2018 ASHS Annual Conference

Muscadine grapes, Vitis rotundifolia Michx. subgenus Muscadinia Planch. (2n=40), are a disease-resistant specialty crop native to the southern United States. Large berries, balanced fruity flavor, dry picking scar, and cold hardiness are important breeding objectives of the University of Arkansas fresh-market muscadine breeding program. The development of predictive molecular markers for these traits would assist breeders in planning crosses and selecting promising seedlings early in the breeding pipeline. The objective of this study was to identify quantitative trait loci (QTL) for fruit quality attributes in two F₁ muscadine populations (‘Supreme’ x ‘Nesbitt’ and ‘Black Beauty x ‘Nesbitt’) segregating for many important traits. Ten mature berries were harvested from 172 progeny in each mapping population and evaluated for berry weight, soluble solids content, pH, and titratable acidity at the University of Arkansas Fruit Research Station during 2011 and 2012. The proportion of berries in each sample with a dry picking scar was recorded during the 2011 season. The severity of winter injury to each vine was visually assessed on a 1-5 scale during June 2017, after low temperatures dipped below -10° C on four nights during December 2016 and January 2017. A high-density consensus linkage map consisting of 2346 markers in 20 linkage groups (LG) with a total length of 2164 cM was created using genotyping-by-sequencing (GBS) data from both populations. Quantitative trait loci were identified by analysis of traits combined over populations based on the consensus map. A large effect QTL explaining 15 to 30% of variation for berry weight in each population during 2011 and 2012 was mapped to LG 2. This QTL co-localized with the muscadine sex locus, with pistillate progeny producing larger fruit on average than perfect-flowered progeny. Overlapping QTL explaining 9 to 16% of variation for soluble solids content, titratable acidity, and pH measured in 2011 were mapped to LG 6. Separate overlapping QTL identified for SSC, TA, and pH in the 2012 season were mapped to LG 17 and explained 10 to 16% of trait variation. Three QTL for dry picking scar were found on LGs 3, 6, and 11, with the largest effect QTL on LG 6 accounting for 22% of trait variation in the ‘Supreme’ x ‘Nesbitt’ population. A QTL explaining 10 to 16% of variance in cold hardiness was also mapped to LG 6. The saturated linkage maps and QTL reported here lay the groundwork for marker-assisted breeding in muscadine grapes.