Effect of water content and temperature on seed longevity of seven Brassicaceae species after 5 years of storage

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 0.01g center dot H2O center dot 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 0.01g center dot H2O center dot g(-1) DW and six temperatures (45, 35, 20, 5, -25, -170 degrees 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 degrees C ranged from 0.02 to 0.03g center dot H2O center dot g(-1). The effect of extreme desiccation at 45 degrees 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 degrees 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.