In 2009, the bicentenary of Charles Darwin's birth on 12 February 1809 is being celebrated. For seed scientists, celebrations of the contributions of the great biologist should also mark his involvement with seeds. Darwin was interested in seeds, particularly in their role in dispersal and distribution of plant species over long distances. His studies of seeds, laid down in several books and articles, contributed to the development of his ideas on evolution and the distribution of living organisms on the planet. In this review, the place of seeds in Darwin's work is surveyed and it is shown how he referred to them to support and illustrate some of his most important ideas.

Eleven sunflower (Helianthus annuus L.) inbred lines were evaluated in field and laboratory studies under drought and irrigation. In the field, lines B59, R419 and B67 had reduced seed and oil yield under drought, while no reduction was observed for R432, HAR4 and B71. Lines HA89, R415, R049, RHA274 and R423 presented intermediate responses. In laboratory tests, seeds of line B59 had reduced germination percentages at 200 and 400 mM mannitol, while germination of seeds of lines R432, B71, HAR4, RHA274 and HA89 was reduced only at 400 mM mannitol. Drought-sensitive B59 and drought-tolerant B71 grown under irrigation and drought conditions in the field were selected for hormone assays. Abscisic acid (ABA) and its catabolites in pericarp, embryonic axis and cotyledons of dry and germinated seeds of B59 and B71 were determined. ABA was the major component of the pericarp of dry seeds from B71 and B59 plants grown under drought. The embryonic axis of B71 dry seeds from drought-grown plants also showed high ABA content. The major findings from this study are: (1) the drought-sensitive and -tolerant lines exhibited different ABA and catabolite profiles; (2) water environment during maternal plant growth affected ABA content and the composition of catabolites in mature and germinated seeds; (3) ABA content did not affect germination performance in our conditions; and (4) the dry and germinated seed parts showed different ABA and catabolite profiles.

Seed shelf-life or longevity is difficult to predict or to measure on a practical time scale. Predictive models suggest that water has the same effect on ageing rate for all seed lots within a species and that initial seed quality is the dominating factor explaining within-species variation. These assumptions are used in ‘accelerated ageing’ or ‘controlled deterioration’ (AA/CD) tests, which are commonly used to predict seed longevity in commercial and research applications. In this study, we describe within-species variation of longevity for seeds of Secale cereale and S. strictum (cultivated rye and its wild progenitor) under typical dry storage conditions of a genebank, and show that initial seed quality is an important, but not sole, factor explaining measured longevity. We also test the correlation of seed longevity, measured under humid and dry conditions, using 50 cultivars of rye, wheat (Triticum aestivum) and the intergeneric cross triticale, to assess how well AA/CD tests predict seed shelf-life during dry storage. Known differences in longevity between wheat and rye were confirmed at all water contents, and triticale seeds demonstrated intermediate behaviour. Longevity measured for humid and dry conditions were weakly correlated when comparisons included all grain types and were not correlated in within-grain-type comparisons. Response to moisture varied among cultivars. These findings do not support assumptions made in seed ageing models that use AA/CD tests. Our results suggest that more traits are involved in the expression of seed longevity than those typically measured in studies of initial seed vigour.

A principal goal of seed germination modelling for wild species is to predict germination timing under fluctuating field conditions. We coupled our previously developed hydrothermal time, thermal and hydrothermal afterripening time, and hydration–dehydration models for dormancy loss and germination with field seed zone temperature and water potential measurements from early summer through autumn to develop predictions of germination timing for Bromus tectorum at a semi-arid site in north-central Utah, USA. Model predictions were tested with a validation dataset based on concomitant seed retrieval experiments in 2 years. Predictions were generally in agreement with observed field germination time courses, even though integration across multiple precipitation events was necessary. Success of the modelling effort hinged on two factors. First, we used a soil capacitance sensor that measured seed zone (5 mm soil depth) water content accurately over a wide range. Second, simulations were built using physiologically based threshold models that can incorporate differences in germination timing for multiple germination fractions and for multiple stages of dormancy loss. Our results suggest that simulation models using hydrothermal time concepts can predict field germination phenology accurately. Seeds in this study integrated their experiences in a widely fluctuating environment in a manner consistent with the assumptions of hydrothermal time. Such threshold-based models also have the advantage of generality, as these concepts can be applied to many different species, environments and weather scenarios.

Arrowleaf sida (Sida rhombifolia) is a tropical weed that grows in disturbed areas. Its control by hand pulling and mowing are only partially effective because arrowleaf sida is difficult to pull and quickly sprouts after cutting. We studied the seed-bank dynamics of S. rhombifolia in the region of Campinas, São Paulo State, Brazil for 2 years, following a known number of seeds placed artificially at five burial depths. Predators and pathogens were responsible for the loss of c. 40% of the seeds during the first year of the experiment. The importance of predation declined with depth. Mortality due to fungal attack did not differ among the burial depths, except for seeds placed at the surface (where it was negligible). Seedling emergence only occurred during the first year, after the beginning of the rainy period and when the study area was still free of a dense vegetation cover. Seedlings did not emerge from depths greater than 5 cm. We conclude that seedling emergence and death are significant causes of seed losses from the seed bank of S. rhombifolia but their relative importance is highly dependent on depth of burial.

The physically dormant seeds of Ipomoea lacunosa and of I. hederacea undergo sensitivity cycling (insensitive ↔  sensitive) to dormancy-breaking treatment. Sensitivity cycling is important to seeds with physical dormancy in sensing appropriate environmental conditions for germination. Seed vigour is also important to seedling establishment, but no study has compared changes in vigour (or not) with changes in sensitivity. This study was conducted to determine the relationship between sensitivity cycling and seed vigour in I. lacunosa and I. hederacea. The seed moisture contents of insensitive and sensitive seeds of I. lacunosa and of sensitive seeds of I. hederacea were measured, and several vigour tests were performed. Vigour of sensitive seeds of I. lacunosa decreased more rapidly than that of insensitive seeds. No significant change in vigour was observed in either permeable or impermeable seeds of I. hederacea. We conclude that sensitivity cycling to physical dormancy break is important in maintaining vigour of I. lacunosa seeds in the soil seed-bank.

Seeds of the iconic Australian baobab Adansonia gregorii display physical dormancy (PY) and germinate readily once they become water permeable, a trait found in most other species in this genus. Highest germination (100%) was observed when seeds were placed in concentrated sulphuric acid (H2SO4) for 24 h, although exposure to H2SO4 for 6–12 h also resulted in >85% germination. Exposure to boiling water for 1–5 min was far less effective in promoting germination (0–23%), although a high number of seeds were water permeable (67–99%) following boiling water treatment. However, the majority of these water-permeable seeds appeared to have been injured by boiling water exposure. Germination at warmer temperatures (30 or 35°C) was found to be optimal (81–83% germination) and proceeded rapidly, with maximum germination occurring after incubation for only 8 d. In comparison, germination at 15–25°C resulted in 3–67% germination over a longer time frame (up to 20 d). While seeds of A. gregorii display PY they are unusually sensitive to dipping in boiling water and are therefore atypical when compared to most other Adansonia species.