Seed Germination Responses Research Articles

Molecular Mechanism Underlying the Synergetic Effect of Jasmonate on Abscisic Acid Signaling during Seed Germination in Arabidopsis

Abscisic acid (ABA) is known to suppress seed germination and post-germinative growth of Arabidopsis (Arabidopsis thaliana), and jasmonate (JA) enhances ABA function. However, the molecular mechanism underlying the crosstalk between the ABA and JA signaling pathways remains largely elusive. Here, we show that exogenous coronatine, a JA analog structurally similar to the active conjugate jasmonate-isoleucine, significantly enhances the delayed seed germination response to ABA. Disruption of the JA receptor CORONATINE INSENSITIVE1 or accumulation of the JA signaling repressor JASMONATE ZIM-DOMAIN (JAZ) reduced ABA signaling, while jaz mutants enhanced ABA responses. Mechanistic investigations revealed that several JAZ repressors of JA signaling physically interact with ABSCISIC ACID INSENSITIVE3 (ABI3), a critical transcription factor that positively modulates ABA signaling, and that JAZ proteins repress the transcription of ABI3 and ABI5. Further genetic analyses showed that JA activates ABA signaling and requires functional ABI3 and ABI5. Overexpression of ABI3 and ABI5 simultaneously suppressed the ABA-insensitive phenotypes of the coi1-2 mutant and JAZ-accumulating (JAZ-ΔJas) plants. Together, our results reveal a previously uncharacterized signaling module in which JAZ repressors of the JA pathway regulate the ABA-responsive ABI3 and ABI5 transcription factors to integrate JA and ABA signals during seed germination and post-germinative growth.

Quantifying seed germination response of deteriorated Trigonella foenum-graecum L. seed to temperatures and water potentials: Thermal time, hydrotime and hydrothermal time models

Quantifying the germination behavior of seeds against variable environmental conditions can use as a useful implement for seed ecological studies. Seed vigor depends on the temperature and moisture conditions during seed development and storage. To quantify the effects of temperature and water potential on germination response of fenugreek seeds, thermal time, hydrotime, and hydrothermal time models were employed. The treatments included 9 temperatures (5, 10, 15, 20, 25, 30, 35, 40 and 45 °C), and five water potentials (0, −0.2, −0.4, −0.6, and −0.8 MPa) on deteriorated (35 h) and non-deteriorated seeds. The results indicated that the segmented model was the best model to describe the germination response of fenugreek seed under different temperatures and water potentials. The cardinal temperatures predicted for germination were 0.48, 21.6, and 46 °C for non-deteriorated seeds, and 0.85, 20.6, and 46.3 °C for deteriorated seeds at 0 MPa. Thermal time constants were 49125 and 56657.9 °C h for non-deteriorated and deteriorated seeds at -0.8 MPa and were 899.6 and 1072 °C h for non-deteriorated and deteriorated seeds at 0 MPa. Hydrotime constants were 50.64 and 72.37 MPa h at 5 °C for non-deteriorated and deteriorated seeds and were 1.97 and 3.07 MPa h at 35 °C. Hydrothermal time constants of non-deteriorated and deteriorated seeds were 264.1 and 263.1 MPa °C h at the supra-optimal temperatures.

Quantifying seed germination responses of Echinops and Centaurea, to salinity and drought stresses

Seed germination may significantly interrupt by water stress due to drought and salinity condition. Salinity can cause osmotic pressure and induce drought stress. Water deficit stress affect normal seed germination and reduce seedling vigor. The objective of this investigation was to determine the effect of drought and salt stresses on germination characteristics of Echinops ritro and Centaurea virgata. Seeds were germinated with the concentrations of sodium chloride (0, 50, 100, 150 and 200 mmol) or in polyethylene glycol PEG6000 (0, -0.2, -0.4, -0.6, -0.8, -1 and -1.2 MPa). The highest values of germination parameters were obtained with no osmotic potential or salinity stress. At treatment by PEG, the germination was severely decreased at -0.6 MPa. While, no germination occurred at- 0.8 MPa by PEG. Results revealed that under 118 Mmol salinity, the seed germination of Centaurea virgata declined to 43% which was as close as half of its total seed germination. However, 50% reduction in seed germination of Echinops ritro was observed at 193 mmol salinity. Results indicated Echinops ritro and Centaurea virgata germination was sensitive to both the stresses. However, seedling growth was more sensitive to PEG than NaCl.

Temperature requirements for guayule seed germination

Guayule (Parthenium argentatum A. Gray) is an alternative source of natural rubber. Direct-seeding is critical to commercialization of guayule and quantifying variability in seed germination response to temperature is necessary. A thermogradient table was used to measure germination rates of the 44 most commonly available Parthenium accessions under 10 temperature gradients. The optimal temperature for seed germination ranged from 17.8–26.9 °C, with an average temperature of 21.8 °C. The sensitivity of seed germination to temperature range varied significantly among accessions. When compared with the highest germination rate at optimal temperature, relative germination rate at 10 °C and 35 °C represented low and high temperature tolerance for seed germination in guayule accessions, respectively. The two accessions with >70 % relative germination rate at 35 °C, R1109 and P. incanum (mariola), had the optimal temperature for germination above 26.6 °C. Six accessions with >70 % relative germination rate at 10 °C, 11591, R1110, PARL 935, CAL-3, 11605, and PARL 920, had a range of 17.8–21.7 °C optimal temperature for germination. This study indicates that guayule and other Parthenium accessions varied significantly in temperature requirements for seed germination. These temperatures can serve as a guide to seasonal timing for direct seeded field planting.

Hydrotime model analysis of lemon balm (Melissa officinalis L.) using different distribution functions

Water potential is an important factor for a successful germination. The hydrotime model can help quantify the seed germination response to water potential (ψ). This present study aimed to investigate the response of lemon balm (Melissa officinalis L.) seed emergence rate to water deficit with six levels (−0.165, −0.35, −0.45, −0.85, −1.25, and Field Capacity (FC) with -0.03 MPa) as a pot experiment. In addition, the germination behavior was studied in six water potentials in PEG solution (0, −0.2, −0.4, −0.6, −0.8 and −1 MPa) as the completely randomized design in 2018. The data were analyzed through the hydrotime model and five distribution functions (Normal, Gumbel, Weibull, Logistic and Loglogistic) were fitted to data for lemon balm. According to the model criteria, the Logistic distribution gave the best fit by the highest adjusted R2 of 0.921 and 0.989, and the lowest Akaike index (AICc) of −1677.855 and −471.777 in the germination and emergence experiments, respectively. According to the results, hydrotime constant (θH) in the two experiments were estimated to be 49.891 and 83.991 MPa h, respectively, which were significantly different (P < .001). However, there was no significant difference between the mean base water potential (ψb(50)), which were estimated as −0.340 and −0.439 MPa in the germination and emergence experiments respectively. The suggested hydrotime modeling in the present study may help predict lemon balm seed germination and emergence in soil under water deficit conditions.

Plant morphology and seed germination responses of seagrass (Zostera japonica) to water depth and light availability in Ailian Bay, northern China

Poor water quality and light reduction owing to anthropogenic impacts are the most widespread causes behind marine submerged angiosperm (seagrass) declines, worldwide. Seagrasses could respond to sustained environmental stresses, such as increasing water depth and light reduction, through morphological changes, particularly shoot density and/or biomass reductions. The seagrass Zostera japonica Asch. and Graebn. has been introduced to the Pacific Coast of North America, but it is widely threatened in its native northwestern Pacific Coast range alongside the east coast of China. The main aims of this study were to determine: 1) the depth limit of Z. japonica growth in its native range, and 2) how light availability affects the growth and recruitment of Z. japonica. To achieve these aims, we investigated the temporal responses of Z. japonica shoots and seeds from an intertidal donor site, Swan Lake, to light availability at water depths ranging from 1 to 6 m using in situ suspended cultures deployed in the experimental site, Ailian Bay, off the coast of Weihai City, China. The results showed that the transplanted Z. japonica shoots and seeds could survive for the duration of their annual growth cycle, permanently underwater, at a depth ≤2 m. There was a significant inverse relationship between water depth and time to complete shoot loss, despite temporally varying water clarity levels. Due to the local turbidity of the waters in Ailian Bay, a depth of 2 m yielded sufficient light deprivation (5%–37% surface irradiance) to negatively affect the seagrass shoot density. Our results suggest that this intertidal species can potentially persist in shallow subtidal areas following transplantation with shoots and seeds. The findings may also serve as useful information for local seagrass distribution limits, and will facilitate their habitat establishment and restoration efforts.

A new halothermal time model describes seed germination responses to salinity across both sub- and supra-optimal temperatures

We quantified the seed germination responses of chicory (Cichorium intybus L.; Asteraceae) to heat, water and salt stresses using hydrothermal time (HTT) and halothermal time (HaloTT) models. We extended the HaloTT model based on NaCl concentration to include supra-optimal temperatures. The HTT and HaloTT models enabled quantitative comparison of the effects of reduced water potentials and increased salinity on germination. Below 30 °C, the median threshold water potential permitting germination estimated by the HTT model (− 0.83 MPa) was higher than that estimated by the HaloTT model (− 1.30 MPa, after converting the median threshold NaCl concentration to osmotic potential). Ion uptake into seeds imbibed in salt solutions accounted for an average osmotic adjustment of 36% in the presence of salt stress compared to seeds imbibed in polyethylene glycol solutions. These thresholds became more positive above 30 °C with a common median ceiling temperature of 43 °C. The HaloTT models developed here accurately described germination responses to NaCl concentrations across all temperatures and incorporated both water potential and osmotic adjustment effects. With respect to seed germination, chicory could be considered as a moderately water stress tolerant species and highly tolerant to salt stress.

Germinación de semillas de Lotus tenuis: efecto del tratamiento pregerminativo, tiempo de almacenamiento y rol de la cubierta dura a largo plazo

Se evaluó el efecto de la escarificación mecánica en dos momentos luego de la cosecha sobre la germinación de semillas de 23 genotipos de Lotus tenuis Waldst et Kit almacenadas en condiciones de laboratorio sin escarificar y el rol de las cubiertas duras sobre dicha respuesta a largo plazo. Se usó un DCA con tres factores [genotipos, tratamiento pregerminativo (E=escarificado; NE=ausencia de escarificado) y tiempo de almacenamiento (t1=0,25 años; t2=22,5 años)] (n=4). Se calculó el porcentaje de germinación acumulada (Gac%) y de semillas duras (Sd%). Para t2 se calculó el índice de velocidad germinativa (IVG). Se aplicó ANOVA no paramétrico (Kruskal-Wallis) y comparación de medianas. Para t2 se analizaron correlación y regresión simple. La interacción triple resultó significativa (p ≤0,01) para ambos parámetros. Gac% tuvo valores mayores en el tratamiento E en t1 y menores en NE en t2. El factor genotipo resultó significativo (p≤0,01) para el E en t2. Sd% tuvo valores mayores en el tratamiento NE en t1 y menores en E independientemente del tiempo de almacenamiento. El factor genotipo resultó significativo (p≤0,01) para NE en t2. La correlación Sd% vs. Gac% e IVG resultó significativa (p≤0,01) y positiva. Las regresiones simples Sd% vs. Gac% e IVG resultaron significativas (p≤0,01). El estudio demostró que la escarificación y el tiempo de almacenamiento afectan de manera positiva y negativa, respectivamente, al comportamiento germinativo de los genotipos estudiados, que el ablandamiento de la cubierta dura es variable entre genotipos y que dicha cubierta estaría vinculada con la conservación de la capacidad germinativa en el largo plazo.

Germination response to temperature and water potential for Sprawling bauhinia (Tylosema fassoglense), a potential crop for Kenya

The knowledge of cardinal temperatures is critical for understanding environmental tolerance limits for germinating plant species. However, this information is not readily available for Tylosema fassoglense [Family: Fabaceae]; despite its potential as a future crop to improve nutrition and enhance sustainable agriculture in Kenya.The objective of this study was to characterise seed germination responses to temperature and water potential of seed lots of T. fassoglenseseeds collected from three counties in Kenya; namely Busia, Migori and Siaya.Scarified seeds were germinated at a wide range of constant temperatures from 10 to 45 °C with intervals of 5 °C and water potentials from 0, -0.25, -0.5, -1.0, -1.5 Megepascal (MPa) at 25 °C.Seeds of T. fassoglense had a wide range of germination temperature of 20 °C (from 15 to 35 °C). Low (10 °C) and high (≥40 °C) temperatures significantly reduced germination in the three seed lots. Busia seed lot had the lowest final germination of 5% at 10 °C while germination was zero at 45 °C in all the seed lots tested. The calculated base, optimal and ceiling temperature (Tb, To and Tc) ranges were 4.05 - 8.0 °C; 33.61 - 35.75 °C; and 46.54 - 47.24 °C, respectively. Suboptimal and supraoptimal thermal time (θT(50)) ranged between 76.19 – 89.02 degree celcius days (°C d) and 30.3–41.89 °C d respectively. Water potential of -0.5 MPa significantly reduced final germination to less than 50% in all seed lots while germination was zero at both -1.0 and -1.5 MPa. The base water potential (Ψb) and hydro time (θH(20)) was between -0.92 to -0.97 MPa and 3.95–4.11 Megapascal days (MPad) respectively.The optimum temperature range for germination was 30–35 °C and seeds were tolerant to low water potential up to -0.5 MPa. However, further studies will need to be carried out on germination in the supraoptimal temperature range and water potential between 0 and -1.0 MPa. The findings in this study will be useful in future research contributing towards domestication of T. fassoglense.

Peanut Seed Germination and Radicle Development Response to Direct Exposure of Flumioxazin Across Multiple Temperatures

ABSTRACT Peanut injury in the field can occur from flumioxazin applied PRE, but this is associated with plants that have emerged, or are about to, emerge from soil. The direct effect of flumioxazin on peanut seed germination and radicle development has not been evaluated. Therefore, research was conducted to determine peanut seed radicle development response to flumioxazin at different concentrations (0.0, 0.01, 0.10, 1.0 and 10.0 ppb) when tested at multiple temperatures (20, 23, 26, and 29 C) in laboratory experiments on a thermogradient table. Data analysis indicated that flumioxazin concentration was not different from the nontreated control (0.0 ppb) for 0.01, 0.1, and 1.0 ppb for peanut germination. Flumioxazin at 10.0 ppb was different from all other treatments and the nontreated control. However, comparing linear regression models for each flumioxazin concentration across all temperatures indicated no differences for slope. These data indicate that when there is direct peanut seed exposure to flumioxazin at field application rates, there is no impact on germination and radicle development. Temperature was noted to affect radicle development greater than field application rates of flumioxazin. As temperature decreased, germination and radicle length was inhibited or decreased, respectively. Nomenclature: Flumioxazin, peanut, Arachis hypogaea (L.), radicle, seed germination

Seasonal germination responses of seeds in fruits of the cold desert shrub Zygophyllum xanthoxylon buried in the field

We hypothesized that seeds of the central Asian cold desert shrub Zygophyllum xanthoxylon exhibit dormancy cycling in nature, which would help ensure that germination occurs at a favorable time for seedling survival. Fresh mature fruits of Z. xanthoxylon were placed on the soil surface and buried at a depth of 3–5 cm in soil in a natural habitat in August 2015. At regular intervals until July 2017, fruits/seeds were taken to the laboratory and evaluated for viability and germination. Fresh seeds in fruits germinated to 22–62% over a range of temperatures. After 6 weeks in the field, seeds on the surface germinated to 72–99% and those in soil to 70–100%. From 12 to 98 weeks, seeds on and in soil germinated to 72–100% at low (15/5 and 20/10 °C) temperatures, but germination at high (25/25 and 30/15 °C) temperatures was higher in summer than in spring. Seeds in fruits on the soil surface had higher germination percentages than those in the soil, especially at high temperatures. Although about half the seeds were dormant at maturity, they became nondormant in the field during summer. There was a decrease in ability to germinate at high temperatures in spring, especially for seeds in buried fruits, which indicates conditional dormancy/nondormancy cycling. Lack of germination at high temperatures in spring would help delay germination until the onset of the summer rainy season in the desert. Burial of fruits in the soil enhances the formation of a short-lived persistent seed bank.

Effective breaking of dormancy of Scaevola sericea seeds with seawater, improved germination, and reliable viability testing with 2,3,5-triphenyl-tetrazolium chloride

Scaevola sericea (Gaertn.) Roxb., which is a semi-mangrove halophyte, displays low seed germination (SG) and poor development. A model system was established to assess seed viability (SV) and enhanced SG in response to 2,3,5-triphenyl-tetrazolium chloride (TTC), and to detect SV under different storage conditions and duration to establish an optional storage method for seeds. Percentage SG (SG%) was also tested with different periods of soaking in water, gibberellic acid (GA3) and seawater after removing fruit pulp. Optimal detection of the percentage of SV (SV%) was possible when seeds were soaked for 3 h in 0.4% TTC. In these conditions, after 15 d, SV% exceeded 90.0%. This indicates that low SG was not related to SV under natural conditions. The nutritious epicarp (pulp) of intact fruit is easily infected by mildew, rotting rapidly in high relative humidity (60–90%). When pulp was removed from fruits, germination period was speeded up by almost 8 d (seeds germinated after sowing for 28 d). This also increased SG%. Seawater broke seed dormancy more efficiently than GA3. The SG% (59.0%) of seeds with their epicarp removed then soaked in seawater for 24 h was higher than seeds soaked in distilled water (24.0%) or in 200 mg/L GA3 (33.7%) after sowing for 40 d The SV% of seeds stored at 4 °C was higher than seeds stored at room temperature (25±3 °C), but when storage period was extended to 180 d or longer, their SV% declined rapidly. In natural conditions, S. taccada seeds have a high SV%. The low SG% is caused by easily rotting pulp and the physiological dormancy of fruits. By removing the pulp and soaking naked seeds in seawater can break seed dormancy and achieve ideal SG which would benefit ecorestoration and landscaping projects.

Seed germination responses for varying KNO3 and NaNO3 stress in Trifolium alexandrinum. L cultivars

Abstract: Egyptian clover (Trifolium alexandrinum L.) is a forage legume considered to be of high nutritional values and palatable as cattle feed. Germination of the seed is affected by water availability and environmental stress prevailing there in. Three cultivars of T. alexandrinum viz. Bundel Berseem 1 (BB1), Bundel Berseem 2 (BB2), and Bundel Berseem 3 (BB3) were germinated under varying NaNO3 and KNO3, concentration range of 0 mM, 25 mM, 50 mM, 75 mM, 100 mM, and 150 mM. Our experiment revealed that up to 50 mM salt concentration, the tested cultivars responded in similar way but when the concentration started to reach 100 mM and 150 mM significant differences between the germination rates of the three cultivars and their respective TI were found for radicle emergence, plumule emergence and cotyledonary leaf appearance. BB1 was found to be more susceptible to the salt stress and the other tested cultivars BB2 and BB3 were comparatively tolerant to salinity.

Population-based threshold models: A reliable tool for describing aged seeds response of rapeseed under salinity and water stress

Rapeseed (Brassica napus L.; Brassicaceae) is the second largest source of oilseed crop which is used for food and industrial applications globally. The production of this plant will be affected by climate change, increasing heat, salt and water stresses, in the future. Therefore, this study aimed to quantify the seed germination responses of two spring (‘Dalgan’ and ‘Hyola 50′) and one winter (‘Ahmadi’) rapeseed cultivars with a range of seed vigor (artificially aged at 42 °C) under water and salt stresses using hydrotime and halotime models, respectively. Germination time courses were recorded and seed germination characteristics were calculated. Seed moisture content and electrical conductivity were measured and also osmotic adjustment value associated with accumulation of salt ions was estimated. Rapeseed germination was negatively influenced by the accelerated aging period (AAP), water potential (ψ) and salinity (NaCl concentration) in all cultivars (P < 0.01). The hydrotime and halotime models accurately describe rapeseed germination at a range of ψs and NaCls at each AAP, with R2 values of 0.80–0.96. The estimated median threshold water potential (ψb(50)) and salinity (NaClb(50)) were −1.291, −1.170 and −1.104 MPa and 373.3, 326.7 and 304.4 mM for Ahmadi, Dalgan and Hyola 50 cultivars at AAP = 0, respectively. With increasing AAP, the ψb(50) increased (become more positive) and NaClb(50) decreased (linearly in both), reached zero at 130, 85.5 and 77.3 h AAP. The ψb(50) estimated by the hydrotime model was higher after converting the NaCl concentrations to ψ as salt ions absorbed by the seeds in response to salt stress (–1.707, –1.455, –1.361 MPa, respectively). The highest osmotic adjustment value observed in Ahmadi (∼21−54 %, depending on AAP) than those obtained in other cultivars, suggesting that the seed mass/size is an effective factor for improving seed germination of rapeseed under saline conditions (r ≥ 0.86, osmotic adjustment value vs. seed mass). However, this value decreased linearly with AAP in all cultivars, reflecting the cell membrane damage and loss of seed vigor. It was confirmed by the increasing conductivity values at higher AAP. In conclusion, the models used in this study were able to accurately predict the rapeseed germination behavior at different levels of water and saline conditions.

Superparamagnetic hematite nanoparticle: Cytogenetic impact on onion roots and seed germination response of major crop plants.

Augmented escape of nanostructures to the ecosystem has necessitated the comprehensive study of their impact, especially on plants. In the current study, hematite nanoparticles were prepared by employing garlic extract and checked for their cytogenetic effect on onion roots and germination characteristics of five agricultural crops (Vigna radiata, Triticum aestivum, Trigonella foenum-graecum, Cicer arietinum and Vicia faba) in the concentration range of 20-100 mg/L. Onion roots exhibited an increased mitotic index till 60 mg/L dosage, beyond which trend decreased marginally. Percentage of aberrant chromosomes reported for 100 mg/L exposure was very low (3.358 ± 0.13%) and included common defects such as clumped/sticky metaphase, ring chromosomes, laggards, spindle abnormality, chromosome bridges etc. Moreover, comet assay, DNA laddering experiment and electron micrograph study confirmed negligible damage to onion roots. Seed germination study indicated a positive response in different agronomic traits (germination index, root length, fold change in weight and vigour index) up to 60 mg/L, beyond which either negative or neutral effect was observed. However, none of the samples showed 50% inhibition in germination index; highest being 33.33% inhibition for V. faba, compared to the control. In brief, biogenic hematite nanoparticles caused insignificant phytotoxicity and were likely assimilated as iron source at lower dosage.

Quantifying seed germination response of melon (Cucumis melo L.) to temperature and water potential: Thermal time, hydrotime and hydrothermal time models

Quantifying the germination behaviour of seeds against fluctuating environmental conditions can use as a useful tool for seed ecological studies. The response of seed germination rate to temperature (T) and water potential (Ψ) can be described using thermal time (TT), hydrotime (HT), and hydrothermal time (HTT) models. The germination behaviour of Persian melons (C. melo L.) were studied over a range of constant temperatures and water availability to assess the performance of hydro-thermal time models and to provide a data set of germination thresholds and parameters for the Persian melons. The seeds of melons were germinated in the laboratory over a water potential range from 0 to –1.25 MPa at 10, 15, 20, 25, 30, 35, 40 and 45 °C. The results showed that germination percentage was affected by water potential, temperature and their interactions. Germination increased with increasing temperature within the range of 15–25 °C, then decreased as temperature increased from 25 to 45 °C. Furthermore, final germination percentages were reduced with decreasing Ψ, although significant reduction was observed at Ψs less than –0.25 MPa. The model analysis showed that the dynamics of seed germination were generally well described by the TT model within Ψs range < –1 MPa (R2 = 83–96), HT (R2= 0.77–0.93) and HTT models (R2=0.89–0.90). Using the models analysis, the base, optimum and ceiling germination temperatures were estimated to be 9.4, 27.3 and 41.4 °C, respectively. Thermal time analysis showed that thermal time required for germination of Persian melon, Tb and Tc were affected by water availability. Furthermore, the estimated minimum water potential threshold for germination was –1.19 MPa using the HT model, but it shifted towards a higher values with temperatures above or below 25 °C. The amount of hydrothermal time required to germinate was 33 MPa °C days on the suboptimal temperatures range and increased by 36% with increasing temperature from the suboptimal temperatures to the supraoptimal temperatures. The HTT model showed that the Ψb(50) increased by 0.09 MPa with every degree increase in temperature above To. The interaction of Ψ and temperature affected the model parameters and finally the performance of germination models, then varying model parameters with changing environmental condition should be considered for predicting germination time in a complex growth environment.

Does nitric oxide protect Eucalyptus urophylla seeds under salt stress conditions?

Abstract: The germination response of seeds under artificial stress conditions is a tool for better understanding of the survival and adaptation ability of species under natural stress conditions. The aims of this study were to evaluate the protective effect of nitric oxide during germination as well as seed vigor and seedling development of Eucalyptus urophylla under salt stress conditions. The experimental design was completely randomized, with five replications, in a 3 × 3 + 1 factorial arrangement, with three priming factors [water, sodium nitroprusside (SNP), and potassium nitrate (KNO3)], three germination conditions (distilled water, and the water potentials of -0.6 and -1.2 MPa), and an additional control treatment (unprimed seeds). The following determinations were made: germination count at seven and fourteen days, germination speed index, primary root length, shoot length, and total length. SNP protects seeds, leading to a higher percentage of germination, as well as greater root growth and total seedling size, whereas KNO3 is not effective in protecting seeds that suffer from salt stress, which affects their physiological and morphological characteristics. E. urophylla seeds are sensitive to salt stress, and physiological priming with SNP leads to an increase in the percentage of germination, vigor, and seedling development under salinity conditions.

Seed size an important factor for the germination response of legume seeds subjected to simulated post-fire soil temperatures

Potential impacts of soil temperatures in a post-fire environment were examined for seeds of legume species with a physical seed dormancy typically found in the eucalypt communities in eastern Australia. Soil temperatures in a post-fire environment may be elevated owing to increased solar radiation and this may influence germination of species with soil-stored seed banks. Seeds were heated at 50, 60 or 70°C, with one unheated control, for 3h per day for 5 days to simulate soil temperatures where canopy gaps existed. More germination of small-seeded species (&amp;lt;12.6mg) occurred owing to changes in simulated soil temperatures than large-seeded species (&amp;gt;14.0mg). Temperatures up to 70°C significantly increased the germination of species with relatively small-sized seeds than large-seeded species (&amp;gt;70°C). This study demonstrated that small-seeded species are able to germinate across a range of temperatures (50–70°C) and can have dormancy broken either during the passage of a fire, or after fire from increased solar radiation, potentially resulting in the decline of the post-fire residual soil seed bank. In contrast, post-fire germination of large-seeded species may be dependent solely on the degree of soil heating during the passage of fire and the species may have a relatively stable residual soil seed bank thereafter.

The influence of temperatures on germination and seedling growth of pyrethrum (Tanacetum cineraiifolium) under drought stress

Pyrethrum is a perennial daisy grown commercially for the insecticide that is extracted from its flowers. In order to evaluate germination and seedling growth of pyrethrum under different temperature and drought stress treatments, an experiment was conducted in seed technology laboratory of Faculty of Agriculture of Islamic Azad University of Isfahan branch in 2018. During this experiment, polyethylene glycol (PEG) at 6 levels (0, -0.2, -0.4, -0.6, -0.8, -1.0 MP) and two temperature treatments (10oC and 15oC) were used. Two separate factorial trials, on the basis of absolute randomized design with three replications were used. Drought stress impact on germination percentage, mean time germination, shoot and root length, abnormal germination, germination uniformity, plumule dry and fresh weight, root dry and fresh weight and seed stamina index was significant. The influence of temperature was meaningful on germination percentage, mean time germination, shoot and root length, plumule dry weight, plumule fresh weight, root dry weight and root fresh weight. The rate of germination, germination percentage, as well as seedling growth and establishment were significantly lowered with the rise of stress levels using PEG. Control treatment and 15oC had obtained the highest germination percentage, mean time germination, shoot and root length, germination uniformity, plumule dry and fresh weight, root dry and fresh weight, and seed stamina index. Taking all traits into account, a clear understanding of the germination responses of seeds is useful in screening for tolerance of species to extreme temperatures.

Seed germination response of a potential rangeland weed Psilocaulon granulicaule to selected environmental conditions

Studies show that just over 620 non-native naturalised plant species have been recorded within the Australian rangelands, some of which have a capacity to cause significant impacts on rangeland flora and grazing activity. Although Psilocaulon granulicaule (Haw.), Schwantes is listed as a highly invasive environmental weed species, there has been no previous research into its seed ecology. Therefore, this study was conducted to investigate the effects of temperature, light, pH, water stress, heat-shock, and salinity on the germination of P. granulicaule. In this study, four temperature regimes covering four different day and night temperature variations (17–7°C, 25–15°C, 30–25°C and 40–30°C) and two light regimes (12-h light–12-h dark, 24-h dark) were investigated. The effects of pH, water stress, heat-shock and salinity were investigated, using pH buffers, polyethylene glycol solutions, three heat shock events under four temperatures and a range of NaCl solutions. These tests were conducted under the identified optimum temperature range (25/15°C) and light regime for seed germination. The results showed that both temperature and photoperiod significantly influenced the germination rate, with 94.2% germination in the 25–15°C range under a 12-h light-12-h dark regime. Higher temperatures (30–40°C) reduced seed germination to &amp;lt;58% germination in both light regimes (57.5%, 12-h light-12-h dark; 54.17%, 24-h dark). The highest germination rates were observed in low pH solutions, high moisture levels, low heat-shocks and low salinity. The study showed that this species is sensitive to environmental factors such as temperature, light, pH, moisture, heat shock and salinity, suggesting that these factors can be used as critical indicators to guide effective management practices to address this weed problem. Given that seeds are sensitive to radiant heat, burning could be used as a tool to effectively manage this species.