Research Project: Basic and Applied Approaches for Pest Management in Vegetable Crops

Location: Vegetable Research

2021 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 new sweetpotato germplasm was developed through open pollinated crosses from a single breeding nursery. Over 25,000 seeds were harvested, and 8,000 seeds were offered to collaborators at Mississippi State University and North Carolina State University. Genome sequencing of DNA from a 48 accession core germplasm set from the USDA-ARS Sweetpotato Germplasm collection was conducted for development of a SNP (single nucleotide polymorphisms) genotyping array in collaboration with Breeding Insight at Cornell University. Ongoing selection of improved sweetpotato germplasm continued with over 5,000 1st year seedlings and over 150 2nd year seedlings, intermediate, advanced, and regional clones were evaluated in the replicated field plots. These seedlings and clones were evaluated for insect resistance and other important horticultural traits. An open pollinated breeding nursery and a bi-parental segregating population were established to create new germplasm with resistance to soil dwelling pests. Also, over 50 sweetpotato clones were maintained in field plantings. The construction of genetic populations of Citrullus using wild germplasm of watermelon were initiated for the development of plant resistance to whiteflies. In collaborative research with the University of Georgia, a study was done on evaluating snap bean resistance to whiteflies and whitefly-transmitted cucurbit leaf crumple virus (CuLCrV) and sida golden mosaic Florida virus (SiGMFV). Twenty types of snap beans were identified with high- to moderate-levels of resistance to CuLCrV and/or SiGMF; however, 21 types were highly susceptible with disease severity. The whole genome of these snap bean genotypes was sequenced and genetic variability among them was identified. Research addressing Objective 2 was conducted in which isoline populations of the sweetpotato whitefly were established in the laboratory; all populations resulted from a single insect. Research addressing Objective 3 was conducted in which gnome sequencing of sweetpotato weevils (n=48) from Georgia, Hawaii, South Carolina, and Texas was conducted in collaboration with Breeding Insight at Cornell University to develop a high throughput genotyping platform (KASP markers) to characterize genetic diversity and population structure. Additional sweetpotato samples were obtained from Jamaica and Vietnam. Optimization of automated DNA isolation was initiated in collaboration with Breeding Insight. ARS researchers in Charleston, South Carolina led a collaborative study with ARS and university researchers in Virginia, North Carolina, South Carolina, Georgia and Florida on several studies on the reproductive biology of click beetles. Research addressed improvement of trapping technology of an important pest of sweetpotato. Using a sex pheromone previously discovered at ARS Charleston, South Carolina, researchers evaluated trap type and placement, lure longevity and killing agents under field conditions. A field study evaluated whether sex pheromones of two important sweetpotato pests could be used together in the same trap to improve efficiency. Another field study evaluated the efficacy of a multi-component blend on attractiveness to an economically important click beetle. In other research, sex attractants for four species of click beetles were identified. A laboratory study assessed the susceptibility of wireworms to entomopathogens (pathogens of arthropods) in the soil. ARS researchers in Charleston, South Carolina completed research that concluded that there is no seed transmission of the sweet potato leaf curl virus (SPLCV) in sweetpotato seed. This result is in agreement with another report on no evidence of seed transmission of another whitefly-transmitted begomovirus, tomato yellow leaf curl virus on tomato. Incorrect reports on seed transmission of SPLCV and other begomoviruses could have a negative impact on strategies in disease management, which might also impose unnecessary burden to the seed companies as well as to governmental regulatory agencies. A strain (GA17) of the entomopathogenic fungus, Isaria javanica, that was found naturally infecting the sweetpotato whitefly in commercial cotton fields in Georgia in late 2017, was studied in the laboratory and field in collaboration with University of Georgia and Fort Valley State University. In collaborative research with the University of Georgia, populations of whiteflies were surveyed across major vegetable landscapes in Georgia; the genetic analysis of the insects revealed little genetic differences among the populations, and a high level of gene flow. In a collaboration by ARS researchers in South Carolina, Florida and Georgia, and researchers at Clemson University and University of Georgia, a study was conducted examining historical research over the past 20 years in the U.S.; the researchers concluded that there are at least 9 generalist predators that significantly affect whitefly populations in the U.S. In collaboration with the University of Georgia, research was continued on the evaluation of the role of insecticides and potential insecticide resistance in the management of the sweetpotato whitefly and whitefly-transmitted viruses, and on-farm research was conducted on the use of row covers for protection against whiteflies. Research concerning Objective 4 was continued in which selections (n=45) from 2019 and 2020 for compact plant growth habit were established into replicated field trials to further select for the most competitive clones against weed pressure. Over 5,000 seedlings were evaluated and 75 selections were made that exhibited compact growth and will be evaluated further in weed competition studies in 2022. An open pollinated breeding nursery and a bi-parental segregating population were established to create new germplasm resistant to soil dwelling pests with modified plant architecture to be competitive with weed pressure.

Accomplishments
1. Root-knot nematode resistance and weed control in sweetpotato. A multidisciplinary team of ARS researchers in Charleston, South Carolina, and Clemson University collaborators, identified sweetpotato germplasm that is resistant to the emerging and invasive Guava root-knot nematode, Meloidogyne enterolobii. The new sources of resistance are being incorporated to develop new resistant sweetpotato germplasm and populations to facilitate marker assisted breeding. Research was also conducted with university collaborators to identify plant hormones that can be used as safeners for herbicide application in sweetpotato. Currently, there are no in-season applicable selective post-emergent herbicides registered for sweetpotato to suppress broadleaves and nutsedge species. These results suggest that the use of safner compounds could improve sweetpotato tolerance to post-applications of bentazon and mesotrione without reducing herbicide efficiency. Expansion of bentazon and mesotrione herbicide labels to include sweetpotato would be beneficial to sweetpotato growers.

2. Snap bean genome to help develop resistance to whiteflies and whitefly-transmitted viruses. The production and quality of snap bean are decreased by whiteflies and leaf crumple disease caused by two whitefly-transmitted viruses -- cucurbit leaf crumple virus and sida golden mosaic Florida virus; these may appear as a mixed infection in fields in the southeastern U.S. A multidisciplinary team of University of Georgia and ARS researchers in Charleston, South Carolina, sequenced the whole genome of selected snap bean genotypes and genetic variability among the genotypes was identified to obtain information that will be helpful in developing snap beans that have resistance to whiteflies and whitefly-transmitted viruses, and this will help protect crops of growers.

Review Publications
Li, Y., Mbata, G.N., Punnuri, S., Simmons, A.M., Shapiro Ilan, D.I. 2021. Bemisia tabaci on vegetables in the southern United States: incidence, impact, and management. Insects. 12:198. https://doi.org/10.3390/insects12030198.
Kheirodin, A., Simmons, A.M., Legaspi, J.C., Grabarczyk, E.E., Toews, M.D., Roberts, P.M., Chong, J., Snyder, W.E., Schmidt, J.M. 2020. Can generalist predators control Bemisia tabaci?. Insects. 11:823. https://doi.org/10.3390/insects11110823.
Gautam, S., Crossley, M.S., Dutta, B., Coolong, T., Simmons, A.M., Da Silva, A., Snyder, W., Srinivasan, R. 2020. Low genetic variability in Bemisia tabaci MEAM1 populations within farmscapes of Georgia, USA. Insects. 11:834.
Agarwal, G., Kavalappara, S.R., Gautam, S., da Silva, A., Simmons, A., Srinivasan, R., Dutta, B. 2021. Field screen and genotyping of Phaseolus vulgaris against two begomoviruses in Georgia, USA. Insects. 12:49
Andreason, S.A., Shelby, E.A., Moss, J.B., Moore, P.J., Moore, A.J., Simmons, A.M. 2020. Whitefly Endosymbionts: Biology, Evolution, and Plant Virus Interactions. Insects. https://doi.org/10.3390/insects11110775.
Andreason, S.J., Olaniyi, O.G., Gilliard, A.C., Wadl, P.A., Williams Iii, L.H., Jackson, M.D., Simmons, A.M., Ling, K. 2021. Large scale seedling grow-out experiments do not support seed transmission of sweet potato leaf curl virus in sweetpotato. Plants. 10(1):139. https://doi.org/10.3390/plants10010139.
Caputo, G.A., Wadl, P.A., Mccarty, L., Adelberg, J., Jennings, K.M., Cutulle, M. 2020. In vitro safening of bentazon by melatonin in sweetpotato. HortScience. 55:1406-1410. https://doi.org/10.21273/HORTSCI15128-20.
Caputo, G.A., Wadl, P.A., Mccarty, L., Adelberg, J., Saski, C., Cutulle, M. 2021. Impact of tank mixing plant hormones with bentazon and mesotrione on sweetpotato injury and weed control. Agrosystems, Geosciences & Environment. https://doi.org/10.1002/agg2.20185.
Hatmaker, E., Wadl, P.A., Rinehart, T.A., Carroll, J.B., Lane, T.S., Trigiano, R.N., Staton, M.E., Schilling, E.E. 2020. Complete chloroplast genome comparisons for Pityopsis (Asteraceae). Frontiers in Plant Science. 55:0241391. https://doi.org/10.1371/journal.pone.0241391.
Nowicki, M., Hadziabdic-Guerry, D., Trigiano, R.N., Boggess, S.L., Kanetis, L., Wadl, P.A., Ojiambo, P.S., Cubeta, M.A., Spring, O., Thines, M., Runge, F., Scheffler, B.E. 2021. ‘Jumping Jack’: Genomic microsatellites underscore the distinctiveness of closely related Pseudoperonospora cubensis and Pseudoperonospora humuli and provide new insights into their evolutionary past. Molecular Plant Pathology. 12:686759. https://doi.org/10.3389/fmicb.2021.686759.
Olaniyi, O.G., Andreason, S.A., Strickland, T.C., Simmons, A.M. 2021. Brassica carinata: new reproductive host plant of Bemisia tabaci (Hemiptera: Aleyrodidae). Entomological News. 129(5):500-511. https://doi.org/10.3157/021.129.0504.
Rutter, W., Wadl, P.A., Mueller, J.D., Agudelo, P. 2021. Identification of sweetpotato germplasm resistant to pathotypically distinct isolates of Meloidogyne enterolobii from the Carolinas. Plant Disease. https://doi.org/10.1094/PDIS-02-20-0379-RE
Shelby, E.A., Moss, J.B., Andreason, S.A., Simmons, A.M., Moore, A.J., Moore, P.J. 2020. Debugging: strategies and considerations for efficient RNAi-mediated control of the whitefly Bemisia tabaci. Insects. 11 (11):723. https://doi.org/10.3390/insects11110723.
Simmons, A.M., Riley, D.G. 2021. Improving whitefly management. Insects. 12:470. https://doi.org/10.3390/insects12050470.
Sparks, T.C., Riley, D.G., Simmons, A.M., Guo, L.G. 2020. Comparison of toxicological bioassays for whiteflies. Insects. 11:789. https://doi.org/10.3390/insects11110789.
Wu, S., Toews, M.D., Hofman, C.O., Behle, R.W., Simmons, A.M., Shapiro Ilan, D.I. 2020. Environmental tolerance of entomopathogenic fungi: a new strain of cordyceps javanica isolated from a whitefly epizootic versus commercial fungal strains. Insects. 11(10). Article 711. https://doi.org/10.3390/insects11100711.
Wu, X., Hulse-Kemp, A.M., Wadl, P.A., Smith, Z., Mockaitis, K., Staton, M.E., Rinehart, T.A., Alexander, L.W. 2021. Genomic resource development for hydrangea (Hydrangea macrophylla (Thunb.) Ser.) – A transcriptome assembly and a high-density genetic linkage map. Horticulturae. https://doi.org/10.3390/horticulturae7020025.