Abstract Cucumber (Cucumis sativus L.) has served as the model system for sex expression in Xowering plants and
its sex type is predominantly controlled by two genetic loci,F and M. Ethylene is the major plant hormone that regulates sex expression in cucumber. The current model predicts that ethylene serves as both a promoter of femaleness
via the F locus and an inhibitor of the male sex via the M locus. In support of this model, genetic, genomic, and transcript analyses indicate that the F gene encodes a key enzyme in ethylene biosynthesis. In this study, we discovered that the M locus co-segregates with an ETHYLENEINSENSITIVE3 (EIN3)-like genomic sequence in an F2
population of 96 individuals. This genetic association agrees with the prediction that the M locus is involved in
ethylene signaling, thus providing another line of evidence in favor of the model. In addition, we generated an ampli-
Wed fragment length polymorphism (AFLP®) map of the M locus, which was delimited into a genetic interval of 2.5
cM. The genetic association and the local map will assist the molecular isolation of the M gene using the combination of positional cloning and candidate gene approach.