Abstract Laila FayyazSummaira RiazRong HuM. Andrew Walker

Map-Based Positional Cloning of Powdery Mildew Resistance Genes from the Chinese Grape Species Vitis piasezkii

Laila Fayyaz, Summaira Riaz, Rong Hu, and M. Andrew Walker* 
*Department of Viticulture and Enology, University of California,
Davis CA 95616 (awalker@ucdavis.edu)

All cultivated grape varieties are highly susceptible to powdery mildew (PM), a fungal disease caused by the pathogen Erysiphe necator, which can evolve rapidly under high selection pressure. The wild Chinese grape species, Vitis piasezkii, is resistant to PM and major resistance loci Ren6 and Ren7 were identified on chromosomes 9 and 19, respectively. Ren6 confers complete resistance, while Ren7 provides partial resistance. In this study, we report a refined positioning of the Ren6 locus and the initial results of V. piasezkii-based BAC library screening. A total of 38 recombinant plants from backcross populations were selected with flanking SSR markers. Plants were evaluated for PM resistance and based on both genotyp-ic and phenotypic scores, the new position of the Ren6 locus is between markers PN9-66.01 and PN9-068. We developed a BAC library from the genomic DNA of the F1 seedling 11373-087, which has an average insert size of ~110 Kb and seven to eight X coverage. DNA probes (600 to 700 bp in length) in close proximity to the flanking markers and without repetitive regions were designed using the reference grape genome PN40024. The BAC library will be screened and clones will be identified and sequenced to develop a physical map of the Ren6 locus capable of identifying candidate powdery mildew resistance genes. Comparisons will be made with the susceptible reference grape genome and the Cabernet Sauvignon genome for this region. This study will be the first attempt to identify candidate resistance genes in V. piasezkii. Candidate genes will be tested in a susceptible V. vinifera cultivar(s) to verify their ability to confer resistance.

Funding Support: PhD Scholarship to Ms. Fayyaz from the Agriculture Innovation Program-Pakistan, funded by the US Agency for International Development through CIMMYT, the International Maize and Wheat Improvement Center