Genetic mapping of a fusarium wilt resistance gene (Fom-2) in melon (Cucumis melo L.)

Fusarium wilt caused by Fusarium oxysporum f.sp. melonis is one of the most devastating diseases in melon production worldwide. The most effective con trol measure available is the use of resistant varieties. Identifying molec ular markers linked to resistance genes can serve as a valuable tool for th e selection of resistant genotypes. Bulked segregant analysis was used to i dentify markers linked to the Fom-2 genes, which confers resistance to race s 0 and 1 of the fungal pathogen. Pooled DNA from homozygous resistant or h omozygous susceptible progeny of F-2 cross between MR-1 and AY was screened using 240 PstI/MseI and 200 EcoRI/MseI primer combinations to identify AFL P markers linked to Fom-2. Fifteen markers potentially linked to Fom-2 were identified, all with EcoRI/MseI primer pairs. These were mapped relative t o Fom-2 in a backcross (BC) population of 60 progeny derived from MR-1 x AY with AY as recurrent parent. Two AFLP markers (ACT/CAT1 and AAC/CAT1) flan ked the gene at 1.7 and 3.3 cM, respectively. Moreover, AFLP marker AGG/CCC and the previously identified RAPD marker 596-1 cosegregated with Fom-2. T hese two dominant markers were converted to co-dominant markers by designin g specific PCR primers that produced product length polymorphisms between t he parents. A survey of 45 melon genotypes from diverse geographic origins with the co-dominant markers demonstrated a high correlation between fragme nt size and the resistance phenotype. These markers may therefore be useful in marker-assisted breeding programs.