Long- and Medium-Term Storage of Germplasm for Conservation of Tree Species

The expanding world population and global climate change has posed several challenges among which degradation of valuable forest resources is a major concern. Trees or woody perennials are an integral part of the forest ecosystem and provide innumerable benefits to humans, wildlife and environment as a whole. Over the years, many forest tree species especially those with high commercial or medicinal importance have faced huge decline in populations and thus require immediate efforts for conservation. Advance biotechnological methods of conservation that ensure in vitro medium- to long-term storage of plant embryonic axes, pollens and in vitro propagules are now increasingly applied for tree species conservation especially, which face poor seed set, low seed germination, have recalcitrant seeds and are typically propagated by vegetative means. The present chapter describes methods and applications of plant tissue culture in conserving tree genetic resources with an emphasis on different approaches to achieve storage under slow growth- and cryo-conditions. In brief, we have discussed how the subculture durations can be extended for short- to medium-term via modifications in chemical (e.g. medium composition, growth retardants) and physical (e.g. light, temperature) environment of cultures whilst maintaining the viability and genetic stability of the stored germplasm. Additionally, long-term storage of tree species under ultralow temperatures (−196 °C) through classical as well as vitrification-based methods are also described with suitable examples. At the end, case studies are presented citing examples of conservation of tree germplasm in the form of pollens and in vitro propagules.