P1130Free the Tannins: The Role of Grape Pathogenesis-Related Proteins in Limiting Condensed Tannin Extraction during Winemaking
Free the Tannins: The Role of Grape Pathogenesis-Related Proteins in Limiting Condensed Tannin Extraction during Winemaking
Grape-derived condensed tannins (CT) are important to the mouthfeel of red wines, but CT concentrations in red wines produced from wild Vitis species or their hybrids are often lower than corresponding wines produced from European wine grapes (V. vinifera), potentially decreasing their utility. These lower CT concentrations in wines arise from not only lower overall and skin tannin concentrations in wild Vitis, but also from lower tannin extractability during fermentation. As part of the USDA-NIFA VitisGen project (www.vitisgen.org) for grapevine cultivar improvement, we investigated the factors limiting CT extraction or retention across species. In one set of experiments, we showed that differences in CT retention following its addition to wines produced from different cultivars are related to the concentration of grape pathogenesis-related proteins (PRPs). A subsequent experiment with 16 site-cultivar combinations showed that under identical winemaking conditions, tannin extractability is well modeled from juice PRP concentration. To study this further, a mapping population from Horizon × Illinois 547-1 (V. rupestris B38 x V. cinerea B9) was phenotyped for juice protein, which ranged from <2 to 121 mg/L. Using a high-resolution genetic map derived from genotyping-by-sequencing markers, one QTL associated with increased PRP concentration was identified from Illinois 547-1 and explained 10% of the variance. Another QTL associated with decreased PRP concentration was identified from Horizon and explained 10% of the variance, but did not pass the significance threshold. These results suggest that limiting PRP accumulation may be a viable strategy for breeding wine grapes that yield high CT wines.