IDENTIFICATION AND DISTRIBUTION OF ALTERNARIA-MALI ON APPLES IN NORTH-CAROLINA AND SUSCEPTIBILITY OF DIFFERENT VARIETIES OF APPLES TO ALTERNARIA BLOTCH

A previously unreported disease characterized by a leaf spot and defoliation of strains of Delicious apple (Malus domestica) occurred in the summers of 1987 and 1988 in western North Carolina. The pathogen was tentatively identified as Alternaria mali, the cause of Alternaria blotch. Morphological characteristics of nine North Carolina isolates were similar to the description of A. mali type A in the literature and a culture obtained from the American Type Culture Collection. The host-specific toxin AM-I was isolated from two North Carolina isolates and appeared identical to standards obtained from Japan. A survey of 60 orchards was conducted in the summers of 1989 and 1990 to determine the distribution of the pathogen and disease incidence in North Carolina. Disease incidence was highest in Henderson County, where it ranged from 0 to 95% in 27 orchards surveyed. Disease incidence and severity increased from 1989 to 1990. Strains of Delicious cultivars were more susceptible than strains of Golden Delicious, whereas Paulared and Idared were the most resistant of 17 varieties and strains of Delicious and Golden Delicious examined.