Comparative germination responses to water potential across different populations of Aegilops geniculata and cultivar varieties of Triticum durum and Triticum aestivum

Variation in seed properties and germination capabilities among populations of the invasive weed Parthenium hysterophorus L. (Asteraceae)

Introduction

Parthenium hysterophorus (Asteraceae) is an invasive weed species that has invaded over 50 countries worldwide. It was first detected in 1980 at Tirat-Zvi, in eastern-northern Israel. In recent years, there has been an increasing concern over the spread of this weed in agricultural and non-agricultural habitats across the country. However, very little is known about the biology of P. hysterophorus and its variation among populations.

Methods

Seeds collected from five locations across Israel were germinated and plants were grown in pollen-proof cages under uniform conditions to produce the progeny populations. Spatial parameters, weight and germination under different environmental conditions were recorded for field and progeny populations.

Results

Seeds originating from field populations were significantly smaller and lighter than seeds of the progeny populations. Germination occurred in the range of 10°C to 30°C (T o ranges from 19°C to 22.3°C, T b ranged from 9°C to 15°C, T c ranged from 24 ℃ to 30.5°C), depending on generation and population. A water potential-based model was developed to estimate germination under different soil water content using specific parameters (b - slope, d - upper limit, e - infliction point). The model suggests a correlation between germination and water potential. Indeed, reduced germination was recorded for the lower water potentials especially for the progeny populations. Spatial parameters, weight and germination under different environmental conditions were recorded for field and progeny populations.

Discussion

We identified differences in seed size and weight, germination under different temperatures, and osmotic potential among P. hysterophorus Israeli populations. Differences across generations may arise due to the transgenerational effects. Our results, may shed light on the germination abilities of P. hysterophorus populations and provide vital insight into understanding the invasive capabilities of this highly noxious weed.

Germination of grass species from dry and wet grasslands in response to osmotic stress under present and future temperatures

PREMISE

Seed germination is controlled by the soil microclimate, which is expected to change with the temperature increase and rainfall irregularity predicted for the future. Because changes in soil characteristics directly affect species recruitment, vegetation dynamics and resilience, we investigated how caryopses of native grasses from dry and wet grasslands respond to water stress under current and future temperature regimes.

METHODS

Caryopses were collected from 10 grass species in dry and wet grasslands, subjected or not to a fire event, and tested for germination at increasing osmotic potential (0 to -1.0 MPa) at current (17°/27°C night/day) and future (23°/33°C) simulated temperatures.

RESULTS

The viability and germination percentages of caryopses from both dry and wet grassland species were progressively reduced as osmotic stress increased, irrespective of temperature regime. The viability of caryopses from wet grassland species was reduced under the future temperature regime, irrespective of osmotic potential. The slow germination of caryopses of dry grassland species at the present temperature regime was absent when they were incubated in the future temperature regime.

CONCLUSIONS

More intense water stress reduced the survival of caryopses for both dry and wet grassland grass species. The predicted future temperature regime reduced the viability of wet grassland species and altered the germination strategy of dry grassland species. These results indicate that increasing water stress and temperature predicted for the future may compromise the recruitment potential of dry and wet grassland species and directly impact the dynamics and resilience of these ecosystems.

Effect of temperature and water potential on the germination of seeds from three different populations of Bidens pilosa as a potential Cd hyperaccumulator

BACKGROUND

Bidens pilosa L., an annual herb, has recently been shown to be a potential Cd-hyperaccumulating plant. The germination characteristics of B. pilosa have been documented, while the difference among populations remains unclear. Understanding variability in seed germination among populations is crucial for determining which populations to use for soil remediation programs.

RESULTS

Present study was conducted to compare the requirements of temperature and water potential for germination of B. pilosa cypselae (the central type, hereafter seeds) from three populations using the thermal time, hydrotime, and hydrothermal time models. Seeds of three populations were incubated at seven constant temperatures (8, 12, 15, 20, 25, 30, and 35 °C) and at each of four water potentials (0, -0.3, -0.6, and -0.9 MPa). The results showed that germination percentage and rate of B. pilosa seeds were significantly by population, temperature, water potential and their interaction except for the interaction of population and water potential. Seeds from Danzhou population displayed a higher base temperature (T_b) for germination than those from Guilin and Baoshan population, however the ceiling temperature (T_c) had no consistent level among the populations but varied according to the water potential. In addition, the median base water potential [ψ_b(50)] for germination of seeds from Danzhou population was higher than that for seeds from Baoshan and Guilin population at low temperatures (< 25 °C), which was opposite at high temperatures (≥ 25 °C).

CONCLUSION

Seed germination requirements of B. pilosa on temperature and water differed significantly among populations. Differences in seed germination among populations may be complicated, which could not be simply explained by the temperature and rainfall conditions where the seeds were produced as previously reported. The results suggested that programme management should consider variation in seed germination traits when select which population could be applied to what kind of target remediation sites.

Comparative seed longevity under genebank storage and artificial ageing: a case study in heteromorphic wheat wild relatives

Seed longevity is a complex trait that depends on numerous factors. It varies among species and populations, and within different seed morphs produced by the same plant. Little is known about variation in longevity in different seed morphs or the physiological and molecular basis of these differences. We evaluated the longevity and oxidative stress status in heteromorphic seeds aged in two different storage conditions. We compared controlled ageing tests (seed storage at 45°C and 60% relative humidity; a method of accelerated ageing used to estimate longevity in genebank conditions) with storage in a genebank for up to 40 years (-18°C and 8% seed moisture content). We employed as study species two wild wheats characterized by seed heteromorphism: Aegilops tauschii and Triticum monococcum subsp. aegilopoides. We estimated the ROS content and the expression of genes coding for enzymes related to the H₂ O₂ scavenging pathway. Results confirmed that seed longevity varies between different seed morphs. Different storage environments resulted in different longevity and survival curves. ROS levels, even if with variable patterns, were higher in several aged seed lots. We observed consistency in the expression of two genes (GSR and CAT) related to ROS scavenging in the late phase of pre-germinative metabolism. Differences in seed longevity between morphs were observed for the first time under genebank conditions. Our results suggest also that controlled ageing tests should be used with caution to infer ranks of longevity under cold storage.

Do marginal plant populations enhance the fitness of larger core units under ongoing climate change? Empirical insights from a rare carnation

Assisted gene flow (AGF) can restore fitness in small plant populations. Due to climate change, current fitness patterns could vary in the future ecological scenario, as highly performant lineages can undergo maladaptation under the new climatic contexts. Peripheral populations have been argued to represent a potential source of species adaptation against climate change, but experimental evidence is poor. This paper considers the consequences of within- and between-population mating between a large core population and the southernmost population, the rare Dianthus guliae, to evaluate optimal AGF design under current and future conditions. We performed experimental self-pollinations and within- and between-population cross-pollinations to generate seed material and test its adaptive value to aridity. Seed germination, seedling growth and survival were measured under current and expected aridity. Effects of population type, pollination treatment and stress treatment on fitness components were analysed by generalized linear models. Relative measures of inbreeding depression and heterosis were taken under different stress treatments. Self-pollination reduced fitness for all the considered traits compared to within- and between-population cross-pollination. Under current aridity regime, the core population expressed higher fitness, and a larger magnitude of inbreeding depression. This indicated the core unit is close to its fitness optimum and could allow for restoring the fitness of the small peripheral population. Contrarily, under increased aridity, the fitness of outbred core lineages decreased, suggesting the rise of maladaptation. In this scenario, AGF from the small peripheral population enhanced the fitness of the core unit, whereas AGF from the core population promoted a fitness loss in the peripheral population. Hence, the small peripheral population could improve fitness of large core units versus climate change, while the contrary could be not true. Integrating reciprocal breeding programmes and fitness analyses under current and predicted ecological conditions can support optimal AGF design in a long-term perspective.

Water Stress Inhibits Germination While Maintaining Embryo Viability of Subtropical Wetland Seeds: A Functional Approach With Phylogenetic Contrasts

Wetland species commonly exhibit a range of strategies to cope with water stress, either through drought tolerance or through avoidance of the period of limited water availability. Natural populations provide a genetic resource for ecological remediation and may also have direct economic value. We investigated the effects of drought stress on the seed germination of wetland species. Nineteen species were germinated in four concentrations of polyethylene glycol 6000 (PEG) and were evaluated daily (12-h light photoperiod) or after 35 days (continuous darkness) to determine seed germination under water stress. Germination percentage decreased with an increase in polyethylene glycol 6000 (PEG) concentration, but species' germination response to PEG concentration varied significantly. Seeds recovered their germinability after the alleviation of water stress, but the extent of recovery was species-dependent.

Characterization of Drought-Responsive Transcriptome During Seed Germination in Adzuki Bean (Vigna angularis L.) by PacBio SMRT and Illumina Sequencing

The full-length single-molecular sequencing and short reads Illumina sequencing were combined to generate the transcripts of adzuki bean with high-quality. A total of 17,636 loci and 60,454 transcripts were detected in this study. To characterize the drought-responsive genes during seed germination in adzuki bean, two varieties, i.e., tolerant and sensitive to drought stress, were selected to conduct analysis of alternative splicing dynamics (AS) and differentially expressed genes (DEGs) by combining the newly assembled draft genome and public adzuki bean reference genome. AS analysis indicated that both the two varieties underwent a little more AS events under control conditions than under drought stress. Among the AS events, IR (intron retention) predominately accounted for 34.3%, whereas AD (alternative donor site) was the least frequent with 15.8%. Meanwhile, 562 long non-coding RNAs, 409 fusion genes and 1208 transcription factors were identified. Moreover, a total of 5,337 DEGs were identified in comparison of the two varieties with drought or control treatments. Notably, 82 DEGs were discovered in the two varieties under drought stress, which might be the candidate in regulation of seed germination to answer for different drought tolerance. The DEGs encoded proteins involved in primary or second metabolism, plant hormone signal transduction, transcript or translation processes, ubiquitin proteasome system, transcription factor, transporters, and so on. The results facilitate to increase the knowledge about the mechanism of drought tolerance during crop seed germination, and provide reference for the breeding of drought-tolerant adzuki bean.

Heteromorphic seeds of wheat wild relatives show germination niche differentiation

Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related. To this end, dispersal units of Triticum urartu and five Aegilops species were X-rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile. Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer-lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations. The results highlight different trait trade-offs in dimorphic seeds of Aegilops and T. urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

SeedStor: A Germplasm Information Management System and Public Database

SeedStor (https://www.seedstor.ac.uk) acts as the publicly available database for the seed collections held by the Germplasm Resources Unit (GRU) based at the John Innes Centre, Norwich, UK. The GRU is a national capability supported by the Biotechnology and Biological Sciences Research Council (BBSRC). The GRU curates germplasm collections of a range of temperate cereal, legume and Brassica crops and their associated wild relatives, as well as precise genetic stocks, near-isogenic lines and mapping populations. With >35,000 accessions, the GRU forms part of the UK's plant conservation contribution to the Multilateral System (MLS) of the International Treaty for Plant Genetic Resources for Food and Agriculture (ITPGRFA) for wheat, barley, oat and pea. SeedStor is a fully searchable system that allows our various collections to be browsed species by species through to complicated multipart phenotype criteria-driven queries. The results from these searches can be downloaded for later analysis or used to order germplasm via our shopping cart. The user community for SeedStor is the plant science research community, plant breeders, specialist growers, hobby farmers and amateur gardeners, and educationalists. Furthermore, SeedStor is much more than a database; it has been developed to act internally as a Germplasm Information Management System that allows team members to track and process germplasm requests, determine regeneration priorities, handle cost recovery and Material Transfer Agreement paperwork, manage the Seed Store holdings and easily report on a wide range of the aforementioned tasks.