Abstract/Summary

Maximising potential seed longevity during harvesting and drying will minimise later testing and regeneration, accumulation of genetic damage, and depletion of seed accessions in genebanks. Experiments with freshly-harvested seeds at the International Rice Genebank determined the effect of drying environment on subsequent longevity in contrasting cultivars of rice (Oryza sativa L.). Genotypes varied considerably in differences in subsequent longevity from initial drying after harvest in a flat-bed dryer at 45°C compared with 15°C/15% RH (standard genebank drying room): from similar longevity up to a 3-fold increase with 45°C. The variation amongst accessions was associated with harvest moisture content: up to 16.2-16.7% longevity was similar, with a progressively greater benefit to subsequent longevity from drying at 45°C the greater the harvest moisture content above this value. Longevity improvement did not appear to be associated with duration of seed development (days after 50% anthesis; DAA), or by total period of exposure to 45°C. Improvement in longevity compared with drying at 15°C/15% RH was also detected when high temperature exposure was delayed after harvest. Drying seeds at 45°C with different relative humidities, revealed a similar beneficial effect to drying for seeds when harvested at a moisture content ≥16.5%. Seeds harvested at a moisture content where they are still metabolically active (≥16.5%) are considered to remain in the desiccation phase of seed development and therefore able to continue to improve longevity ex planta when exposed to drying at 45°C. The consistent relationship between relative improvement in longevity and harvest MC when seeds from different harvest seasons and at different stages of maturity were dried at different durations under different regimes at 45°C confirmed that the temperature of drying is the most important factor which enables seeds to continue to accrue longevity ex planta.