Plant, Animal & Microbe Genomes X Conference Plant, Animal & Microbe Genomes X ConferenceJanuary 12-16, 2002
Town & Country Convention Center
San Diego, CA
Poster: Gene Isolation
The soil-borne fungus Fusarium oxysporum f.sp. melonis causes significant losses in melon production worldwide. The only economically feasible control measure available is the use of resistant cultivars. In melon, resistance to F. oxysporum races 0 and 1 is conferred by a single dominant gene, Fom-2. Previously, two co-dominant PCR markers (FM and AM) and an AFLP marker (ACT/CAT1) were found to be tightly linked to Fom-2 in backcross population of 60 plants. The AFLP marker was used to screen filters of a Bacterial Artificial Chromosome (BAC) library and PCR-based markers, SSR6 and SSR138, were developed using the BAC end sequences of the positive clones. Fine mapping based on 156 recombinant inbred lines derived from a cross between PI161375 and "Vedrantais" which segregate for Fom-2, strongly indicated that FM and SSR138 flank the gene at 0.7 and 0.4 cM, respectively. Interestingly, SSR6 cosegregated with Fom-2 in the same population. In order to construct a physical map of the region containing Fom-2 gene, the identified markers AM, FM, SSR6 and SSR138 were used to screen the HindIII BAC library. Using a chromosome walking approach, a single contig of BAC clones covering the genetic interval encompassing Fom-2 was constructed. The physical order of the markers was as predicted by the genetic map and confirmed the established genetic position of Fom-2. End sequencing of BAC clones in the contig revealed the presence of three sequences with homology to characterized resistance genes in other species. Two sequences had homology to NBS-LRR R-genes. The third sequence had homology to the resistance gene Cf-2 in tomato.