Where Flowers Bloom, so Do Downy Mildews: New Species and New Records of Hyaloperonospora , Peronospora , and Plasmopara Species on Ornamental and Wild Plants in the United States

Le résumé fourni par la source

Downy mildews are biotrophic plant pathogens of low- and high-value crops that can cause significant damage and economic losses. The floral and nursery crops industries are particularly susceptible to downy mildews, especially when annuals, herbaceous perennials, and woody plants are growing in protected environments. Downy mildews are also a common but poorly documented occurrence on wild relatives or noncultivated plant hosts. The role these play, however, as pathogen reservoirs and in the emergence or reemergence of downy mildew epidemics is still unknown. In this study, we report downy mildew observations on several annual, herbaceous perennial, and woody shrub plants in several states in the Eastern United States. Based on morphological observations and phylogenetic analyses of two nuclear loci (internal transcribed spacer, nuclear ribosomal large subunit) and two mitochondrial loci ( cox2, cox1), we report Peronospora and Plasmopara occurrences on frost grape (Ohio), Lenten rose (North Carolina, Virginia), mock strawberry (Maryland), redbud (North Carolina), snapdragon (Virginia), viburnum (North Carolina), and Virginia creeper (Maryland, Ohio). The phylogenetic analysis indicated that the Peronospora isolates on snapdragon ( Antirrhinum majus) from Virginia were clearly separated from other P. antirrhini isolates collected on Misopates orontium, indicating that they constitute a separate species here described as Pe. ceperoae. The phylogenetic analyses also supported the combination of Peronospora matthiolae, a pathogen of Matthiola incana (stock), into Hyaloperonospora, based on specimens collected in Ohio. Collectively, our results suggest a wider geographic distribution for the downy mildew species reported, highlighting the need for continuous surveillance of these pathogens to prevent outbreaks and their introduction to naïve environments.

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