Klepka, L. | bioRxiv Science

bioRxiv2025

Limitations of p50 as a measure of seed longevity and the way forward

PremiseComparative studies of seed longevity assess how environmental conditions, species identity, populations, or genotypes affect seed viability loss in stored seeds. These studies commonly use the time it takes for seed viability to drop to 50% - known as p50, - as a measure of seed longevity. However, p50 is influenced by the initial seed viability. To allow comparisons regardless of the initial seed viability, standard protocols for comparative studies of seed longevity recommend using seed lots with "similar and high" initial viability, typically between 85 and 100%. However, even such range of initial seed viabilities might result in substantial variation in p50. MethodsHere, we use a modelling approach to illustrate how variation in initial viability affects p50 estimates, and to propose alternative, more robust measures of seed longevity in storage. ResultsWe show that for hypothetical accessions with identical rates of seed viability loss, variation in initial viability between 85 and 100% leads to a threefold variation in p50 estimates. Most of the unintended variation is introduced by accessions with very high viability (>95%). Restricting the initial viability to a narrower range (e.g., 85-95%) reduces but does not eliminate this bias. Alternatively, p50 can be recalculated to a standardized value of initial viability (e.g., 90%), which makes it proportional to the rate of probit viability loss without any noise. However, the most straightforward measure of seed longevity for comparative studies is the rate of viability loss itself, represented by {sigma} (sigma) from the viability equation. ConclusionThe common measure of seed longevity, p50, is affected by unintended, substantial variation caused by varying initial viability of the seed lot, and is thus suboptimal for comparative studies of seed longevity among seed accessions. More robust measures of seed longevity include the rate of viability loss, or p50 standardized to a certain initial seed viability.

ecology↗

bioRxiv2025

Large interspecific and intraspecific variation in seed longevity in storage

PremiseConservation seed banks are essential for ex-situ plant conservation, but stored seeds slowly deteriorate and lose viability. Seed longevity in storage is determined by the initial seed viability and the rate of seed viability loss. The rate of seed viability loss in storage varies between species, and there is possibly also some variation between populations or even genotypes within species. However, the extent of this intraspecific variability and its drivers remain unclear. MethodsWe investigated both inter- and intraspecific variability in seed longevity and its predictors in 41 common grassland species and 188 seed accessions from across Europe. We exposed the seeds to artificial ageing conditions (60% RH, 45{degrees}C) and used probit analysis to obtain the rate of seed viability loss ({sigma}) as a measure of seed longevity. We then related {sigma} to both accession- and species-specific factors. Key resultsSeed longevity ({sigma}) varied significantly among accessions within 58% of the species, and the probability of detecting such intraspecific differences increased with the number of accessions available for a given species. This suggests that within-species variation in seed longevity is widespread. Accession-specific predictors explained only 14.4% of the within-species variability. Specifically, seed longevity increased with the mean annual temperature at the accession origin and decreased with the accession-specific seed weight. Across species, seed longevity differed among plant families but was unrelated to seed weight or seed chemical composition. ConclusionsOur findings highlight substantial within-species variation in seed longevity in storage, which, however, is difficult to predict.

ecology↗