IN VITRO CONSERVATION OF GENETIC RESOURCES
Brian V. Ford-Lloyd
University of Birmingham, UK
The maintenance in vitro of plant material has an important role to play as an alternative to field genebanks in conserving clonally propagated species (eg. potato, cassava, yam, taro, cocoyam, banana, garlic), and those species which produce recalcitrant seeds (eg. cacao, mango, coconut, avocado, hops). Increasingly, in vitro conservation is even required for seed crops as barley, rice and maize, where because the possibility for transformation in governed by genotype, there is a need to conserve competent cell cultures for continued experiments.
Various techniques now exist for in vitro conservation including slow grwth storage and cryopreservation, the latter being the most promising for long-term conservation of germplasm. While slow growth storage is dependent upon the ability to culture shoots under conditions which reduce the growth rate to a minimum, cryoperservation depends upon the manipulation of meristems, callus, cell cultures or somatic embryos. Success may depend upon preconditioning, cryoprotection, rate of freezing, and the use of vitrification and dessication strategies before storage.
In vitro storage of germplasm of potato, cassava and banana is now underway. Research continues to find ways of conserving mango, coconut and Xanthosoma. In vitro techniques for collecting germplasm are well advanced and have beebn succesfully applied to cotton, cassava, coconut and citrus fruits.
Genetic stability of germplasm stored in vitro culture, and may occur at very high levels. For instance, in bananas and plantains up to 60% of in vitro progeny can be offtypes. Despite this, in vitro techniques are still preferred for propagation and maintenance of germplasm. Because of the significance that in vitro techniques have in Musa germplasm conservation and propagation, a case study of bananas and plantains is worthy of deeper consideration.
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