@article{duin_montalban_joglekar_d'amico-willman_ritchie_fagen_huerta_2024, title={First Report of Bacterial Leaf Spot Disease on Sesame (<i>Sesamum indicum</i>) Caused by <i>Pseudomonas syringae</i> pv. <i>sesami</i> in North Carolina}, volume={6}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-02-24-0292-PDN}, abstractNote={In July 2022, dark brown to black, angular, water-soaked lesions were observed on sesame leaves (Sesamum indicum L.) in a research plot established to assess yield potential for eight varieties at the North Carolina (NC) Sandhills Research Station (Chavez 2023). Symptoms were indicative of a bacterial leaf spot (BLS). At early flowering stage, leaf spots were present on scattered plants; varieties ES108, SS3301, and ES201 exhibited up to 75% disease prevalence, with lower frequency in ES103, S39, S4302, S3251, and S3276. Symptomatic leaves from 3-4 plants were collected on four different dates from July through September. A section of symptomatic tissue was excised and macerated in sterile deionized water (SDW). A 10 µL aliquot was streaked onto SPA medium (15 g sucrose, 5.0 g proteose peptone, 0.50 g MgSO4 7H2O, 0.25 g K2HPO4, 15 g agar per liter of SDW) and incubated at 28ºC. After 72 h, numerous, smooth, white-cream colored, convex-shaped, colonies were individually isolated. Five randomly selected isolates from the different collection dates, designated as AHP108-AHP111 and AHP116, were genotyped. The 16S rRNA, gyrB, rpoD, and gapA genes were sequenced (Heuer et al. 1997; Hwang et al. 2005) and deposited to NCBI (GenBank Accessions: P213467- PP213470; OQ628040-OQ628042; PP214983-PP214994; and PP255798). These five isolates shared 100% sequence identity for gyrB and rpoD. AHP108-AHP111 shared 100% sequence identity for 16S rRNA and gapA, with 99.7% and 90.8% identity, respectively, for AHP116. A phylogenetic tree was inferred from a maximum-likelihood analysis of concatenated gyrB, rpoD, and gapA sequences of the five isolates and the top 11 hts from a blastn search of the NCBI nucleotide database. Those hits included closely related sequences from Pseudomonas syringae pv. sesami type strains ICMP 763T and ICMP 7459T. Based on this phylogenetic analysis AHP108-AHP111 and AHP116 are P. syringae pv. sesami. Recent genomic analysis suggests this pathovar is part of P. amygdali (Gomila et al. 2017), but an official name change has not been proposed. Each of the five isolates were infiltrated into leaves of sesame varieties ES108, ES103, and S327, consistently resulting in similar symptoms. Thus, strain AHP116, as a representative, was used to fulfill Koch's postulates using five, 30-day-old potted sesame plants (var. S3301). Plants were spray-inoculated with a bacterial suspension of ~108 CFU/ml until runoff; plants were incubated in moist chambers 24 h pre and post inoculation at 28ºC with 80% relative humidity and a 12 h photoperiod. At 13 days post inoculation, symptoms resembling those on plants at the Sandhills Research Stations in 2022 were evident. Reisolated bacteria were confirmed to be AHP116 through 16S rRNA and gyrB amplification and sequencing. No symptoms were observed on the five water-inoculated plants. BLS of sesame has been reported in Asia and is thought to be seedborne (Firdous et al. 2009; Prathuangwong and Yowabutra 1997). To our knowledge, this is the first report of P. syringae pv. sesami causing BLS on sesame in North Carolina. Sesame cultivation in the state increased from approximately 2,000 acres in 2022 to 13,000 acres in 2023 and there is interest in cultivating sesame as a rotational and alternative crop because it requires minimal input costs. Potential outbreaks of BLS in this warm, humid region could negatively affect sesame production, where little is known about the economic impact of the disease.}, journal={PLANT DISEASE}, author={Duin, Izabela Moura and Montalban, Kimberly M. and Joglekar, Prasanna and D'Amico-Willman, Katherine and Ritchie, David F. and Fagen, Jennie R. and Huerta, Alejandra I.}, year={2024}, month={Jun} }
 @article{adaskaveg_schnabel_ritchie_forster_2023, title={Common Preharvest Diseases of Peach and Nectarine Caused by Fungi and Bacteria: Biology, Epidemiology and Management}, ISBN={["978-1-78924-843-2"]}, DOI={10.1079/9781789248456.0012}, journal={PEACH}, author={Adaskaveg, James E. and Schnabel, Guido and Ritchie, David F. and Forster, Helga}, year={2023}, pages={261–342} }
 @article{katherine m. d'amico-willman_joglekar_luna_ritchie_fagen_huerta_2022, title={Complete Genome Sequence of Xanthomonas arboricola pv. pruni Strain Xcp1 Isolated in 1984 from a Bacterial Spot Spring Canker on Prunus persica var. nucipersica cv. "Redgold"}, volume={11}, ISSN={["2576-098X"]}, DOI={10.1128/mra.00209-22}, abstractNote={
            Xanthomonas arboricola
            pv.
            pruni
            is an important plant pathogen and the causal agent of bacterial spot of stone fruits (
            Prunus
            spp). Here, we report a complete genome of
            X. arboricola
            pv.
            pruni
            strain Xcp1 generated from hybrid PacBio Sequel and Illumina NextSeq2000 sequencing.
          }, journal={MICROBIOLOGY RESOURCE ANNOUNCEMENTS}, author={Katherine M. D'Amico-Willman and Joglekar, Prasanna and Luna, Emily K. and Ritchie, David F. and Fagen, Jennie and Huerta, Alejandra I.}, year={2022}, month={Nov} }
 @article{schappe_ritchie_thiessen_2020, title={First Report of Serratia marcescens Causing a Leaf Spot Disease on Industrial Hemp (Cannabis sativa)}, volume={104}, ISBN={1943-7692}, DOI={10.1094/PDIS-04-19-0782-PDN}, abstractNote={In the 2017 and 2018 growing seasons (between May and October), several cultivars of industrial hemp plants grown for flowers in greenhouse production from four North Carolina counties showed symptoms of an angular leaf spot on leaves, stems, and flower parts. Lesions were initially small, dark brown, 1 to 3 mm in size, and vein-limited. As the disease progressed, lesions coalesced to form larger regions of necrosis that engulfed large portions of leaves, and whole plants were lost to disease. Red bacterial ooze was observed streaming from the plant tissues. Bacterial colonies growing on potato dextrose agar (PDA) were raised and dark-pink colored. The Gram stain indicated gram-negative bacilli. A representative isolate (called strain T2) was used to inoculate Cannabis sativa L. ‘Carmagnola’. Two-week-old seedlings (n = 6) were inoculated with a bacterial suspension (OD₆₀₀ = 0.1, approximately 10⁸ CFU/ml) using a PreVal hand sprayer; additional seedlings (n = 6) were inoculated with sterile water to serve as the negative control. Plants were incubated at 23°C for 21 days in a growth chamber with a 12-h photoperiod. After 8 days, dark brown-black lesions similar to those described above were observed on inoculated leaves. Control plants remained symptomless. The pathogen of interest was the only microorganism reisolated from lesions, and after transferring onto PDA, colonies were identical in morphology to those isolated from the original diseased plants. Molecular identification was conducted by first extracting DNA from the representative isolate T2 using the DNeasy Powersoil kit (Qiagen, Hilden, Germany). The 16S ribosomal RNA region (Klindworth et al. 2013) and the RNA polymerase β-subunit (rpoB) gene (Mollet et al. 1997) were PCR amplified. Amplicons were sequenced at the North Carolina State Genomic Sciences Laboratory, and sequences for each gene from the isolate assessed (T2) were deposited to GenBank (accessions MK598699 and MN400982 for 16S rRNA and rpoB, respectively). NCBI-BLAST searches (Altschul et al. 1997) showed the highest similarity (99.6% identity) with 16S rRNA of Serratia marcescens subsp. sakuensis and 99.6% pairwise identity to rpoB of S. marcescens strain B3R3 (GenBank accession KU894791). Based on pathogenicity, morphology, and molecular identification, the unknown bacterial isolate was identified as S. marcescens. Because industrial hemp is increasingly grown across the United States for cannabidiol production, this disease could pose significant challenges and cause yield reduction in affected plants. Additionally, this pathogen could be of human health concern should it survive hemp processing practices, because there are strains that affect humans.}, number={4}, journal={PLANT DISEASE}, author={Schappe, T. and Ritchie, D. F. and Thiessen, L. D.}, year={2020}, month={Apr}, pages={1248–1249} }
 @article{zhang_wang_yuan_xu_tu_fisk_zhang_chen_ritchie_hu_2018, title={Irrigation and weed control alter soil microbiology and nutrient availability in North Carolina Sandhill peach orchards}, volume={615}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2017.09.265}, abstractNote={Orchard management practices such as weed control and irrigation are primarily aimed at maximizing fruit yields and economic profits. However, the impact of these practices on soil fertility and soil microbiology is often overlooked. We conducted a two-factor experimental manipulation of weed control by herbicide and trickle irrigation in a nutrient-poor peach (Prunus persica L. cv. Contender) orchard near Jackson Springs, North Carolina. After three and eight years of treatments, an array of soil fertility parameters were examined, including soil pH, soil N, P and cation nutrients, microbial biomass and respiration, N mineralization, and presence of arbuscular mycorrhizal fungi (AMF). Three general trends emerged: 1) irrigation significantly increased soil microbial biomass and activity, 2) infection rate of mycorrhizal fungi within roots were significantly higher under irrigation than non-irrigation treatments, but no significant difference in the AMF community composition was detected among treatments, 3) weed control through herbicides reduced soil organic matter, microbial biomass and activity, and mineral nutrients, but had no significant impacts on root mycorrhizal infection and AMF communities. Weed-control treatments directly decreased availability of soil nutrients in year 8, especially soil extractable inorganic N. Weed control also appears to have altered the soil nutrients via changes in soil microbes and altered net N mineralization via changes in soil microbial biomass and activity. These results indicate that long-term weed control using herbicides reduces soil fertility through reducing organic C inputs, nutrient retention and soil microbes. Together, these findings highlight the need for alternative practices such as winter legume cover cropping that maintain and/or enhance organic inputs to sustain the soil fertility.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Zhang, Yi and Wang, Liangju and Yuan, Yongge and Xu, Jing and Tu, Cong and Fisk, Connie and Zhang, Weijian and Chen, Xin and Ritchie, David and Hu, Shuijin}, year={2018}, month={Feb}, pages={517–525} }
 @article{roberts_ritchie_kerns_2016, title={Plant Growth Regulator Effects on Bacterial Etiolation of Creeping Bentgrass Putting Green Turf Caused by Acidovorax avenae}, volume={100}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-04-15-0419-re}, abstractNote={ Bacterial etiolation, caused by Acidovorax avenae, is a widespread problem in creeping bentgrass putting green turf. The symptoms normally appear as abnormally elongated turfgrass stems and leaves. Observations at multiple field sites suggest the involvement of plant growth regulators (i.e., GA-biosynthesis inhibitors) commonly applied to turf, alluding to a phytohormone imbalance caused by the bacterium. A 2-year field study examined the effects of trinexapac-ethyl, flurprimidol, and paclobutrazol on bacterial etiolation severity caused by A. avenae. Trinexapac-ethyl applied at 0.05 kg a.i. ha−1 every 7 days and 0.10 kg ha−1 every 14 days increased etiolation compared with all other treatments in both years. Flurprimidol and paclobutrazol were not different from the control but high-rate applications caused phytotoxicity that lowered turf quality early in 2014. When the etiolated turfgrass was removed with mowing, turfgrass treated with trinexapac-ethyl exhibited the highest turfgrass quality on most rating dates. Results from this work illustrate that using plant growth regulator materials with different modes of action is a solution to managing creeping bentgrass growth while limiting the potential for bacterial etiolation outbreaks. }, number={3}, journal={PLANT DISEASE}, author={Roberts, Joseph A. and Ritchie, David F. and Kerns, James P.}, year={2016}, month={Mar}, pages={577–582} }
 @article{roberts_kerns_ritchie_2015, title={Bacterial etiolation of creeping bentgrass as influenced by biostimulants and trinexapac-ethyl}, volume={72}, ISSN={["1873-6904"]}, DOI={10.1016/j.cropro.2015.03.009}, abstractNote={Bacterial etiolation, caused by Acidovorax avenae and Xanthomonas translucens, has become a widespread problem in turfgrass throughout the U.S. Various management tactics are used in managing this disease and differ among turfgrass managers. The use of biostimulants and trinexapac-ethyl (TE) has become a staple in putting green management and many products have been associated with etiolation outbreaks. Experiments performed in field and controlled environments evaluated the impact of commercial biostimulants and TE on etiolation of creeping bentgrass (Agrostis stolonifera L. c.v. ‘Penn A-1’) caused by both A. avenae and X. translucens. In the field, a factorial study was arranged as a split-plot randomized complete block design with 4 replications. The main plot consisted of biostimulants (Knife Plus, CytoGro, Astron, Nitrozyme, PerkUp, BioMax, and none) applied at label rates while the subplot treatments consisted of TE application frequency (0.049 kg ha−1 applied at 7 d, 14 d, and none). For controlled environment experiments, biostimulant and TE treatments were arranged in a randomized complete block design with 4 replications. Bacterial etiolation was measured regularly when present using a grid count to determine the percent area exhibiting etiolation in the field while etiolated turfgrass plants were counted individually in controlled environments. Turf quality was also rated using a scale of 1–9 with 1 = completely dead, 9 = best, and 5 = minimum acceptable turf quality for all experiments. Biostimulant treatments did not have a significant effect on etiolation caused by either bacterium. Trinexapac-ethyl decreased etiolation caused by X. translucens and increased etiolation caused by A. avenae. These results support the necessity of identifying bacteria associated with etiolation as variable effects were observed with TE treatments. These factors should be considered when developing plant growth regulator programs if etiolation is problematic. Future research to evaluate phytohormone production in these bacteria may improve our understanding of etiolation development while improving methods for control.}, journal={CROP PROTECTION}, author={Roberts, Joseph A. and Kerns, James P. and Ritchie, David F.}, year={2015}, month={Jun}, pages={119–126} }
 @article{schwartz_potnist_milsina_wilson_patane_martins_minsavage_dahlbeck_akhunova_almeida_et al._2015, title={Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity}, volume={6}, ISSN={["1664-302X"]}, DOI={10.3389/fmicb.2015.00535}, abstractNote={Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type III effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of 67 Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Xg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type III effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion of AvrBsT and XopQ allows a host range expansion for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors.}, journal={FRONTIERS IN MICROBIOLOGY}, author={Schwartz, Allison R. and Potnist, Neha and Milsina, Sujan and Wilson, Mark and Patane, Jose and Martins, Joaquim, Jr. and Minsavage, Gerald V. and Dahlbeck, Douglas and Akhunova, Alina and Almeida, Nalvo and et al.}, year={2015}, month={Jun} }
 @article{yang_reighard_ritchie_okie_gasic_2013, title={Mapping quantitative trait loci associated with resistance to bacterial spot (Xanthomonas arboricola pv. pruni) in peach}, volume={9}, ISSN={["1614-2950"]}, DOI={10.1007/s11295-012-0580-x}, abstractNote={Bacterial spot, caused by Xanthomonas arboricola pv. pruni (Xap), is a serious disease that can affect peach fruit quality and production worldwide. This disease causes severe defoliation and blemishing of fruit, particularly in areas with high rainfall, strong winds, high humidity, and sandy soil. The molecular basis of its tolerance and susceptibility in peach is yet to be understood. An F2 population of 63 genotypes derived from a cross between peaches “O’Henry” (susceptible) and “Clayton” (resistant) has been used for linkage map construction and quantitative trait loci (QTL) mapping. Phenotypic data for leaf and fruit response to Xap infection were collected over 2 years at two locations. A high-density genetic linkage map that covers a genetic distance of 421.4 cM with an average spacing between markers of 1.6 cM was developed using the International Peach Single Nucleotide Polymorphism Consortium (IPSC) 9K array v1. Fourteen QTLs with an additive effect on Xap resistance were detected, including four major QTLs on linkage groups (LG) 1, 4, 5, and 6. Major QTLs, Xap.Pp.OC-4.1 and Xap.Pp.OC-4.2, on LG4 were associated with Xap resistance in leaf; Xap.Pp.OC-5.1 on LG5 was associated with Xap resistance in both leaf and fruit, while Xap.Pp.OC-1.2 and Xap.Pp.OC-6.1 on LG1 and LG6, respectively, were associated with Xap resistance in fruit. This suggested separate regulation of leaf and fruit resistance for Xap in peach as well as participation of genes involved in general plant response to biotic stress. The potential for marker-assisted selection for Xap resistance in peach is discussed.}, number={2}, journal={TREE GENETICS & GENOMES}, author={Yang, Nannan and Reighard, Gregory and Ritchie, David and Okie, William and Gasic, Ksenija}, year={2013}, month={Apr}, pages={573–586} }
 @article{worthington_rogers_huigens_melander_ritchie_2012, title={Foliar-Applied Small Molecule that Suppresses Biofilm Formation and Enhances Control of Copper-Resistant Xanthomonas euvesicatoria on Pepper}, volume={96}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-02-12-0190-re}, abstractNote={ We report a small molecule additive, a member of the 2-aminoimidazole (2AI) group that is an analogue of the marine sponge natural product oroidin that suppresses resistance of Xanthomonas euvesicatoria to copper and decreases biofilm formation in an in vitro system. In laboratory experiments, 2AI combined with copper reduced both bacterial multiplication in broth and bacterial recovery on pepper leaf discs of a copper-resistant strain of X. euvesicatoria to a level close to that of a copper-sensitive strain. Compound 2AI used alone exhibited minimal bactericidal activity. In 3 years of field experiments, when combined with a copper-containing material, copper hydroxide (Kocide 3000), and other antibacterial materials, these spray mixtures resulted in decreased bacterial spot foliar disease and increased fruit yields using hybrid bell pepper (Capsicum annuum) cultivars and copper-resistant strains of X. euvesicatoria. This study demonstrates the concept for using small molecules as additives to antibacterial compounds at nonbactericidal concentrations under field conditions that, in the laboratory, were demonstrated to suppress bacterial biofilms and copper-resistant strains. }, number={11}, journal={PLANT DISEASE}, author={Worthington, R. J. and Rogers, S. A. and Huigens, R. W., III and Melander, C. and Ritchie, D. F.}, year={2012}, month={Nov}, pages={1638–1644} }
 @article{pothier_pagani_pelludat_ritchie_duffy_2011, title={A duplex-PCR method for species- and pathovar-level identification and detection of the quarantine plant pathogen Xanthomonas arboricola pv. pruni}, volume={86}, ISSN={["1872-8359"]}, DOI={10.1016/j.mimet.2011.03.019}, abstractNote={A PCR-based method was developed for the stone fruit quarantine pathogen Xanthomonas arboricola pv. pruni (Xap), which provides rapid, sensitive and specific in planta detection and isolate identification. Primers specific for Xap were identified using random amplified polymorphic DNA (RAPD). Simplex PCR with these primers had a limit of detection per PCR reaction of approximately 10CFU for isolate cultures and 50CFU for plant material when used on tenfold dilutions of isolate culture or genomic DNA extracted from spiked samples, respectively. The primers were adapted as a high-throughput single-step screening based on a digoxigenin-labeled DNA probe assay with a detection limit of 4×10(2)CFU from isolate cultures. A duplex-PCR method was designed that includes the pathovar-level with species-level primers based on species-specific regions of the quinate metabolic gene qumA, increasing diagnostic confidence and offering the first molecular test for all X. arboricola pathovars.}, number={1}, journal={JOURNAL OF MICROBIOLOGICAL METHODS}, author={Pothier, J. F. and Pagani, M. C. and Pelludat, C. and Ritchie, D. F. and Duffy, B.}, year={2011}, month={Jul}, pages={16–24} }
 @article{wichmann_ritchie_kousik_bergelson_2005, title={Reduced genetic variation occurs among genes of the highly clonal plant pathogen Xanthomonas axonopodis pv. vesicatoria, including the effector gene avrBs2}, volume={71}, ISSN={["1098-5336"]}, DOI={10.1128/AEM.71.5.2418-2432.2005}, abstractNote={ABSTRACT}, number={5}, journal={APPLIED AND ENVIRONMENTAL MICROBIOLOGY}, author={Wichmann, G and Ritchie, D and Kousik, CS and Bergelson, J}, year={2005}, month={May}, pages={2418–2432} }
 @article{romero_ritchie_2004, title={Systemic acquired resistance delays race shifts to major resistance genes in bell pepper}, volume={94}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO.2004.94.12.1376}, abstractNote={ The lack of durability of host plant disease resistance is a major problem in disease control. Genotype-specific resistance that involves major resistance (R) genes is especially prone to failure. The compatible (i.e., disease) host-pathogen interaction with systemic acquired resistance (SAR) has been studied extensively, but the incompatible (i.e., resistant) interaction less so. Using the pepper-bacterial spot (causal agent, Xanthomonas axonopodis pv. vesicatoria) pathosystem, we examined the effect of SAR in reducing the occurrence of race-change mutants that defeat R genes in laboratory, greenhouse, and field experiments. Pepper plants carrying one or more R genes were sprayed with the plant defense activator acibenzolar-S-methyl (ASM) and challenged with incompatible strains of the pathogen. In the greenhouse, disease lesions first were observed 3 weeks after inoculation. ASM-treated plants carrying a major R gene had significantly fewer lesions caused by both the incompatible (i.e., hypersensitive) and compatible (i.e., disease) responses than occurred on nonsprayed plants. Bacteria isolated from the disease lesions were confirmed to be race-change mutants. In field experiments, there was a delay in the detection of race-change mutants and a reduction in disease severity. Decreased disease severity was associated with a reduction in the number of race-change mutants and the suppression of disease caused by the race-change mutants. This suggests a possible mechanism related to a decrease in the pathogen population size, which subsequently reduces the number of race-change mutants for the selection pressure of R genes. Thus, inducers of SAR are potentially useful for increasing the durability of genotype-specific resistance conferred by major R genes. }, number={12}, journal={PHYTOPATHOLOGY}, author={Romero, AA and Ritchie, DF}, year={2004}, month={Dec}, pages={1376–1382} }
 @article{romero_kousik_ritchie_2002, title={Temperature sensitivity of the hypersensitive response of bell pepper to Xanthomonas axonopodis pv. vesicatoria}, volume={92}, DOI={10.1094/PHYTO.2002.92.2.197}, abstractNote={ When bacterial spot-resistant pepper plants carrying resistance gene Bs2 and infiltrated with incompatible strains of Xanthomonas axonopodis pv. vesicatoria carrying a functional avrBs2 gene (races P1 and P3) were incubated at 32°C, they exhibited an electrolyte leakage and bacterial multiplication pattern in planta similar to that obtained with a compatible strain (race P4) carrying a nonfunctional avrBs2 gene. They also developed disease-like symptoms. Pretreatment of incompatible bacteria at 32°C before infiltration caused a delay in electrolyte leakage less pronounced than that caused by exposing plants to 32°C. Also, plants had to be exposed to 32°C for an hour prior to inoculation to increase symptom expression. These data suggest that the Bs2 gene is temperature sensitive. In other experiments, the avrBs1-Bs1 interaction appeared to be the most heat tolerant and thus the least likely to revert to compatible, whereas the avrBs3-Bs3 interaction had an intermediate sensitivity to elevated temperatures. }, number={2}, journal={Phytopathology}, author={Romero, A. M. and Kousik, C. S. and Ritchie, D. F.}, year={2002}, pages={197–203} }
 @article{romero_kousik_ritchie_2001, title={Resistance to bacterial spot in bell pepper induced by acibenzolar-S-methyl}, volume={85}, ISSN={["0191-2917"]}, DOI={10.1094/pdis.2001.85.2.189}, abstractNote={ Bell pepper plants sprayed with the chemical acibenzolar-S-methyl (ABM, Actigard 50 WG) showed resistance to subsequent infections with the bacterial spot agent Xanthomonas axonopodis pv. vesicatoria. Induction of resistance was independent of the cultivar used, and was expressed as early as 3 days after treatment and continued for at least 2 weeks. In the field, applications of ABM every 2 weeks, alone or in combination with copper, resulted in disease control similar to the standard treatment of copper plus maneb. Yield response was variable, with certain combinations of chemical treatments and cultivars producing yields as large as the copper plus maneb treatment. In contrast, weekly applications during the entire crop season had a negative impact on yield. In plots maintained free of bacterial spot, applications of ABM every 2 weeks caused a reduction in yield for one cultivar of six tested. The use of chemical inducers for the control of bacterial spot on bell pepper, while generally promising, may result in an unpredictable loss in fruit yield. }, number={2}, journal={PLANT DISEASE}, author={Romero, AM and Kousik, CS and Ritchie, DF}, year={2001}, month={Feb}, pages={189–194} }
 @article{kousik_ritchie_1999, title={Development of bacterial spot on near-isogenic lines of bell pepper carrying gene pyramids composed of defeated major resistance genes}, volume={89}, ISSN={["0031-949X"]}, DOI={10.1094/phyto.1999.89.11.1066}, abstractNote={Disease severity caused by races 1 through 6 of Xanthomonas campestris pv. vesicatoria on eight near-isogenic lines (isolines) of Early Calwonder (ECW) with three major resistance genes (Bs1, Bs2, and Bs3) in different combinations was evaluated in the greenhouse and field. Strains representing races 1, 3, 4, and 6 caused similar high levels of disease severity, followed by races 2 and 5 on susceptible ECW. Race 3 caused severe disease on all isolines lacking resistance gene Bs2. Race 4, which defeats Bs1 and Bs2, caused less disease on isoline ECW-12R (carries Bs1 + Bs2), than on isolines ECW, ECW-10R (carries Bs1), and ECW-20R (carries Bs2). Similar results were obtained with race 4 strains in field studies conducted during 1997 and 1998. In greenhouse studies, race 6, which defeats all three major genes, caused less disease on isoline ECW-13R (carries Bs1 + Bs3) and ECW-123R (carries Bs1 + Bs2 + Bs3) than on isolines ECW, ECW-10R, ECW-20R, and ECW-30R (carries Bs3), but not on ECW-23R (carries Bs2 + Bs3). In greenhouse studies with commercial hybrids, strains of races 4 and 6 caused less disease on Boynton Bell (carries Bs1 + Bs2) than on Camelot (carries no known resistance genes), King Arthur (carries Bs1), and X3R Camelot (carries Bs2). Race 6 caused less disease on hybrid R6015 (carries Bs1 + Bs2 + Bs3) and Sentinel (carries Bs1 + Bs3) than on Camelot. Residual effects were not as evident in field studies with race 6 strains. Defeated major resistance genes deployed in specific gene combinations (i.e., gene pyramids) were associated with less area under the disease progress curve than when genes were deployed individually in isolines of ECW or commercial hybrids. Successful management of bacterial spot of pepper is achieved incrementally by integrating multiple tactics. Although there is evidence of residual effects from defeated genes, these effects alone likely will not provide acceptable bacterial spot control in commercial production fields. However, when combined with sanitation practices and a judicious spray program, pyramids of defeated resistance genes may aid in reducing the risk of major losses due to bacterial spot.}, number={11}, journal={PHYTOPATHOLOGY}, author={Kousik, CS and Ritchie, DE}, year={1999}, month={Nov}, pages={1066–1072} }
 @article{kousik_ritchie_1998, title={Response of bell pepper cultivars to bacterial spot pathogen races that individually overcome major resistance genes}, volume={82}, ISSN={["0191-2917"]}, DOI={10.1094/pdis.1998.82.2.181}, abstractNote={The effect of major resistance genes (Bs1, Bs2, and Bs3) or gene combinations for resistance to bacterial spot of bell peppers (Xanthomonas campestris pv. vesicatoria) in 15 commercial cultivars on disease reduction and yield were studied during 1995 and 1996. Reaction of cultivars to specific races (races 1, 2, or 3) of the pathogen corresponded with seed company claims for resistance against these races. Races 1 to 4 were used as initial inoculum in 1995, and races 1 to 6 in 1996 field experiments. Cultivars with no known resistance genes to bacterial spot (e.g., Camelot, Jupiter, and Valiant), a single resistance gene (X3R Camelot, King Arthur), or a combination of Bs1 and Bs3 genes (Guardian, Sentinel, and Admiral) were severely diseased. Yields were reduced in all inoculated cultivars compared to non-inoculated cultivars used as controls. Although races 4 and 6 caused significant disease in cultivars with only Bs1 (King Arthur) or Bs2 (X3R Camelot) genes, cultivars with a combination of Bs1 and Bs2 (Boynton Bell, PR9300-8) had much lower levels of bacterial spot. Roger 4178, a hybrid with a combination of Bs1, Bs2, and Bs3 genes, had the lowest disease ratings. Overall, race 3 was predominant during 1995, while races 3 and 6 were recovered most frequently in 1996.}, number={2}, journal={PLANT DISEASE}, author={Kousik, CS and Ritchie, DF}, year={1998}, month={Feb}, pages={181–186} }
 @article{ritchie_werner_hammerschlag_1993, title={Field evaluation of tissue culture-derived peach trees for susceptibility to bacterial spot (Xanthomonas campestris pv. pruni)}, ISBN={9066053852}, DOI={10.17660/actahortic.1993.336.19}, number={336}, journal={Acta Horticulturae}, author={Ritchie, D. F. and Werner, D. J. and Hammerschlag, F. A.}, year={1993}, pages={155} }
 @article{ritchie_averre_milholland_1993, title={First report of angular leaf spot, caused by Xanthomonas fragariae, on strawberry in North Carolina}, volume={77}, number={12}, journal={Plant Disease}, author={Ritchie, D. F. and Averre, C. W. and Milholland, R. D.}, year={1993}, pages={1263} }
 @article{ritchie_dittapongpitch_1991, title={COPPER-RESISTANT AND STREPTOMYCIN-RESISTANT STRAINS AND HOST DIFFERENTIATED RACES OF XANTHOMONAS-CAMPESTRIS PV VESICATORIA IN NORTH-CAROLINA}, volume={75}, ISSN={["0191-2917"]}, DOI={10.1094/PD-75-0733}, abstractNote={Copper- and streptomycin-resistant strains of xanthomonas campestris pv. vesicatoria were detected in diseased pepper and tomato plants. In surveys of 32 noncontiguous fields during four growing seasons, 63% of 70 strains were copper resistant and 30% were resistant to at least 100 μg/ml of streptomycin. All streptomycin-resistant strains were copper resistant. Strains of pepper races 1, 2, and 3, as well as strains from the tomato group, were detected (...)}, number={7}, journal={PLANT DISEASE}, author={RITCHIE, DF and DITTAPONGPITCH, V}, year={1991}, month={Jul}, pages={733–736} }