist. 67(4):57–64. https://doi.org/10.1093/ae/tmab053.
