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Geographic Distribution of Cryptic Species of Plasmopara viticola Causing Downy Mildew on Wild and Cultivated Grape in Eastern North America

First, fifth, tenth, and thirteenth authors: INRA, ISVV, UMR1065 Santé et Agroécologie du Vignoble, F-33883, Villenave d'Ornon, France; second author: INRA, UMR1131 Santé de la Vigne et Qualité du Vin, F-68000, Colmar, France; third author: Virginia Tech, Department of Plant Pathology, Physiology, and Weed Science, 417 Price Hall, Blacksburg 24061; fourth author: Agriculture and Agri-Food Canada, 430 Gouin Boulevard, Saint-Jean-sur-Richelieu, Quebec J3B 3E6, Canada; sixth author: Ohio State University, Department of Plant Pathology, 224 Selby Hall, Wooster; seventh author: Cornell University, Plant Pathology and Plant-Microbe Biology, 115 Barton Laboratory, NYSAES, Geneva, NY; eighth author: Florida Agricultural and Mechanical University, Center for Viticultural Sciences and Small Fruit, Tallahassee 32307; ninth author: Virginia Tech, Department of Plant Pathology, Physiology, and Weed Science, 595 Laurel Grove Road, Winchester 22602; eleventh author: Department of Plant Pathology, Michigan State University, East Lansing 48824; and twelfth author: Cornell University, Long Island Horticultural Research & Extension Center, 3059 Sound Avenue, Riverhead, NY 11901.

The putative center of origin of Plasmopara viticola, the causal agent of grape downy mildew, is eastern North America, where it has been described on several members of the family Vitaceae (e.g., Vitis spp., Parthenocissus spp., and Ampelopsis spp.). We have completed the first large-scale sampling of P. viticola isolates across a range of wild and cultivated host species distributed throughout the above region. Sequencing results of four partial genes indicated the presence of a new P. viticola species on Vitis vulpina in Virginia, adding to the four cryptic species of P. viticola recently recorded. The phylogenetic analysis also indicated that the P. viticola species found on Parthenocissus quinquefolia in North America is identical to Plasmopara muralis in Europe. The geographic distribution and host range of five pathogen species was determined through analysis of the internal transcribed spacer polymorphism of 896 isolates of P. viticola. Among three P. viticola species found on cultivated grape, one was restricted to Vitis interspecific hybrids within the northern part of eastern North America. A second species was recovered from V. vinifera and V. labrusca, and was distributed across most of the sampled region. A third species, although less abundant, was distributed across a larger geographical range, including the southern part of eastern North America. P. viticola clade aestivalis predominated (83% of isolates) in vineyards of the European winegrape V. vinifera within the sampled area, indicating that a single pathogen species may represent the primary threat to the European host species within eastern North America.

Additional keywords: plant pathogen.