The J. Derek Bewley Career Lectures presented at the triennial meetings of the International Society of Seed Science support early-career seed scientists by providing retrospective views, from those late in their careers, of lessons learned and future implications. Ambition, ability, inspiration, foresight, hard work and opportunity are obvious career requirements. The importance of mentoring and teamwork combined with the clear communication of results, understanding and ideas are emphasized. The role of illustration in research, and its dissemination, is outlined: illustration can support hypothesis development, testing and communication. Climate change may perturb the production of high-quality seed affecting conservation as well as agriculture, horticulture and forestry. An illustrative synthesis of the current understanding of temporal aspects of the effects of seed production environment on seed quality (assessed by subsequent seed storage longevity) is provided for wheat (Triticum aestivum L.) and rice (Oryza sativa L.). Seed science research can contribute to complex global challenges such as future food supplies from seed-propagated crops in our changing climate whilst conserving biological diversity (through seed ecology and technologies such as ex situ plant genetic resources conservation by long-term seed storage in genebanks), but only if that research can be – and then is – applied.

The long-standing hypothesis that seed quality improves during seed filling, is greatest at the end of seed filling, and declines thereafter (because seed deterioration was assumed to begin then), provided a template for research in seed quality development. It was rejected by investigations where seed quality was shown to improve throughout both seed development and maturation until harvest maturity, before seed deterioration was first observed. Several other temporal patterns of seed quality development and decline have also been reported. These are portrayed and compared. The assessment suggests that the original hypothesis was too simple, because it combined several component hypotheses: (a) the seed improvement (only) phase ends before seed deterioration (only) commences; (b) there is only a brief single point in time during seed development and maturation when, in all circumstances, seed quality is maximal; (c) the seed quality improvement phase coincides perfectly with seed filling, with deterioration only post-seed filling. It is concluded that the search for the single point of maximum seed quality was a false quest because (a) seed improvement and deterioration may cycle (sequentially if not simultaneously) during seed development and maturation; (b) the relative sensitivity of the rates of improvement and deterioration to environment may differ; (c) the period of maximum quality may be brief or extended. Hence, when maximum quality is first attained, and for how long it is maintained, during seed development and maturation varies with genotype and environment. This is pertinent to quality seed production in current and future climates as it will be affected by climate change and a likelihood of more frequent coincidence of brief periods of extreme temperatures with highly sensitive phases of seed development and maturation. This is a possible tipping point for food security and for ecological diversity.

Drying reduces seed moisture content, which improves subsequent seed survival periods. Diverse maximum temperatures have been recommended to limit or avoid damage to seeds, but some high-temperature drying regimes may improve subsequent seed quality. Seeds from 20 different accessions of five rice (Oryza sativa L.) variety groups (aromatic, Aus, Indica, temperate Japonica, tropical Japonica) were harvested over several seasons at different stages of maturation and either dried throughout at 15°C/15% relative humidity (RH) or for different initial periods (continuous or intermittent) in different drying regimes at 45°C before final equilibrium drying at 15°C/15% RH. Subsequent seed longevity in hermetic storage at 45°C with 10.9% moisture content was determined. In no case did initial drying at 45°C provide poorer longevity than drying at 15°C/15% RH throughout. There was a split-line relation, which did not differ amongst investigations, between longevity after initial drying at 45°C relative to that at 15°C/15% RH throughout and harvest moisture content, with a break point at 16.5% (a seed moisture status of about –14 MPa). Below 16.5%, relative longevity did not differ with harvest moisture content with little or no advantage to longevity from drying at 45°C. Above 16.5%, relative longevity showed a positive relation with harvest moisture content, with substantial benefit from drying at 45°C to subsequent longevity of seeds harvested whilst still moist. Hence, there are temporal (immediately ex planta cf. subsequent air-dried storage) and water status discontinuities (above cf. below 16.5%) in the effect of temperature on subsequent air-dried seed longevity.

Post-harvest drying prolongs seed survival in air-dry storage; previous research has shown a benefit of drying moist rice seeds at temperatures greater than recommended for genebanks (5–20°C). The aim of this study was to determine whether there is a temperature limit for safely drying rice seeds, and to explore whether the benefit to longevity is caused by high-temperature stress or continued seed development. Seeds of two rice varieties were harvested at different stages of development and dried initially either over silica gel, or intermittently (8 h day–1) or continuously (24 h day–1) over MgCl2 at temperatures between 15 and 60°C for up to 3 days. Seeds dried more rapidly the warmer the temperature. Subsequent seed longevity in hermetic storage (45°C and 10.9% moisture content) was substantially improved by increase in drying temperature up to 45°C in both cultivars, and also with further increase from 45 to 60°C in cv. ‘Macassane’. The benefit of high-temperature drying to subsequent longevity tended to diminish the later the stage of development at seed harvest. Intermittent or continuous drying at high temperatures provided broadly similar improvements to longevity, but with the greatest improvements detected in a few treatment combinations with continuous drying. Heated-air drying of rice seeds harvested before maturity improved their subsequent storage longevity by more than that which occurred during subsequent development in planta, which may have resulted from the triggering of protection mechanisms in response to high-temperature stress.

Little barley (Hordeum pusillum Nutt.) seeds germinated readily without pregermination chilling on substrates moistened with either water or 0.2% aqueous KNO3. Little barley seeds were physiologically mature and viable as early as 11 days after flowering. Pregermination chilling induced dormancy in mature seeds moistened with water, but not those moistened with 0.2% KNO3. Mature seeds frequently germinated better at alternating temperatures from 20C (16 h) to 30C (8 h) than at constant 20C. Germination of seeds after 1 week in a thermogradient table varied from 1% at 34C to 77% at 21C. Seeds were able to germinate over an extended period in the fall and spring. Forage and seed production were highest from the first fall planting date and decreased with later plantings. Plants emerging from seeds planted in March and April did not produce seed.

Mile-a-minute weed or devil's tearthumb (Polygonum perfoliatum, syn. = Persicaria perfoliata) is an invasive annual vine in the Mid-Atlantic and Northeastern United States that reproduces solely through seeds. Our study aimed to identify how mile-a-minute seed viability is affected by time of year and the maturity of the fruit surrounding the achene. Full-sized immature (green) and mature (blue) fruits were collected from five field sites every 2 wk over a 3 mo period, and seed viability was assessed using a triphenyl tetrazolium chloride (TZ) assay. At the onset of seed production in mid-August, 35% of seeds from immature fruits were viable. This percentage increased steadily, peaking at 84% in late September before declining at some sites around the time of the first frost. In contrast nearly all seeds with mature fruits (96%) were viable at all collection dates. Thus land managers who apply physical or chemical control methods for mile-a-minute weed should do so before the onset of any seed production and not simply before fruit maturation. If it is necessary to apply control methods after fruit set, it should be done as early in the season as possible.

Chlorophyll fluorescence (CF) analysis was explored as a potential tool to identify the optimal time to harvest rice seed germplasm for maximum storage longevity. Seeds of 20 diverse genebank accessions were harvested at 24, 31, 38 and 45 d after peak flowering (DAF) and half of each seed lot was sorted by hand, following normal practice at the T.T. Chang Genetic Resources Center. CF analysis was carried out on both non-sorted and sorted seeds, while storage experiments were carried out on sorted seeds. Seed longevity (the time for viability to fall to 50%, p50) was significantly correlated with the skewness, kurtosis, mode and mean of the CF histograms when the data for every accession at all the harvest times were included in the correlation analysis. However, these correlation coefficients were ≤ 0.481. The correlation coefficient between p50 and DAF was similarly low (0.461). For individual accessions, there was wide variation in the correlation coefficients. While for some accessions, there appeared to be a strong relationship between p50 and mean CF that could be used to guide when to harvest seeds in the field, for other accessions, a unique mean CF to inform when to harvest seeds or for use in seed sorting could not be identified; this was also true for DAF over the harvesting schedule used in this study. Given the number and diversity of accessions managed by a genebank, it seems unlikely that CF analysis would be an appropriate tool to help manage the regeneration or processing of seeds intended for storage in the genebank.

Controlled aging experiments were carried out in order to evaluate the changes in seed longevity occurring following the attainment of maximum seed dry weight in foxglove (Digitalis purpurea L.). Seeds harvested in three successive years were stored at ~5% moisture content (fresh weight basis) and 50°C. Seed longevity was greater the later the seeds were harvested. When the data were modelled using the predictive viability model of Ellis and Roberts, these increases were attributable to increases in both the theoretical initial viability (in probits) of the seed-lot, Ki, and in the standard deviation of the normal distribution of seed deaths in time, σ. Furthermore, there was a positive relationship between Ki and σ which was independent of the year of harvest (r = 0.9016, for 11 d.f., P < 0.001). These results do not support the predictive model which relies on the assumption that σ will not differ between seed lots of the same species stored under identical conditions. When seeds were stored at a range of moisture contents (between 5 and 10%) at 50°C, increases in σ during seed development were manifest as changes in the negative logarithmic relationship between σ and moisture content; below an upper limit, the regressions for seed lots at different stages of maturity were significantly different (P < 0.05) but could be constrained to either a common intercept or to a common slope (P < 0.05). It is proposed that it was the inherent variation in individual seed lifespans which increased during seed development. These results raise important concerns regarding the use of predetermined ‘species constants’ to predict the longevity of seed lots during long-term storage in seed banks.