Evaluation of table grape genetic resources for sugar, organic acid, and amino acid composition of berries

Abstract

Variations in the sugar, organic acid, and amino acid composition of table grape berries were determined in three successive years in 129 grape cultivars. Three regional groups were represented among these cultivars; European, North American, and Japanese. All cultivars are conserved at the Fukuoka Agricultural Research Center in Japan. Three representative ripe average-sized bunches were selected from one vine per cultivar. Ripeness was judged by visual observation of seed color change to dark brown, without senescence of berry tissue. Soluble solids content (SSC) was weakly correlated with other berry traits, but strongly correlated with total sugar content. Genotypic variance (σ g 2) was significant for all berry traits, especially for α ratio (sugar composition) and γ ratio (amino acid composition). The yearly effect (σ y 2) was significant for SSC, total sugar content, and total amino acid content but not for α ratio, titratable acidity, β ratio (organic acid composition) and γ ratio. Repeatabilities over the 3 years were very high for α ratio and γ ratio, while they were low for SSC, total sugar content, titratable acidity, β ratio, and amino acid content. Correlation coefficients between the values of each individual year and the 3-year mean were relatively high for the α ratio and γ ratio. We highlight the varietal differences in the α ratio and γ ratio because of the low environmental variation. Two types of grape were distinguished on the basis of sugar composition: hexose accumulators (α ratio ≥ 0.81) and sucrose accumulators (α ratio ≤ 0.80). The hexose- and sucrose-accumulating traits were related to genetic or regional differences. Cultivars were classified into five types on the basis of the γ ratio. Like the α ratio, variation in the γ ratio is closely related to cultivar parentage and regional differences. Vitis vinifera cultivars exhibited a skewed distribution with a γ ratio below 1.0 because they contain low levels of sweet amino acids. In contrast, the γ ratio frequently exceeded 1.5 in American hybrid cultivars because they contain high levels of sweet amino acids.