Viability of Oryza sativa L. seeds stored under genebank conditions for up to 30 years

Germination ability, equilibrium relative humidity (eRH), and moisture content of 'control' seed samples representing 183 rice accessions stored in the active (2-4 A degrees C) and base (-10 A degrees C until 1993, then -20 A degrees C) collections of the T. T. Chang Genetic Resources Center were determined after storage for 20.5-30.5 years. Germination of seeds that had been stored in the base collection was generally high (> 70 %), whereas germination was more variable for seeds stored in the active collection. Samples with lower viability after storage in the active collection were likely to have lower viability after storage in the base collection. There were significant differences in the moisture content-eRH relationship of the seeds depending on whether the seeds had been stored in the active or base collection. Based on re-test data for regular seed samples regenerated in 1979-1980 and stored in the active collection for up to 31 years, estimates of the time for ability to germinate to fall to 50 % (p (50)) ranged from 54 to 997 years. For the same seed samples stored in the base collection for approximately 31 years, ability to germinate has been maintained and germination increased due to improved procedures. The ability to germinate of base collection samples was also generally higher than that of 'safety duplicate' samples of the same seed lots that had been sent to the National Center for Genetic Resources Preservation, USA in 1981 and stored at -18 A degrees C. This may have been due to uptake of moisture either during processing for dispatch or as a consequence of poor packaging material. The results are discussed in relation to long-term seed storage and genebank management.