As part of conservation of plant genetic resources, long-term storage of seeds is highly relevant for genebanks. Here we present a systematic review and a meta-analysis of studies on seed longevity focusing on half-life (P 50) under different storage conditions. Six studies were selected for the meta-analysis; in addition, a high number of additional references were included in the discussion of the results. The results show that under ambient conditions, half-life is short, from 5 to 10 years, while under more optimal conditions, which for orthodox seeds is at low humidity and low temperature, half-life is more in the 40−60 years range, although with large interspecies variation. Under longterm genebank conditions, with seeds dried to equilibrium and thereafter kept at minus 18 −20°C in waterproof bags or jars, half-life can be twice or three times as long. In general, many of the grain legume seeds, as well as corn, common oat, and common barley are long-lived, while cereal rye, onion, garden lettuce, pepper, and some of the forage grasses are more short-lived. Conditions during maturation and harvesting influence longevity, and proper maturation and gentle handling are known to be of importance. Seed longevity models have been developed to predict final germination based on initial viability, temperature, humidity, storage time, and species information. We compared predicted germination to results from the long-term experiments. The predicted values were higher or much higher than the observed values, which demonstrate that something in the seed handling in the genebanks have not been optimal. Long-term studies are now available with data at least up to 60 years of storage. Our review shows that the knowledge and methodology developed for the conservation of plant genetic resources should also work for wild species of orthodox seed nature.

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Ex situ seed banks provide an effective conservation and utilization system for crops and their wild relatives. Efforts are made to reduce genetic drift in conservation, where regeneration is a critical step. In the present study, we examined eight wild populations of red clover (Trifolium pratense L.) according to 13 morphological and phenological traits. Samples of original collected seed were grown and compared with plants from first and second ex situ generation, with commercial cultivars and landraces being included for purposes of comparison. Variance analysis and Tukey multiple comparisons of means showed that the commercial cultivars and landraces were clearly distinct from the wild populations and were excluded from the further analysis. Despite the fact that the wild accessions were collected from a geographically delimited region in Norway, they exhibited significant differences in several of the measured traits. The main phenotypic patterns remain after ex situ regenerations. However, the mean values for four of the examined traits (across accessions) did change significantly from one generation to the next. Two of the eight accessions had significantly changed from one generation to the next, a tendency was observed across all the studied traits. The results were discussed in terms of regeneration circumstances. Observed changes appeared to be directional, going from populations with predominantly wild morphological types towards plants more closely resembling the commercial cultivars. Such a directional change implies that selection or gene flow has been acting on the accessions during regeneration, rather than random changes owing to genetic drift.

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Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) is one of the most devastating sugar beet diseases. Sugar beet plants engineered to express a 0.4 kb inverted repeat construct based on the BNYVV replicase gene accumulated the transgene mRNA to similar levels in leaves and roots, whereas accumulation of the transgene-homologous siRNA was more pronounced in roots. The roots expressed high levels of resistance to BNYVV transmitted by the vector, Polymyxa betae. Resistance to BNYVV was not decreased following co-infection of the plants with Beet soil borne virus and Beet virus Q that share the same vector with BNYVV. Similarly, co-infection with the aphid-transmitted Beet mild yellowing virus, Beet yellows virus (BYV), or with all of the aforementioned viruses did not affect the resistance to BNYVV, while they accumulated in roots. These viruses are common in most of the sugar beet growing areas in Europe and world wide. However, there was a competitive interaction between BYV and BMYV in sugar beet leaves, as infection with BYV decreased the titres of BMYV. Other interactions between the viruses studied were not observed. The results suggest that the engineered resistance to BNYVV expressed in the sugar beets of this study is efficient in roots and not readily compromised following infection of the plants with heterologous viruses.

More than 30 years ago, the Nordic Gene Bank established a long-term experiment on seeds stored under permafrost conditions in an abandoned mine corridor in Svalbard, as a tool to monitor storage life under these conditions. The study included seeds from 16 Nordic agricultural and horticultural crops, each represented by two or three cultivars (altogether 38 accessions). All seeds were ultra-dried to 3–5% moisture before being sealed in glass tubes. Germination tests were performed in accordance with the International Seed Testing Association (ISTA) protocols. At the initiation of the experiment, the samples showed good germination with the median value at 92%. The overall picture remained stable over the first twenty to twenty-five years. However, the variation became larger over time and at 30 years, the median value had dropped to 80%. At the lower end, with a high drop in germination, we found rye, wheat, and English ryegrass. At the upper end, we found Kentucky bluegrass and cucumber. The lowest germination was found in samples with the highest initial seed moisture levels. Pre-storage conditions are likely to be of major importance for longevity.