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Vitis aestivalis-derived ‘Norton’ is the official grape of the State of Missouri, grown in regions with high disease pressure and cold winter temperatures, where Vitis vinifera is not adapted. It reportedly offers an abundance of traits, including resistance to powdery and downy mildew as well as botrytis bunch rot, which can be used to naturally improve existing V. vinifera germplasm. To identify genetic determinants for resistance to downy mildew caused by Plasmopara viticola and botrytis bunch rot caused by Botrytis cinerea in V. aestivalis-derived ‘Norton’, a mapping population of 182 individuals was constructed from a cross between ‘Norton’ and V. vinifera ‘Cabernet Sauvignon’. A consensus genetic map was constructed with 411 simple sequence repeat (SSR) markers. In collaboration with VitisGen (http://www.vitisgen.org), approximately 43,320 single-nucleotide polymorphism (SNP) markers generated by genotyping-by-sequencing (GBS) were identified, and a consensus map of 3825 SNPs was developed. Of these, 1665 SNP and 407 SSR markers were clustered into 19 linkage groups, for a total of 2072 markers spanning a genetic distance of 2203.5 cM. In preparation for placing traits on this integrated high-resolution map, disease progression and resistance reaction in response to P. viticola and B. cinerea were evaluated in this population for 2 years. The quantitative trait loci (QTL) analysis indicated major resistance loci on linkage group 18 for downy mildew and linkage group 2 for botrytis bunch rot, respectively. The ultimate goal of this program is to use genetic markers to rapidly deploy favorable alleles and accelerate breeding cycles for new cultivar releases.

‘Cynthiana’/‘Norton’ is considered the best American native grape variety for fine wine with suspected to have tolerance to PD (Pierce’s disease) and proven low susceptibility to foliar and fruit disease. The variety has been very successfully grown for commercial wine production for more then a century in the eastern United States and for the past decade in Louisiana within PD zone as well. Most of the grapevine varieties in existence today are centuries old and are considered to have arisen by various means: domestication of wild vines, spontaneous crosses between wild vines and varieties, and crosses between two or more varieties. Using the methods of molecular analysis, the pedigree describing the genetic history of grape variety can be reconstructed. DNA microsatellites have proved to be the markers of choice for this purpose since they are transmitted in a codominant Mendelian manner. It is assumed that ‘Cynthiana’/‘Norton’ is originated from Vitis aestivalis, Michaux. We are investigating the phylogenetics of the ‘Cynthiana’/‘Norton’ grape via data mining in the North American grape germplasm collections, ampelographic analysis and specifically expressed in the variety microsatellite markers. We are using an already-published set of ten pairs of SSR primers designed for Vitis riparia. For the purpose developing more specific markers, ‘Norton’ publicly available expressed sequence tags (ESTs) were used to screen for SSR. Two 202 SSRs out of 2,101 ESTs were located and the promising SSR primers were synthesized for specific amplification in the targeted grape accessions. This study is designed to identify the pedigree and genetic make up of ‘Cynthiana’/‘Norton’ grape and to verify that this particular grape variety carry tolerance to Pierce’s disease and is appropriate for high quality red wine production under Florida environmental conditions.

Stilbene synthase (StSy), encoded by a multigene family of several members, is the key enzyme to form resveratrol, the major component of the grapevine phytoalexin response. Genes encoding stilbene synthases have previously been described for several plant species including grapevine. Pierce's disease (PD), anthracnose and downy mildew are the limiting factors for growing European grape (V. vinifera) in the southeastern United States. Native American grape species such as V. shuttleworthii, V. aestivalis and V. rotundifolia present strong resistance to these diseases. In order to understand the role of StSy in grapevine disease resistance, several hundred stilbene synthase gene sequences from among Vitis species were retrieved from the NCBI database. These stilbene synthase sequences were blasted against about 9,000 unigenes of V. shuttleworthii grape. Homologous relationships among the stilbene synthase (StSy 1) from five Vitis species were analyzed by multiple alignments.