Short- and long-term effects of ultra-drying on germination and growth of vegetable seeds

Before ultra-dry technology can be adopted in China, the short- and long-term effects of drying seeds to very low water contents must be evaluated. To do this, the viability and vigour of seeds of five vegetable species (Chinese cabbage, Brassica campestris L. ssp. pekinensis; green Chinese onion, Allium fistulosum L. var. Gaganeum makino; chive, Allium tuberosum; cucumber, Cucumis sativus; and pepper, Capsicum frutescens L.) were measured immediately after drying to water contents between 5 and 1%, and after 3 years' storage at constant temperatures of 40, 4 and -20 degrees C and ambient temperatures of 25+/-10 degrees C (day) and 15+/-10 degrees C (night). Percentage germination of seeds after 1 day (early count) and 2 weeks (final count), emergence in soil, seedling mass and conductivity of leachate following imbibition were used to evaluate seed performance. There were no differences in initial germination percentages and only minor differences in leakage rates of seeds dried to different levels, indicating that imbibitional damage was not problematic in these seeds. After 3 years' storage, there was no evidence of deterioration in samples stored at ambient temperatures, 4 degrees C or -20 degrees C. Final germination percentage was lower in Chinese cabbage and pepper seeds stored at 40 degrees C and water contents greater than 4%. Reductions in early germination counts, soil emergence and/or seedling mass of Chinese cabbage, cucumber, pepper and Chinese onion seeds stored for 3 years at 40 degrees C and water contents less than about 2% suggested that drying to extremely low water contents had detrimental effects on longevity. In contrast, storage at 40 degrees C had a promoting effect on the germination of chive seeds, suggesting that they were after-ripened at the elevated temperature. Our results suggest that there may be an optimum water content for seed storage and that different germination assays have different sensitivities in detecting deterioration.