Evaluation of Onion (Allium cepa L.) Seed after 10 Years of Storage at 5, −18, and −196°C

Long-term storage strategies for seed germplasm are needed to assure preservation of diminishing plant genetic resources. Cryopreservation in liquid nitrogen (−196°C) is being studied as a potential method to reduce the rate of seed deterioration and thus increase the storage life of the seed. Onion (Allium cepa L.) seed was stored for 10 yr at 5, −18, and −196°C (liquid nitrogen) and evaluated for germination, seedling root length, electrolyte leakage, and O₂ uptake to determine long-term storage response. Average germination of seed stored at −18 and −196°C did not decline over the 10 yr period, while germination of seed stored at 5°C dropped from 94 to 68%. Variation in moisture content was observed in seed stored at 5 and −18°C, with no variation noted at the −196°C-storage temperature. The variation in moisture content may have influenced seed deterioration at the 5°C-storage temperature. It is less likely that the variation in seed moisture content was a contributing factor at the −18°C-storage temperature. Electrolyte leakage results, an indication of seed membrane integrity, were inconclusive. Average seedling root lengths of 2.8, 5.7, and 6.6 mm and seedling O₂ uptake rates of 124, 156, and 176 pmol mg⁻¹ min⁻¹ (5, −18, and −196°C storage, respectively) were observed, suggesting less physiological deterioration at the −196°C-storage temperature. Based on seedling root length, O₂ uptake rates, maintenance of seed moisture content and seed germination, it was concluded that seed deterioration was greater at 5 > −18 > −196°C. Maintenance of seed germplasm at 5°C in this experiment was not satisfactory. Liquid nitrogen and −18°C storage for up to 10 yr was acceptable. Cryopreservation of seed germplasm appeared to result in superior seed vigor compared with the −18°C storage; however, longer-term experiments are needed to determine if cryopreservation results in extended seed preservation.