Abstract
To the standard methods currently used to make grapevine virus-free, apex micrografting on hypocotyls of somatic embryos is proposed as an alternative procedure. The study defines optimal conditions to produce hypocotyl fragments suitable for micrografting. Interruption of the process by storage of tissues or embryos at low temperature (+ 4 degreesC) was assessed at different stages and for durations up to 6 months. Best procedure to produce somatic embryos were: long-term maintenance of embryogenic cultures on C1 medium (5 muM 2.4-D + 1 muM BAP, solidified with 4 g(.)l(-1) agar and 4 g(.)l(-1) Phytagel); differentiation of embryogenic callus for 2 months on C2 medium (5 muM NOA + 1 muM BAP, gelling agents same as above); transfer of single embryos on plant growth regulator-free medium for 2-3 weeks for germination. At different steps of the process, embryogenic tissues or differentiated embryos can be stored for up to 180 d for some cultivars. Micrografting assays Were performed with various types of embryo and with apices from. several V. vinifera cultivars. White to slightly coloured. hypocotyls, excised from embryos germinated in darkness, gave best results for micrografting, while hypocotyl shape had little influence. For all genotypes tested the success rate ranged from 18 to 30 %