† Background and Aims Most priming studies have been conducted on commercial seed lots of unspecified uniformity and maturity, and subsequent seed longevity has been reported to both increase and decrease. Here a seed lot of Digitalis purpurea L. with relatively uniform maturity and known history was used to analyse the effects of priming on seed longevity in air-dry storage. † Methods Seeds collected close to natural dispersal and dried at 15 % relative humidity (RH), 15 8C, were placed into experimental storage (60 % RH, 45 8C) for 14 or 28 d, primed for 48 h at 0, 21, 22, 25, 210 or 215 MPa, re-equilibrated (47 % RH, 20 8C) and then returned to storage. Further seed samples were primed for 2 or 48 h at 21 MPa and either dried at 15 % RH, 15 8C or immediately re-equilibrated for experimental storage. Finally, some seeds were given up to three cycles of experimental storage and priming (48 h at 21 MPa). † Key Results Priming at 21 MPa had a variable effect on subsequent survival during experimental storage. The shortest lived seeds in the control population showed slightly increased life spans; the longer lived seeds showed reduced life spans. In contrast, seeds first stored for 14 or 28 d before priming had substantially increased life spans. The increase tended to be greatest in the shortest lived fraction of the seed population. Both the period of rehydration and the subsequent drying conditions had significant effects on longevity. Interrupting air-dry storage with additional cycles of priming also increased longevity. † Conclusions The extent of prior deterioration and the post-priming desiccation environment affect the benefits of priming to the subsequent survival of mature seeds. Rehydration-dehydration treatments may have potential as an adjunct or alternative to the regeneration of seed accessions maintained in gene banks for plant biodiversity conservation or plant breeding.

Variation in individual seed behaviours within a developing population is inherent and inevitable. In this outbreeder, there is significant variation in seed longevity which appears dependent on embryo genotype with little effect of maternal genotype or architectural factors.

Maturation continued ex planta in these post-abscission, pre-dispersal seeds of D. purpurea dried at 15-80 % RH at a rate correlated positively with RH (cf. ageing of mature seeds). Subsequent re-hydration at 95 % RH enabled a further improvement in quality. Priming seeds initially stored air-dry for 3 months also allowed maturation events to resume. However, once individual seeds within the population had reached maximum longevity, priming had a negative impact on their subsequent survival.