The duration that seeds stay vigorous during storage is difficult to predict but critical to seed industry and conservation communities. Production of volatile compounds from lettuce seeds during storage was investigated as a non-invasive and early detection method of seed ageing rates. Over 30 volatile compounds were detected from lettuce seeds during storage at 35 degrees C at water contents ranging from 0.03 to 0.09 g H(2)O g(-1) dw. Both qualitative and quantitative differences in volatile composition were noted as a function of water content, and these differences were apparent before signs of deterioration were visible. Seeds stored at high water content (L >or=0.06 g H(2)O g(-1) dw) emitted molecular species indicative of glycolysis (methanol+ethanol), and evidence of peroxidation was apparent subsequent to viability loss. Seeds containing less water (0.03-0.05 g H(2)O g(-1) dw) produced volatiles indicative of peroxidation and survived longer compared with seeds stored under more humid conditions. Production of glycolysis-related by-products correlated strongly with deterioration rate when measured as a function of water content. This correlation may provide a valuable non-invasive means to predict the duration of the early, asymptomatic stage of seed deterioration.

HighlightSpecies, storage products, and moisture have large effects on the nature and quantity of volatile emission from dry seeds, but storage time and seed viability do not.

Final germination percentages of 25 accessions of Brassicaceae from the UPM (Universidad Politécnica de Madrid) seed bank were evaluated after 38-40 years of storage. The seeds were preserved at temperatures between-5°C and-10°C in flame sealed vials containing dehydrated (blue) silica gel. Seed moisture content ranged between 0.3 and 3% (f.w.b) after storage. Most accessions (ten out of twelve) with high initial (before storage) germination rate (low initial dormancy) maintained these high values almost intact after storage (91-100% germination). In two accessions, seeds had developed a secondary dormancy, which was successfully overcome by scarification. A second set of 13 accessions had low initial germination rates (0-20%, i.e. high initial dormancy). In one accession, dormancy had been broken during storage (92% germination) and in nine accessions germination was significantly enhanced by GA 3 and or scarification. Seed dormancy most often decreases during storage but it may also increase or remain unchanged. The consideration of these dormancy variations is very important when evaluating seed longevity in wild species. The preservation method based on silica gel and low temperature (-5°C and-10°C) has proved highly efficient at least for Brassicaceae. Vials with seeds of 12 additional accesssions had remained at room temperature during 34-39 years and those seeds showed germination percentages that were similar to those preserved in the cold room. This result suggests that temperature might not be as important as expected-at least for medium-term preservation-and supports the possibility of using ultra-dry methods.

The aim of the present study was to determine whether the loss of seed germination capacity and vigour in seeds of four wild Brassicaceae species (Brassica repanda, Moricandia arvensis, Rorippa nasturtium-aquaticum and Sinapis alba) during ageing at 45°C and 90% relative humidity was related to changes in lipid peroxidation and membrane integrity. For all of the species, ageing reduced the final germination percentage and increased the length of time required to reach 50% of final germination (T 50 ). Large differences in longevity were observed among the species. The times required for viability to be reduced to 80 and 50% of maximum germination (P80 and P50) were the lowest for B. repanda, and these values were two times longer for M. arvensis and R. nasturtium-aquaticum and five times longer for S. alba compared with B. repanda. A loss of seed viability was not associated with malondialdehyde accumulation, suggesting that lipid peroxidation did not cause seed deterioration under these conditions. However, the conductivity test effectively detected seed deterioration in these wild Brassicaceae species, and membrane permeability correlated with both germination and vigour loss. This correlation may provide a valuable mean for early detection of seed viability in wild Brassicaceae species.

Maximising seed longevity is crucial for genetic resource preservation and longevity of orthodox seeds is determined by environmental conditions (water content and temperature). The effect of water content (down to 0.01 g·H₂O·g(-1) ) on seed viability was studied at different temperatures for a 5-year storage period in taxonomically related species. Seeds of seven Brassicaceae species (Brassica repanda, Eruca vesicaria, Malcolmia littorea, Moricandia arvensis, Rorippa nasturtium-aquaticum, Sinapis alba, Sisymbrium runcinatum) were stored at 48 environments comprising a combination of eight water contents, from 0.21 to 0.01 g·H₂O·g(-1) DW and six temperatures (45, 35, 20, 5, -25, -170 °C). Survival curves were modelled and P50 calculated for those conditions where germination was reduced over the 5-year assay period. Critical water content for storage of seeds of six species at 45 °C ranged from 0.02 to 0.03 g·H₂O·g(-1) . The effect of extreme desiccation at 45 °C showed variability among species: three species showed damaging effects of drying below the critical water content, while for three species it was neither detrimental nor beneficial to seed longevity. Lipid content could be related to longevity, depending on the storage conditions. A variable seed longevity response to water content among taxonomically related species was found. The relative position of some of the species as long- or short-lived at 45 °C varied depending on the humidity at which storage behaviour was evaluated. Therefore, predictions of survival under desiccated conditions based on results obtained at high humidity might be problematic for some species.