In vitro induction of hexaploid forms and generation of hexaploid forms from induced mixoploids in triploid grape cultivars (vitis vinifera complex)

Several triploid cultivars have been bred in Japan and other countries. We also have bred three promising triploid cultivars and hybrids. Because of the triploidy, however, these grapes hardly produced next generations by crossings. The aim of this study was to induce chromosome doubling in vitro in newly bred triploid hybrids 'BK seedless' and 'BRI seedless' grapes, restore their fertility and make it possible for further breeding with them. Ploidy level of the obtained hexaploid plantlets was confirmed by flow cytometry. A hexaploid plant was produced in vitro when triploid 'BRI seedless' shoots were treated with 625 μM colchicine solution for 72 hours, indicating that hexaploid forms of triploid grapes could be produced by using this method. Further, hexaploid plants were also derived from colchicine-induced mixoploid shoots (triploid- hexaploid-chimeras) following three times of successive subcultures of the shoot apices transplanting 16 weeks intervals in vitro. The hexaploid grapes obtained in vitro showed behind in growth and were difficult to acclimatize.