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Pathogenic Races of Gymnosporangium juniperi-virginianae on Apple. Herb S. Aldwinckle, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva 14456; Phytopathology 65:958-961. Accepted for publication 1 April 1975. DOI: 10.1094/Phyto-65-958.

Fourteen apple cultivars were inoculated under controlled conditions with standardized suspensions of basidiospores of Gymnosporangium juniperi-virginianae, collected in ten areas of the U.S. and in Ontario, Canada. Five pathogenic races were distinguished by cultivars on which aecia developed. Race 1 (Indiana and Michigan) was most restricted in host range, and incited aecia on only three test cultivars. Race 2 incited aecia on four cultivars, and Race 3 (Alabama and Arkansas) on six cultivars. Race 4 (New Jersey, New York, Maine, Iowa, and Kentucky) incited aecia on seven cultivars. Race 5 (Ontario) incited aecia on eight cultivars, the widest host range of any race. Within races, individual collections differed in production of pycnia and nonsporulating flecks on certain cultivars.

Additional keywords: Malus, disease resistance, cedar apple rust.