Genetics of Resistance to Benomyl inVenturia inaequalisIsolates from Israel and New York

Abstract

Fourteen single-spore cultures of V. inaequalis isolated from apple [Malus sylvestris] scab lesions at 2 sites in Israel and at 3 sites in New York state, USA, showed resistance to benomyl. Four levels of resistance were determined in vitro: 5 isolates with low resistance grew at 0.5 but not at 5 .mu.g of benomyl/ml; one moderately resistant isolate grew at 5 but not at 50 .mu.g/ml; 3 highly resistant isolates grew and sporulated at 50 .mu.g/ml but more slowly than at 5 .mu.g/ml; and 5 isolates with very high resistance grew and sporulated abundantly at benomyl concentrations higher than 50 .mu.g/ml. In crosses between different resistant isolates and between sensitive wild-types and resistant isolates, the levels of benomyl resistance are controlled by a polymorphic series consisting of 4 allelic mutations, in a single Mendelian gene. No effect of modifying genes or cytoplasmic components on benomyl resistance was evident in the isolates from their country.