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Title: PHYSICAL MAPPING OF THE FOM-2 REGION IN MELON (CUCUMIS MELO L.) USING A BACTERIAL ARTIFICIAL CHROMOSOME (BAC) LIBRARY

Author
item WANG, YI-HONG - CLEMSON UNIVERSITY
item Thomas, Claude
item DEAN, RALPH - CLEMSON UNIVERSITY

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Molecular markers are needed to facilitate and expedite the development of melon cultivars with resistance to Fusarium wilt which is one of the most important, production-limiting fungal diseases of melon throughout the world, because genetic resistance is the most effective, economical, and environmentally-benign method of disease control. Previous research under this project in cooperation with Clemson University identified two DNA markers that co-segregate with Fom-2, a gene conferring resistance to races 0 and 1 of Fusarium wilt. In further, recently completed cooperative studies, these two markers linked to Fom-2 were used to screen a bacterial artificial chromosome (BAC) library made from multi-disease resistant ARS melon line MR-1, including identification of clones which were fingerprinted, physically mapped, end-sequenced, and searched against GenBank for characteristics of other cloned resistance genes. Confirmation nof identity of this resistance gene will allow direct introgression into susceptible melon and other germplasm to provide the most efficient development of Fusarium wilt resistant cultivars.

Technical Abstract: Large-insect genomic libraries such as Bacterial Artificial Chromosome (BAC) libraries represent valuable tools for gene localization, cloning, and physical and genetic studies of the genome. Previously, the authors genetically mapped the Fom-2 gene that confers resistance to Fusarium wilt race 1 of melon. Two markers (596-1 and AGG/CCC) cosegregating with the gene in a backcross population of 60 individuals were converted to codominance (FM and AM, respectively). In studies reported here, these markers were used to screen a melon BAC library. Marker FM identified 14 and AM identified 23 BAC clones, respectively. These clones were fingerprinted and ends sequenced. Alignment of sequences at GenBank produced four matches (E value 8e-06) to leucine-rich repeats (LRRs) of resistance genes (R-genes)in the clones identified by FM and five nucleotide-binding sites (NBSs) of R-genes (E value 2e-28) in the clones identified by AM. The evidence is not conclusive, but fingerprinting and assembly by FPC software suggests that all clones belonged to one contig at relaxed stringency. Hybridization analysis also suggests that they may form one contig. Furthermore, if Fom-2 belongs to the class of cloned R- genes that contains both NBS and LRR domains then the sequence evidence is also consistent with a single overlapping contig. Further studies are needed to prove that this region contains Fom-2 and that this R-gene is the Fom-2 gene.