Longevity of Nicotiana seeds conserved at low temperatures in ex situ genebanks

Seeds of Nicotiana tabacum and N. rustica stored for up to 38 years at temperatures of -15 / -18 degrees C (IPK, Gatersleben, Germany - experiment 1) and 33 years at 0 degrees C (IHAR, Radzikow, Poland - experiment 2) were germinated using a Jacobsen apparatus at a temperature of 30 +/- 2 degrees C. Seven days after sowing, the percentage of seedlings exhibiting a normal appearance was scored. Variation in germination was compared with initial viabilities (historic data). In addition, a logistic regression analysis was used to model the proportion of seed lots (accessions) that had germination higher than 75% over time. After 38 years, this proportion was 60% in Experiment 1 but less than 10% in Experiment 2, even though the initial viability levels in the two experiments were high and very similar. The reduced seed longevity obtained in Experiment 2 might not be due to higher storage temperature alone.