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Abstract
Seeds of 14 vegetable and 2 flower species were placed in paper envelopes and submerged in liquid nitrogen (LN2, –196°C) for periods up to 180 days with no adverse effects on germination. Vigor tests with beans (Phaseolus vulgaris L.), lettuce (Lactuca sativa L.), and peas (Pisum sativum L.) also indicated no reduction in germination or vigor after exposure to LN 2. Liquid nitrogen offers promise as a medium for long-term storage of seed germplasm.
Long-term preservation of seed germplasm is a high agricultural priority. It assures that genetic diversity will be available for future generations for continued plant improvement. This experiment reports on the affect that storage temperature had on the viability of 65 selections of lettuce seed stored for 30 years. The average seed moisture content was 5.5% ± 0.5% (fresh weight basis). Fresh seed samples were placed at 5 °C storage in 1969. In 1975 they were then transferred to -18 °C storage. Viability remained at 98% ± 5% for the first 14 years of 5 /-18 °C storage, then viability declined. At 17 years storage, the average viability had dropped to 75% and continued to drop at about 4%/year. At the 17-year mark, individual samples were split, one-half remained at -18 °C the other half was placed under liquid nitrogen vapor (lnv) conditions (about -150 to -190 °C). The -18 °C stored samples continued to deteriorate to 14% viability at the 30 year test period (1999). The samples placed in lnv did not decrease further in viability and remained at 75% viability at the 30-year mark. Seed vigor was reduced in the -18 °C stored seeds that were still viable. The lnv-preserved samples were significantly more vigorous. It is clear from this experiment that lnv preservation was significantly superior to -18 °C storage and, in fact, stopped or significantly reduced the rate of viability loss in samples that are rapidly deteriorating.