Research Project: Mitigating High Consequence Domestic, Exotic, and Emerging Diseases of Fruits, Vegetables, and Ornamentals

Location: Subtropical Plant Pathology Research

2019 Annual Report

Objectives
1. Develop a risk-based index to analyze potential emerging pathogens/pests to identify those with greatest negative impact on agriculture to guide future research. 2. Characterize ecology, biology, epidemiology, genetics, and vector and host (crop and weed) interactions of exotic, newly emerging, re-emerging, and domestic pathogens. 2a. Characterize the basic biology, molecular biology and genetics of ‘Candidatus Liberibacter asiaticus (Las),’ the bacterium associated with citrus huanglongbing (HLB), and molecular mechanisms of host resistance/tolerance to Las infection. 2b. Characterize the basic biology, molecular biology, vector interactions and/or epidemiology of Tomato chlorotic spot virus (TCSV) and other tospoviruses, Squash vein yellowing virus (SqVYV), ilarviruses and other viruses of vegetables, ornamentals, and weeds, and Xanthomonas fragariae [causing angular leaf spot (ALS) on strawberry]. 2c. Characterize meteorological components affecting the epidemiology of Asiatic citrus canker (ACC), and the interactions of the Asian leaf miner with ACC, citrus black spot (CBS), the Asian citrus psyllid with HLB, the interaction of thrips with TSV. 3. Develop/refine and deliver rapid, sensitive reliable detection/sampling methods for high consequence/economic limiting pathogens, including but not limited to citrus canker, huanglongbing, black spot, plum pox virus, seedborne pathogens, and insect vectored viruses of vegetables and ornamentals. 3a. Develop improved detection methods for tospoviruses, Las and Xanthomonads on citrus and strawberry. 3b. Develop new and augment existing surveillance methods and protocols for HLB and the other newly introduced diseases such as CBS and PPV. 4. Develop or improve comprehensive integrated disease management strategies to rapidly find and delimit new disease introductions and develop quarantine and control/mitigation/eradication programs for exotic pathogens. 4a. Develop and use stochastic models to test various disease control strategies for citrus and prunus diseases caused by exotic pathogens. 4b.Develop and implement the most efficacious strategies for disease management of HLB, Xanthomonads of citrus and strawberry, CBS, PPV, and viruses of vegetables and ornamentals.

Approach
The overall approach is to thoroughly characterize plant pathogens causing domestic, exotic and emerging diseases at multiple levels: assessment and prioritization of economic, production and political risk; cellular, molecular and/or biochemical levels of host-pathogen-vector interaction; and traditional and newer stochastic epidemiological analysis at regional and plantation levels. New pathogens will be identified and characterized by biological and traditional cultural methods. Recombinant DNA and genomics technologies will be applied to study host-pathogen interactions. Resulting knowledge will be used to develop new detection and sampling methods, and management strategies, for these pathogens.

Progress Report
Culture of Candidatus Liberibacter asiaticus (Las) in vitro was greatly improved, Las was maintained and propagated in liquid media for months, and caused Huanglongbing (HLB) via feeding psyllid and inoculating to citrus. Selections of citrus seedlings and bud sports were evaluated for HLB resistance/tolerance via graft-based and psyllid inoculations. The resistant/tolerant selections from greenhouse evaluations were further propagated, and planted in Picos Research Farm and commercial grove for field trials. From Las pathogenesis standpoint, we demonstrated that Las 5315 effector induced extreme starch accumulation and chlorosis, typical symptoms of HLB, which provides new targets for interference. Experiments with a controlled experimental system to study aspects of tissue colonization and population development showed bacterial populations and physiological activity peaked early after colonization of new tissues. A small scale, short term protocol for assessing antimicrobial compounds showed only beta-lactam and tetracycline antibiotics were effective against Las. Transmission of tospoviruses, ilarviruses and Squash vein yellowing virus (SqVYV) is continuing to be elucidated. Production scale monitoring of tospoviruses and ilarviruses were investigated. Seeds of fruits from watermelon plants infected with SqVYV were collected for virus testing and seed transmission studies. A novel tobamovirus (Hoya chlorotic spot virus) was isolated from the ornamental crop, Hoya spp., and its biology, host range and genome were characterized. To identify potential inoculum sources for the strawberry angular leaf spot pathogen Xanthomonas fragariae, its survival was examined on 10 common surfaces found in strawberry nurseries at both room temperature and -4 °C (the cold storage temperature for dormant plants in strawberry nurseries) in a designed experiment. The bacteria were artificially inoculated and then collected from each surface with buffer-soaked cotton balls at 10 time points up to 1 year after inoculation. Survival rate was tested with a specialized quantitative polymerase chain reaction (qPCR) procedure and the likelihood of disease transmission was evaluated by rub-inoculating strawberry leaves with the cotton balls. Results showed that X. fragariae survived on several different surfaces for various lengths of time. The longest survival and highest disease transmission rate (up to 9 months after inoculation) was observed on cardboard at -4°C. The information provided by this study can be used to develop improved sanitation protocols for angular leaf spot management in strawberry nurseries. Plots to test the interaction of Asiatic citrus canker (ACC), leafminer, and wind breaks were established in Brazil and data collection continues with Brazilian collaborators. Results indicated that combinations of windbreaks and leafminer control are highly efficacious for canker mitigation. Fourier transform infrared spectroscopy (FTIR) was fully evaluated as a Huanglongbing (HLB) detection tool and found to be of marginal use requiring no further study. Fear of spread by hurricanes of both ACC in Texas and Citrus Black Spot (CBS) in Florida led to development of predictive models to estimated hurricane spread of the pathogens. These are being used by state and federal regulatory agencies to target detection survey. Model accuracy will be assessed in future years when data of hurricane spread is collected. A stochastic simulation risk-based model for CBS spread by trade pathways has been developed. It has been tested against trade pathway data sets, reviewed by collaborators, and is now completed. Meteorological, insect count, and virus incidence data for Tobacco streak virus (TSV) continue to be collected in cucurbit and solanaceous crops. New sets of conventional reverse transcription-polymerase chain reaction (RT-PCR) and qRT-PCR primers for all three genomic RNAs of Tomato chlorotic spot virus (TCSV), Groundnut ringspot virus (GRSV) and Tomato spotted wilt virus (TSWV) have been developed and validated. These primers were used for first detection of TCSV in soybean. Full genome sequence of TCSV isolate from peanut was determined. A new detection method based on two different biomarkers from host response to Candidatus Liberibacter asiaticus infection was developed, which may significantly reduce diagnostic time and cost for citrus Huanglongbing, and serves as pre-symptomatic diagnosis. A multi-pest surveillance method for statewide sweeps for Huanglongbing (HLB) and its vector and several other diseases including Citrus black spot (CBS) has been very successful, is continuously adapted to new disease priorities as requested by USDA APHIS, and is re-deployed yearly. Risk-based residential and commercial survey methods for Asian Citrus psyllid (ACP) and Huanglongbing are in the eighth year of deployment in California. Model validation indicated the models and linked surveillance are highly successful as they continually detect new introductions in Southern California which have now exceeded 1500 as of July 1, 2019. At the request of California Dept. of Food and Agriculture (CDFA), a spatiotemporal analysis of HLB detections resulted in a recommendation of delimiting surveys around new detections to be reduced from 800m to 400m with great savings in manpower and fiscal resources. CDFA now routinely uses the reduced delimiting survey methodology. A risk-based survey to detect plum pox virus (PPV) outbreaks in New York State is integrated into the State/Federal NY PPV eradication program and is in the seventh year of deployment. A risk-based model and survey to detect new PPV introduction is 90% developed and will be deployed in California and perhaps other states when complete. Our surveys developed for multiple pathogens are being used by regulatory agencies and commodity groups to target disease/vector hotspots for existing Huanglongbing and predict new outbreak locations. These are revised each year to optimize surveys to changing disease/vector conditions and will be used for multiple years into the future. Models for Asiatic citrus canker (ACC), Huanglongbing, PPV and Citrus tristeza continue to be augmented and extended in unique ways to address specific regulatory issues as they arise. These models and their refinement continues to be the foundation for future work. Solar thermotherapy reduces the titer of Candidatus Liberibacter asiaticus (Las) and enhances canopy growth by altering gene expression profiles in Huanglongbing- (HLB-) affected citrus plants. Despite the presence of Las in heat-treated commercial citrus, many trees produced abundant flush and grew vigorously for two to three years after treatment. Transcriptome analysis comparing healthy trees to HLB-affected citrus both before and after heat treatment demonstrated that post-treatment transcriptional expression patterns more closely resembled the expression patterns of healthy controls. Overall, these results indicate that solar thermotherapy can be an effective component of an integrated control strategy for citrus HLB. An agent-based model has also been developed to examine the efficacy of Huanglongbing (HLB) control strategies in selected locations in California. A census-travel model to predict introductions of pathogens from foreign sources has been integrated into HLB, Plum Pox Virus (PPV), and other surveys as an added risk factor and has recently published as a stand-alone method. A Bayesian Belief Network model to assess phytosanitary health of seed commodities has been developed, and has been validated for a tomato seed-borne disease and is currently being extended to other seed bacterial, viral and fungal pathosystems. For strawberry, a commercial-scale “Plant Sauna” was constructed at a commercial nursery in California. Heat-treatment research trials were repeated in California with three nursery collaborators. Results reinforced use of the current sauna protocol over traditional hot water treatment. As a result of the California successes, Plant Sauna’s were constructed at two commercial nurseries in North Carolina and Canada in 2019 by the proprietors, and a portion of the planting stock was treated to evaluate the performance under their operational guidelines and environment. Watermelon and pepper germplasm evaluations for Squash vein yellowing virus (SqVYV), powdery mildew and/or tospoviruses are continuing. Virus sanitation trial continued.

Accomplishments
1. Canine detection of Huanglongbing (HLB) in California potentially mitigates an impending state-wide epidemic. HLB epidemics continue to spread worldwide and devastate all citrus industries. The key to mitigation of HLB is early detection and rapid response. Through the HLB MAC (Multi-Agency Coordination) grants program ARS researchers at Fort Pierce, Florida, have trained 20 dogs for early detection (within 2-4 weeks post infection) of HLB where the prior gold standard, polymerase chain reaction (PCR), requires months to detect. The dogs can also detect with 99.06% accuracy whereas PCR detection is ~30-35%, not because the assay is poor, but due to sampling and the problem of selecting the precise infected tissue in a tree with 1-200,000 leaves. In 2018-19 California growers and the California Department Food and Agriculture (CDFA) initiated a team of researchers, industry leaders and regulatory personnel to conduct final validation of the canines in residential citrus environments and concluded that the canines were >92 accurate even under highly variable and in hospitable conditions. The canines are being integrated and deployed into CDFA survey to detect asymptomatic incipient infections of HLB for early response (tree removal). Simulations demonstrate how the impending epidemic is greatly mitigated by the incorporation of canine detection teams for early detection.

2. Risk model and resulting risk-based survey direct California program to combat Huanglongbing (HLB). To effectively mitigate the devastating effects of the HLB epidemic on the California citrus industry, ARS researchers at Fort Pierce, Florida, devised and deployed models and surveillance methods to search the large (300,000 acre) commercial citrus industry in addition to the vast residential plantings of citrus (60 % of residences have at least one citrus tree). At present the state of California has 75-100 surveyors dedicated to this task but they cannot reach all commercial and residential properties. ARS researchers have developed a risk-model which uses 10-15 risk criteria to rank each 1 square mile area in California. Via this model ARS researchers have designed and deployed a risk-based survey in California to target and optimize survey efforts. ARS researchers have also designed a 3-cycle survey based on the risk model to survey the entire state 3 times per year. The risk-based residential and commercial survey methods for Asian Citrus psyllid (ACP) and HLB are in the eighth year of deployment in California and validation indicated they have highly successful and have become the mainstay of the large state-wide survey in California. The survey continually detects new introductions in Southern California, which have now exceeded 1500 as of July 1, 2019. These new introductions are immediately removed and result in a quarantine surrounding the detection. At present the survey is done visually with PCR confirmation of suspicious trees, however, canine detection (see above accomplishment) will likely be integrated into the risk-based survey.

3. Epidemiological models predict the spread of two severe citrus diseases by hurricanes. Asiatic citrus canker (ACC) and citrus black spot (CBS) are two serious diseases that are not only causing economic damage but are severe impediments to international trade of citrus as a commodity. ACC, caused by a bacterium, and CBS, caused by a fungus, are both dispersed by rain splash. In the presence of hurricanes such rain splash can be spread over many miles. Two such hurricanes, Harvey in southeast Texas, and Irma in Southwest Florida potentially spread ACC and CBS, respectively in 2017. ARS researchers at Fort Pierce, Florida, adapted and extended a previously developed hurricane dispersal model to address both diseases and make predictions for where these infections may have spread due to the hurricanes. The results of these model predictions were presented to the appropriate regulatory agencies and science advisory committees. ARS researchers also developed risk-based surveys to target areas rejected by the hurricane models. As result Texas and Florida state regulatory agencies in collaboration with USDA, APHIS have deployed the surveys for early detection of potential spread of these diseases in both states.

4. Spatial and temporal dynamics of Tomato yellow leaf curl virus (TYLCV) and its whitefly vector were characterized in tomato epidemics. Tomato crops in the southeastern U.S. have continuously been impacted by TYLCV since its first detection in Florida in the late 1990s. Current strategies for management focus on farm-centric tactics that rely mainly on strategic insecticide application for whitefly vector control, use of TYLCV-resistant tomato cultivars, rogueing infected plants and various cultural controls. With the exception of resistant cultivars, these approaches have had limited success for controlling both TYLCV and the whitefly. Areawide pest management (AWPM) may be a viable alternative but spatial and temporal dynamics of the virus and vector must be defined for it to be successful. Scouting reports from cooperating growers located across ~20,000 acres in southwest Florida from 2006-2013 and weather data were used to analyze the relationships between weather, whitefly and TYLCV by ARS scientists in Fort Pierce, Florida, in collaboration with university scientists. A strong correlation between virus disease and insect pressure was found in neighboring fields and tended to be more prevalent in the second half of the season. Correlations extended to approximately 2 kilometers. Results are intended to foster development of AWPM as a new and improved strategy for TYLCV epidemic management.

5. Xanthomonas fragariae causes angular leaf spot in strawberry. The pathogen’s association with its host tissue is thought to be a condition for its survival. Consequently, transmission of the pathogen to field production sites occurs almost exclusively through the movement of contaminated planting stock. The aim of this study by ARS scientists in Ft. Pierce, Florida, was to develop a propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR) protocol for specific detection of viable X. fragariae cells. The PMA-qPCR procedure was developed for two different primer pairs: one producing a long amplicon (863 basepairs) and the other a short amplicon (61 basepairs). Both primer pairs were tested with mixtures of viable and heat-killed bacteria cells and with bacteria-spiked strawberry petiole samples. Results showed that long-amplicon PMA-qPCR enabled specific and sensitive detection of X. fragariae with a detection limit of 103 CFU/ml, and it significantly improved the PMA efficiency on differentiating viable from dead bacterial cells relative to short-amplicon PMA-qPCR. PMA-qPCR with long amplicon was able to completely suppress the detection of dead X. fragariae cells from 104-107 colony forming units/milliliter (CFU/ml) in pure bacterial suspensions and from 103-107 CFU/ml in bacteria-spiked strawberry petiole samples. The quantification results from PMA-qPCR for mixtures of viable and dead cells were highly correlated with the predicted bacterial concentrations in a linear relationship (R2 = 0.981). This assay can be useful for identifying inoculum sources in the strawberry production cycle, which may lead to improved disease management strategies.

6. The citrus industry maintains an interest in identifying antimicrobial compounds effective against Candidatus Liberibacter asiaticus (Las) the cause of Huanglongbing (HLB). A vacuum-assisted infiltration assay developed by ARS scientists in Ft. Pierce, Florida, with individual HLB-symptomatic leaves followed by grafting demonstrated that only two classes of antibiotics affected Las viability. This is in contrast with previous published studies that indicated other classes of antibiotics were effective.

7. Field evaluation of integrated management for mitigating citrus Huanglongbing (HLB) in Florida. ARS and University of Florida researchers in Ft. Pierce, Florida, implemented an integrated strategy that includes chemotherapy, thermotherapy, and additional nutrition treatment in field trials over three years. To assess the complex interactions, they used several methods for evaluating the effectiveness of integrated management, including the slopes of the cycle threshold (Ct) increase, the pathogenic index and the decline index from Ct value and tree scores, and the antimicrobial efficacies from pathogenic and decline indices. This comprehensive analysis showed that most of the tested chemicals were effective to some degree in killing or suppressing the Candidatus Liberibacter asiaticus (Las) bacterium. Trunk-injected penicillin was the most effective chemical treatment in all groves, followed by oxytetracycline, and silver nitrate delivered as foliar sprays. Although the steam heat treatment and additional nutrition did not eliminate or suppress Las bacteria over the long term, these treatments did positively affect tree growth and recovery in the short term. Overall, our results provide new insights into HLB control method and strategy for integrated management for HLB epidemic plantations.

8. Symptom determinants for Candidatus Liberibacter asiaticus (Las) infection determined. LasDelta5315 effector induces extreme starch accumulation and chlorosis in Las infection in Nicotiana benthamiana, and the effector SDE1 (5315) targets DEAD-box RNA 2 helicase DDX3 to modulate chlorosis. ARS researchers at Fort Pierce, Florida, demonstrated that the key function of the LasDelta5315 effector induced excessive starch accumulation. Furthermore, by cooperating with other scientists, it was revealed SDE1 gene was comprised of 11 putative promoters localized in three distinct regions, and they act in a complex regulation mode. Four SDE1-interacting proteins were identified from N. benthamiana. This study demonstrated that SDE1 is controlled by a complex promoter, and targets DEAD-box RNA helicase DDX3 to induce chlorosis.

Review Publications
Estevez De Jensen, C., Funderburk, J., Skarlinsky, T., Adkins, S.T. 2019. First report of tomato chlorotic spot virus in soybean (Glycine max L.). Plant Disease. https://doi.org/10.1094/PDIS-05-19-0979-PDN.
Shrestha, D., McAuslane, H.J., Ebert, T.A., Cervantes, F.A., Adkins, S.T., Smith, H.A., Dufault, N., Webb, S.E. 2019. Assessing the temporal effects of Squash vein yellowing virus infection on settling and feeding behavior of Bemisia tabaci (MEAM1) (Hemiptera: Aleyrodidae). Journal of Insect Science. 19(3):5. https://doi.org/10.1093/jisesa/iez036.
Adegbola, R.O., Kemerait, R.C., Adkins, S.T., Naidu, R.A. 2019. Complete genome segment sequences of Tomato chlorotic spot virus from peanut in Haiti. Microbiology Resource Announcements. 8:e00306-19. https://doi.org/10.1128/MRA.00306-19.
Maes, P., Adkins, S.T., Alkhovsky, S.V. et al. 2019. Taxonomy of the order Bunyavirales: second update 2018. Archives of Virology. 164(3):927-941. https://doi.org/10.1007/s00705-018-04127-3.
Abudurexiti, A., Adkins, S.T., Alioto, D. et al. 2019. Taxonomy of the order Bunyavirales: update 2019. Archives of Virology. https://doi.org/10.1007/s00705-019-04253-6.
Rojas, M.R., Macedo, M.A., Maliano, M.R., Soto-Aguilar, M., Souza, J.O., Briddon, R.W., Kenyon, L.A., Rivera Bustamante, R.F., Zerbini, M.F., Adkins, S.T., Legg, J.P., Kvarnheden, A., Wintermantel, W.M., Sudarshana, M.R., Peterschmitt, M., Lapidot, M., Martin, D.P., Moriones, E., Inoue-Nagata, A.K., Gilbertson, R.L. 2018. World management of geminiviruses. Annual Review of Phytopathology. 56:637-677. https://doi.org/10.1146/annurev-phyto-080615-100327.
Tyler-Julian, K., Funderburk, J., Srivastava, M., Olson, S., Adkins, S.T. 2018. Evaluation of a push-pull system for the management of Frankliniella species (Thysanoptera: Thripidae) in tomato. Insects. 9(4):187. https://doi.org/10.3390/insects9040187.
Hilf, M.E., Luo, W. 2018. Behavior of ‘Candidatus Liberibacter asiaticus’ in new growth of citrus suggests the application of a small tree system for evaluating anti-microbial compounds. Journal of Phytopathology. 108(10):1165-1171. https://doi.org/10.1094/PHYTO-12-17-0408-R.
Milne, A.E., Teiken, C., Deledalle, F., van den Bosch, F., Gottwald, T.R., McRoberts, N. 2018. Growers’ risk perception and trust in control options for huanglongbing citrus-disease in Florida and California. Crop Protection. 114(December 2018):177-186. https://doi.org/10.1016/j.cropro.2018.08.028.
Graham, J., Meyers, M., Gottwald, T.R., Bock, C.H. 2018. Effect of windbreaks on wind speed and canker incidence on grapefruit. International Citrus Congress Proceedings. 37:item 2.
Bourhis, Y., Gottwald, T.R., Lopez-Ruiz, F.J., Patarapuwadol, S., van den Bosch, F. 2019. Sampling for disease absence - deriving informed monitoring from epidemic traits. Journal of Theoretical Biology. 461:8-16. https://doi.org/10.1016/j.jtbi.2018.10.038.
Bourhis, Y., Gottwald, T., van den Bosch, F. 2019. Translating surveillance data into incidence estimates. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 374(1776). https://doi.org/10.1098/rstb.2018.0262.
Gottwald, T.R., Luo, W., Posney, D., Riley, T., Louws, F. 2019. A probabilistic census-travel model to predict introduction sites of exotic plant, animal and human pathogens. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 374(1776). https://doi.org/10.1098/rstb.2018.0260.
McRoberts, N., Garcia Figuera, S., Olkowski, S., McGuire, B., Luo, W., Posny, D., Gottwald, T.R. 2019. Using models to provide rapid programme support for California's efforts to suppress Huanglongbing disease of citrus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 374(1776). https://doi.org/10.1098/rstb.2018.0281.
Yang, C., Zhong, Y., Powell, C., Doud, M.S., Duan, Y., Zhang, M. 2018. Antimicrobial compounds effective against Candidatus Liberibacter asiaticus discovered via graft-based assay in citrus. PLoS One. 8(1):17288. https://doi.org/10.1038/s41598-018-35461-w.
Hao, G., Ammar, D., Duan, Y., Stover, E.W. 2019. The 'Candidatus Liberibacter asiaticus' effector LasP235 targeting the citrus chloroplast induces Huanglongbing-like symptoms in transgenic citrus. AGRI GENE. 12:100085. https://doi.org/10.1016/j.aggene.2019.100085.
Zhang, M., Yang, C., Powell, C., Pasco, A., Wang, J., Huang, Y., Duan, Y. 2019. Field evaluation of integrated management for mitigating citrus huanglongbing in Florida. Frontiers in Plant Science. 9(1890):1-12. https://doi.org/10.3389/fpls.2018.01890.
Pitino, M., Allen, V.W., Duan, Y. 2018. Las 5315 effector induces extreme starch accumulation and chlorosis as Ca. Liberibacter asiaticus infection in Nicotiana benthamiana. Frontiers in Plant Science. 9:113.
Ding, F., Allen, V.W., Zhang, S., Duan, Y., Lou, W. 2018. Molecular mechanisms underlying heat or tetracycline treatments for citrus HLB control. Horticulture Research. 5:30. https://doi.org/10.1038/s41438-018-0038-x.
Madden, L., Hughes, G., Bucker-Moraes, W., Xu, X-M., Turechek, W. 2018. Twenty-five years of the binary power law for characterizing heterogeneity of disease incidence. Phytopathology. 108:656-680. https://doi.org/10.1094/PHYTO-07-17-0234-RVW.
Wang, H., McTavish, C., Turechek, W. 2018. Colonization and movement of Xanthomonas fragariae in strawberry Tissues. Phytopathology. 108:681-690. https://doi.org/10.1094/PHYTO-10-17-0356-R.
Pitino, M., Armstrong, C.M., Duan, Y. 2017. Molecular mechanisms behind the accumulation of adenosine triphosphate (ATP) and H2O2 in citrus plants in response to ‘Candidatus Liberibacter asiaticus’ infection. Horticulture Research. 4(Article number 17040). https://doi.org/10.1038/hortres.2017.40.
Keinath, A.P., Ling, K., Adkins, S.T., Hasegawa, D.K., Simmons, A.M., Hoak, S., Mellinger, C., Kousik, C.S. 2018. First report of cucurbit leaf crumple virus infecting three cucurbit crops in South Carolina. Plant Health Progress. 19:322-323. https://doi.org/10.1094/PHP-07-18-0039-BR.
Johns, C., Lee, A., Springer, T., Rosskopf, E.N., Hong, J.C., Turechek, W., Burelle, N.K., Finley, N. 2017. Using NMR-based metabolomics to monitor the biochemical composition of agricultural soils: a pilot study. European Journal of Soil Biology. 83:98-105. https://doi.org/10.1016/j.ejsobi.2017.10.008.
Webster, C.G., Turechek, W., Li, W., Kousik, C.S., Adkins, S.T. 2017. Development and evaluation of ELISA and qRT-PCR for identification of Squash vein yellowing virus in cucurbits. Plant Disease. 101(1):178-185. https://doi.org/10.1094/PDIS-06-16-0872-RE.
Kousik, C.S., Ikerd, J.L., Turechek, W. 2017. Development of Phytophthora fruit rot caused by Phytophthora capsici on resistant and susceptible watermelon fruit of different ages. Plant Disease. 102(2)370-374. https://doi.org/10.1094/PDIS-06-17-0898-RE.
Kousik, C.S., Ikerd, J.L., Mandal, M., Adkins, S.T., Turechek, W. 2018. Watermelon germplasm lines: USVL608-PMR, USVL255-PMR, USVL313-PMR and USVL585-PMR with broad resistance to powdery mildew. HortScience. 53(8):1212-1217. https://doi.org/10.21273/HORTSCI12979-18.
Kousik, C.S., Ikerd, J.L., Mandal, M., Adkins, S.T., Webster, C.G., Turechek, W. 2018. Powdery mildew resistant bottle gourd germplasm lines: USVL351-PMR and USVL482-PMR. HortScience. 53(8):1224-1227. https://doi.org/10.21273/HORTSCI13067-18.
Gent, D.H., Mahaffee, W.F., Turechek, W., Ocamb, C.M., Twomey, M.C., Woods, J.L., Probst, C. 2018. Risk factors for bud perennation of Podosphaera macularis on hop. Phytopathology. https://doi.org/10.1094/PHYTO-04-18-0127-R.