SEED MATURITY AND THE EFFECTS OF DIFFERENT DRYING CONDITIONS ON DESICCATION TOLERANCE AND SEED LONGEVITY IN FOXGLOVE (DIGITALIS-PURPUREA L)

The effects of different drying methods on desiccation tolerance and longevity in seeds of foxglove (Digitalis pur pu, ea L.) were assessed from just prior to mass maturity (when seeds have attained maximum dry weight), and at intervals during the post-abscission phase of development. Tolerance of drying under seed conservation conditions (15% relative humidity, RH, and 15 degrees C), was acquired close to mass maturity at 36 d after flowering (DAF). Increases in desiccation tolerance were induced when drying was delayed for 4 d by placing seeds in a near-saturated atmosphere (approx. 100% RH), or if seeds were pre-dried for 7 d at either approx. 32% or approx. 73: % RH. Irrespective of the drying treatment, seed longevity increased throughout the sampling period, i.e, beyond the point of mass maturity and throughout the post-abscission phase, up to the point of incipient natural dispersal. At each developmental stage, delayed drying or pre-drying led to an increase in seed longevity under controlled ageing conditions compared with seeds dried directly under seed conservation conditions. Increases in longevity were apparent as increases in the estimates for the intercept of transformed seed survival curves (K-i) and for the standard deviation of the normal distribution of seed lifespans, and also in the mean time to death of individuals in storage, consistent with a continuation of ripening events. The results are discussed in relation to the assessment of seed longevity and to current post-harvest drying practices for seeds intended for long-term ex-situ conservation. (C) 1995 Annals of Botany Company