Investigating Evolution and Balance of Grape Sugars and Organic Acids in Some New Pathogen-Resistant White Grapevine Varieties

Abstract

Breeding technologies exploiting marker-assisted selection have accelerated the selection of new cross-bred pathogen-resistant grapevine varieties. Several genotypes have been patented and admitted to cultivation; however, while their tolerance to fungal diseases has been the object of several in vitro and field studies, their productive and fruit composition traits during ripening are still poorly explored, especially in warm sites. In this study, five white pathogen-resistant varieties (PRV) listed as UD 80–100, Soreli, UD 30–080, Sauvignon Rytos, Sauvignon Kretos were tested over two consecutive seasons in a site with a seasonal heat accumulation of about 2000 growing degree days (GDDs), and their performances were compared to two Vitis vinifera L. traditional varieties, Ortrugo and Sauvignon Blanc. Berries were weekly sampled from pre-veraison until harvest to determine total soluble solids (TSS) and titratable acidity (TA) dynamics. All tested PRV exhibited an earlier onset of veraison and a faster sugar accumulation, as compared to Ortrugo and Sauvignon Blanc, especially in 2019. At harvest, Sauvignon Blanc was the cultivar showing the highest titratable acidity (8.8 g/L). Ortrugo and PRV showed very low TA (about 4.7 g/L), with the exception of Sauvignon Rytos (6.5 g/L). However, data disclose that Sauvignon Rytos higher acidity at harvest relies on higher tartrate (+1.1 to +2.2 g/L, as compared to other PRV), whereas in Sauvignon Blanc, high TA at harvest is due to either tartaric (+1 g/L, compared to PRV) and malic (+2.5 g/L, compared to PRV) acid retention. Overall, Sauvignon Rytos is the most suited PRV to be grown in a warm climate, where retaining adequate acidity at harvest is crucial to produce high-quality white wines. Nevertheless, canopy and ripening management strategies must be significantly adjusted, as compared to the standard practice employed for the parental Sauvignon Blanc.