Cadle-Davidson, L. .
Evidence for race-specificity in resistance to grape powdery mildew.
Powdery mildew, caused by Uncinula necator (syn. Erysiphe necator), is economically the most important disease of grapes and can be particularly devastating on high quality Vitis vinifera grapes, which are almost universally susceptible to powdery mildew. Wild Vitis spp. are widely used as powdery mildew resistant parents in interspecific crosses, but knowledge about the genetic mechanisms of resistance and about the diversity of virulence in pathogen populations is lacking. While race-specific resistance to powdery mildews of other crops is common (though rarely durable), previous studies in grapevine have not tested the race specificity of grape powdery mildew resistance. In the current study, 120 genotypes of Vitis spp. were inoculated in a controlled environment with a single conidial isolate of U. necator, and 74 genotypes were classified as resistant. The same genotypes were assayed for resistance to a natural vineyard population of U. necator in Fredonia, NY, and 37 of the 74 previously resistant individuals were susceptible to the natural population, suggesting the presence of race-specific resistance. All 46 genotypes that were susceptible to the single isolate were also susceptible to the natural vineyard population of U. necator. Subsequent light microscopy experiments revealed varying levels of ontogenic resistance in all genotypes tested (resistant and susceptible) and the occurrence of penetration resistance in all wild Vitis spp. tested. These results suggest that many of the available and commonly used sources of grape powdery mildew resistance are race-specific and will be rapidly overcome by U. necator isolates that are already prevalent in New York State. However, germplasm is available for the development of grape cultivars with potentially durable resistance to grape powdery mildew.
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1 - USDA-ARS, Grape Genetics Research Unit, 630 W. North St., Geneva, NY, 14456, USA
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM