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Title: Isolation, Sequence Analysis, and Linkage Mapping of NBS-LRR Disease Resistance Gene Analogs in Watermelon

Author
item Harris-Shultz, Karen
item Wechter, William - Pat
item Levi, Amnon

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2009
Publication Date: 12/1/2009
Citation: Harris, K.R., Wechter, W.P., Levi, A. 2009. Isolation, Sequence Analysis, and Linkage Mapping of NBS-LRR Disease Resistance Gene Analogs in Watermelon. Journal of the American Society for Horticultural Science. 134:649-657.

Interpretive Summary: The watermelon is vulnerable to numerous plant pests and diseases such as viruses, bacteria, fungi, and nematodes. However, only limited information is known about genes that confer resistance to diseases and pests in watermelon. In this study, we used DNA technologies to identify genes of watermelon with DNA sequences similar to those found in genes conferring disease or pest resistance in other plant species. We identified several key groups of these resistance gene sequences in wild type watermelon accessions known to possess disease or pest resistance. We developed DNA markers for each of these resistance gene groups. These DNA markers may be useful to plant breeders interested in developing watermelon varieties that are resistant to diseases and pests, resulting in a healthier plant, safer food supply, and a reduced need for pesticides.

Technical Abstract: Cultivated watermelon (Citrullus lanatus var. lanatus) is susceptible to a wide range of pathogens. Sixty-six watermelon resistance gene homologs were cloned from ‘Calhoun Gray’, PI 296341, and PI 595203 using degenerate primers to select for the nucleotide binding site (NBS) from the NBS-LRR resistance gene family. After contig assembly, eight groups of watermelon resistance gene homologs (WRGH) were identified and amino acid sequence alignment revealed that these groups contained motifs characteristic of NBS-LRR resistance genes. Using cluster analysis, the eight WRGH were further classified as having homology to Drosophila Toll and mammalian interleukin-1 receptor (TIR) and non-TIR domains. Three of these WRGH, as well as three disease related watermelon ESTs, were placed on a testcross map. Linkage mapping of WRGH identified linkage group XIII as an area in watermelon where resistance gene homologs cluster. In addition, these WRGH sequence tagged sites (WRGH-STS) were amplified among the various genera of the Cucurbitaceae indicating that conservation of R-gene homologs exist among cucurbit species. These WRGH-STS markers may be useful in marker-assisted selection for the improvement of disease resistance in watermelon.