Proposed descriptors for organic acids to evaluate grape germplasm

Abstract

A total of 259 grapevine accessions consisting of 169 varieties, 81 bred lines, 5 rootstocks and 4 clones of 2 wild species were surveyed for content and composition of organic acids in grape juice. Free acid content ranged from 0.13 g to 2.79 g/100 ml, and total acid content ranged from 0.36 g to 3.95 g/100 ml. The acid contents (both free and total acid) of the varieties and bred lines were lower than those of rootstocks and wild species. Furthermore, ratios of free to total acid of the varieties and bred lines were significantly lower than those of rootstocks and wild species. As tartaric and malic acids were major components in acid composition, the ratio of tartaric to malic acid (designated as β ratio) varied from 0.25 to 7.23, and the varieties and bred lines were superior to the rootstocks and wild species in the β ratio. Varietal difference in the β ratio was also observed in the cultivated species (Vitis vinifera and hybrids of V. labrusca x V. vinifera). The ripening period was associated with sharp decrease in free acid content, while β ratio was continued to increase. Although their change during ripening was remarkable, less variation in free acid content and the β ratio was observed near the ripening stage. The variations in free acid content and the β ratio as the descriptors between years were not negligble, indicating that evaluation for the two descriptors should be made in several years, at least three years.