Ex-situ seed longevity of Nepeta spp.

Extended seed longevity in the dry state is the basis for the ex-situ conservation of orthodox seeds (desiccation-tolerant seeds). However, even under identical storage conditions, there is wide variation in seed longevity between species. The results of the artificial aging test provide seed bank managers a tool to assess the potential longevity of seed sets of these species under seed bank conditions, to enable the selection of appropriate viability retest intervals and, as a result, better management of conservation accessions. In the present work, seeds of nine wild species of Nepata spp. were aged at elevated temperature and relative humidity (45°C and 60% RH) for 120 days. Seeds were removed at various times (1, 2, 5, 9, 20, 30, 50, 75, 100 and 125 days) and their viability was determined through standard germination tests. The time taken in storage for viability to fall to 50% (p50) was determined using Probit analysis and used as a measure of relative seed longevity between species. Among Nepeta species, p50 at 45°C and 60% RH varied from 4.38 d to 16 d. Results indicated that based on the artificial aging longevity, in the gene banks the germination test intervals of species N. pogonosperma, N. haussknechtii, N. glomerulosa, N. cataria, N. depauperata can be ten years. But the germination test intervals of N. menthoides, N. nuda, N. schirazana and N. oxydonata should be five years, and even re-collecting their seeds can be a more appropriate strategy to protect them in ex-situ conditions.