Five independent loci each control monogenic resistance to gummy stem blight in melon ( Cucumis melo L.).

Inheritance and segregation analysis demonstrated that five independent genes in melon confer monogenic resistance to foliar infection by the fungal pathogen Didymella bryoniae, resulting in the disease known as gummy stem blight (GSB). In this study, two new monogenic sources of GSB resistance were characterized. Resistance in Cucumis melo PI 482398 was monogenic dominant based on segregation analysis of F(1), F(2) and backcross populations, while resistance in C. melo PI 482399 showed monogenic recessive inheritance. Four accessions, PI 482398, PI 157082, PI 511890, and PI 140471, each previously known to carry monogenic dominant resistance to GSB, were intercrossed to determine genetic relationships among these resistance sources. Recovery of susceptible individuals in F(2) populations confirmed that these accessions possess different resistance genes. Resistance loci were designated Gsb-1 (formerly Mc, monogenic dominant resistance from PI 140471), Gsb-2 (monogenic dominant resistance from PI 157082), Gsb-3 (monogenic dominant resistance from PI 511890), Gsb-4 (monogenic dominant resistance from PI 482398) and gsb-5 (monogenic recessive resistance from PI 482399).