Zygotic embryos for the efficient long-term conservation of a Georgian provenance of sweet chestnut: an overview

Forest ecosystems are of considerable significance for the conservation of plant biodiversity. Sweet chestnut (Castanea sativa Mill.) belongs to the hardwood forest species within the genus Castanea. It is dominant in mountainous forests of western Georgia occupying the majority of areas covered with forests. Because of low self-renewal and diseases, the large massifs of chestnut forests are threatened by extinction. Castanea sativa is included in the 'Red List' of Georgia under state vulnerable (VU) and has been subjected to conservation measures in response to the Global Strategy for Plant Conservation (GPSC). Rapidly developing in vitro techniques open new possibilities for the safe ex-situ conservation of woody plant material. Various tissue culture-derived explants, such as shoot tips, nodal explants, somatic embryos, embryogenic cell lines, and embryonic axes have been widely used for conservation purposes to ensure the sustainability of the genetic pool of the genus Castanea. The study summarizes the recent achievements in species protection in Georgia via long-term preservation of a Georgian provenance of sweet chestnut using embryonic axes (EA) as an explant. The present overview focuses on the successful utilization of zygotic embryos for the conservation of a Georgian provenance of sweet chestnut germplasm and summarizes the recent achievements via long-term preservation. The efficacy of different techniques for cryopreservation of EAs, such as specimen dehydration - 'one-step freezing', PVS2-vitrification, and encapsulation-vitrification are evaluated. The advantages of the utilization of zygotic embryos for safe and effective long-term conservation of threatened hardwoods concerning the post-cryopreservation recovery of explants are discussed.