Progress and Challenges in the Application of Synthetic Seed Technology for Ex Situ Germplasm Conservation in Grapevine (Vitis spp.)

Although grapevine (Vitis spp.) is one of the most ancient and important fruit crops, there is no concerted international effort to conserve its genetic resources, which are estimated to consist of 10-14,000 cultivars. Synthetic seed technology offers opportunities to conserve clonal genetic resources either in the form of quiescent somatic embryos or as encapsulated regenerable somatic tissue. Since the first report of somatic embryogenesis in grapevine in 1976, much research has been conducted into synchronising the process, maturation, dehydration, encapsulation and testing longevity under cold storage. Since the development of vitrification-based cryopreservation methods, both somatic embryos and other somatic tissue with meristematic regions have been used in cryopreservation experiments, and methods have been optimised to reach post-thaw regeneration percentages that satisfy gene bank standards for implementing cryopreservation. Nevertheless, improved protocols for 'difficult' genotypes are still needed for induction of somatic embryos and synchronising their formation, maturation and germination, as well as cryopreservation. As a result of these difficulties, conservation by cryopreservation has progressed using encapsulated shoot tips or axillary buds of tissue culture plants. Some vitrification-based methods use a droplet of vitrification solution to protect the shoot tips on an aluminium strip allowing faster freezing of tissue, an important factor for post-cryo-survival. The novel V cryo-plate method combines the advantages of both encapsulating the shoot tips in alginate beads that then adhere to the aluminium of the V cryo-plate, meaning manipulations can be performed easily, and the high thermal conductivity of aluminium speeding processed of freezing and thawing. Cryopreservation of somatic embryos has been suggested as a way to conserve the diversity of wild V. vinifera ssp. sylvestris, and limited results obtained to date are promising.