Alice Wise

Geographic distribution of cryptic species of Plasmopara viticola causing downy mildew on wild and cultivated grape in eastern North America.

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.

Mitigating the Economic Impact of Grapevine Red Blotch: Optimizing Disease Management Strategies in U.S. Vineyards

Grapevine red blotch disease (GRBD) is a recently-recognized viral disease found across some of the major grapegrowing regions in the United States. Vineyard managers were surveyed to (i) estimate the economic impact of GRBD on Vitis vinifera cv. Cabernet Sauvignon in Napa and Sonoma Counties in California and on V. vinifera cv. Merlot in eastern Washington and Long Island in New York, and (ii) to identify cost-minimizing management strategies under various disease incidence rates, price penalties for suboptimal fruit composition, timing of disease onset relative to vineyard age, and costs of control. The economic cost of GRBD was estimated to range from

Impact of Severity and Timing of Basal Leaf Removal on 3-Isobutyl-2-Methoxypyrazine Concentrations in Red Winegrapes

2213/ha in eastern Washington, when disease onset occurs at a low initial infection level and there is a low price penalty, to

Growing Vitis vinifera grapes in New York State. I - Performance of new and interesting varieties

68,548/ha in Napa County, when initial infection rates and quality penalties are both high. Our results further suggest that roguing symptomatic vines and replanting with clean vines derived from virus-tested stocks minimize losses if GRBD incidence is low to moderate (below 30%), while a full vineyard replacement should be pursued if disease incidence is higher, generally above 30%. These findings should help vineyard managers in the four examined viticultural regions adopt optimal GRBD management strategies.