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

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 (sigma (g) (2)) was significant for all berry traits, especially for alpha ratio (sugar composition) and gamma ratio (amino acid composition). The yearly effect (sigma (y) (2)) was significant for SSC, total sugar content, and total amino acid content but not for alpha ratio, titratable acidity, beta ratio (organic acid composition) and gamma ratio. Repeatabilities over the 3 years were very high for alpha ratio and gamma ratio, while they were low for SSC, total sugar content, titratable acidity, beta ratio, and amino acid content. Correlation coefficients between the values of each individual year and the 3-year mean were relatively high for the alpha ratio and gamma ratio. We highlight the varietal differences in the alpha ratio and gamma ratio because of the low environmental variation. Two types of grape were distinguished on the basis of sugar composition: hexose accumulators (alpha ratio a parts per thousand yen 0.81) and sucrose accumulators (alpha ratio a parts per thousand currency sign 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 gamma ratio. Like the alpha ratio, variation in the gamma ratio is closely related to cultivar parentage and regional differences. Vitis vinifera cultivars exhibited a skewed distribution with a gamma ratio below 1.0 because they contain low levels of sweet amino acids. In contrast, the gamma ratio frequently exceeded 1.5 in American hybrid cultivars because they contain high levels of sweet amino acids.