SHABI, E., Division of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50-250, Israel
KATAN, T., Division of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50-250, Israel
MARION, K., Division of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50-250, Israel

Ten single‐spore cultures of benomyl‐resistant Venturia inaequalis were isolated from apple scab lesions at two sites in Israel. According to the ability of the isolates to germinate and grow at varying benomyl concentrations, three levels of resistance were determined in vitro: two moderately resistant (MR) isolates were resistant to 5 μg/ml but sensitive to 50 μg/ml benomyl; five highly resistant (HR) isolates, grew and sporulated at 50 μg/ml more slowly than at 5 μg/ml; and three isolates with very high resistance (VHR) grew and sporulated as freely at 50 μg/ml as at 5 μg/ml. Crosses between resistant isolates and sensitive wild types, as well as between different resistant isolates, showed that the various levels of benomyl resistance are conferred by three allelic mutations that constitute a polymorphic series in a single Mendelian gene. In these isolates benomyl resistance is not affected by modifying genes or cytoplasmic components. Copyright © 1983, Wiley Blackwell. All rights reserved