BP Singh

Medium and Long-term Storage of Seed Material in Gene Bank 57The second requirement is to keep the seed dry. If bags areused, storage on pallets will keep the seed "from direct contact witha damp floor. Sealing the floor against moisture penetration is alsouseful. Storage of seeds in steel bins with tight fitting lids or inmoisture proof bags will solve the problem of moisture penetrationprovided the seeds are already dry enough for sealed storage.(b) Medium Term Storage: The siz~ of the accessions kept inthe medium term are generally larger than those meant for longterm storage. These working collections have higher rate of usageas they are distributed regularly for evaluation and breedingpurposes. The accessions have to be regenerated periodically dueto depletion of stocks, rather than hom loss of viability. Therefore,the time period for storage is about 5 to 10 years and the pressureof extending the longevity as for the base collections is not existing.The active collections are stored at temperatures ranging from O°Cto 10 e e. The seed samples in these collections are stored in varioustypes of containers such as cloth bags, metal cans or glass jars. Ifthe containers are hermetically sealed after drying the samplesthen the relative humidity of the medium term storage is notimportant . If the unsealed containers are used then the relativehumidity should be brought down. This shall, however, increasethe running costs. The method adopted, thus shall be decided bythe frequency of withdrawal of the samples ( A temperature of SOCand 35~40% RH is adequate for maintaining the viability of mostorthodox seeds for 5-10 years).Long Term StorageThe base collections and duplicate base collections aregenerally kept in stores where the strict storage environment aremaintained.The conditions recommended by IBPGR (now IPGRI) forstorage of base collections are probably most suitable andeconomical to maintain by conventional mechanical refrigerationmethods. The preferred standard for base collections is storage at5% ± 1 % seed moisture content in hermetically sealed, moistureproof containers at -20°e. In fact -2oDe is an arbitrary temperature.The 1976 Working Group ofIBPGR suggested that the temperaturestandard could be relaxed to -lOee if the seed bank was restrictedto a few species with good storage characteristics such as the