Incorporating Natural, Non-toxic Arthropod Resistant Tomato Varieties into Southern Production Systems

Final report for LS19-305

Project Type: Research and Education
Funds awarded in 2019: $299,963.00
Projected End Date: 09/30/2022
Grant Recipient: Clemson University
Region: Southern
State: South Carolina
Principal Investigator:
Juang-Horng Chong
Clemson University
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Project Information


Arthropod pests critically limit yields and quality of tomatoes in the Southeast. Whiteflies and thrips transmit viruses that can result in 100 percent crop loss. Additionally, whiteflies, thrips and spider mites reduce yield through foliar feeding, and spider mites and thrips cause fruit scarring. The management of these major pests and the viral diseases they vector to tomatoes relies heavily on pesticides. But tomato producers are caught in a classic “pesticide treadmill” — using frequent pesticide applications that increase the risks of resistance development (due to pests’ rapid life cycles) and cause secondary pest outbreaks (due to the pesticides’ non-target effects on natural enemies), which necessitate further pesticide applications. Therefore, the introduction of new, pest-repellent tomato lines and hybrids can break this cycle at its roots by reducing pest abundance (through repellency to pests) and solving the shortcomings of existing TSWV-resistant lines (which are not arthropod resistant and can still suffer feeding damage).

Such new pest-repellent tomato lines and hybrids, which incorporate natural non-toxic insect resistance from wild tomato, are available from Cornell University tomato breeding program. The leaves and stems of the new lines have trichomes that produce acylsugars, which are highly repellent to many pest species (including thrips and whiteflies) and reduce pest feeding, oviposition, and virus prevalence. But new lines require field testing to integrate into current production practices. Therefore, the proposed project will assess a selection of four experimental thrips-and whitefly-resistant tomato lines and hybrids (varying in acylsugar type and level) for resistance to spider mites, and compatibility with natural enemies of these major pests in the tomato production systems of the Southeast.

We will determine in laboratory studies if select experimental acylsugar lines/hybrids known to control whiteflies and thrips also control twospotted spider mites, which have not yet been directly verified. We will also evaluate non-target effects of these lines on selected natural enemies to confirm that acylsugar-mediated insect resistance can be integrated with biological control. We will measure the effects of acylsugars on pest and natural enemy abundance and virus prevalence in commercial fields in GA and SC. We will consult with our collaborating growers and field test the tomatoes lines in their farms, scale and small, and spring and fall production. We have planned for a variety of outreach activities to engage our stakeholders directly.

A summary of project results prepared for seed companies will encourage mass production of seeds, and will be posted on the Cooperative Extension websites of Clemson University and the University of Georgia. In addition, project updates will occur at vegetable grower meetings, and demonstrations are planned to coincide with the annual Vegetable Field Days in GA and SC. Finally, we will organize workshops on natural plant traits for agriculture for improved pest management at the Southeast Vegetable and Fruit Expo and Southeast Regional Fruit and Vegetable Conference. Therefore, our coordinated research and outreach efforts will help break the “pesticide treadmill” currently challenging sustainable production of tomatoes.

Project Objectives:
  • Determine if acylsugar producing tomato lines provide sufficient resistance to twospotted spider mites and select the most spider mite-resistant line.
  • Determine the compatibility of acylsugar producing lines with biological control of thrips and whiteflies by four known biological control agents.
  • Determine the compatibility of acylsugar producing lines with biological control of spider mites by three predatory mites.
  • Examine impacts of acylsugar producing lines on pest and natural enemy abundance, and virus incidence in southern commercial tomato fields.


Click linked name(s) to expand/collapse or show everyone's info
  • Zachary Snipes (Educator)
  • Dr. David Riley (Researcher)
  • Dr. Gunbhaphur (Gunn) Gill
  • Swikriti Pandey
  • Darlene DeJong
  • Paul Baker
  • James Lisenby
  • John Paulk
  • Andy Carter
  • Matthew Brown
  • Dawn Sikora


Materials and methods:

Objective 1: Determine if acylsugar producing tomato lines provide sufficient resistance to twospotted spider mites and select the most spider mite-resistant line.

Acylsugar tomato lines that produce different types and/or levels of acylsugars were provided by the tomato breeding program at Cornell University led by Mutschler. Since the initial lines with CU071026 background suffered from reduced fruit set, seed set and germination, a new set of lines with greatly improved seed production and germination was created with CU17NBL background. These improved seeds were provided to co-PIs. The new acylsugar lines in CU17NBL background were developed by backcross breeding transferring acylsugar QTL from the lines in CU071026 background to CU17NBL using marker assisted selection. Seed production was performed in greenhouses, for maximum control of plant conditions and to protect against possible seed borne pathogens.

A series of laboratory, greenhouse and field experiments were conducted at facilities of the University of Georgia and Clemson University to evaluate the resistance of selected acylsugar-producing tomato lines against sweetpotato whiteflies and twospotted spider mites from 2019 to 2022.

Research team at Clemson University, under Chong and Gill, compared the susceptibility of acylsugar tomato lines (CU071026, CU17NBL, QTL6/CU17 and QTL6/AS) to a commercial cultivar (Amelia) for twospotted spider mite and sweetpotato whiteflies in a series of laboratory and greenhouse bioassays. In no-choice tests, a scintillation vial filled with water was glued to the bottom of a plastic cup and a hole was drilled in its lid to insert the petiole of fully expanded leaf (third from the top) from each line. A total of 12 leaves from each line were used in this experiment. Five pairs of whiteflies were introduced into each arena to lay eggs, and after 72 hours the whiteflies (adults, nymphs and eggs) were counted under microscopes.  In two-choice tests, the five tomato lines were paired and exposed to twospotted spider mite. Each tomato line was paired with itself or another line, resulting in 10 comparisons. Ten adult female spider mites were introduced to the plastic platform connecting both leaves. Each pair was replicated eight times. The numbers of spider mite motiles (i.e., adults and nymphs) and eggs on each leaf were recorded after 72 hours. In all-choice tests, the acceptance of the five tomato lines to twospotted spider mites and sweetpotato whiteflies was evaluated in the greenhouse. To test for spider mite preference, potted plants from each experimental line were randomly placed together in a block, resulting in a total eight blocks. Spider mites dispersing from infested plants maintained in the same greenhouse were allowed to infest the experimental plants for 12 weeks. After that, three fully expanded leaves (one each from top, middle and bottom thirds) were randomly collected from each plant weekly for three weeks, and the numbers of spider mites (eggs, nymphs and adults) were counted under microscopes. For the no-choice test for whiteflies, one potted plant of each acylsugar and commercial line was isolated in each cage covered with fine mesh. A total of 40 plants (eight from each line) were used. Five pairs of whiteflies were introduced to the plant from each line. Three fully expanded leaves (one each from top, middle and bottom thirds) were randomly collected from each plant biweekly for 8 weeks, and the numbers of whiteflies (eggs, nymphs and adults) were counted under the microscope. Leaf samples of all acylsugar and commercial lines used this these experiments were collected and dried at PDREC, and sent to Cornell University for acylsugar analysis using standard assay developed in the Mutschler lab. The analysis will enable co-PIs to correlated different levels ad types of acylsugars with the observed experimental data on the susceptibility of these selected lines.

Research team at the University of Georgia, under Schmidt and Pandey, conducted a series of greenhouse and laboratory experiments to further evaluate the resistance of selected acylsugar-producing tomato lines against sweetpotato whiteflies. The tomato lines used in the choice and no-choice tests were five acylsugar lines (CU071026, CU17NBL, QTL6/sw5/AS, QTL6/CU17, QTL6/sw5/CU17NBL) and a commercial tomato cultivar (Amelia F1 Hybrid). Whiteflies were obtained from a greenhouse colony maintained on “Red Snapper” tomato plants at the University of Georgia-Tifton Campus. The tomato plants with whitefly colonies were isolated in bugdorms (60x60x60 cm WxDxH, and mesh size 150x150ǀ160 µm aperture). The no-choice test was conducted in a greenhouse by placing a tomato plant from each line in a bugdorm, and then isolating two leaflets per plant with a leaf cage. Ten whitefly adults were introduced into each leaf cage. The leaflets were carefully removed six days after infestation and the number of whitefly eggs and nymphs on each leaflet were recorded. Each line was repeated five times, with ten leaflet samples per tomato line. The choice test was conducted with detached leaflets in a temperature-controlled environmental chamber (30°C, 100 µml photoperiod 16L:8D hours). Petioles of a fully expanded leaflet of all six lines were obtained from tomato plants maintained in a greenhouse. The leaflets were checked for the presence of arthropods or infestation. Only clean leaflets were used in the experiment. A transparent cylindrical cage (20 cm long and 13.7 cm in diameter) was made from a transparent plastic sheet, within which a leaflet from a tomato line was inserted (kept vigorous by inserting the petiole into a scintillation vial with water). Twenty whitefly adults were introduced per cage and allowed the whiteflies six days to interact with the leaflets. The experiment was repeated three times. Hence, we obtained 15 replicates per line. At the end of six days, we removed the cages from the environmental chamber and collected the adult whiteflies and leaflets. Each leaflet was observed under a stereo microscope. We counted and recorded the number of eggs and nymphs present on a leaflet.


Objective 2: Determine the compatibility of acylsugar producing lines with biological control of thrips and whiteflies by four known biological control agents.

Research team at the University of Georgia (UGA), under Schmidt, conducted a greenhouse study to evaluate the efficacy of suppressing whitefly abundance on selected acylsugar tomato lines with the predatory mite, Amblyseius swirskii. (Amblyseius swirskii is also a predator of thrips.) The tomato varieties used in this experiment were three acylsugar lines (CU071026, FA7/AS and QTL6/AS) and two commercial varieties (Amelia and Florida 47). Tomato plants were grown inside the bug dorms (W60 x D60 x H60 cm; mesh size = 150 x 150 | 160 µm aperture). Tomato seedlings at five-leaf stage were infested with whiteflies that were obtained from a clean non-virus colony maintained on the cotton seedlings at Riley’s lab at UGA. Whiteflies were allowed to colonize the plants in a choice test, all varieties in same enclosed area, for a period of three weeks. Each of the six bug dorms contained five plants, one plant of each variety (total of 30 plants). After release of whitefly adults into the dorms, the team sampled whitefly populations weekly by removing one leaflet and counting all eggs, nymphs and adults for three weeks. Each plant received a treatment of one mite sachet, which hung on each plant. After predatory mite introduction, weekly samples of whitefly populations were taken by removing one leaflet per plant variety from each of the cages, for a total of 30 leaves per time period over four weeks. The leaflet samples were transported to the lab for the count of whitefly eggs and nymphs, and count of A. swirskii eggs and adults under stereomicroscopes.

Research team at Clemson University, under Chong and Gill, conducted a series of laboratory bioassays to detect potential reduction in biological control efficacy of selected tomato lines (CU071026, CU17NBL, QTL6/CU17, QTL6/AS and Amelia) to three natural enemies—Delphatus catalinae (whitefly predator), Orius insidiosus (thrips predator) and Eretmocerus eremicus (whitefly parasitoids). The biological control agents were purchased from commercial suppliers. For the Delphastusbioassays, leaflets of each tomato lines were collected and placed in an arena (described for whitefly preference bioassay in Objective 1). The leaflets were infested with adult whiteflies for three days, after which the adult whiteflies were removed, leaving only whitefly eggs on the leaf. One predator was released into each arena and the numbers of consumed whitefly eggs were recorded after 24 hours. For Orius and Eretmocerus bioassays, whole tomato plants were infested with adult whiteflies and leaflets were collected from the tomato plants after whitefly nymphs had reached the third instar. The leaflets were placed individually in arena (described in Objective 1) and one Orius and female Eretmocerus was introduced into the arena for 24 hours. After Orius removal, the leaflets were examined to count the numbers of nymphs consumed. After Eretmocerusremoval, the leaflets were kept in the arena until whitefly nymphs reached the “pupal” stage. The numbers of parasitized pupae were recorded.


Objective 3: Determine the compatibility of acylsugar producing lines with biological control of spider mites by three predatory mites.

Research team at Clemson University, under Chong and Brown, conducted a series of laboratory and greenhouse experiments to determine the compatibility between acylsugar producing tomato lines and three predatory mite species—Phytoseiulus persimilis, Neoseiulus californicus and Neoseiulus andersoni. The predatory mites were purchased from commercial suppliers. Because laboratory and greenhouse bioassay in Objective 1 demonstrated that only CU071026 suffered some level of infestation, and therefore, will require additional intervention in the field to prevent damage and yield loss, this team decided to focus assessments in this objective on CU071026 and Amelia. The laboratory bioassays were conducted as two-choice tests where a pair of tomato leaflets, one of a selected tomato line, infested with twospotted spider mite adults and eggs were placed in an arena described spider mite preference bioassays in Objective 1. The numbers of predatory mites and consumed spider mites or spider mite eggs on each leaflet were recorded after 24 hours. The greenhouse bioassays were conducted as a no-choice test on whole tomato plants of CU071026 (because this is the only variety that had suffered some level of spider mite infestation) and Amelia (the commercial cultivar) to assess if the addition of predatory mites can complement suppression of spider mite population provided by acylsugars. Whole tomato plants were grown in greenhouse and infested with spider mites for 4 weeks before the bioassays. The infested tomato plants were placed individually in plastic tubs filled with water so that the spider mites and predatory mites could not leave the tomato plants and interfered with the biological control activities on the other plants. The spider mite and predatory mite population were sampled weekly over 6 weeks to detect potential interference or complementation of acylsugar-producing tomato line with biological control.


Objective 4: Examine impacts of acylsugar producing lines on pest and natural enemy abundance, and virus incidence in southern commercial tomato fields.

Initially we had secured three commercial growers (Bill Brim of Lewis Taylor Farms, Will Harris of White Oak Pastures, and Matthew Horry of Kindlewood Farms) to participate in field trials in Georgia and South Carolina. The COVID pandemic prevented field research and outreach activities planned for 2020 and 2021. Once travel and field work restrictions were lifted in 2021, we reached out to ten growers in Georgia and South Carolina to plan for implementation of our research results in commercial farms. However, discoveries from the breeding program and our greenhouse trials suggested that the pest resistant varieties are still not producing flowers, fruits and taste at a comparable level to current commercial varieties, and they do not prevent whitefly-transmitted diseases. After reviewing these discoveries, our grower, Extension specialist and agent partners voiced their concerns about the commercial value of these pest resistant varieties at this time and advised the project team to wait until the varieties have been further improved to rival commercial cultivars before conducting the field trials. Paraphrasing of one participating growers: Nothing kills a variety faster than not having the desirable quality even if the variety is resistant to all pests and diseases in the world. Instead of generating poor reputation for an incomplete product (in this case, the tomato lines), the project team decided to suspend the field demonstration of the project based on cooperators’ inputs.

Resistance of the tomato lines to sweetpotato whiteflies were evaluated in the field at the University of Georgia in 2019 to 2022. During these times, insufficient infestation by spider mites limited our ability to assess the resistance of acylsugar-producing lines against spider mites in the field. For whiteflies, five acylsugar-producing lines (CU071026, CU17NBL, QTL6/sw5/AS, QTL6/CU17 and QTL6/sw5/CU17NBL) and a commercial cultivar (Grand Marshall) were evaluated. Seedlings at 5-6 leaf stage were transplanted to raised bed plots covered with white plastic mulch. Each plot represented a replicate of the tomato line and received 10 plants each. Four replicates of each line and the plots were randomly assigned for each line. Whiteflies were allowed to infest the tomato plants naturally after transplant. Radiant® @ 0.7L/ha insecticide was applied once and hand-picking was conducted twice to manage tobacco hornworms and fall armyworms. Weekly sampling was conducted two weeks after transplanting for ten weeks. Three plants from a plot were selected and the number of adult whiteflies were counted. A leaflet sample was taken by selecting three plants randomly in a plot and taking a leaflet from the middle portion of the selected plants. The leaflets were then observed under a stereomicroscope to count whitefly eggs, nymphs and adults. Visual inspections were also conducted to assess the presence of Tomato Yellow Leaf Curl Virus (TYLCV) weekly. However, only two plants out of ten plants in a plot with the experimental acylsugar line QTL6/sw5/CU17NBL displayed symptoms of TYLCV. Disease ratings from bacterial leaf spots caused by Xanthomonas spp. were conducted on all plants at the end of the sampling period.

 The diversity of arthropods (pest and non-pest) in the tomato field was sampled to understand the effect of the acylsugar-producing tomato lines on non-pest arthropods. A 30-second suction sample from the canopy of the middle three tomato plants in each plot using a modified reverse-flow leaf blower into a fine mesh bag at the end of the field experiment period. The contents were transported to the laboratory, where each was sieved, individuals sorted, and categorized to taxa (order level or higher) to provide estimates of arthropod counts in each tomato line.

The abundances of whiteflies and natural enemies on selected acylsugar and commercial lines had been evaluated in an organic field at UGA’s Tifton Campus. In addition to the target predatory mite, A. swirskii, the research team at UGA (led by Schmidt and Dutta) also monitored for other endemic natural enemies colonizing the tomato plants. The tomato varieties used for this experiment were two acylsugar lines (CU071026 and FA7/AS) and two commercial lines (SV7631TD, which is susceptible to Tomato Yellow Leaf Curl Virus, and Skyway 687, which is resistant to TYLCV). The seeds were sown in the greenhouse and planted to the fields at four- to five-leaf stage. Whiteflies were allowed to infest the plants naturally and the mite treatments were applied to the plants right after transplant. In this field experiment the research team tried three different mite application types, i.e. dusting the mites on the top of the plants (top), dusting the mites on the base of the plants (basal) and hanging the mite sachets on the plants (sachet), and prepared a treatment without biological control. The team documented the abundances of whiteflies and A. swirskii over time by removing leaflets from plants then assessing the numbers of arthropods colonizing the plants. The presence of TYLCV was quantified using an immunostrip test.

We have very compelling data on the “deterrent” effects of acylsugar-producing tomato lines on multiple pests in the laboratory bioassays and greenhouse experiments. In lieu of a trial in commercial fields, this project team developed a semi-field trial where tomato lines were planted in fields at experiment stations so that pest management of the experimental tomato lines can be assessed in semi-field conditions. Our results are promising for deterring whiteflies and spider mites, and therefore, our stakeholders and Extension cooperators are very excited by the possibilities of these new tomatoes lines with resistance/ deterrence to whiteflies and spider mites. Once fruit set and quality reaches current commercial levels, and disease is bred into the lines, these will be great for future field trials with cooperators.

Research results and discussion:

Objective 1: Determine if acylsugar producing tomato lines provide sufficient resistance to twospotted spider mites and select the most spider mite-resistant line.

In two-choice laboratory experiments conducted by research team at Clemson University, the abundance of twospotted spider mite founded on all acylsugar lines was significantly lower compared to the commercial line (Amelia). Among the acylsugar lines, QTL/CU17 harbored fewer spider mites compared to CU07, whereas equal numbers of mites were found on CU17, QTL6/CU17 and QTL6/AS. In all-choice test, more spider mites were found on the commercial line than on all acylsugar lines throughout the experiment.

In the first no-choice test to assess the susceptibility of the acylsugar lines to sweetpotato whitefly, conducted at Clemson University, the per capita numbers of whitefly eggs at 72 hours were not significantly different among the acylsugar and commercial line (Amelia). However, in the repeat of the no-choice test, the per capita numbers of eggs after 72 hours were significantly lower on QTL6/CU17 and CU07 compared to the commercial line. Throughout the duration of experiment (72 hours), the presence of acylsugars (i.e. washed vs. unwashed leaves) did not significantly affect whitefly egg numbers in both laboratory no-choice tests. Similarly, the detached leaf (choice) and leaf cage (no-choice) experiments conducted at the University of Georgia also reported no significant difference in whitefly oviposition and nymphs across different lines in the no-choice test. Conversely, in the choice-test (detached-leaf experiment), tomato lines had significantly higher numbers of whiteflies eggs and nymphs on the leaflets of the commercial cultivar, as compared to the acylsugar lines. The number of whiteflies eggs and nymphs was not significantly different between the different acylsugar lines.

In the greenhouse no-choice test conducted at Clemson University, the team found that the numbers of eggs were significantly lower on all acylsugar lines compared to the commercial line. An interaction between line × time was significant for the numbers of nymphs, which could be explained by higher number of nymphs on commercial line compared to the acylsugar lines at four weeks after whitefly introduction. The numbers of adults were also significantly higher on the commercial line than all the acylsugar lines at all sampling times.

These studies showed that when assessed in a small isolated space during the first 72 hours of introduction, sweetpotato whiteflies did not exhibit marked preference for commercial lines over acylsugar lines. However, when assessed over a longer duration and provided with full plants, all acylsugar lines appeared to have significantly lower numbers of whitefly eggs, nymphs and adults. All acylsugar lines were highly resistant to spider mites. These results demonstrate that the acylsugar lines, when planted in the field, will likely be able to harbor lower abundance of whiteflies and spider mites.


Objective 2: Determine the compatibility of acylsugar producing lines with biological control of thrips and whiteflies by four known biological control agents.

Consistent with field results generated under Objective 4, the populations of whiteflies were lower in acylsugar lines (lowest in FA7/AS) compared to the commercial lines in a field in Georgia. The whitefly egg and nymph populations were particularly low in the later sampling dates. Predatory mite recovery was very low during the entire experiment. As a result, the decrease of whitefly population likely could not be attributed to control by the predatory mites, but more likely related to acylsugar lines. This study suggested that A. swirskii established equally poorly on all tomato varieties (similar among the acylsugar lines). This result indicates that while acylsugar lines are good at reducing whitefly numbers, they did not improve the establishment of a known and highly effective whitefly predator, putting in doubt the practicality of combining a highly resistant host plant with biological control.

In laboratory bioassays conducted at Clemson University, the research team found that the foraging efficacy and effectiveness of large predators, i.e., Orius insidiosus and Delphastus catalinae, were not affected by the presence of acylsugars in the experimental lines. These predators consumed as much whitefly eggs or nymphs on the acylsugar-producing lines as they did on the commercial variety. ON the other hand, the parasitoid Eretmocerus eremicus were not successful in parasitizing whitefly nymphs on all the acylsugar-producing tomato lines when compared to the commercial variety. It is likely that the trichomes and sticky acylsugar droplets were repellent or a hindrance to foraging by the parasitoids.


Objective 3: Determine the compatibility of acylsugar producing lines with biological control of spider mites by three predatory mites.

In laboratory bioassay, the three predator mite species (P. persimilis, N. californicus and N. andersoni) demonstrated reduction in the numbers of spider mite motiles and eggs consumed on leaves of CU071026, indicating that CU071026 (and likely other acylsugar producing lines) may interfere with the biological control of spider mites with predatory mites. In the greenhouse experiment, there were no differences between CU071026 and Amelia receiving P. persimilis and N. californicus in percent reduction of spider mite motiles or eggs. Plants where A. andersoni was released had higher percent reduction in spider mite eggs on CU071026 than Amelia. More predatory mites (of all species) survived better on Amelia than CU071026, but the differences were significant only for P. persimilis. There were no differences in predatory mite eggs between cultivars for any mite species. Results from this study indicate that CU071026 likely is not compatible with predatory mites. Therefore, if spider mites break through resistance in this experimental line, another pest management approach (other than biological control with predatory mites) may have to be employed.


Objective 4: Examine impacts of acylsugar producing lines on pest and natural enemy abundance, and virus incidence in southern commercial tomato fields.

In the organic field experiment conducted in 2020, whitefly abundance was significantly affected by tomato variety, with lower numbers observed on acylsugar lines than on the commercial lines. The University of Georgia team observed low recovery of A. swirskii from all tomato varieties, and few endemic natural enemies. Due to poor establishment of predatory mites on tomato plants, A. swirskii application methods had no significant effect on reducing whiteflies on all tomato lines. Although acylsugar lines significantly reduced whitefly abundance compared to commercial lines, they were not effective in reducing disease incidence. In the field experiments in 2021 and 2022, tomato lines had significant effects on the number of whiteflies observed on leaves. The commercial cultivar had significantly higher whitefly pressure as compared to any of the experimental acylsugar lines. Of the acylsugar lines, the CU17NBL had the highest whitefly numbers, and the QTL6/CU17 had the lowest. However, the three with the lowest were not significantly different. Furthermore, results show that from an overall leaf collection level of 702 leaves sampled, all of the acylsugar lines commonly had below 10 whiteflies, and only the CU17NBL or the QTL6/sw5/AS lines had whitefly counts on leaves greater than 20. Conversely, the commercial line had upwards of 60 and commonly greater than 10. It is also during this experiment that we determined that acylsugar-producing tomato lines differed in caterpillar abundance. The highest tobacco hornworm abundance was observed on lines CU071026 and CU17NBL and with no significant difference between the two lines. The lowest tobacco hornworm abundance was observed on QTL6/sw5/AS. Furthermore, tomato lines were observed to have a variety of other arthropods inhabiting these open field plots. We observed Hemiptera including high numbers (3827) of Miridae. Predatory bug families such as Geocoridae (76) and Anthocoridae (4) were also observed. Diptera was the second most abundant with a count of 722. A total of 121 parasitic wasps (order: Hymenoptera) were also observed.

Tomato lines had a significant effect on bacterial leaf spot severity. The research team at the University of Georgia observed significantly high disease incidence in the commercial cultivar Grand Marshall. Of the five experimental acylsugar lines, QTL6/sw5/AS and CU17NBL were observed to have the lowest bacterial leaf spot severity.

Whiteflies also host viruses that are transmitted to plants causing various diseases. None of the acylsugar lines used in these experiments possessed Tomato Yellow Leaf Curl virus-resistant genes yet the TYLCV incidence. When whiteflies were very high in abundance in 2019/2020 studies, high rates of disease were observed in both commercial and acylsugar-producing lines, but in 2021/2022 studies, only two plants out of all the plants in the field experiment were infected. It was difficult to conclude overall disease effects, but appears that disease will spread and no resistance is present in the current acylsugar lines.

The studies demonstrated that whiteflies prefer tomato plants that lack enhanced defensive traits such as high density of glandular trichomes and acylsugar levels. Significantly higher whitefly abundance was found on commercial or non-acylsugar lines. Acylsugars, a secondary metabolite secreted from type IV glandular trichomes in tomato plants is associated with decreased survival and fitness of whiteflies. These defense traits are, however, found non-functional in cultivated/commercial tomato lines. In both the open field tests, greenhouse tests, and choice tests, whiteflies accumulated at higher numbers or preferred non-acylsugar varieties. The results of the laboratory and greenhouse experiments were validated in the controlled field experiments.

Participation Summary


Educational approach:

The project team originally planned to disseminate research findings and recommendations to the vegetable growers and allied industry groups in GA, FL, SC and NC via several routes and outlets. COVID-19 pandemic severely limited the project team’s ability to deliver training opportunities, field demonstrations and on-farm research. The proposal to deliver a hands-on workshop on biological control in vegetable production was also not selected by the organizing committee of a regional vegetable growers meeting and trade show. The plan to develop research and demonstration plots in commercial fields was also suspended based on cooperators’ advices not to demonstrate tomato varieties that are not ready for commercial release. The team resorted to delivering education and contents through county and state grower meetings, and demonstration plots for the annual Vegetable Field Days at university campuses. Data were also provided to seed companies to encourage the mass production of acylsugar-producing tomato varieties. To allow for the adoption of the acylsugar technology even after the end of this project, seeds of several experimental lines (including improved lines from the CU17NBL background) have been deposited in USDA Germplasm System and the Rich Tomato Research Germplasm Bank. The newest lines, which have far less pennellii DNA and look like commercial tomato variety (albeit with yellow fruit), will be released in March or April 2023.

Additional opportunities for scientific outreach included the annual meetings of Entomological Society of America (ESA). Results from this project had been submitted for publication in peer-reviewed journals (currently in review).

This project also provided training opportunities to graduate students, post-doctoral research associates and technicians on plant breeding, host plant resistance screening, and entomological research.

Educational & Outreach Activities

4 Consultations
1 Journal articles
1 Online trainings
7 Webinars / talks / presentations
5 Workshop field days

Participation Summary:

288 Farmers participated
173 Ag professionals participated
Education/outreach description:

This project was introduced to the attendees of the South Carolina Organic and Sustainable Grower Meeting, held virtually 8 December 2020. The attendees received introductory information on the role of host plant resistance in pest management and sustainable agriculture in general and the specific attribute of the tomato lines evaluated in this project during the meeting. The team also presented educational information generated from this project to stakeholders (vegetable growers, extension agents, industry partners, and others) via Pee Dee REC Field Day in 2021 (virtual) and 2022 (in-person). Research plots were demonstrated during the field days (video if virtual) and results from the project were provided to demonstrate the potential of acylsugar tomato lines as a sustainable approach to pest management, particularly spider mites, in field tomato productions.

The Vegetable Breeder Institute Field Day (held virtually due to COVID-19 restriction in 2020 and 2021) was held in August 2020 to 2022. Mutschler presented reports on the progress in creating and characterizing new acylsugar lines to seed companies and breeders, such as Johny’s Selected Seeds, Clover Seeds, Sakata Seed America, and others. The experience of VBI Field Day suggested that the most effective route for this project to disseminate its project results might be through virtual meetings, conferences and field days.

Paper presentations have been provided at the virtual annual meetings of the Entomological Society of America (ESA) and at the Southeastern Branch of ESA. Manuscripts and factsheets generated based on results from this project are been prepared or in review.

Learning Outcomes

38 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation

Project Outcomes

1 New working collaboration
Project outcomes:

Our laboratory and greenhouse experiments have demonstrated high resistance levels of acylsugar-producing lines against twospotted spider mite and sweetpotato whiteflies, two of the most important pests of tomato production in the southeastern United States. The results on whiteflies were validated in controlled field experiment, but the resistance against spider mites could not be confirmed in the fields because of low infestation level during the project years. Despite the demonstrated resistance and excitement by our cooperators, we were not able to establish research and demonstration plots in the commercial fields because of significant yield and quality deficits as well as poor resistance to whitefly-transmitted viral diseases of the current experimental lines. As a result, we were not able to assess the actual value of the acylsugar-producing tomato lines to commercial production, in terms of pest management cost, yields and sustainability. (Hence, the report of 0 growers adopt or change practice.) We are confident, however, that acylsugar-producing tomato lines are significant breakthroughs in incorporating host plant resistance in pest management on tomatoes in the southern United States. Acylsugar-producing lines evaluated in the experiment were highly resistant to twospotted spider mites. In fact, several tested lines were completely void of spider mite infestation. If a commercial cultivar can be developed to express an elevated acylsugar level, there is a possibility that twospotted spider mite may no longer be a major pest of tomatoes. When management of spider mites is no longer a need, growers can save significant cost, time and risk from applying pesticides, thus contributing to the economic and environmental sustainability of their operations. Acylsugar-producing lines also have resistance against whiteflies and are compatible with large biological control agents of whiteflies. The compatibility with biological control will allow growers to adopt biological control to further suppress the whitefly populations that are already low on acylsugar-producing tomatoes. Again, the successful implementation of a combination of host plant resistance and biological control will contribute to economic and environmental sustainability of southern tomato production system. We hope that this project has demonstrated conclusively the potential of acylsugar-producing tomato lines that commercial varieties with the acylsugar traits and desirable yield and fruit characteristics could be developed in the future. We will be glad to see the grower community reap the rewards as a result of this project.

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