Abstract
Species in the genera Hyaloperonospora and Peronospora (Oomycota, Peronosporaceae) are obligate biotrophic pathogens responsible for destructive downy mildew diseases of ornamental horticulture plants worldwide. Throughout the past decade, newly emergent downy mildew diseases have become increasingly prevalent, but often the identity of the pathogen is unknown or poorly defined. In this study we set out to identify the downy mildew pathogens infecting three widely grown ornamental plants: Agastache spp. (hyssops), Tarenaya hassleriana (syn. = Cleome hassleriana; spider-flower) and Monarda didyma (bee balm or bergamot). Phylogenetic analysis of the internal transcribed spacer rDNA and cox2 revealed two new species, which are described here as Peronospora monardae infecting both Monarda didyma and A. mexicana, and Hyaloperonospora daughtreyae infecting T. hassleriana. One sample of Peronospora collected from Agastache sp. ‘Bolero’ did not cluster with P. monardae, but its relationship to other species in the clade was not sufficiently resolved for taxonomic determination. Phylogenetic analysis also supported the combination of Peronospora iberidis, a pathogen of Iberis spp. (candytuft), into Hyaloperonospora. To assess intrasample ITS sequence variation from P. monardae, data were generated using high-throughput amplicon sequencing (HTAS). Multiple haplotypes were identified from the P. monardae samples, with less than 1% intrasample variation observed. From a core set of haplotypes shared across the HTAS the variant frequencies could not be completely explained by heterozygosity alone.
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Data availability
The dataset(s) supporting the conclusions of this article are available in the [repository name] repository, [unique persistent identifier and hyperlink to dataset(s) in http:// format]. Voucher specimens are available through the U.S. National Fungus Collections (BPI).
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The authors wish to thank Sara May for providing samples included in this study.
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This work was funded by the U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS) project 8042-22000-298-00-D and the USDA Animal and Plant Health Inspection Service (APHIS) Farm Bill 10007 program. CSS, NL and EW were participants in the ARS Research Participation Program administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy (DOE) and the USDA. ORISE is managed by ORAU under DOE contract number DEAC05-06OR23100. USDA-APHIS provided support in the form of stipend for one author (EW), but did not have any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of this author are articulated in the “author contributions” section. ORISE, DOE and ORAU did not have any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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CSS, NL, EW and MLD performed data generation and analysis. JAC conceived, supervised and administered the study and acquired funding. CSS, NL and JAC drafted and revised the original manuscript. All authors contributed to the interpretation of data, and read and approved the final manuscript.
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Salgado-Salazar, C., LeBlanc, N., Wallace, E.C. et al. Peronospora monardae, Hyaloperonospora daughtreyae and H. iberidis: new species associated with downy mildew diseases affecting ornamental plants in the United States. Eur J Plant Pathol 157, 311–326 (2020). https://doi.org/10.1007/s10658-020-01989-9
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DOI: https://doi.org/10.1007/s10658-020-01989-9