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Background and Aims: Understorey species in temperate deciduous woodlands such as wild daffodil (Narcissus pseudonarcissus) and common snowdrop (Galanthus nivalis) have complex dormancy: seeds that are shed in late spring require warm summer temperatures for embryo elongation and dormancy alleviation, but then cooler temperatures for germination in autumn. As seasons warm and tree canopies alter, how will different seasonal temperature sequences affect these complex dormancy responses?, Methods: The effect of different sequences of warmer (+5 °C), current or cooler (-5 °C) seasons (summer to spring) on seed germination patterns over seven successive seasons were investigated, with all sequences combined factorially to determine the consequences of differential seasonal temperature change for the temporal pattern of germination (and so seedling recruitment)., Key Results: Little (<1 %, G. nivalis) or no (N. pseudonarcissus) seed germination occurred during the first summer in any treatment. Germination of N. pseudonarcissus in the first autumn was considerable and greatest at the average (15 °C) temperature, irrespective of the preceding summer temperature; germination was also substantial in winter after a warmer autumn. Germination in G. nivalis was greatest in the warmest first autumn and influenced by preceding summer temperature (average > warmer > cooler); the majority of seeds that germinated over the whole study did so during the two autumns but also in year 2's cooler summer after a warm spring., Conclusions: Warmer autumns and winters delay first autumn germination of N. pseudonarcissus to winter but advance it in G. nivalis; overall, warming will deplete the soil seed bank of these species, making annual seed influx increasingly important for recruitment and persistence. This study provides a comprehensive account of the effects of temperature changes in different seasons on seed germination in these early spring-flowering geophytes and consequently informs how these and other temperate woodland species with complex seed dormancy may respond to future climate change., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background and Aims: Seeds of the moist temperate woodland species Galanthus nivalis and Narcissus pseudonarcissus, dispersed during spring or early summer, germinated poorly in laboratory tests. Seed development and maturation were studied to better understand the progression from developmental to germinable mode in order to improve seed collection and germination practices in these and similar species., Methods: Phenology, seed mass, moisture content and ability to germinate and tolerate desiccation were monitored during seed development until shedding. Embryo elongation within seeds was investigated during seed development and under several temperature regimes after shedding., Key Results: Seeds were shed at high moisture content (>59 %) with little evidence that dry mass accumulation or embryo elongation were complete. Ability to germinate developed prior to the ability of some seeds to tolerate enforced desiccation. Germination was sporadic and slow. Embryo elongation occurred post-shedding in moist environments, most rapidly at 20 °C in G. nivalis and 15 °C in N. pseudonarcissus. The greatest germination also occurred in these regimes, 78 and 48 %, respectively, after 700 d., Conclusions: Seeds of G. nivalis and N. pseudonarcissus were comparatively immature at shedding and substantial embryo elongation occurred post-shedding. Seeds showed limited desiccation tolerance at dispersal.

Rising temperatures due to climate change are expected to interplay with biological invasions, and may enhance the spread and growth of some alien species upon arrival in new areas. To successfully invade, a plant species needs to overcome multiple biological barriers. Among the crucial life stages, seed germination greatly contributes to the final species assembly of a plant community. Several studies have suggested that alien plant success is related to their high seed germination and longevity in the soil. Hence, our aim is to test if the germination potential of alien seeds present in the seed bank will be further enhanced by future warming in temperate dry grasslands, an ecosystem that is among those most prone to biological invasions. We designed a laboratory germination experiment at two temperatures (20 and 28 °C), to simulate an early or late heat wave in the growing season, using seeds from nine common grassland Asteraceae species, including native, archaeophyte and neophyte species. The test was performed on both single and mixed pools of these categories of species, using a full-factorial orthogonal design. The warmer germination temperature promoted neophyte success by increasing germination probability and germination speed, while negatively impacting these parameters in seeds of native species. The co-occurrence of native and archaeophyte seeds at the lower temperature limited the invasiveness of neophytes. These results provide important information on future management actions aimed at containing alien plant invasions, by improving our knowledge on the possible seed-bank response and interaction mechanisms of common species occurring in disturbed natural areas or restored sites. Summary of the experimental results. The colour of the flowers represent the status, divided as native (blue), neophyte (red) and archaeophyte (green). Each flower symbol represents the species pool for each plant category (i.e. NA = Buphthalmum salicifolium, Carlina vulgaris, Centaurea scabiosa; NE = Artemisia annua, Symphyotrichum novi-belgii, Senecio inaequidens; AR = Centaurea cyanus, Cichorium intybus, Tripleurospermum inodorum). The number of flowers represent the germination percentage of the various category assembly. In the columns are divided the various combination. From up to bottom the trend of germination percentage at 20 and 28 °C are shown. [ABSTRACT FROM AUTHOR]

The length of time for which seed lots maintain their viability and vigour in storage has become a trait of interest for rice and other crop and model species. However, different research groups have taken different approaches to measuring this trait, including storing seeds under 'natural ageing', accelerated ageing, and controlled deterioration test conditions. There has also been a tendency to use only a single germination test result to assess the relative longevity of different genotypes. Here, we explain why we have taken a different approach in a genome-wide association study of seed longevity in Oryza sativa (Indica Group), and offer suggestions as to how, in the future, this trait should be assessed to make it possible to develop varieties with improved seed longevity, depending on the target storage environment. [ABSTRACT FROM AUTHOR]

Resilience of rice cropping systems to potential global climate change will partly depend on the temperature tolerance of pollen germination (PG) and tube growth (PTG). Pollen germination of high temperature-susceptible Oryza glaberrima Steud. (cv. CG14) and Oryza sativa L. ssp. indica (cv. IR64) and high temperature-tolerant O. sativa ssp. aus (cv. N22), was assessed on a 5.6-45.4 °C temperature gradient system. Mean maximum PG was 85% at 27 °C with 1488 μm PTG at 25 °C. The hypothesis that in each pollen grain, the minimum temperature requirements (Tn) and maximum temperature limits (Tx) for germination operate independently was accepted by comparing multiplicative and subtractive probability models. The maximum temperature limit for PG in 50% of grains (Tx(50)) was the lowest (29.8 °C) in IR64 compared with CG14 (34.3 °C) and N22 (35.6 °C). Standard deviation (sx) of Tx was also low in IR64 (2.3 °C) suggesting that the mechanism of IR64's susceptibility to high temperatures may relate to PG. Optimum germination temperatures and thermal times for 1 mm PTG were not linked to tolerating high temperatures at anthesis. However, the parameters Tx(50) and sx in the germination model define new pragmatic criteria for successful and resilient PG, preferable to the more traditional cardinal (maximum and minimum) temperatures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Seed dormancy induction and alleviation in the winter-flowering, moist temperate woodland species Galanthus nivalis and Narcissus pseudonarcissus are complex and poorly understood. Temperature, light and desiccation were investigated to elucidate their role in the germination ecophysiology of these species. The effect of different seasonal temperatures, seasonal durations, temperature fluctuations, the presence of light during different seasons and intermittent drying (during the summer period) over several 'years' on seed germination was investigated with outdoor and laboratory experiments. Warm summer-like temperatures (20 °C) were necessary for germination at subsequent cooler autumn-like temperatures (greatest at 15 °C in G. nivalis and 10 °C in N. pseudonarcissus). As the warm temperature duration increased, so did germination at subsequent cooler temperatures; further germination occurred in subsequent 'years' at cooler temperatures following a second, and also third, warm period. Germination was significantly greater in darkness, particularly in G. nivalis. Dormancy increased with seed maturation period in G. nivalis, because seeds extracted from green capsules germinated more readily than those from yellow capsules. Desiccation increased dormancy in an increasing proportion of N. pseudonarcissus seeds the later they were dried in 'summer'. Seed viability was only slightly reduced by desiccation in N. pseudonarcissus, but was poor and variable in G. nivalis. Shoot formation occurred both at the temperature at which germination was greatest and also if 5 °C cooler. In summary, continuous hydration of seeds of both species during warm summer-like temperatures results in the gradual release of seed dormancy; thereafter, darkness and cooler temperatures promote germination. Cold temperatures, increased seed maturity ( G. nivalis) and desiccation ( N. pseudonarcissus) increase dormancy, and light inhibits germination. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177, 246-262. [ABSTRACT FROM AUTHOR]

Probit-based models relating a proportional response variable to a temporal explanatory variable, assuming that the times to response are normally distributed within the population, have been used in seed biology for describing the rate of loss of viability during seed ageing and the progress of germination over time in response to environmental signals (e.g. water, temperature). These models may be expressed as generalized linear models (GLMs) with a probit (cumulative normal distribution) link function, and, using GLM fitting procedures in current statistical software, parameters of these models are efficiently estimated while taking into account the binomial error distribution of the dependent variable. The fitted parameters can then be used to calculate the ‘traditional’ model parameters, such as the hydro- or hydrothermal time constant, the mean or median response of the seeds (e.g. mean time to death, median base water potential), and the standard deviation of the normal distribution of that response. Furthermore, through consideration of the deviance and residuals, performing model evaluation and modification can lead to improved understanding of the underlying physiological/ecological processes. However, fitting a binomial GLM is not appropriate for the cumulative count data often collected from germination studies, as successive observations are not independent, and time-to-event/survival analysis should be considered instead. This review discusses well-known probit-based models, providing advice on how to collect appropriate data and fit the models to those data, and gives an overview of alternative analysis approaches to improve understanding of the underlying mechanisms of seed dormancy and germination behaviour. [ABSTRACT FROM PUBLISHER]

In obligate seeding species, the germination niche is crucial for colonization and population survival. It is a high-risk phase in a plant's life cycle, and is directly regulated by temperature. Seeds germinate over a range of temperatures within which there is an optimum temperature, with thresholds above and below which no germination occurs. We suggest that abrupt changes in temperature associated with a warming climate may cause a disconnect between temperatures seeds experience and temperatures over which germination is able to occur, rendering obligate seeding species vulnerable to decline and extinction. Using a bidirectional temperature gradient system, we examined the thermal constraints in the germination niche of some geographically restricted species from the low altitude mountains of the Stirling Range, southern Western Australia, including seedlots from lowland populations of four of these species. We demonstrated that high temperatures are not a limiting factor for germination in some restricted species, signifying a lack of relationship between geographic range size and breadth of the germination niche. In contrast, we identified other restricted species, in particular Sphenotoma drummondii, as being at risk of recruitment failure as a consequence of warming: seeds of this species showed a strong negative relationship between percentage germination and increasing temperature above a relatively low optimum constant temperature (13°C). We found some ecotypic differences in the temperature profiles between seeds collected from montane or lowland populations of Andersonia echinocephala, and while specific populations may become more restricted, they are perhaps at less risk of extinction from climate warming. This seed-based approach for identifying extinction risk will contribute tangibly to efforts to predict plant responses to environmental change and will assist in prioritizing species for management actions, directing limited resources towards further investigations and can supplement bioclimatic modelling. [ABSTRACT FROM AUTHOR]

Fritillaria tubiformis subsp. moggridgei (Liliaceae) is a rare, endemic species that inhabits open mountains and alpine grasslands of the Ligurian Alps. At the time of seed dispersal, the underdeveloped embryos were 27% the length of the seed. Here we report the results of laboratory experiments carried out to determine the temperature preferences for embryo growth and radicle emergence. Embryo growth commenced immediately after sowing at 4°C. Once the embryo had grown the length of the seed, the radicle emerged. The time required for embryo growth and radicle emergence was longer when seeds were placed through a seasonal sequence of temperatures, commencing with late summer (10/20°C), compared with seeds immediately placed at a temperature to simulate winter conditions (4°C). Prematurely transferring seeds from winter to spring temperatures (5/10°C) also slowed the progress of germination. Radicle emergence did not occur at 10 or − 5°C and less than 20% germination occurred in seeds placed at constant 0°C. Addition of gibberellic acid (GA3) did not promote embryo growth of seeds placed at 20°C. Overall, the temperature preferences for embryo growth and subsequent radicle emergence are such that, in situ, seed germination may occur during the winter under snow cover or at the end of winter to coincide with snow melt and warming temperatures. [ABSTRACT FROM AUTHOR]

Seeds from ten terrestrial orchid species, nine from the south-west Australian biodiversity hotspot ( Caladenia arenicola, Caladenia flava, Caladenia huegelii, Diuris laxiflora, Microtis media ssp. media, Pterostylis recurva, Pterostylis sanguinea, Thelymitra crinita and Thelymitra macrophylla) and one from south-east Australia ( Diuris fragrantissima), were placed into experimental storage to assess their relative longevity and likely optimal conditions for long-term conservation seed banking. Seeds from all species were desiccation tolerant, germinating after drying at 23% relative humidity ( C. arenicola, C. huegelii, P. sanguinea and T. macrophylla) or 5% relative humidity ( C. flava, D. laxiflora, M. media ssp. media, P. recurva and T. crinita) at 23 °C. From automatedly determined moisture adsorption and desorption isotherms at 23 °C, these equate to tolerance of drying to 0.03-0.06 g water g−1 dry weight or 0.013-0.028 g water g−1 dry weight, respectively. Results of storage experiments at a range of moisture contents and temperatures suggest conventional seed bank storage at −18 °C after equilibration at c. 23% relative humidity (at 23 °C) may be suitable for most of the species, although there was higher germination of P. recurva seeds stored at −80 °C and of M. media ssp. media seeds equilibrated at 75% relative humidity. However, there was considerable variation in germination of seeds sampled after different storage periods, making it difficult to identify optimal storage conditions definitively. Results of comparative longevity storage experiments at 60% relative humidity and 40 °C suggest seeds from these orchid species are short-lived compared with non-orchid species, and with Australian species in particular. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164, 26-41. [ABSTRACT FROM AUTHOR]

Genebank management is a field in its own right; it is multifaceted, requiring a diverse set of skills and knowledge. Seed physiology is one area that is critical to the successful operation of seed genebanks, requiring understanding of seed quality during development and maturation, seed dormancy and germination, and seed longevity in storage of the target species. Careful management of the workflow between these activities, as seeds move from harvest to storage, and the recording and management of all relevant associated data, is key to ensuring the effective conservation of plant genetic resources. This review will discuss various aspects of seed physiology that genebank managers should be aware of, to ensure appropriate decisions are made about the handling and management of their seed collections. [ABSTRACT FROM AUTHOR]