Progress 01/01/24 to 12/31/24
Outputs
Target Audience:The target audience reached during this project period include peach producers, Extension personnel, and researchers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?A PhD student, a high school student, and one technician were trained to conduct experiments and research in this project. The PhD student presented results from this project at the annual conference of American Phytopathological Society (APS), the Southern Division (SD)-APS meeting, and Clemson CAFLS Graduate Research Symposium. The PI attended SD-APS meetings, SC peach production meeting, and presented project results at the 15th International Conference on Plant Pathogenic Bacteria and the 5th International Symposium of Biological Control of Bacterial Plant Diseases. How have the results been disseminated to communities of interest?Project results were presented to Extension personnel and researchers at annual APS, SD-APS, the Clemson CAFLS Graduate Research Symposium, and the 5th International Symposium of Biological Control of Bacterial Plant Diseases. Project results were communicated to growers via personal visits. What do you plan to do during the next reporting period to accomplish the goals?Finish developing the epidemiological model. Publish the remaining manuscripts from this project and communicate the results to stakeholders.
Impacts
What was accomplished under these goals?
Objective 1. Examine the prevalence of oxytetracycline-resistant and copper-tolerant Xap strains in southeastern peach orchards and evaluate the impact of these strains on current chemical control programs. The 2024 summer sampling was done in June and July from the same trees in the seven commercial peach orchards (20-30 trees per orchard) sampled in 2023. On each tree, bacterial spot incidence and severity were rated on 20 fruit and the leaves of 10 one-year-old twigs; one sample each of symptomatic leaf and fruit were used for Xap isolation. A total of 406 Xap isolates were collected and screened on nutrient agar amended with copper sulphate pentahydrate (CSP: 0, 150, 175, and 200 ppm) or oxytetracycline (25 ppm). The prevalence of oxytetracycline resistance in Xap populations was similar as last year but the prevalence of high copper tolerance increased. All the oxytetracycline resistant isolates were further screened on nutrient agar amended with up to 250 ppm of oxytetracycline and for the presence of tet genes in PCR assays. A manuscript is being prepared for submission. Objective 2. Identify genetic determinants of oxytetracycline resistance and copper tolerance in Xap. Gene functional analysis revealed the core genes conferring copper resistance in a Xap strain. Duplication of this copper resistance gene cluster increased the resistance level compared to the single copy, while deletion of both copies of this cluster caused the loss of copper resistance. The copper resistant genes and phenotypes were able to be transferred to other bacterial species via conjugation. A manuscript is being prepared for submission. Objective 3. Evaluate novel chemicals for improved control of Xap populations. The interaction between nano-borate zinc product and other novel chemicals for Xap control were evaluated in the greenhouse and field. The data are being analyzed. Objective 4. Compare the overwintering capability of chemical-resistant strains and sensitive strains and develop an epidemiological model based on environmental factors during the dormant season to predict the inoculum levels for the subsequent growing season. No difference was observed in overwintering capability of XAP strains with different chemical sensitivities, suggesting that these OTC-resistant and copper-tolerant strains may persist and accumulate in peach orchards across seasons. A manuscript has been submitted. The inoculum prediction model is being developed.
Publications
- Type:
Peer Reviewed Journal Articles
Status:
Published
Year Published:
2024
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2024. Development of a long amplicon PMA-qPCR assay for detection of viable Xanthomonas arboricola pv. pruni cells in peach trees. Plant Dis. DOI: 10.1094/PDIS-01-24-0012-RE.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2024
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2024. Exploring the winter survival of Xanthomonas arboricola pv. pruni strains with different chemical sensitivities in peach trees. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2024
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2024. Overwintering capability of Xanthomonas arboricola pv. pruni strains with different chemical sensitivities in peach trees. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2024
Citation:
Panth, M.#, E. Noh#, G. Schnabel, and H. Wang. Overwintering capability of Xanthomonas arboricola pv. pruni strains with different chemical sensitivities in peach trees. Southern Division APS Meeting, Columbia, SC, February 2024.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2024
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. Exploring the overwintering survival of Xanthomonas arboricola pv. pruni strains with different chemical sensitivities in peach trees. CAFLS Graduate Research Symposium, Clemson, SC, August 2024.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2024
Citation:
Panth, M., E. Noh, G. Schnabel, D. Anco, and H. Wang. Exploring the overwintering survival of Xanthomonas arboricola pv. pruni strains with different chemical sensitivities in peach trees. APS Annual Meeting, Memphis, TN, July 2024.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2024
Citation:
Wang, H., M. Panth, J. Pereira, D. Moreno#, C. N. Hancock, R. Carvalho, G. Schnabel, P. Brannen, S. Santra, and J. Jones. Exploring mechanisms of chemical resistance in Xanthomonas arboricola pv. pruni and strategies to mitigate resistance and improve disease control. 15th International Conference on Plant Pathogenic Bacteria and the 5th International Symposium of Biological Control of Bacterial Plant Diseases, Blacksburg, Virginia, July 2024.
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Progress 01/01/23 to 12/31/23
Outputs
Target Audience:The target audience reached during this project period includepeach producers, Extension personnel, and researchers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two graduate students and one technician were trained to conduct experiments and research in this project. One student presented results from this project at the annual conference of American Phytopathological Society (APS), the southern division (SD)-APS meeting, Southeastern Professional Fruit Worker's Conference (SPFWC), Clemson CAFLS Graduate Research Symposium, and CU-CAT Ag Tech Spotlight Event. The PI attended annual APS and SD-APS meetings, SC peach production meeting, and presented project results at the NIFA PD meeting and an invited seminar at Brigham Young University. A co-PI attended the annual APS meeting. How have the results been disseminated to communities of interest?Project results were presented to Extension personnel and researchers at annual APS, SD-APS, and SPFWC conferences, NIFA PD meeting, the Clemson CAFLS Graduate Research Symposium, and CU-CAT Ag Tech Spotlight Event. The project was also presented in an invited seminar to researchers and students at Brigham Young University. Project results were communicated to growers via personal visits. What do you plan to do during the next reporting period to accomplish the goals?Objective 1. The annual survey will be continued in Year 4 in the seven commercial peach orchards; disease ratings will be collected and Xap isolates will be evaluated for sensitivity to copper and oxytetracycline. A manuscript will be prepared for publication. Objective 2. We plan to finish the functional analysis of the copper tolerance genes in Xap and prepare a manuscript for publication. Objective 3. Lab and greenhouse assays for more combinations of novel chemicals will be completed. A manuscript will be prepared for publication. Objective 4. The viable Xap overwintering on peach trees in both the research field and commercial orchards will be quantified by PMA-qPCR and/or culturing in spring 2023. A model will be built to predict the inoculum levels on peach trees based on the weather factors.
Impacts
What was accomplished under these goals?
Objective 1. Examine the prevalence of oxytetracycline-resistant and copper-tolerant Xap strains in southeastern peach orchards and evaluate the impact of these strains on current chemical control programs. The 2023 summer sampling was done in early June and late July/early August from the same trees in the seven commercial peach orchards (20-30 trees per orchard) sampled in 2021 and 2022. On each tree, bacterial spot incidence and severity were rated on 20 fruit and the leaves of 10 one-year-old twigs; one sample each of symptomatic leaf and fruit were used for Xap isolation. A total of 439 Xap isolates were collected and screened on nutrient agar amended with copper sulphate pentahydrate (CSP: 0, 150, 175, and 200 ppm) or oxytetracycline (25 ppm). The prevalence of oxytetracycline resistance and copper tolerance in Xap populations was similar as last year. All the oxytetracycline resistant isolates were further screened on nutrient agar amended with up to 250 ppm of oxytetracycline and for the presence of tet genes in PCR assays. Objective 2. Identify genetic determinants of oxytetracycline resistance and copper tolerance in Xap. This year, we tried cloning different combination of candidate genes from the copper resistant plasmid into a copper sensitive strain. Four of the copper resistant genes together were shown to confer copper resistance up to 200 ppm of CSP, which is lower than the resistant level in the wild type strain. More combinations of copper resistant candidate genes are being tested now. Objective 3. Evaluate novel chemicals for improved control of Xap populations. We published a manuscript featuring the new nano-borate zinc product for Xap control on Environmental Science: Nano. The interaction between this nano-borate zinc product and other novel chemicals for Xap control are being evaluated in the lab and greenhouse. Objective 4. Compare the overwintering capability of chemical-resistant strains and sensitive strains and develop an epidemiological model based on environmental factors during the dormant season to predict the inoculum levels for the subsequent growing season. From the analysis of the overwintering Xap population in 2022, peach twigs inoculated during the leaf drop period had the most spring cankers and the highest number of overwintered XAP populations. There were significant differences in overwintering capability among XAP strains with different chemical sensitivities. In March 2023, ten twigs per tree were collected and rated for spring canker from the same trees in the seven commercial peach orchards described in objective 1. Thirty buds from ten twigs (~3 buds per twig) per tree were pooled for PMA treatment and DNA extraction. The twig samples from the 2022 inoculated trees in the research orchard were also collected in March 2023, rated for spring canker, and processed for bacterial isolation, PMA treatment and DNA extraction. The DNA is stored in -20°C for future qPCR analysis. During the 2023 growing season, each tree inoculated in the previous years developed bacterial spot symptoms thus no further inoculation was conducted. To study the spread and distribution of Xap strains in the research orchard, bacterial extracts from the peach leaves collected from four directions per tree during the leaf drop period were plated on media amended with CSP (0 and 200 ppm) or oxytetracycline (25 ppm) for colony count. The DNA from the bacterial extracts were stored at -20 °C for further qPCR analysis. The quantity of Xap on five twigs per tree during the leaf drop period was assessed with PMA-qPCR. A manuscript featuring the PMA-qPCR assay is in submission.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2023
Citation:
Pereira, J., D. Moreno, G.G. Giannelli, E. Davidson, J.R. Huertas, H. Wang, and S. Santra. 2023. Targeted delivery of oxytetracycline to the epidermal cell junction and stomata for crop protection. Environ. Sci. Nano. DOI:10.1039/D3EN00140G.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2023
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2023. Examining the overwintering capability of Xanthomonas arboricola pv. pruni on peach trees using PMA-qPCR. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2023
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2023. Development of a PMA-qPCR assay for detection of viable Xanthomonas arboricola pv. pruni cells in peach trees. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2023
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2023. Quantification of viable Xanthomonas arboricola pv. pruni cells in peach trees using propidium monoazide quantitative PCR (PMA-qPCR). SEPFWC Proceedings. In press.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
Wang, H. Exploring mechanisms of chemical resistance in Xanthomonas arboricola pv. pruni and strategies to mitigate resistance and improve disease control. NIFA PD Meeting, National Harbor, MD, November 2023.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
Panth, M., G. Schnabel, and H. Wang. Exploring mechanisms of chemical resistance in Xanthomonas arboricola pv. pruni and strategies to mitigate resistance and improve disease control. CAFLS Graduate Research Symposium, Georgetown, SC, October 2023.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
Panth, M., E. Noh, G. Schnabel, and H. Wang. 2023. Examining the overwintering capability of Xanthomonas arboricola pv. pruni on peach trees using PMA-qPCR. CU-CAT Ag Tech Spotlight Event, Clemson, SC, September 2023.
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Progress 01/01/22 to 12/31/22
Outputs
Target Audience:The target audience reached during this project period include peach producers, Extension personnel, and researchers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Three graduate students and two undergraduate students were trained to conduct experiments and research in this project. Two students attended the annual conference of American Phytopathological Society (APS) to present the results from this project. One student presented at the southern division-APS meeting and Clemson CAFLS Graduate Research Symposium. Two students presented at the Southeastern Professional Fruit Worker's Conference (SPFWC). The PI attended the annual APS and SPFWC meetings and was invited to present the project results at the SC Statewide Peach meeting, SC peach production meeting, GA Plant Pathologists Association Meeting, and the Materials Innovation for Sustainable Agriculture Symposium. A co-PI attended the annual APS meeting. How have the results been disseminated to communities of interest?PI Wang presented the project results to the peach producers, Extension personnel, and researchers at the SC Statewide Peach meeting and SC peach production meeting. The PI and students also presented results to the researchers and Extension personnel at the GA Plant Pathologists Association Meeting, the Materials Innovation for Sustainable Agriculture Symposium, annual APS and SPFWC conferences, the southern division-APS meeting, and the Clemson CAFLS Graduate Research Symposium. What do you plan to do during the next reporting period to accomplish the goals?Objective 1. The annual survey will be continued in Year 3 in the seven commercial peach orchards; disease ratings will be collected and Xap isolates will be evaluated for sensitivity to copper and oxytetracycline. Objective 2. We will keep conducting the functional analysis of the copper tolerance genes in Xap. Objective 3. The best performing novel chemicals from the previous lab and greenhouse assays will be tested in combination and in different dosages in the greenhouse and field. Objective 4. We will spray chemicals in the dormant season to study their impact on the overwintering Xap population. The viable Xap overwintering on peach trees in both the research field and commercial orchards will be quantified by PMA-qPCR and/or culturing in spring 2023. We will keep maintaining the weather stations and collecting weather data to build a model to predict the inoculum levels on peach trees based on the weather factors.
Impacts
What was accomplished under these goals?
Objective 1. Examine the prevalence of oxytetracycline-resistant and copper-tolerant Xap strains in southeastern peach orchards and evaluate the impact of these strains on current chemical control programs. The 2022 summer sampling was done in early June and late July/early August from the same trees in the seven commercial peach orchards (20-30 trees per orchard) sampled in 2021. On each tree, bacterial spot incidence and severity were rated on 20 fruit and the leaves of 10 one-year-old twigs; one sample each of symptomatic leaf and fruit were used for Xap isolation. A total of 379 Xap isolates were collected and screened on nutrient agar amended with copper sulphate pentahydrate (0, 150, 175, and 200 ppm) or oxytetracycline (25 ppm). Low copper tolerance is still prevalent in all orchards and the number of high copper tolerant isolates increased in 2022. The three orchards where oxytetracycline resistant Xap populations were found in 2021 were still the ones harboring the resistance but the percentage of resistant isolates was slightly higher in 2022. All the oxytetracycline resistant isolates were further screened on nutrient agar amended with up to 250 ppm of oxyetetracycline and for the presence of tet genes in PCR assays. Objective 2. Identify genetic determinants of oxytetracycline resistance and copper tolerance in Xap. Illumina sequencing revealed cop gene clusters in a Xap strain with high copper tolerance, however, these cop genes were not able to be assembled into chromosome or plasmid with the short sequence reads. We tried to knock out two operons, one at a time, to verify their contribution to copper tolerance with sucrose counter selection, however, it was not successful. Then we did the nanopore sequencing of the strain and found duplication of these cop genes on the same plasmid, which explains why our knockout experiments failed. Thus, instead of gene knockout, we are currently inserting genes into sensitive strains to evaluate their contribution to copper tolerance. We also did the conjugation assay and were able to successfully transfer the copper tolerance genes and phenotype from Xap to a copper sensitive X. perforans strain. Objective 3. Evaluate novel chemicals for improved control of Xap populations. More lab and greenhouse assays were conducted on different dosages of novel chemicals. A new nano-zinc product developed by Dr. Santra's group in UCF was found to inhibit Xap growth in both lab and greenhouse without causing phytotoxicity. The SEM and laser scanning confocal microscopy analysis at UCF revealed that this nano-zinc product tends to deposit in the junction between epidermal cells and stomata on peach leaves, the major sites for bacterial colonization. It also pulled oxyetracycline to these leaf features after the spray of both chemicals combined and increased the oxytetracycline coverage on peach leaves. The lab assays at CU showed an overall additive effect between the nano-zinc and oxytetracycline against all five Xap strains tested. A manuscript is being prepared for submission. Objective 4. Compare the overwintering capability of chemical-resistant strains and sensitive strains and develop an epidemiological model based on environmental factors during the dormant season to predict the inoculum levels for the subsequent growing season. We optimized the PMA-qPCR assay for quantifying overwintering Xap in peach trees. The assay was tested against Xap and 25 other closely-related bacterial species. It was able to specifically detect as low as 103 and 104 CFU/ml of viable Xap cells in pure bacterial suspension and bacteria-spiked twig extracts, respectively, with the presence of up to 107 CFU/ml of dead Xap cells. In March 2022, ten twigs per tree were collected and rated for spring canker from the same trees in the seven commercial peach orchards described in objective 1. Thirty buds from ten twigs (~3 buds per twig) per tree were pooled for PMA treatment and DNA extraction. The twig samples from the 2021 inoculated trees in the research field were also collected in March 2022, rated for spring canker, and processed for bacterial isolation, PMA treatment and DNA extraction. The DNA is stored in -20°C for future qPCR analysis. We repeated the inoculation trial in the research field in 2022 and have collected the twigs at 3 h after each inoculation to quantify the baseline level of Xap inoculum on twigs.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2022
Citation:
Herbert, A., C.N. Hancock, B. Cox, G. Schnabel, D. Moreno, R. Carvalho, J. Jones, M. Paret, X. Gene, and H. Wang. 2022. Oxytetracycline and streptomycin resistance genes in Xanthomonas arboricola pv. pruni, the causal agent of bacteria spot in peach. Front. Microbiol. doi:10.3389/fmicb.2022.821808.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Panth, M., G. Schnabel, and H. Wang. 2022. Examining the prevalence and persistence of oxytetracycline resistant and copper tolerant strains of Xanthomonas arboricola pv. pruni in the southeastern peach orchards. Phytopathol. 112:S2.13.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2022
Citation:
Moreno, D., G. Schnabel, and H. Wang*. 2022. Evaluation of novel chemicals for bacterial spot management in peach. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2022
Citation:
Panth, M., E. Noh, G. Schnabel, P. Brannen, and H. Wang*. 2022. Prevalence and persistence of oxytetracycline resistant and copper tolerant strains of Xanthomonas arboricola pv. pruni in peach orchards of southeastern USA. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2022
Citation:
Panth, M., E. Noh, G. Schnabel, P. Brannen, and H. Wang*. 2022. Examining the prevalence and persistence of oxytetracycline resistant and copper tolerant Xanthomonas arboricola pv. pruni in peach orchards of the Southeastern US. SEPFWC 2022 Proceedings. In press.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2022
Citation:
Pereira, J., D. Moreno, G.G. Giannelli, E. Davidson, J.R. Huertas, H. Wang**, and S. Santra. 2022. Safeguarding the leaves through targeted delivery of oxytetracycline. SEPFWC 2022 Proceedings. In press.
- Type:
Theses/Dissertations
Status:
Awaiting Publication
Year Published:
2022
Citation:
Herbert, A. 2022. Identification and genetic characterization of oxytetracycline resistance in Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot in peach.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Panth, M., G. Schnabel, and H. Wang. Incidence and prevalence of chemical resistant Xanthomonas arboricola pv. pruni in the southeastern peach orchards. CAFLS Graduate Research Symposium, Florence, SC, August 2022.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Wang, H. Management of bacterial spot in the southeastern peach production. 2022 Materials Innovation for Sustainable Agriculture (MISA) Symposium, Orlando, FL, October 2022.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Wang, H. Oxytetracycline resistance in Xanthomonas arboricola pv. pruni: mechanisms and current status. 2022 GA Plant Pathologists Association (GAPP) Meeting, Keynote speaker, Savannah, GA, May 2022.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Wang, H. Updates on peach bacterial spot. SC Statewide Peach Meeting, virtual, March 2022.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2022
Citation:
Wang, H. Updates on peach bacterial spot. SC Peach Production Meeting, Edgefield, SC, February 2022.
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Progress 01/01/21 to 12/31/21
Outputs
Target Audience:The target audience reached during this project period includepeach producers, Extension personnel, and researchers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two graduate students were trained to conduct experiments and research in this project. A graduate student attended the annual conference of American Phytopathological Society to present the results from this project. The PI attended the Southeast Regional Fruit & Vegetable Conference, SC peach production meeting, Michigan peach production meeting, and the southeastern professional fruit workers conference and presented this project. How have the results been disseminated to communities of interest?PI Wang presented this project atthe Southeast Regional Fruit & Vegetable Conference, SC peach production meeting, and Michigan peach production meeting to the peach producers, Extension personnel, and researchers. Theresults from this project also were presented to the researchers at the annual conference of American Phytopathological Society and the southeastern professional fruit workers conference. What do you plan to do during the next reporting period to accomplish the goals?Objective 1. The association of different spray programs with chemical resistance/tolerance levels and prevalence in the Xap populations collected from Year 1 will be analyzed. A subset of resistant/tolerant Xap strains will be evaluated for impact on current chemical control programs by inoculation of peach trees in the greenhouse. Xap isolates will be collected from the same commercial farms in South Carolina and Georgia and evaluated for chemical sensitivity to copper and oxytetracycline in Year 2. Objective 2. We will keep conducting the functional analysis of the copper resistance genes in Xap. The functional tet and cop genes identified in the sequenced Xap strains will be screened via PCR in the rest of resistant/tolerant strains collected in Objective 1 to determine the relationship between strain genotype and phenotype for both copper and oxytetracycline resistance. Objective 3. We will keep screening more novel chemicals in the lab and greenhouse. The novel chemicals showing the best disease control with the least phytotoxicity from the greenhouse assay will be further tested in the field. Objective 4. The viable Xap overwintering on peach trees in both the research field and commercial orchards will be quantified by PMA-qPCR and the culturing method. Twigs developing canker in early spring will be counted and bacteria will be isolated from active twig cankers and evaluated for resistance/tolerance to oxytetracycline and copper. Association between the quantity of viable bacteria overwintered on peach trees and the disease incidence/severity ratings during the subsequent growing season will be analyzed. The best novel chemicals identified from Objective 3 will be evaluated on some inoculated trees during dormancy for their effect on reducing the inoculum level before the subsequent growing season. We will keep maintaining the weather stations and collecting weather data to build a model to predict the inoculum levels on peach trees based on the weather factors.
Impacts
What was accomplished under these goals?
Objective 1. Examine the prevalence of oxytetracycline-resistant and copper-tolerant Xap strains in southeastern peach orchards and evaluate the impact of these strains on current chemical control programs. Bacterial spot was rated on peach leaves and fruit three times during May-August in seven farms inSouth Carolina and Georgia. In each farm, 20-30 trees of an O'Henry orchard were sampled. On each tree, bacterial spot incidence and severity were rated on 20 fruit and the leaves of 10 one-year-old twigs; one sample each of symptomatic leaf and fruit were used for Xap isolation. A total of 506 Xap isolates were collected and screened on oxytetracycline- and copper-amended media. Isolates with low levels of copper tolerance were prevalent in all the farms sampled and the isolates with oxytetracycline resistance were found in three of the farms. Objective 2. Identify genetic determinants of oxytetracycline resistance and copper tolerance in Xap. A subset of oxytetracycline-resistant and copper-tolerant strains were sequenced for their whole genomes. The genome sequence analysis revealed a plasmid-borne tetracycline resistance gene in oxytetracycline-resistant Xap strains and clusters of copper resistance genes in a Xap strain with high level of copper tolerance. Gene functional analysis revealed that the tetracycline resistant gene was the determinant of oxytetracycline resistance in Xap and it can be transferred to other Xanthomonas species via conjugation. Functional analysis of the copper resistance genes is being conducted. Objective 3. Evaluate novel chemicals for improved control of Xap populations. A number of nanomaterials and other chemicals that have shown promising results in controlling other Xanthomonas pathogens were tested against Xap with different chemical sensitivity phenotypes in the lab and greenhouse. The nano-zinc products showed the best antibacterial effect in vitro, and they were shown to reduce bacterial spots on leaves inoculated with copper- and oxytetracycline-sensitive Xap. The addition of EBDC was found to significantly increase the copper efficacy on controlling Xap. We also investigated the mode of action of the chemicals by examining the bacteria using epi-fluorescence microscopy and scanning electron microscopy after exposure to chemicals. Objective 4. Compare the overwintering capability of chemical-resistant strains and sensitive strains and develop an epidemiological model based on environmental factors during the dormant season to predict the inoculum levels for the subsequent growing season. The Xap-specific PMA-qPCR assay has been designed and is currently being optimized to quantify the live overwintering Xap populations on twigs and buds. In the research field, peach trees were spray-inoculated with four Xap strains representing four different phenotypes of chemical sensitivity in June, August, and November. We installed the weather stations in the research field and seven commercial peach orchards where we sampled in Objective 1. The weather data (temperature, humidity, precipitation, wind, leaf wetness, and solar radiation) are being monitored in real time.
Publications
- Type:
Journal Articles
Status:
Submitted
Year Published:
2021
Citation:
Herbert, A., C.N. Hancock, Cox, B., Schnabel, G., Moreno, D., Carvalho, R., Jones, J. Paret, M., Geng, X., and Wang, H. Oxytetracycline and streptomycin resistance genes in Xanthomonas arboricola pv. pruni, the causal agent of bacteria spot in peach. Frontiers in Microbiology. Submitted.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2021
Citation:
Wang, H., Herbert, A., Hancock, C.N., Cox, B., Schnabel, G., Moreno, D., Carvalho, R., Jones, J., and Paret, M. Oxytetracycline and streptomycin resistance in Xanthomonas arboricola pv. pruni, the causal agent of bacterial spot in peach. Proceedings of the 2021 Southeastern Professional Fruit Workers Conference.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2021
Citation:
Herbert, A., Hancock, C.N., Negrete, D., Schnabel, G., Cox, B., and H. Wang. 2021. First report of oxytetracycline and streptomycin resistance genes in Xanthomonas arboricola pv. pruni, the causal agent of bacteria spot in peach. Phytopathol. In press.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Wang, H. Chemical and biological control of peach bacterial spot. Southeast Regional Fruit and Vegetable Conference, Virtual, 2021.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Wang, H. Management of peach bacterial spot. SC Peach Production Meeting, Virtual, 2021.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2021
Citation:
Wang, H. Bacterial spot management and discussion. Michigan Spring Peach Meeting, Virtual, 2021.
- Type:
Other
Status:
Published
Year Published:
2021
Citation:
Attaway, D. 2021. Clemson researcher leads effort against new Xap strains that threaten peaches and other stone fruits. https://news.clemson.edu/clemson-researcher-leads-effort-against-new-xap-strains-that-threaten-peaches-and-other-stone-fruits/. Also appeared on Market Bulletin and as a top hit on Southeast FarmPress Daily Sunday edition.
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