Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2001
Publication Date: N/A
Interpretive Summary: Fusarium wilt is one of the most important, production-limiting fungal diseases of melon throughout the world and resistant varieties are needed to provide the most efficient and environmentally compatible control of this disease. To facilitate the development of these resistant melon varieties, USDA, ARS and university researchers are conducing cooperative research to characterize the gene in melon that confers resistance. The studies in this paper compare the Fusarium wilt resistance gene that the researchers have identified from melon to other resistance genes that have been characterized from plants in an effort to fully sequence this gene. It was found to be very similar to certain other resistance genes, such as one for resistance to a virus disease in tobacco. Full characterization of this resistance gene will allow scientists to directly introgress it into susceptible melon, thus providing the most efficient method of developing Fusarium wilt resistant varieties.
Technical Abstract: Disease resistance has not yet been characterized at the molecular level in cucurbits, a group of high-value, nutritious horticultural plants. Previously, we genetically mapped the Fom-2 gene that confers resistance to Fusarium wilt races 0 and 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 this paper, these markers were used to screen a melon Bacterial Artificial Chromosome (BAC) library. FM identified 14 and AM identified 18 BAC clones, respectively. These clones were fingerprinted and ends sequenced. Fingerprinting analysis showed that clones identified by each marker assembled together into separate contigs at high stringency by FPC (Fingerprint Contig) analysis. GenBank searches produced matches to leucine-rich repeats (LRRs) of resistance genes (R-genes), retroelements and cellulose synthase in the clones identified by FM, and matches to nucleotide-binding sites (NBSs) of R-genes, retroelements and cytochrome P450 in the clones identified by AM. A 6.5 kb fragment containing both NBS and LRR sequences was identified from clones found by marker AM and sequenced. Sequence analysis indicates that the deduced amino acid sequences shares high homology to known R-genes such as N, L6, M, RPP1, RPP5, RPS4, all containing TIR (Toll/interleukin1 receptor)-NBS-LRR. Highest homology was found with the tobacco N gene, which had 42% identify and 58% similarity in the TIR-NBS and LRR regions. The sequence information would be useful for identifying NBS-LRR class of R genes in other cucurbits.