Seed Science Research最新文献

For many decades, seed germination data have been modelled by probit analysis. In particular, it is the basis of the seed viability equation used, in the first instance, to describe the decline in germination of seeds in storage, but then also the rate of the decline, depending on seed moisture content and the temperature of storage. The underlying assumption of a probit model is that the response follows a normal distribution, in this case, loss of the ability to germinate over time. Probit analysis also takes into account the binomial error associated with germination data. Many statistical packages have probit analysis as an option within the generalized linear modelling framework; here, we present code for applying probit analysis in the free software, R. Codes are provided for fitting a single survival curve, for a single seed lot stored in a constant storage environment; for fitting multiple survival curves and evaluating the effect of constraining parameters for the different seed lots; and lastly, to model the moisture relations of seed longevity. The code bases provided could also be used in pollen and fern/bryophyte spore longevity modelling.

Seeds rely on temperature to adjust their germination timing by modulating primary and secondary dormancy. The knowledge regarding an intraspecific variation in the germination responses to supra-optimal temperatures during imbibition within the Solanum lycopersicon species and its relation with pre- and post-harvest environments is limited. Here, we studied the impact of imbibition at 35°C in 17 genotypes selected from a multiparent advanced generation intercross (MAGIC) population. We discovered a high genetic variability in the germination responses to heat, leading to thermotolerance, thermoinhibition or thermodormancy with different depths. While thermodormancy appeared more profound than primary dormancy, there was no correlation between the deepness of primary and thermodormancy. Post-harvest treatments influenced considerably germination at supra-optimal temperatures. Dry storage beyond the apparent loss of primary dormancy led to an increased proportion of thermotolerant or thermoinhibited seeds at the expense of thermodormancy in a genotype-dependent manner, thereby revealing cryptic genetic variation. Prolonged cold imbibition also led to increased thermodormancy in genotypes that produced thermotolerant and thermoinhibited seeds. The thermal history before and after flowering influenced primary dormancy and the germination response to heat during imbibition in a genotype-dependent manner, with high temperatures leading to increased thermotolerance or thermoinhibition at the expense of thermodormancy, suggesting transgenerational plasticity despite the domestication of the species. The high potential of the MAGIC population for quantitative trait loci mapping and causal polymorphism identification will be helpful in deciphering the regulatory mechanisms that lead to the plasticity of thermoinhibition or thermodormancy, as well as their connection to the parental environment.

We have reviewed seed dormancy and germination in the Rubiaceae, the fourth-largest angiosperm family (in terms of species richness), in relation to ecology, life form, biogeography and phylogeny (subfamily/tribe). Life forms include trees, shrubs, vines and herbs, and tropical rainforest trees have the greatest number of tribes and species. The family has five kinds of embryos: investing, linear-full, linear-underdeveloped, spatulate and spatulate-underdeveloped, and seeds are non-dormant (ND) or have morphological (MD), morphophysiological (MPD) or physiological (PD) dormancy. Except for the occurrence of the investing embryo only in dry fruits of Dialypetalanthoideae, each kind of embryo is found in dry and fleshy fruits of Dialypetalanthodies and of Rubioideae. In tropical and temperate regions, there are species with ND seeds and others whose seeds have MD, MPD or PD. A complete seed dormancy profile (i.e. some species with ND seeds and others whose seeds have MD, MPD or PD) was found for tropical rainforest trees and shrubs and semi-evergreen rainforest shrubs. Dormancy-break occurs during cold or warm stratification or dry-afterripening, depending on the species. Some tropical species have long periods of dormancy-break/germination extending for 4–5 to 30–40 weeks. Soil seed banks are found in 5 and 15 tribes of Rubiaceae in tropical and temperate regions, respectively. With increased distance from the Equator, diversity of life forms and seed dormancy decreases, resulting in only herbs with PD at high latitudes. We conclude that the low species richness of Rubiaceae in temperate regions is not related to low diversity of seed dormancy/germination.

Although seed trait variations and their relationship to the ecological niche have been studied extensively at the species level, they do not necessarily reflect variations at the population level. In this study, we explored the intra-specific variation in relative embryo length, seed mass and germination speed in 40 populations of Daucus carota distributed across Europe and North America. By including information on local climate conditions, we aimed to examine the impact of the geographical origin on various seed functional traits and to detect potential local adaptation. No significant difference was observed in final seed germination for European and North American seeds incubated at 20°C, nor in seed viability. In European populations, relative embryo length significantly increased with increasing seed mass, but no such relation was found in North American populations. Larger relative embryo length at dispersal resulted in increased germination speed in both European and North American populations. Populations in drier areas typically had seeds with larger relative embryo lengths. Precipitation-related climate variables showed a negative relationship with relative embryo length, indicating a reduction in relative embryo length with increased precipitation. No clear relationship between climate and seed mass was observed. We can conclude that seed functional traits of D. carota are adapted to local climate conditions, as a clear gradient was observed in the relative embryo length of D. carota, which was associated with germination speed and climate. This gradient was less pronounced in North America, which can be explained by its relatively recent introduction to the continent.