Mapping Alternaria cucumerina Resistance in Cucumis melo

Alternaria Leaf Blight (Alternaria cucumerina) is a serious fungal pathogen affecting worldwide production of melon (Cucumis melo). Introgression of resistance genes and selection for resistance requires identification of resistant varieties and would be greatly facilitated by the availability of molecular markers. We are attempting to identify markers linked to Alternaria resistance in a recombinant inbred line (RIL) from an initial cross of MR-1 (resistant) and Ananas Yokneam (susceptible). The resistance gene Ac has been reported in USDA breeding line MR-1, but molecular markers have yet to be identified. Utilizing bulked segregant analysis, we have been conducting marker discovery using 176 RAPD and 295 High Frequency Oligonucleotides-Targeting Active Genes (HFO-TAG) primers. Ninety-nine RAPD and 38 HFO-TAG primers were screened using agarose gel electrophoresis, yielding 212 polymorphisms. Additionally, HFO-TAG primers were modified for screening on a fragment analysis system resulting in an additional 544 polymorphisms. Three hundred of the most prominent polymorphisms identified during BSA have been used to construct a linkage map of a population of 94 RILs. This map will have immediate utility in marker identification of gene loci associated with Alternaria resistance, as well as other resistance genes found in MR-1.