Quantitative trait locus mapping of downy mildew and botrytis bunch rot resistance in a Vitis aestivalis-derived ‘Norton’-based population

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.