| Résumé | Tissue culture techniques, especially meristem culture, have been employed to clonally propagate many crop species in a disease-free condition and also to maintain plantlets in vitro for short to medium term duration. Few plant species such as grape, strawberry, potato, ryegrass, cassava, sweet potato, coffee, etc., have been maintained in vitro as plantlets for various periods. The storage duration is increased by reducing the vegetative growth of the plantlets by different manipulations in culture such as exposure to low temperature and application of chemicals to induce osmotic stress etc. Only preservation at ultra-low temperature can guarantee preservation of germplasm for extended periods of time. Shoot apical or lateral meristems have been identified as excellent material for long-term preservation of germplasm by cryogenic methods. Meristems of a few plant species, viz. carnation, potato, strawberry, pea, chickpea, peanut, etc., have been successfully frozen and stored in liquid nitrogen. Since all metabolic activities of plant cells are arrested at the temperature of liquid nitrogen (-196 ᵒC) the germplasm could be indefinitely stored in a genetically unaltered condition. This prospect opens up new possibilities for the long-term preservation of genetic material. A combination of in vitro storage strategies and cryopreservation approaches should satisfy the current need for germplasm preservation. |
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