Germination Rate of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] Seeds Affected by Their Orientation

Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seeds developwith the adaxial surface continuous with the cone scale. Onseparation, the scale side of the seed is lighter coloured andflatter than the side not previously in contact with the scale.Seeds oriented scale-side-up on a moist surface germinate morerapidly than seeds placed scale-side-down. When seeds were germinatedunder laboratory conditions, the response to orientation variedamong seeds of different geographic origin. Most of the geographicvariation in germination rate occurred when seeds were orientedscale-side-up. Pseudotsuga menziesii (Mirb.) Franco, Douglas-fir germination, orientation of seeds     

The Role of the Lens in Seed Imbibition and Seedling Vigour of Sesbania punicea (Cav.) Benth. (Leguminosae: Papilionoideae)

Seeds of Sesbania punicea (Cav.) Benth. are largely impermeable,and the natural, low, percentage which germinate are permeableat the lens. Scarifying seed in acid stimulates germinationand causes various types of damage to the testa, including thelens. Placing seeds in boiling water stimulates germinationby rendering the seeds permeable at the lens. Seeds were mechanicallyscarified at precise sites on the testa to assess influenceof the site and degree of damage on germination. Results indicatethat both the site of initial water entry and the rate of waterentry are important in determining seed and seedling vigour.Damaging the lens is more effective in stimulating germinationand reducing seedling abnormalities than complete excision ofthe lens. This effect can be reversed if seeds from which thelens was excised are allowed to imbibe gradually in inert osmotica.The leguminous lens thus acts as the site of initial water entryand regulates the rate of water uptake, thereby increasing seedand seedling vigour. Sesbania punicea (Cav.) Benth., hardseededness, lens, seed germination, imbibition damage, seedling vigour     

The Effect of Desiccation on the Longevity of Seeds of Araucaria hunsteinii and A. cunninghamii

Seeds of Araucaria hunsteinii K. Schum. dried quicker at 29°Cthan at 19°C and quicker with the seed-coat removed thanwhen intact; seeds enclosed in polyethylene bags increased inmoisture content. At 15°C, seeds in a flow of air driedquicker than seeds in a box with silica gel, which in turn driedquicker than seeds in a box with no desiccant. No loss of germinationability occurred on drying fresh seed from 53 to about 32 percent moisture content (fresh weight basis); during further desiccationthe percentage germination was related to percentage moisturecontent in the form of a sigmoid curve, culminating in a completefailure to germinate at approximately 14 per cent moisture content.A consistent relationship was observed for all treatments andthe mean critical moisture content for seed death (failure togerminate) was near 23 per cent. Excised embryos grew on 1 percent agar but died if previously subjected to 14 h of desiccationat 15°C. In contrast, no relationship was found between germination andmoisture content of A. cunninghamii D. Don on desiccation from21 to 7 per cent moisture content. Possible causes for the observeddifference in response to desiccation are discussed and methodsfor seed storage are considered. Araucaria hunsteinii, Klinkii pine, Araucaria cunninghamii, Hoop pine, desiccation, seed longevity, storage of seeds     

Reproductive allocation,seed dispersal and germination of <Emphasis Type="Italic">Myricaria laxiflora</Emphasis>, an endangered species in the Three Gorges Reservoir area

Myricaria laxiflora is an endangered plant that grows in the flood zone along the Yangtze River in the Three Gorges area from 70 m to 155 m above sea level. To understand the spatial distribution patterns of the species and to provide information for developing conservation strategies, we used field surveys to study its seed reproduction and dispersion, and used growth chambers to study seed germination. Results showed that M. laxiflora produced many flowering branches, inflorescences and seeds. Seeds were very small and output was high although biomass allocation to reproduction was low (∼4%). Reproductive allocation was strongly correlated with the biomass of stems and leaves. Seeds were dispersed either by the wind or the river current. Wind-dispersed seeds usually settled within 25 m from parent plants leading to a clumped distribution of individuals in populations. Water-dispersed seeds often landed and established on strands of firth where the fine sediment and gentle sloping were available. Seedlings that emerged from water-dispersed seeds were distributed along the water flood line. The life-span of M. laxiflora seeds was about 7 days. Seeds could germinate within 24 h when they absorbed adequate amounts of water. Soil water content was a key factor limiting the establishment ability of M. laxiflora. Experiments showed that the minimum soil water content for germination to occur was 10% on sand or 17% on sandy soil substrates, and the optimal conditions were on saturated soils. The water content of sandy soils on the riverbank was lower than 10% in autumn, the dry season, and seeds were able to germinate only on sandy beaches that were intermittently inundated by the fluctuating river current. These characteristics of seed dispersal and germination limit the ability for M. laxiflora to expand its distribution. These results provide information essential for the conservation and reintroduction of this endangered species.     

Influence of Salinity and Temperature on the Germination of Haloxylon recurvum Bunge ex. Boiss.

The stem succulent perennial halophyteHaloxylon recurvum Bungeex. Boiss. grows and produces seed under highly saline conditionsand seeds are deposited in saline soils. Experiments were conductedto determine the effect of salinity and temperature on the germinationof seeds. Results indicate that seeds can germinate at veryhigh salt concentrations (500 mM). However, highest germinationpercentages were obtained in distilled water. Cooler thermoperiodspromoted germination, while high temperatures significantlyinhibited the germination of seeds at all NaCl concentrationstested. Rate of germination decreased with increases in salinity.At higher thermoperiods the rate of germination was significantlylower in comparison to lower thermoperiods. Seeds recover afterbeing transferred to distilled water and recovery was higherfrom higher salinity concentrations and lower thermoperiods.Final recovery germination percentages in high salt treatmentswere significantly lower than non-saline controls, indicatingthat exposure to high concentration of NaCl permanently inhibitedgermination. Germination; halophyte; Haloxylon recurvum recovery of germination; salinity; temperature     

Responses of Vegetable Seeds to Controlled Hydration

Leek, onion and carrot seeds were imbibed in water and in solutionsof polyethylene glycol (PEG) 6000 over the range –0.5to –4.0 MPa osmotic potential, for periods up to 28 dat 15 C. Seeds started to germinate after 7 and 14 d at –0.5MPa and –1.0 MPa PEG, respectively, but in the lattercase, germination did not exceed 5%. No germination occurredin solutions of lower (more negative) osmotic potential. Seedmoisture content increased with osmotic potential in all threespecies and the relationships were unaffected by the durationof imbibition in solutions of –1.0 to –4.0 MPa,though leek seeds had higher moisture contents than the otherspecies for any given osmotic potential. Linear relationships between response to priming (differencebetween mean germination times of primed and untreated seeds)and seed moisture content were obtained for each species, positiveresponses being obtained above 30–35% seed moisture contentwith optima at 46, 44.5 and 44% seed moisture contents in leek,onion and carrot, respectively. Priming had no effect on embryovolume or cell number per embryo in leek and onion. Carrot embryovolume increased by 43% and cell number per embryo doubled inprimed compared with untreated seeds, whereas seeds imbibedin water showed only a slight increase in cell number per embryoat the stage when radicles were beginning to penetrate the seedcoat. Allium cepa L. cv. Rijnsburger Robusta, onion, Allium porrum L. cv. Winterreuzen, leek, Daucus carota L. cv. Nantaise, carrot, germination, priming, polyethylene glycol, seed moisture, cell number, embryo volume     

A Model of the Effects of a Wide Range of Constant and Alternating Temperatures on Seed Germination of FourOrobanche Species

Seeds of the obligate parasitic plants, Orobanche spp., wereconditioned in water or GA₃for 2 or 12 weeks and then stimulatedto germinate by the synthetic stimulant GR24. Temperature treatmentsduring the germination tests comprised 169 different constantand alternating temperature regimes on a two-dimensional gradientplate. Optimum temperatures for germination of seeds of O. aegyptiacaand O. crenata were 18–21 °C and 18 °C, respectively.However, longer conditioning periods slightly lowered the optimain both species, and the maximum germination percentage wasalso reduced due to an induction of secondary dormancy. At agiven mean temperature, more seeds germinated at constant thanat alternating temperatures. Results were analysed in termsof characteristics of alternating temperatures that appearedto control germination, i.e. mean temperature, maximum temperature,amplitude (difference between daily maximum and minimum temperatures)and thermoperiod (the time spent at the maximum temperatureeach day). Final germination was modelled on the basis of therebeing two prerequisites for germination: a minimum mean temperaturewhich must be exceeded and a maximum temperature above whichthe seed will not germinate. These two requirements were assumedto be independent and to be normally distributed in the seedpopulation so that final germination could be described by amultiplicative probability model. Because of the response tomaximum temperature, inhibitory effects were more evident atalternating temperatures. Amplitude and thermoperiod influencedthis effect of maximum temperature. The implications of thedetrimental effect of alternating temperatures for germinationofOrobanche spp. in the field are discussed. Copyright 1999Annals of Botany Company Orobanche aegyptiaca, O. crenata, O. cernua, O. minor, broomrape, seed germination, temperature, germination model, secondary dormancy.     

Effect of salinity and chemical factors on seed germination in the halophyte Crithmum maritimum L.

Seeds of the halophyte Crithmum maritimum L. were exposed to salt stress and chemical pretreatments in order to improve germination. Seeds submitted to salt stress did not germinate but they recovered rapidly upon transfer to distilled water, recovery being higher after a low salinity pretreatment. Chemical treatments resulted in differential effects on seed germination. Known dormancy breakers such as potassium nitrate and thiourea had no effect on sea fennel seed germination. Conversely, l-ascorbic acid (40 or 60 mM) and ethanol (96%) significantly improved germination rate by 10, 30 and 30%, respectively. Pretreatment of seeds with l-ascorbic acid at 40 mM was shown to alleviate the negative effects of low NaCl concentration on germination. These findings indicate that the application of ascorbic acid may be used to improve sea fennel seed germination, which is of great interest for cultivating this plant.     

Studies on the Development of the Desiccation-sensitive (Recalcitrant) Seeds of Avicennia marina (Forssk.) Vierh.: The Acquisition of Germinability and Response to Storage and Dehydration

Germinability and responses to storage and dehydration werestudied throughout the development of the desiccation-sensitiveseeds of Avicennia marina. Seeds acquired the ability to produceroots at 55 d after fruit set (DAFS) which is shortly afterhistodifferentiation, but the capacity for full germinability(seedling establishment) was not attained until 70 DAFS, whichis midway through the phase of growth and reserve accumulation.Pre-mature seeds showed a germination lag that was equivalentto the period between harvest and full maturity, but, followingshort-term storage, this was reduced to that of mature seeds.At no stage, however, would seeds with an intact pericarp germinate. Once seeds were fully germinated, storage lifespan under non-desiccatingconditions was independent of developmental stage, but was considerablyreduce by the presence of the pericarp, probably because offungal contamination. Prior to the acquisition of full germinationcapacity, the seeds were unable to tolerate any dehydrationbut became tolerant to slight water loss once they became fullygerminable, after which desiccation sensitivity was not influencedby the stage of development. If rapidly dried, excised axesof germinable seeds survived to lower water contents than didaxes removed from seeds following slower drying.Copyright 1993,1999 Academic Press Desiccation-tolerance/sensitivity, germination, mangrove, recalcitrant, seed development, seed storage     

Sensitivity of seed germination to water stress in high-altitude populations of a threatened palm species

• Divergence in seed germination patterns among populations of the same species is important for understanding plant responses to environmental gradients and potential plant sensitivity to climate change. In order to test responses to flooding and decreasing water potentials, over 3 years we germinated and grew seeds from three habitats of Euterpe edulis Mart. occurring along an altitudinal gradient.
• Seed germination and root growth were evaluated under different water availability treatments: control, flood, −0.4 MPa, −0.8 MPa, in the years 2012, 2013 and 2014, and in the final year of the experiment (2014) at −1.0 MPa and −1.5 MPa.
• Seeds from the montane habitat did not germinate in the flooding treatment. Seed germination of all three habitats decreased in the −1.5 MPa treatment and the montane habitat had lowest germination in this treatment. Time required for half of the seeds to germinate increased up to −0.8 MPa. Seeds from montane habitats germinated more slowly in all treatments. The only difference in seed germination synchrony was an increase in the submontane population under the flooding treatment. However, synchrony decreased at the lowest water potentials. Roots of the montane population were more vigorous in most treatments, except at −0.8 MPa.
• The unusual ability of these seeds to germinate at low water potentials might be related to early seed germination at the onset of the rainy season, which potentially decreases seed predation pressure. Seeds of the montane population were more sensitive to both types of water stress. A predicted increase in the frequency and intensity of extreme high rainfall or drought events may predispose early stages of this population to adverse factors that might negatively affect population viability with elevational in future climate change scenarios.

     

GENETIC EFFECTS OF GERMINATION TIMING AND ENVIRONMENT: AN EXPERIMENTAL INVESTIGATION

Seeds of many species do not germinate immediately after dispersal, but instead may remain indefinitely in a dormant but viable state. Although it is well established that seeds often exhibit diversified patterns of dormancy and germination, the causes and consequences of this variation remain poorly understood. In this study, we investigate the extent to which seed genotypes of the desert mustard Lesquerella fendleri differentially germinate and establish under experimental conditions in a greenhouse. We used a two-way factorial design to compare genotypes of Lesquerella plants derived from seeds that germinated and established at different times and under different soil water regimes. Overall allozyme allele frequencies of Lesquerella plants varied significantly with both germination time and initial soil water availability. Single-locus heterozygosity analyses revealed that seeds sown into initially low water conditions produced plants that were significantly more heterozygous than plants derived from seeds experiencing constantly high water conditions, but heterozygosity did not differ significantly among plants originating from early- and late-germinating seeds. This is the first study to experimentally demonstrate that germination timing and environment can significantly affect the genetic structure of emerging plant populations. The study suggests that germination and survival behavior may (1) play an important role in generating and maintaining the genetic structure of natural plant populations and (2) set the stage for subsequent evolution.     

Seed Germination and Seedling Development in Cyclamen persicum

Cyclamen persicum Mill, seeds germinate in a narrow range oftemperature and germination is strongly inhibited by continuousirradiation with white light. The thermal optimum is approx.15 °C in both darkness and light. Seed germination is alsovery sensitive to oxygen deprivation and this sensitivity ismore pronounced at 20 °C than at the optimum 15 °C.Very immature seeds cannot germinate at any temperature, butgerminability increases during seed maturation Seedling development is unusual since seed reserves are usedimmediately for tuber formation. Tuberization is optimal at15–20 °C in light and in darkness. Supra-optimal temperatures(25–30 °C) or hypoxia inhibit tuber formation andlead to very elongated tubers These results allow the producers to improve the productionof homogeneous populations of cyclamen seedlings Wheat seeds, Triticum aestwum L., acetylcholinesterase, electrophoresis, germination, assay     

Germination ecology of the polycarpic grassland perennials Primula veris and Trollius europaeus

The seed germination behaviour of Primula veris and Trollius europaeus , both perennial, polycarpic grassland plants was compared The species have similar-sized seeds that are dormant at dispersal Seeds buried in soil and exhumed at regular intervals showed that for both species, primary seed dormancy was overcome by cold-stratification Hence, their germination in the field should occur in spring, following dispersal, or later Seeds of P veris became dormant again in the late spring/early summer, and dormancy was broken again in the second winter Seeds of T europaeus did not exhibit such changes in dormancy
Seeds of P veris did not germinate in darkness This suggests that P veris can accumulate a persistent seed bank because buried seeds are prevented from germinating Trollius europaeus , on the other hand, germinated equally well in darkness and in light which suggests that seeds might germinate even when they are too deep in the soil for seedlings to emerge Two lines of evidence confirm this difference in seed bank behaviour (1) Primula veris was detected in the persistent seed bank of a grassland site, whereas T europaeus was not (n) After 16 months burial, 85% of the P veris seeds but only 8% of the T europaeus seeds remained viable     

Seed Germination Ecology of the Cold Desert Annual Isatis violascens (Brassicaceae): Two Levels of Physiological Dormancy and Role of the Pericarp

The occurrence of various species of Brassicaceae with indehiscent fruits in the cold deserts of NW China suggests that there are adaptive advantages of this trait. We hypothesized that the pericarp of the single-seeded silicles of Isatis violascens restricts embryo expansion and thus prevents germination for 1 or more years. Thus, our aim was to investigate the role of the pericarp in seed dormancy and germination of this species. The effects of afterripening, treatment with gibberellic acid (GA₃) and cold stratification on seed dormancy-break were tested using intact silicles and isolated seeds, and germination phenology was monitored in an experimental garden. The pericarp has a role in mechanically inhibiting germination of fresh seeds and promotes germination of nondormant seeds, but it does not facilitate formation of a persistent seed bank. Seeds in silicles in watered soil began to germinate earlier in autumn and germinated to higher percentages than isolated seeds. Sixty-two percent of seeds in the buried silicles germinated by the end of the first spring, and only 3% remained nongerminated and viable. Twenty to twenty-five percent of the seeds have nondeep physiological dormancy (PD) and 75–80% intermediate PD. Seeds with nondeep PD afterripen in summer and germinate inside the silicles in autumn if the soil is moist. Afterripening during summer significantly decreased the amount of cold stratification required to break intermediate PD. The presence of both nondeep and intermediate PD in the seed cohort may be a bet-hedging strategy.     

Role of Brycinus lateralis (Teleostei: Alestidae) in dispersal and germination of Nymphaea nouchali (Angiospermae: Nymphaeaceae) seeds on a seasonal floodplain of the Okavango Delta,Botswana

Seed passage through the gut of vertebrates can be important for seed dispersal, but might influence seed viability. The ability of seeds to germinate after ingestion by seed-eating fish is important for the population dynamics of some plant species, and significant in the evolution of plant–fish interactions. Certain fish in the Okavango Delta, Botswana, are fruit- and seed-eaters and could act as seed dispersers. We sampled 14 fish species in 2013, finding Nymphaea nouchali var. caerulea seeds in the digestive tracts of eight, most commonly in the striped robber Brycinus lateralis. Seeds extracted from the gut of this species had an overall mean germination success of 11.7%. This fish species might well be a legitimate seed disperser, having a positive effect on seed dispersal from parent plants in the Okavango Delta. The current study represents one of the first investigations of the likelihood of seed dispersal by fish on the African continent.     

Effect of Endogenous Coumarin on the Germination of Seeds of Coumarouna odorta Aublet

Seeds of Coumarouna germinate readily at 33?C in darkness orlight in spite of high levels of endogenous coumarin. The concentrationof coumarin on a dry-weight basis remained constant in the cotyledonsand increased in the embryos during germination. Applied coumarin(0.4 and 4 mM) did not inhibit germination of Coumarouna butenhanced the growth of embryos; yet a single seed of Coumarouna,placed at the centre of a Petri-dish, drastically inhibitedgermination of other neighbouring seeds (lettuce, radish, andtomato). The presence of coumarin in the soil of potted seedlingssuggest that coumarin exuded by the radicle can inhibit germinationand growth of other species in its vicinity, thus eliminatingcompetition during the first stages of growth.     

Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Seed conditioning and germination in witchweed (Striga asiatica(L.) Kuntze) were temperature-dependent. With higher conditioningtemperatures, shorter conditioning time was required for germinationwith terminal dl-strigol (strigol) treatment at 30 °C. Maximumgermination (80–100%) was obtained by conditioning inwater at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively,and terminally treating with 10^–6 M strigol at 30 °C.Seeds conditioned in 10^–8 M strigol instead of water germinatedmuch less with the same terminal strigol treatment. Generally,conditioning was slower when seeds were conditioned in strigolrather than water. The reduction in germination rate by pretreatmentin strigol or pretreatment at low temperatures could be overcomeby increasing the terminal strigol concentration in the germinationtest. Conditioned seeds did not germinate at 10 and 15 °Cwith a terminal 10^–6 M strigol treatment but yielded closeto maximum germination at 25, 30 and 35 °C with the sameterminal strigol treatment. To obtain maximum germination, boththe minimum conditioning temperature and the minimum germinationtemperature for conditioned seeds were 20 °C. Factors suchas conditioning time, and strigol concentration and temperatureduring conditioning and/or germination determine whether seedsremain in the conditioning phase or shift to a germination phase. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica, temperature, weed control     

Recovery of Germination from Different Osmotic Conditions by Four Halophytes from Southeastern Spain

Seeds of four halophytes from southeastern Spain (the perennialsHalocnemum strobilaceum,Arthrocnemum macrostachyum and Sarcocorniafruticosa, and the annual Salicornia ramosissima) were exposedto iso-osmotic stress with NaCl, MgCl₂, MgSO₄and Na₂SO₄. Theosmotic potential that enforced dormancy in the majority ofseeds was determined. The percentage of ungerminated seeds thatrecovered when they were transferred to distilled water didnot differ significantly from the percentage germination ofseeds in distilled water controls, irrespective of the saltused to impose the stress. Therefore, the factor responsiblefor the dormancy of seeds seems to be the decrease in osmoticpotential. Such osmotic pretreatments promoted an increase inthe rate of recovery germination which, inArthrocnemum macrostachyumand Sarcocornia fruticosa, doubled their rates of germinationcompared to distilled water controls. The osmotic potentialsof the soils where the four species occur naturally were morenegative than those allowing seeds to germinate after osmoticstress. Copyright 2000 Annals of Botany Company Arthrocnemum macrostachyum, Halocnemum strobilaceum, halophytes, osmotic stimulation, recovery of seed germination, Salicornia ramosissima, Sarcocornia fruticosa.     

Germination behaviour of Astroloma xerophyllum (Ericaceae), a species with woody indehiscent endocarps

The dispersal unit of many Ericaceae comprises an ovoid drupe with a woody indehiscent endocarp, and diaspores of this type are notoriously difficult to germinate for most members of this widely distributed family. Within the biodiverse south‐west of Western Australia, more than 200 drupaceous species of Ericaceae have been described, more than 50 of which are considered to be rare and threatened, requiring significant conservation action in the near future. In this paper, we investigate the germination ecology of the common Australian endemic, Astroloma xerophyllum, as a proxy for closely related threatened taxa, focusing on the ex situ and in situ germination requirements of seeds and indehiscent endocarps. Each endocarp possessed up to seven locules and means of 2.0–3.4 seeds per endocarp from the two collections used in this study. Seeds were up to 2.74 mm in length and 100% viable. Embryos were linear, differentiated and approximately 1.3 mm in length. Seeds within endocarps imbibed water to 28%, whereas excised seeds became hydrated to 44%. Fifty‐five per cent of seeds extracted from endocarps germinated on water agar alone and 100% germinated when presoaked in gibberellic acid. Seeds remaining inside intact endocarps failed to germinate unless treated with a germination promoter and incubated for more than 20 weeks. Rapid germination of seeds in intact endocarps was promoted by soaking endocarps in gibberellic acid and incubating them in 100% O₂. Embryos grew substantially in length within seeds prior to germination, and thus seeds have morphophysiological dormancy. Seeds under natural conditions required several seasons to germinate to any degree. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 299–311.     

Post‐Dispersal Seed Removal and Germination Selected Tree Species Dispersed by Cebus capucinus on Barro Colorado Island,Panama1

Dispersal quality, an important component of seed disperser effectiveness, may strongly affect the rate of plant recruitment. Here we evaluated the quality of Cebus monkey dispersal by comparing the secondary removal fate and germination of fresh and Cebus‐ingested seeds of nine tree species on Barro Colorado Island, Panama. Overall, rates of secondary seed removal by vertebrates were low, with most Cebus defecations remaining undisturbed for extended periods on the forest floor. Only four of 30 feces were completely buried by dung beetles, and we found significantly higher vertebrate removal of defecated seeds than control seeds for only one species, Cordia bicolor. Seed germination varied greatly between plant taxa. Seeds of 3 out of 9 species showed significantly higher percent germination after monkey gut passage than control fresh seeds. Germination times tended to be shorter for defecated than for control seeds but were significantly different only for one of nine species, Cecropia insignis. Low rates of seed removal from Cebus feces, coupled with high germination probabilities, suggest high dispersal effectiveness for Cebus and contrasts strongly with patterns of post‐dispersal seed fate recorded for other primate species.