STORAGE OF SEEDS - POTENTIAL AND LIMITATIONS FOR GERMPLASM CONSERVATION

Objectives of seed storage are primarily either short-term for forestry operations, or long-term for germplasm conservation. Seeds can be grouped into four classes of storage characteristics: 'true orthodox' seeds can be stored for long periods at seed moisture contents of 5-10% and sub-freezing temperatures; 'sub-orthodox' seeds can be stored under the same conditions, but for shorter periods due to high lipid content or thin seed coats; 'temperate recalcitrant' seeds cannot be dried at all, but can be stored for 3-5 years at near-freezing temperatures; and 'tropical recalcitrant' seeds also cannot be dried, and they are killed by temperatures below 10-15°C. Cryogenic storage in liquid nitrogen at -196°C holds promise, but needs more research. Some genetic damage may occur during seed storage, but the extent and effect of this damage has yet to be determined. Seed storage, by both conventional and cryogenic technologies, offers a relatively cheap method of conserving a broad range of germplasm. It will likely play an essential, complementary role, in germplasm conservation as temporary conservation until ex-situ stands are established, and as a safety measure against disastrous losses for limited numbers of seedlots. To fulfill the conservation roles, seed storage life must exceed the natural interval between germination and seed production for the next generation. Most true orthodox and many sub-orthodox seeds offer no problem, but neither recalcitrant seed class can meet this criterion with present technology. However, even short gains in viability retention of recalcitrant species can be useful (e.g., in transporting seed collections from remote areas to nurseries or laboratories). © 1990.