Effect of phyllotactic position and cultural treatments toward successful direct shoot organogenesis in dwarf ‘Pixie’ grapevine (Vitis vinifera L.)

In Vitis spp. where somatic embryogenesis-based regeneration predominates, an efficient, reproducible and robust method of direct shoot organogenesis from leaf explant material has been established in the dwarf wine grape ‘Pixie’ (Vitis vinifera). This regeneration system was achieved by testing the response of leaf material in two stages of development, and pre-conditioning the explant material in dark conditions and/or in liquid media prior to excising from the plant and placing it on solidified media. The pre-excision treatments included (1) a dark period of 24 h, with no regeneration medium; (2) soaking in regeneration medium followed by a dark period of 24 h; (3) a dark period of 24 h followed by soaking in liquid VRM (Vitis Regeneration Medium); (4) vacuum infiltration in liquid VRM followed by a dark period of 24 h; and (5) a control of no pre-conditioning treatment. Excised leaves from pre-treated intact plants in vitro significantly increased the frequency of shoot organogenesis. The most responsive explant material consisted of young semi-translucent apical leaves varying in size from 3 to 8 mm in length. The most successful combinations of factors contributing to shoot organogenesis involved the solely dark-exposed apical leaves or the soaking in VRM followed by a dark period. These results are expected to facilitate Vitis-related research in genetics, functional genomics, physiology, and other fields.