Evaluation of Grape Germplasm for Downy Mildew Resistance

Abstract

Grape accessions from the University of Arkansas table grape collection at the Fruit Substation, Clarksville, Ark., and the USDA-ARS grape germplasm repositories in Geneva, N.Y., and Davis, Cal. were evaluated for downy mildew resistance. Evaluations were done in two trials, in a fungicide-free vineyard, established in 1993 and 1994 at Fayetteville, Ark. Ratings for sporulation, chlorosis, and necrosis were taken twice, once in August and once in September, in 1994, 1995, and 1996. Several grape accessions, including ‘Bacchus,’ ‘Ives,’ ‘Lady Patricia,’ ‘Oberlin 595,’ ‘Mid-South,’ ‘Atoka,’ ‘Cottage,’ ‘Long John,’ ‘Loretto,’ ‘Aurelia,’ ‘Patricia,’ ‘Lutie,’ ‘Cynthiana,' V. riparia, V. vulpina, V. thunbergii, V. champinii, V. cinerea helleri, V. cinerea, V. flexuosa, V. aestivalis argentifolia, V. cordata, V. mustangensis, and D-210 were rated as downy mildew resistant in all three years. Certain accessions showed good resistance in 1994, but showed less resistance in 1995 and 1996. Differences in downy mildew ratings on some accessions were found between Fayetteville and other reported locations, while some showed no location effects. In general, susceptible grape accessions had much higher levels of sporulation, chlorosis, and necrosis by the second rating in September.