ヤマブドウ研究― 樹及び果実の特性 ―

Vitis coignetiae Pulliat is one of the naturally growing grape vines in the Japanese Islands, of which the fruit has been utilized as a healthy juice and wine. In Hiruzen Highlands, the vines have been cultivated for wine making since the 1980's. We have studied the physiology of berry set and berry maturation of the vines to improve the fruit production and fruit quality for last 14 seasons. V. coignetiae vines are dioecious and need insect pollination, mainly by two species of Diptera, Eristalis tenax and Eristalis cerealis, and one species of Hymenoptera, Ceratina japonica, indicating that mix planting with male vines and reservation of such insects are recommended. Once pollen grains have pollinated onto the stigma, most of them grow a pollen tube to penetrate into ovule tissue and finally reach the embryo sac to complete ovule fertilization. There are several types of coignetiae vines in Hiruzen vineyards that have different genetic backgrounds. RAPD analysis of 15 vines revealed that they can be divided into three groups and two individuals. Coignetiae vines have been found to have a lower tolerance for water logging than other cultivars, whereas they have moderate drought tolerance. Furthermore, coignetiae vines are not very disease tolerant, especially toward downy mildew, indicating that growers must take sufficient care over drainage and fungus control. V. coignetiae vines accumulate high levels of sugar and acid into the flesh and anthocyanins in the berry skin when they reach the full ripe stage, which is mid and late October in Hiruzen. Tartaric acid, the main acid constituent in coignetiae berries, is contained at levels as high as 1.0%. Amino acid concentration in the juice is much lower in most coignetiae vines than other wine grapes, although a special coignetiae vine with berries with high amino acid content has been found. V. coignetiae berries have been proved to have several functional properties such as high free radical scavenging activity and anti-photodecomposition of anthocyanin pigments. As commercial products of coignetiae berries, beautiful wines, pure juice, and wine vinegar with a rich and fruity taste are produced.

岡山県真庭市蒜山で，地域特産物として1980年代から栽培が始められたヤマブドウ（Vitis coignetiae Pulliat）について，1993年から現在で，系統の識別，結実と果実発育の特性，果実成分の分析を行った．その結果，雌雄異株であるヤマブドウの結実安定のためには，受粉昆虫の活動が必要で，有用な数種の訪花昆虫が同定された．ヤマブドウの雌ずいは形態的に発育がよく，確実に受粉されれば，結実安定は達成される．しかし，ヤマブドウ樹は乾燥には強いが，耐湿性は低く，また，ベト病抵抗性も高くないので，ブドウ園の立地条件が重要である．成熟果実には糖，酸が高濃度で含まれるが，アミノ酸濃度は低い．しかし，探索の結果，一般の赤ワイン用品種 と同程度のアミノ酸含量を持つ樹が発見された．また，ヤマブドウ果実には高濃度の色素が含まれるが，同時にこの色素の光分解を抑制する成分が含まれていることが明らかになった．今後，この成分の同定と食品添加物としての利用が期待される．蒜山地区内のひるぜんワイン㈲ではヤマブドウワイン製造の技術改善が続けられ，赤およびロゼワインとして高い評価を得るようになった．また，「おかやまバイオアクティブ」の開発プロジェクトとしてワインビネガーの試作も行われた．現在，発ガン抑制などの機能性研究も進められており，健康食品としての生産拡大が期待される．