Characterization and phylogenetic analysis of the ancient Japanese grape cultivar ‘Juraku’

The ‘Juraku’ grape was cultivated in Kyoto as early as the 17^th century, but as far as we now know, commercial orchards have not been cultivated after the 1940s. Recently, a grapevine over 100 years old was found in the garden of a private house, and this vine was estimated to be the ancient Japanese grape cultivar ‘Juraku’ or its offspring. The fruit quality assessment and the phylogenetic study of this old grape cultivar were made in order to preserve and use the germplasm. The following parameters were considered: berry weight, length and width, soluble solids content (TSS), sugar composition, juice pH, total phenolics, and amino acid composition. These parameters were compared with the Japanese wine grape cultivar ‘Koshu’. Berry size of the ‘Juraku’ (about 2 g fw) was smaller than that of ‘Koshu’ (about 5 g fw). The average TSS of the juice was 18.2 °Brix. The sucrose was not detected, but reducing sugars (glucose and fructose) were detected in the juice. ‘Juraku’ had a higher tartaric acid content and a lower malic acid content than the ‘Koshu’. ‘Juraku’ also had a higher content of several amino acids in the skin. The phylogenetic analysis was done based on the genome sequence data derived from 30 cultivars and wild species accessions, including European, American, and Asian origin. The ‘Juraku’ showed a close genetic relationship with ‘Koshu’ and belonged to the same cluster. Our results indicate that ‘Juraku’ was a hybrid between Vitis vinifera and unknown species.