@article{d'arcangelo_wallace_miles_quesada-ocampo_2022, title={Carboxylic Acid Amide but Not Quinone Outside Inhibitor Fungicide Resistance Mutations Show Clade-Specific Occurrence in Pseudoperonospora cubensis Causing Downy Mildew in Commercial and Wild Cucurbits}, volume={8}, ISSN={["1943-7684"]}, url={https://doi.org/10.1094/PHYTO-05-22-0166-R}, DOI={10.1094/PHYTO-05-22-0166-R}, abstractNote={Since its reemergence in 2004, Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew (CDM), has experienced significant changes in fungicide sensitivity. Presently, frequent fungicide applications are required to control the disease in cucumber due to the loss of host resistance. Carboxylic acid amides (CAA) and quinone outside inhibitors (QoI) are two fungicide groups used to control foliar diseases in cucurbits, including CDM. Resistance to these fungicides is associated with single nucleotide polymorphism (SNP) mutations. In this study, we used population analyses to determine the occurrence of fungicide resistance mutations to CAA and QoI fungicides in host-adapted clade 1 and clade 2 P. cubensis isolates. Our results revealed that CAA-resistant genotypes occurred more prominently in clade 2 isolates, with more sensitive genotypes observed in clade 1 isolates, while QoI resistance was widespread across isolates from both clades. We also determined that wild cucurbits can serve as reservoirs for P. cubensis isolates containing fungicide resistance alleles. Finally, we report that the G1105W substitution associated with CAA resistance was more prominent within clade 2 P. cubensis isolates while the G1105V resistance substitution and sensitivity genotypes were more prominent in clade 1 isolates. Our findings of clade-specific occurrence of fungicide resistance mutations highlight the importance of understanding the population dynamics of P. cubensis clades by crop and region to design effective fungicide programs and establish accurate baseline sensitivity to active ingredients in P. cubensis populations.}, journal={PHYTOPATHOLOGY}, author={D'Arcangelo, K. N. and Wallace, E. C. and Miles, T. D. and Quesada-Ocampo, L. M.}, year={2022}, month={Aug} }
 @article{salgado-salazar_leblanc_wallace_daughtrey_crouch_2020, title={Peronospora monardae, Hyaloperonospora daughtreyae and H. iberidis: new species associated with downy mildew diseases affecting ornamental plants in the United States}, volume={157}, ISSN={["1573-8469"]}, DOI={10.1007/s10658-020-01989-9}, number={2}, journal={EUROPEAN JOURNAL OF PLANT PATHOLOGY}, author={Salgado-Salazar, Catalina and LeBlanc, Nicholas and Wallace, Emma C. and Daughtrey, Margery L. and Crouch, Jo Anne}, year={2020}, month={Jun}, pages={311–326} }
 @article{wallace_quesada-ocampo_2017, title={Analysis of microsatellites from the transcriptome of downy mildew pathogens and their application for characterization of Pseud operonospora populations}, volume={5}, ISSN={["2167-8359"]}, DOI={10.7717/peerj.3266}, abstractNote={Downy mildew pathogens affect several economically important crops worldwide but, due to their obligate nature, few genetic resources are available for genomic and population analyses. Draft genomes for emergent downy mildew pathogens such as the oomycetePseudoperonospora cubensis, causal agent of cucurbit downy mildew, have been published and can be used to perform comparative genomic analysis and develop tools such as microsatellites to characterize pathogen population structure. We used bioinformatics to identify 2,738 microsatellites in theP. cubensispredicted transcriptome and evaluate them for transferability to the hop downy mildew pathogen,Pseudoperonospora humuli, since no draft genome is available for this species. We also compared the microsatellite repertoire ofP. cubensisto that of the model organismHyaloperonospora arabidopsidis, which causes downy mildew in Arabidopsis. Although trends in frequency of motif-type were similar, the percentage of SSRs identified fromP. cubensistranscripts differed significantly fromH. arabidopsidis. The majority of a subset of microsatellites selected for laboratory validation (92%) produced a product inP. cubensisisolates, and 83 microsatellites demonstrated transferability toP. humuli. Eleven microsatellites were found to be polymorphic and consistently amplified inP. cubensisisolates. Analysis ofPseudoperonosporaisolates from diverse hosts and locations revealed higher diversity inP. cubensiscompared toP. humuliisolates. These microsatellites will be useful in efforts to better understand relationships withinPseudoperonosporaspecies andP. cubensison a population level.}, journal={PEERJ}, author={Wallace, Emma C. and Quesada-Ocampo, Lina M.}, year={2017}, month={May} }
 @article{wallace_quesada-ocampo_2017, title={Examining the population structure of the cucurbit downy mildew pathogen, Pseudoperonospora cubensis, by host, location and time}, volume={107}, number={7}, journal={Phytopathology}, author={Wallace, E. and Quesada-Ocampo, L.}, year={2017}, pages={6–6} }
 @article{wallace_choi_thines_quesada-ocampo_2016, title={First Report of Plasmopara aff. australis on Luffa cylindrica in the United States.}, volume={100}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-06-15-0684-PDN}, DOI={10.1094/pdis-06-15-0684-pdn}, abstractNote={HomePlant DiseaseVol. 100, No. 2First Report of Plasmopara aff. australis on Luffa cylindrica in the United States PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Plasmopara aff. australis on Luffa cylindrica in the United StatesE. Wallace, Y. J. Choi, M. Thines, and L. M. Quesada-OcampoE. Wallace, Y. J. Choi, M. Thines, and L. M. Quesada-Ocampohttp://orcid.org/0000-0002-9072-7531AffiliationsAuthors and Affiliations E. Wallace , Department of Plant Pathology, North Carolina State University, Raleigh 27695 Y. J. Choi , Department of Biological Science, College of Natural Sciences, Kunsan National University, Gunsan 54150, Korea M. Thines , Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft fur Naturforschung, and Johann Wolfgang Goethe University, Department of Biological Sciences, Institute of Ecology, Evolution and Diversity, D-60325 Frankfurt (Main), Germany L. M. Quesada-Ocampo , Department of Plant Pathology, North Carolina State University, Raleigh 27695. Published Online:8 Jan 2016https://doi.org/10.1094/PDIS-06-15-0684-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Luffa, or the sponge gourd, is a subtropical member of the Cucurbitaceae family. The fibrous nature of the fruit's vascular system creates a functional sponge and is mainly cultivated for this purpose. Asia and Central America lead in commercial luffa production, but the United States has recognized the demand and economic potential for luffa and efforts have been made to implement luffa as a specialty crop (Davis 2008). In August 2014, luffa leaves exhibiting irregular to angular chlorotic lesions were collected from Haywood County, North Carolina. All five luffa plants, located in a sentinel plot part of the CDM IPM pipe, were infected with 20% disease severity. The abaxial surface revealed water-soaked lesions and white sporulation consistent with downy mildew symptoms. Sporangiophores and sporangia were collected from field samples by pipetting up and down on the lesion with water, then observed and measured using a light microscope. Papillate, hyaline sporangia were primarily ovoid-spherical in shape, having dimensions of (13–) 14–15–17 (–18) × (11–) 12–13–13 (–15) (n = 54). The sporangiophore length had dimensions of (348–) 438–550–661 (–771) (n = 54). The trunk's width was (8–) 10–12–14 (–16) (n = 46), with the base slightly wider and becoming narrow just below the first branch. Branching pattern was monopodial with secondary branches and branchlets occurring at 90° angles from primary branches and secondary branches, respectively. Morphology was consistent with Plasmopara australis according to Constantinescu (2002). DNA was extracted from sporulating lesions on luffa leaves. PCR was used to amplify the nuclear gene D1-D3 region of 28S large subunit ribosomal RNA (LSU), and the mitochondrial gene cytochrome c oxidase subunit 2 (cox2) (Choi et al. 2009). Products were sequenced and submitted to GenBank (Accession Nos. KT159460 to KT159463). There is no previous sequence data available for Plasmopara australis in GenBank for BLAST analyses as occurs with many downy mildew pathogens; however, the D1-D3 nrLSU sequences were used to generate a phylogenetic tree as seen in Choi et al. 2009. Cox2 sequences were not used in phylogenetic analysis. This data, along with morphological characteristics, is sufficient to designate this pathogen P. aff. australis. Remaining tissue was preserved and submitted to the Larry F. Grand Mycological Herbarium (Catalog No. 20864). In 2006, Plasmopara australis was first reported on Luffa cylindrica in Brazil (Soares et al. 2006). In the United States, P. australis reportedly occurs on Echinocystis lobata and Sicyos angulatus, two wild cucurbit species commonly found across the country (Farr and Rossman 2015). It is unclear how L. cylindrica came to be a host for P. australis in the United States. However, this new disease is of concern for small-scale luffa growers. Certainly, more investigation may shed light on the disease cycle, epidemiology, and host-specificity of the pathogen.References:Choi, Y. J., et al. 2009. Mycol. Res. 113:1127. Crossref, Google ScholarConstantinescu, O. 2002. Sydowia 54:129. ISI, Google ScholarDavis, J. 2008. Commercial luffa sponge gourd production. Hortic. Inf. Leaflet. North Carolina State Univ. Coop. Ext., Raleigh, NC. Retrieved from http://content.ces.ncsu.edu/commercial-luffa-sponge-gourd-production, 24 March 2015. Google ScholarFarr, D. F., and Rossman, A. Y. Fungal Databases, Syst. Mycol. Microbiol. Lab., ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/, 24 March 2015. Google ScholarSoares, D. J., et al. 2006. Plant Pathol. 55:295. https://doi.org/10.1111/j.1365-3059.2006.01328.x. Crossref, ISI, Google ScholarDetailsFiguresLiterature CitedRelated Vol. 100, No. 2 February 2016SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 15 Feb 2016Published: 8 Jan 2016First Look: 15 Oct 2015Accepted: 6 Oct 2015 Pages: 537-537 Information© 2016 The American Phytopathological SocietyCited byFantastic Downy Mildew Pathogens and How to Find Them: Advances in Detection and Diagnostics25 February 2021 | Plants, Vol. 10, No. 3Population Analyses Reveal Two Host-Adapted Clades of Pseudoperonospora cubensis, the Causal Agent of Cucurbit Downy Mildew, on Commercial and Wild CucurbitsE. C. Wallace, K. N. D'Arcangelo, and L. M. Quesada-Ocampo7 July 2020 | Phytopathology®, Vol. 110, No. 9Diagnostic Guide for Cucurbit Downy MildewAndres Salcedo, Mary Hausbeck, Stacey Pigg, and Lina M. Quesada-Ocampo14 May 2020 | Plant Health Progress, Vol. 21, No. 3Molecular approaches for biosurveillance of the cucurbit downy mildew pathogen, Pseudoperonospora cubensis9 August 2017 | Canadian Journal of Plant Pathology, Vol. 39, No. 3}, number={2}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Wallace, E. and Choi, Y. J. and Thines, M. and Quesada-Ocampo, L. M.}, year={2016}, month={Feb}, pages={537–537} }
 @article{wallace_adams_ivors_ojiambo_quesada-ocampo_2014, title={First Report of Pseudoperonospora cubensis Causing Downy Mildew on Momordica balsamina and M. charantia in North Carolina}, volume={98}, ISSN={["1943-7692"]}, url={http://europepmc.org/abstract/med/30699625}, DOI={10.1094/pdis-03-14-0305-pdn}, abstractNote={ Momordica balsamina (balsam apple) and M. charantia L. (bitter melon/bitter gourd/balsam pear) commonly grow in the wild in Africa and Asia; bitter melon is also cultivated for food and medicinal purposes in Asia (1). In the United States, these cucurbits grow as weeds or ornamentals. Both species are found in southern states and bitter melon is also found in Pennsylvania and Connecticut (3). Cucurbit downy mildew (CDM), caused by the oomycete Pseudoperonospora cubensis, was observed on bitter melon and balsam apple between August and October of 2013 in six North Carolina sentinel plots belonging to the CDM ipmPIPE program (2). Plots were located at research stations in Johnston, Sampson, Lenoir, Henderson, Rowan, and Haywood counties, and contained six different commercial cucurbit species including cucumbers, melons, and squashes in addition to the Momordica spp. Leaves with symptoms typical of CDM were collected from the Momordica spp. and symptoms varied from irregular chlorotic lesions to circular lesions with chlorotic halos on the adaxial leaf surface. Sporulation on the abaxial side of the leaves was observed and a compound microscope revealed sporangiophores (180 to 200 μm height) bearing lemon-shaped, dark sporangia (20 to 35 × 10 to 20 μm diameter) with papilla on one end. Genomic DNA was extracted from lesions and regions of the NADH dehydrogynase subunit 1 (Nad1), NADH dehydrogynase subunit 5 (Nad5), and internal transcribed spacer (ITS) ribosomal RNA genes were amplified and sequenced (4). BLAST analysis revealed 100% identity to P. cubensis Nad1 (HQ636552.1, HQ636551.1), Nad5 (HQ636556.1), and ITS (HQ636491.1) sequences in GenBank. Sequences from a downy mildew isolate from each Momordica spp. were deposited in GenBank as accession nos. KJ496339 through 44. To further confirm host susceptibility, vein junctions on the abaxial leaf surface of five detached leaves of lab-grown balsam apple and bitter melon were either inoculated with a sporangia suspension (10 μl, 104 sporangia/ml) of a P. cubensis isolate from Cucumis sativus (‘Vlaspik' cucumber), or with water as a control. Inoculated leaves were placed in humidity chambers to promote infection and incubated using a 12-h light (21°C) and dark (18°C) cycle. Seven days post inoculation, CDM symptoms and sporulation were observed on inoculated balsam apple and bitter melon leaves. P. cubensis has been reported as a pathogen of both hosts in Iowa (5). To our knowledge, this is the first report of P. cubensis infecting these Momordica spp. in NC in the field. Identifying these Momordica spp. as hosts for P. cubensis is important since these cucurbits may serve as a source of CDM inoculum and potentially an overwintering mechanism for P. cubensis. Further research is needed to establish the role of non-commercial cucurbits in the yearly CDM epidemic, which will aid the efforts of the CDM ipmPIPE to predict disease outbreaks.  References: (1) L. K. Bharathi and K. J. John. Momordica Genus in Asia-An Overview. Springer, New Delhi, India, 2013. (2) P. S. Ojiambo et al. Plant Health Prog. doi:10.1094/PHP-2011-0411-01-RV, 2011. (3) PLANTS Database. Natural Resources Conservation Service, USDA. Retrieved from http://plants.usda.gov/ , 7 February 2014. (4) L. M. Quesada-Ocampo et al. Plant Dis. 96:1459, 2012. (5) USDA. Index of Plant Disease in the United States. Agricultural Handbook 165, 1960. }, number={9}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Wallace, E. and Adams, M. and Ivors, K. and Ojiambo, P. S. and Quesada-Ocampo, L. M.}, year={2014}, month={Sep}, pages={1279–1279} }