Edaphic constraints on seed germination and emergence of three <Emphasis Type="Italic">Acacia</Emphasis> species for dryland restoration in Saudi Arabia

In situ edaphic factors affecting seed germination and seedling emergence of three framework species of Acacia were investigated with the intent of developing fundamental and scalable restoration capacity for Arabian dryland restoration. Direct seeding represents the most efficient means to restore vegetation at the landscape scale and this study provides insight into edaphic and ecological limitations, as well as effective protocols governing the use of native seeds for restoration in hyper-arid environments. The study was conducted in extant Acacia woodland habitat on conserved land (Thumamah Nature Park) in close proximity to Riyadh, Saudi Arabia. Broad-scale direct seeding using un- and pretreated Acacia gerrardii, A. tortilis, and A. ehrenbergiana seed, and two seed burial depths were implemented across three sites with distinct soil surface characteristics. Eight weeks post-sowing, random samples for each species × seed treatment × burial depth combination were excavated, sieved, and categorized as follows: failed to germinate, germinated but died prior to emerging, or successfully emerged. We show that germination and emergence of Acacia gerrardii, A. tortilis, and A. ehrenbergiana were driven by a three-way interaction among species, site, and seed burial depth. Treating seed with the signaling compound Moddus did not have a definitive effect, positive or negative, on any of the species investigated. Acacia gerrardii was the only species that exhibited widespread emergence, though emergence was not consistent across sites or burial depths. Germination was highest in disturbed soil (up to 69% for A. gerrardii), but very few (<2%) successfully emerged; a greater proportion of germinants in sandy soil emerged (up to 44% for A. gerrardii) even though the overall germination was less. Though species-dependent, a 2-cm sowing depth was most effective in sand; while in disturbed soil, sowing depths of 1 and 2 cm were comparable; and no germination was observed in gravelly clay soil. Sandy soil exhibited rapid water infiltration (107.6 mm min^?1), and post-sowing surface crusting was a non-factor (0.44 kg cm^?2). Disturbed soil exhibited moderate water infiltration (1.46 mm min^?1) and post-sowing surface crusting was double that of sand (0.88 kg cm^?2) and restrictive on seedling emergence. Gravelly clay exhibited extremely poor water infiltration (0.12 mm min^?1), and surface crusting was severe (4.49 kg cm^?2) and an order of magnitude greater than sand. The medium-coarse sand fraction, a key driver of the observed soil surface processes, was greatest in sand (55%) and significantly less and uniform in the disturbed (22%) and gravelly clay (22%) soils. Our findings demonstrate that soil surface characteristics and associated processes can dictate ecological processes at depths as shallow as 1–2 cm, and that soil crusts that slow water infiltration and impede seedling emergence rapidly reconstitute after disturbance; both are important considerations for restoring dryland vegetation.     

Water entry for the black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> L.) seeds observed by dedicated micro-magnetic resonance imaging

Water entry at germination for black locust (Robinia pseudoacacia L.) seeds which are known as hard seeds with impermeable seed coat to water, was examined using micro-magnetic resonance imaging (MRI). The MRI apparatus equipped with a low-field (1 T; Tesla) permanent magnet was used, which is open access, easy maintenance, operable and transportable. The excellent point of the apparatus is that T ₁-enhancement of water signals absorbed in dry seeds against steeping free water is stronger than the apparatuses with high-field superconducting magnets, which enabled clear detection of water entry. Water hardly penetrated into the seeds for more than 8 h but approximately 60 % of seeds germinated by incubating on wet filter papers for several days. Hot water treatments above 75 °C for 3 min effectively induced water gap; scarification was 70 % at 100 °C and 75 °C, declined to 15 % at 50 °C and decreased further at room temperature. Water entered into the scarified seeds exclusively through the lens, spread along the dorsal side of the seeds and reached the hypocotyl, whereas water migrated slowly through hilum side to radicle within 3 h.     

Positive responses of strawberry (<Emphasis Type="Italic">Fragaria</Emphasis> × <Emphasis Type="Italic">ananassa</Emphasis> Duch.) explants to salicylic and iron nanoparticle application under salinity conditions

Mucuna bracteata DC. ex Kurz is an important cover crop in plantations across the tropics. However, low germination rate and poor viability of Mucuna seeds pose significant challenges of using the seeds as starting material. To address these limitations, we have optimized seed germination conditions (such as scarification period, surface sterilization protocols and imbibition period) and in vitro propagation protocols for M. bracteata. We found that seeds treated with sulphuric acid for 30 min, imbibed for 6 h and incubated in dark conditions on a wet cotton roll (10 mL of sterile distilled water) supplemented with 0.1% activated charcoal produced the highest percentage of seed germination (44%) and seed vigor index. In vitro-derived cotyledonary nodes showed the highest number of shoots per explant (5.60) and rooting response (92.9%) when cultured on Murashige and Skoog medium containing 4.44 µM 6-benzylaminopurine and 10.7 µM 1-naphthaleneacetic acid, respectively. Of the 100 rooted plantlets acclimatized, 89.0% survived after 4 weeks of transplanting. Single sequence repeat and flow cytometry analysis were performed to confirm the genetic fidelity of the plants. Our protocol offers, for the first time, a simple and effective seed germination and scalable propagation procedures for M. bracteata. Furthermore, we have also estimated the genome size (1448?±?9 Mb) and DNA content (1.48?±?0.01 pg) for M. bracteata that can be used for future cytogenetic studies on genetic diversity and gene exchange.     

Modeling seed germination of unprimed and primed seeds of sweet sorghum under PEG-induced water stress through the hydrotime analysis

The effects of reduced water potential (ψ) on seed germination at 25 and 15 °C in unprimed (UP) and primed (P) seeds of two cultivars of sweet sorghum (cv. Keller and cv. Makueni local), were analyzed through the hydrotime model. Six ψ (from 0 to ?1.0 MPa) in polyethylene glycol 6000 (PEG) solutions were used for the tests. Seeds were primed in 250 g/L PEG solution at 15 °C for 48 h. Decreasing ψ of imbibition solution reduced and delayed germination. At 15 °C seeds germinated less and slower than at 25 °C at any ψ. Seeds of cv. Makueni local exhibited a greater sensitivity to water stress in terms of germination percentage, than seeds of cv. Keller, but they were faster in germination. Osmopriming was beneficial for seed germination, both in terms of final percentage and rate, at any temperature and ψ. The hydrotime analysis revealed that predicted θ _H constant was increased when temperature was reduced to 15 °C and at this temperature median base water potential [ψ _b(50)] for germination was higher (less negative) than at 25 °C. Seed priming shifted ψ _b(50) towards more negative values and reduced θ _H requirements for germination. At 25 °C the two cultivars behaved similarly while at 15 °C cv. Keller exhibited a ψ _b more negative but required a greater θ _H to germinate, indicating a greater water-stress tolerance but a slower germination, than cv. Makueni local. The application of the model allows to identify water stress tolerant cultivars during germination, to include into breeding programs for the selection of well-performing cultivars under stress conditions.     

Environmental cues for germination of the invasive bunch grass <Emphasis Type="Italic">Pennisetum ciliare</Emphasis> (L.) Link

Responses of seed germination to air temperature, water potential, light, and smoke were studied in the laboratory for seeds of the invasive bunch grass Pennisetum ciliare (L.) Link (syn. Cenchrus ciliare L.; buffel grass). First introduced to North America during the mid-twentieth Century for establishing pastures, this African bunch grass has become an invasive species of concern. Across all the experiments conducted, a low germination was observed for P. ciliare fascicles that never exceeded 30 % at 21 days after sowing. Optimal day/night air temperatures for germination, controlled with an environmental chamber, were 25/15 and 30/20 °C, while extreme temperatures of 15/5 and 45/35 °C inhibited germination. By sowing seeds of P. ciliare under different water potentials, created with aqueous solutions of polyethylene glycol, an optimum of ?0.03 MPa led to the highest germination, while no germination was observed at ?1.0 MPa. Monochromatic optical filters were utilized to germinate seeds under various wavelengths, of which red (650 nm) and far red (730 nm) led to the highest germination. In addition, seeds that were incubated in the dark had higher germination than those incubated under white light. Incubation in smoke water, which can stimulate germination of pyrophytic species, resulted in a marginal inhibition of germination compared with imbibition with distilled water.     

Effect of cold stratification on seed germination in <Emphasis Type="Italic">Solidago</Emphasis> × <Emphasis Type="Italic">niederederi</Emphasis> (<Emphasis Type="Italic">Asteraceae</Emphasis>) and its parental species

In this study, we investigated the influence of cold stratification on seed germination in S. × niederederi, a hybrid between the North American S. canadensis and the European S. virgaurea, using fruit samples collected in 2016 in Poland. We aimed to test the hypothesis that the low temperature exposure decreases the final percentage and speed of seed germination in the hybrid and its parental species. For each species, sets of 100 achenes in three replications were mixed with dry sand and stored in Petri dishes in darkness for 12 weeks, at ?18 °C and?+?4 °C, and?+?25 °C. The seeds were incubated for 21 d at room temperature (+25 °C), under the 12 h photoperiod (630 lx). We showed a lack of significant differences in: (i) the final percentage of germinated seeds of studied species stored at the same conditions, (ii) the final percentage of germinated seeds between the applied stratification conditions in the hybrid and its parental species, and (iii) the mean values of Timson’s index, mean germination time, and coefficient of velocity of germination between the stratification conditions in each species. The statistically significant inter-specific differences in the mean germination time parameter after the +25 °C treatment suggest that the seeds of S. × niederederi are able to germinate faster than the seeds of its parental species. However, to improve our knowledge of naturalization and invasion abilities of S. × niederederi by sexual reproduction, the seed germination and seedling survival of the hybrid should be tested in the field.     

Desiccation-induced ROS accumulation and lipid catabolism in recalcitrant <Emphasis Type="Italic">Madhuca latifolia</Emphasis> seeds

Loss of viability in desiccation-sensitive seeds of Madhuca latifolia (Roxb.) J. F. Macbr., an important multipurpose tropical tree, was correlated with seed water content (WC). WC declined from 0.59 to 0.19 g g^?1 fresh mass, 35 days after harvest from mother plant, at ambient conditions (temperature 25 ± 2 °C, relative humidity 50 ± 2%). The desiccation-induced reduction in viability was related with an accumulation of reactive oxygen species (ROS) that promoted lipid peroxidation associated loss of membrane integrity. Conducted study revealed 1.6–19 folds rise in lipid peroxidized products in desiccated M. latifolia seeds, and was found to be linked inversely with WC and germination percentage. Additionally, increased activities (7 and 13 folds) of lipid hydrolyzing enzymes; lipase (EC 3.1.1.3) and lipoxygenase (EC 1.13.11.12) respectively, were discernible in desiccating M. latifolia seeds. In summary, increased ROS, lipid oxidation, lipase and lipoxygenase were strongly correlated with viability loss in desiccating M. latifolia seeds.     

Role of indehiscent pericarp in formation of soil seed bank in five cold desert Brassicaceae species

The dispersal and germination unit of some Brassicaceae species is the fruit, and we hypothesized that it could affect germination phenology and promote formation of a soil seed bank. We determined the effects of the indehiscent pericarp on germination and longevity of buried seeds of five Brassicaceae species native to cold deserts of central Asia. Germination phenology (seedling emergence) was monitored for intact dispersal units and isolated seeds of Chorispora sibirica, Goldbachia laevigata, Spirorrhynchus sabulosus, Tauscheria lasiocarpa (annuals), and Sterigmostemum fuhaiense (perennial) at natural temperatures in watered and non-watered (natural precipitation) soil. Intact dispersal units and isolated seeds were buried under natural conditions and exhumed at regular intervals for 35 months to monitor germination, viability and moisture content of isolated seeds, seeds in dispersal units, and seeds removed from dispersal units after burial. Isolated seeds of Goldbachia, Spirorrhynchus, and Tauscheria germinated only the first autumn and those of Chorispora and Sterigmostemum the first autumn and first spring, with higher germination percentages in all species in watered than in non-watered soil. A high percentage of seeds in buried dispersal units of Chorispora, Goldbachia, and Sterigmostemum was viable after 35 months, and seeds exhibited a 6-month dormancy cycle, being non-dormant only in autumn and spring. Seeds in buried dispersal units of Spirorrhynchus and Tauscheria germinated when exhumed in the first spring, but all non-germinated seeds were dead after 1 year. Thus, the presence of the pericarp allows Chorispora, Goldbachia, and Sterigmostemum to form a persistent seed bank but not Spirorrhynchus and Tauscheria.     

Seed dormancy and germination of the rare,high elevation Balkan endemic <Emphasis Type="Italic">Cerastium dinaricum</Emphasis> (Caryophyllaceae)

Short or long-term ex situ conservation is becoming increasingly important in conservation of plants in today’s changing environments. One of the important steps in ex situ conservation is the collection and storage of seeds and the consequent establishment of seed germination protocols. Cerastium dinaricum (Caryophyllaceae) is an endemic, high elevation and rare species of European conservation concern. Because of its severely fragmented distribution along the Dinaric Alps, the populations are likely to undergo further shrinkage in the future, which addresses the need of a long-term effective conservation management. From the potential ex situ population management perspective, we focused our study on germination ecology of C. dinaricum. The study revealed that temperature considerably affected the germination of seeds, which germinate better at 20 °C rather than 10 °C. A period of cold-wet stratification also significantly improved the final germination percentage with more pronounced increase at 20 °C, while addition of GA3 increased the final germination percentage by breaking the dormancy of non-stratified seeds. Mechanical scarification did not improve germination; on the contrary, it resulted in the lowest germination success. Seeds grown in complete darkness germinated significantly better compared to control when they were exposed to cold-wet stratification. Contrary to previous studies on some alpine species, which germinate better when exposed to light, dark treatment resulted in the highest germination percentages with 70 and 90% germination success after 4 and 8 weeks of stratification, respectively.     

Hydrothermal time analysis of watermelon (<Emphasis Type="Italic">Citrullus vulgaris</Emphasis> cv. ‘Crimson sweet’) seed germination

This study evaluated the ability of a hydrothermal time model (HTT) to describe the kinetics of watermelon (Citrullus vulgaris cv. ‘Crimson sweet’) seed germination under different temperatures (T) and water potentials (ψ) and also to determine the cardinal temperatures of watermelon. Results indicated that ψ influenced germination rate and germination percentage. For this seed lot, cardinal temperatures were 10 °C for T _b, 28.34 °C for T _o and 40.8 °C for T _c in the control (0 MPa) treatment. There was a decrease in hydrotime constant (θ _H) when T was increased to T _o and then remained constant at supra-optimal temperatures (30 MPah^?1). Also, at temperatures above T _o, ψ _b(50) values increased linearly with T. The k _T value (the slope of the relationship between ψ _b(50) and T exceeds T _o) of this seed lot was calculated as 0.076 MPa°Ch^?1. Results this study show that when the HTT model is applied, it can accurately describe ψ _b(g) and the course of germination around Ts (R ² = 0.82). Moreover, the ψ _b(50) was estimated to be ?0.96 MPa based on this model. Consequently, the germination response of watermelon for all Ts and ψs can be adequately described by the HTT model and enabling it to be used as a predictive tool in watermelon seed germination simulation models.     

Different plant provenance same seed tolerance to abiotic stress: implications for <Emphasis Type="Italic">ex situ</Emphasis> germplasm conservation of a widely distributed coastal dune grass (<Emphasis Type="Italic">Uniola paniculata</Emphasis> L.)

Preservation of genetic diversity within germplasm repositories represents an important tool for plant conservation. However, seeds must tolerate extreme levels of post-harvest desiccation and cold to realize benefits of ex situ storage. Factors including local climate and habitat impact expression of desiccation and freezing tolerance especially for widely distributed species. Our aim here was to understand the influence of a latitudinal gradient on seed desiccation and cryo-freezing tolerance. We sampled mature U. paniculata seeds from two geographically and genetically distinct populations then examined seed-water relations and germination following desiccation via equilibrium drying assays (0.5 to 91% RH; ?797 to ?12.9 MPa). Germination ability after drying and subsequent cryo-freezing treatments (?196?°C, 1 to 1440 min) was also evaluated. Seeds of both populations displayed similar reverse sigmoid moisture sorption isotherms characteristic of desiccation tolerant tissues. Furthermore, initial seed water potential (?63 and ?90 MPa) was considerably lower than the lethal limit (?20 MPa) identified for desiccation sensitive tissues. Final germination (range 58–93%) and temporal patterns differed significantly between populations following desiccation and cryo-freezing stress, but these germination responses were similar to initial germination. A higher proportion of non-germinated, yet viable seeds remained for the northern compared to southern population. Location does influence germination response, but differential germination is related to seed dormancy rather than desiccation or cryo-freezing sensitivity. Ex situ conservation of U. paniculata is therefore feasible across the latitudinal gradient studied here.     

A comparison of partial dehydration and hydrated storage-induced changes in viability,reactive oxygen species production,and glutathione metabolism in two contrasting recalcitrant-seeded species

This study compared the responses of Avicennia marina and Trichilia dregeana seeds, both of which are recalcitrant, to partial dehydration and storage. Seeds of A. marina exhibited a faster rate of water and viability loss (± 50% viability loss in 4 days) during partial dehydration, compared with T. dregeana (± 50% viability loss in 14 days). In A. marina embryonic axes, reactive oxygen species (ROS) production peaked on 4 days of dehydration and was accompanied by an increase in the GSH:GSSG ratio; it appears that the glutathione system alone could not overcome dehydration-induced oxidative stress in this species. In A. marina, ROS and axis water content levels increased during hydrated storage and were accompanied by a decline in the GSH:GSSG ratio and rapid viability loss. In T. dregeana embryonic axes, ROS production (particularly hydrogen peroxide) initially increased and thereafter decreased during both partial dehydration and hydrated storage. Unlike in A. marina embryonic axes, this reduced ROS production was accompanied by a decline in the GSH:GSSG ratio. While T. dregeana seeds may have incurred some oxidative stress during storage, a delay in and/or suppression of the ROS-based trigger for germination may account for their significantly longer storage longevity compared with A. marina. Mechanisms of desiccation-induced seed viability loss may differ across recalcitrant-seeded species based on the rate and extent to which they lose water during partial drying and storage. While recalcitrant seed desiccation sensitivity and, by implication, storage longevity are modulated by redox metabolism, the specific ROS and antioxidants that contribute to this control may differ across species.     

Differences in reward removal efficiency and its consequences for seed germination in the ant-dispersed sedge <Emphasis Type="Italic">Carex tristachya</Emphasis> (Cyperaceae)

Reward removal is an essential step for seed dispersal mutualism because residual rewards inhibit germination. Nevertheless, variation in the reward removal efficiency (RRE) among dispersers and its consequences for germination have rarely been reported. In this study, we compared the RREs of two sympatric seed-dispersing ants, Formica japonica and Pheidole noda, using seeds of the ant-dispersed sedge Carex tristachya. Then, we conducted seed sowing experiments in a non-heated glasshouse to evaluate the effect of RRE on the percentage and speed of germination. The majority (85%) of seeds handled by F. japonica had residual elaiosomes, while elaiosomes were completely removed from all seeds handled by P. noda, demonstrating that P. noda has much higher RRE than F. japonica. The seed sowing experiments revealed that RRE, defined by the presence or absence of residual elaiosomes, was not associated with the percentage germination within a year. However, high RRE seeds with no residual elaiosomes germinated significantly faster than low RRE seeds with residual elaiosomes. Similarly, artificial removal of elaiosomes from C. tristachya seeds accelerated germination speed without affecting germination percentage. These results suggest that RRE is one of the most important parameters determining the effectiveness of a seed dispersal agent.     

Quantification of soybean seed germination response to seed deterioration under PEG-induced water stress using hydrotime concept

This experiment was arranged to investigate the ability of hydrotime model (θ_H) for estimating soybean seed germination (cv. ‘JK’) under different accelerated aging periods (AAP, 0, 24, 48, and 72 h) at each of the following water potentials (ψ, 0, ??0.12, ??0.24, and ??0.36 MPa). Results indicated that both germination percentage (GP) and germination rate (GR) significantly influenced by ψ, AAP, and their interactions (P?<?0.01). GP and GR decreased by 62.6 and 47.3% with longer AAP from 0 to 72 h and by 90.7 and 81.5% with lower ψ from zero to ??0.36 MPa as compared to the control, respectively. Therefore, the effect of ψ on GP and GR was more than AAP. The θ_H value was constant (~?6.71 MPa h^?1) till 50.6 h AAP and then linearly declined with the rate of 0.1545 MPa h^?1 per hour increase in AAP until 72 h (~?50% lower than its initial value). The ψ_b(50) value was ? 0.343 MPa in the control and then increased (became more positive) by ~?70% until 72 h AAP (? 0.104 MPa). In general, GP and GR of soybean declined with the increasing ψ_b(50) which can be due to cell membrane damage and reduce the activity of enzymes and organelles during AAP. Based on our findings, the θ_H model could describe well these relationships and their parameters can nicely be used for simulating soybean seed germination under this condition.     

Development of a powder formulation based on <Emphasis Type="Italic">Bacillus</Emphasis><Emphasis Type="Italic">cereus</Emphasis> sensu lato strain B25 spores for biological control of <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> in maize plants

Maize is an economically important crop in northern Mexico. Different fungi cause ear and root rot in maize, including Fusarium verticillioides (Sacc.) Nirenberg. Crop management of this pathogen with chemical fungicides has been difficult. By contrast, the recent use of novel biocontrol strategies, such as seed bacterization with Bacillus cereus sensu lato strain B25, has been effective in field trials. These approaches are not without their problems, since insufficient formulation technology, between other factors, can limit success of biocontrol agents. In response to these drawbacks, we have developed a powder formulation based on Bacillus B25 spores and evaluated some of its characteristics, including shelf life and efficacy against F. verticillioides, in vitro and in maize plants. A talc-based powder formulation containing 1 × 10⁹ c.f.u. g^?1 was obtained and evaluated for seed adherence ability, seed germination effect, shelf life and antagonism against F. verticillioides in in vitro and in planta assays. Seed adherence of viable bacterial spores ranged from 1.0 to 1.41 × 10⁷ c.f.u. g^?1. Bacteria did not display negative effects on seed germination. Spore viability for the powder formulation slowly decreased over time, and was 53 % after 360 days of storage at room temperature. This formulation was capable of controlling F. verticillioides in greenhouse assays, as well as eight other maize phytopathogenic fungi in vitro. The results suggest that a talc-based powder formulation of Bacillus B25 spores may be sufficient to produce inoculum for biocontrol of maize ear and root rots caused by F. verticillioides.     

Characterization of As(III) oxidizing <Emphasis Type="Italic">Achromobacter</Emphasis> sp. strain N2: effects on arsenic toxicity and translocation in rice

Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented plant growth promoting traits (ACC deaminase activity, production of indole-3-acetic and jasmonic acids, siderophores secretion, and phosphate solubilization) and arsenic transformation abilities. Achromobacter sp. strain N2 was resistant to different metals and metalloids, including arsenate (100 mM) and arsenite (5 mM). The strain was resistant to ionic stressors (i.e., arsenate and NaCl), whereas bacterial growth was impaired by osmotic stress. Strain N2 was able to oxidize 1.0 mmol L^?1 of arsenite to arsenate in 72 h. This evidence was supported by the retrieval of an arsenite oxidase AioA gene highly homologous to arsenite oxidases of Achromobacter and Alcaligenes species. Rice seeds of Oryza sativa (var. Loto) were bio-primed with ACCD-induced and non-induced cells in order to evaluate the effect of inoculation on rice seedlings growth and arsenic uptake. The bacterization with ACCD-induced cells significantly improved seed germination and seedling heights if compared with the seeds inoculated with non-induced cells and non-primed seeds. Enhanced arsenic uptake was evidenced in the presence of ACCD-induced cells, suggesting a role of ACCD activity on the mitigation of the toxicity of arsenic accumulated by the plant. This kind of responses should be taken into account when proposing PGP strains for improving plant growth in arsenic-rich soils.     

Reproductive ecology of <Emphasis Type="Italic">Agave colorata</Emphasis>: the importance of nectar-feeding bats and the germination consequences of self-pollination

Agave colorata is a paniculate agave distributed along the migratory route of the nectar-feeding bat Leptonycteris yerbabuenae. In this paper, we evaluate the importance of nectar-feeding bats in the reproduction of A. colorata in a population in Sonora, Mexico, and describe the germination consequences of self-pollination. We estimated abundance using five plots and set pollination treatments to evaluate the importance of bats. We recorded 14.8?±?6.8 plants/400 m², with a bimodal size distribution. Flowers are protandrous and visited mainly (>?20 visits/plant/30 min) by L. yerbabuenae. Pollination exclusion experiments showed that flowers excluded from diurnal visitors had maximum fruit set values (0.49?±?0.42), while the autonomous self-pollination treatment had the lowest value (0.03?±?0.06). Similarly, the greatest number of viable seeds per fruit was recorded in the diurnal exclusion treatment, while the greatest number of empty seeds was observed in the self-pollination treatment. Fruit set values among untreated plants varied from 32 to 54%, with a mean value of 41.8%. Seeds derived from self-pollination had a narrower window of opportunity for germination compared to seeds derived from nocturnal pollination. Self-pollinated seeds had lower germination, rate of germination or lag time in response to light, osmotic potential and heat shock treatments, compared to other pollination treatments, revealing an inbreeding cost. Overall, our results show that L. yerbabuenae is the likely major pollinator of the studied A. colorata population. However, under pollinator limitation A. colorata may produce seeds by autonomous self-pollination, at a cost expressed as lower germination.     

Using hydrothermal time concept to describe sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) seed germination response to temperature and water potential

To quantify both temperature (T) and water potential (ψ) effects on sesame (Sesamum indicum L.) seed germination (SG) and also to determine the cardinal T _s for this plant, a laboratory experiment was carried out using hydrothermal time model (HTT). For this purpose, four sesame cultivars (‘Asbomahalleh’, ‘Darab’, ‘Dashtestan’ and ‘Yellowhite’) were germinated at seven constant T _s (20, 25, 30, 35, 37, 39 and 43 °C) at each of the following ψ _s (0, ? 0.12, ? 0.24 and ? 0.36 MPa; provided by PEG 8000). Germination rate (GR) and germination percentage (GP) significantly influenced by ψ, T and their interactions in all cultivars (P ≤ 0.01). There was no significant difference, based on the confidence intervals of the model coefficients, between cultivars, so an average of cardinal T _s was 14.7, 35.4 and 47.2 °C for the minimum (T _b), optimum (T _o) and maximum (T _c) T _s, respectively, in the control condition (0 MPa). Hydrotime values in all cultivars decreased when T was increased to T _o and then remained constant at T _s > T _o (15 MPa h^?1). An average value of ψ _b(50) was estimated to be ? 1.23 MPa at T _s ≤ T _o and then increased linearly (0.1041 MPa°Ch^?1, the slope of the relationship between ψ _b(50) and supra-optimal T _s) with T when T _s increased above T _o and finally reached to zero at T _c. The T _b and T _o values were not influenced by ψ, but T _c value decreased (from 47.2 for zero to 43.5 °C for ? 0.36 MPa) at supra-optimal T _s as a result of the effect of ψ on GR. Based on our findings, this model (as a predictive tool) and or the estimated parameter values in this study can easily be used in sesame SG simulation models to quantitatively characterize the physiological status of sesame seed populations at different T _s and ψ _s.