Studies on the Inheritance of Stemphylium Resistance in Tomatoes

Abstract

Gray leaf spot of tomatoes, caused by Stemphylium solani Weber, is widespread and highly destructive in Hawaii. Control by application of fungicides is expensive and, in many instances, only partially successful. All the locally adapted, commercial varieties are susceptible. In a program to develop gray leaf spot resistant commercial varieties, tiny-fruited, resistant tomato lines (Lycopersicon pimpinellifolium and Targinnie Red - L. esculentum) were introduced. These were crossed with locally adapted susceptible varieties. Seed from such crosses was further propagated and back crossed to the two parents. First, second, and third generation seedlings, as well as backcross generations, were examined in greenhouse tests to determine the mode of inheritance of resistance. The data obtained indicate that resistance is governed by a single dominant genetic factor pair. This factor pair is assigned the symbol "Sm-sm."