BP Singh

Medium and Long-term Storage of Seed Material in Gene Bank 55The seeds of many important tropical plantation crops, suchas rubber, cocoa, coconut, many tropical fruits and a number oftimber species of both the tropics and of the temperate latitudesfall into the second group known as the 'recalcitrant' seeds. Theseseeds suffer subcellular damage and cosequent loss of viabilitywhen dried. Moreover, lowering the temperatures to lOoC causeschilling injury and cooling to sub zero temperatures causesfreezing injury in these seeds. In comparison to orthodox seeds,therefore, the storage life of recalcitrant seeds cannot be easilyincreased by manipulating the storage environment.Indian National Gene BankThis national facility for long term ex-situ conservation ofbase collections, set up by NBPGR at New Delhi, has four majorcomponents:a) Seed Repository: Samples of orthodox type seeds aredehydrated at 15°C and 15% RH to around 5% moisture content,sealed in laminated aluminium foils under vacuum and depositedin cold storage at -20°C.b) Tissue Culture Repository: Disease-free tissue cultures ofrecalcitrant seeds (those not capable of withstanding dehydrationand very low temperatures) and vegetatively propagated plantspecies, developed from meristem explants, are maintained usingappropriate growth-limiting media and by subculturing at suitableintervals.c) Cryopreservation facility: Seed samples of selected species'synthetic ~eeds' embryos and gametes are being preserved usingcryopreservation technique, either by immersion in liquid nitrogen(-196°C) or by keeping in its vapour phase (around -150°C)following protocols using computerised freezing-thawing ratesand chemical cryoprotectants.d) Clonal Repository: Germplasm collections of vegetativelypropagated crops like turmeric, ginger, sweet potato find bananaare being maintained under field conditions following suitablecrop rotations and backed by tissue-culture safety duplication.Gene 'Bank Standardsi) Seed sample size: About 3,000 viable seeds in case of selfpollinated crops and twice that number for cross pollinated.