Seed dimorphism and germination behaviour in Salicornia patula

One of the annual species of the genus Salicornia from the Mediterranean coast, Salicornia patula presents a seed dimorphism. This morphological seed dimorphism is linked with a physiological ‘dimorphism’ with regard to some requirements for germination. Central seeds, in the inflorescence, are larger, are dispersed attached to the perianth, have no light requirement for germination and seem to have a low germination response to salinity. The lateral seeds, which are free from perianth envelopes, require light and cold pretreatment and seem to have a high sensitivity to salinity. Salicornia patula colonizes unstable transition zones between permanently flooded muds and perennial vegetation. These zones have a winter flooding period. The beginning of the flooding period and of the dry period may vary from year to year, depending on the erratic distribution of autumn and winter rains on the Mediterranean coast. So, in some years, a seedling population may be destroyed before reaching the stage of seed production. Seed dimorphism might cause germination to the more distributed in time, thus reducing the chances of extinction of a complete generation. In the present paper salinity and temperature response are described more precisely, are investigated, some aspects of the longevity of the two types of seed, and the adaptative significance of the corresponding dispersal and germination syndromes are discussed in more detail.     

Seed ecology and germination treatments in Magnolia dealbata: An endangered species

Magnolia dealbata is a deciduous tree species in danger of extinction. Seed ecology data and successful germination treatments are important for conservation and species reintroduction programs. This study reports about seed ecology and germination treatments of M. dealbata Zucc. The results showed that the seeds, influence of vertebrates excluded, persisted viable after 1 year, suggesting the presence of a semi-persistent seed pool. There was no significant difference (p>0.05) in survival of seeds with or without sarcotesta after a year. Significant differences (p<0.05) were found in the number of seeds surviving after a year at different levels of burial. There was no significant interaction upon survival (p>0.05) between sarcotesta presence or absence in the seed and burial depth. If vertebrates were not excluded the seeds had a removal rate of 100% 8 months after being exposed. Seed survival curve was of Type II, that is, with constant mortality throughout the time. The most successful germination treatment (p<0.05) with 100% germination was soaking of seeds without sarcotesta for 24 h at room temperature (18–20 °C).     

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment (sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.     

Seed germination of the halophyteSuaeda japonica under salt stress

Suaeda japonica Makino belonging to the family Chenopodiaceae, is a halophyte and grows at the shore of Ariake sea in Japan. This plant presumably possesses high salt resistant nature, thus, we examined the mechanisms of seed germination under salt stress. The seeds maintained 80% germination rates on the medium containing 0.7 M NaCl. Germination rates varied depending on salt type; the germination rates under NaCl or KCI exhibited relatively lower values than ones under sodium gluconate or potassium gluconate. This different responses for salts seemed to be as a result of the presence of Cl⁻ ions. Although very high levels of betaine (compatible solute), were kept in the seedlings grown under no salt stress, the contents gradually increased as concentration of NaCl increased. Betaine is a factor present in plants that works to alleviate the effects of excessive soil salts. It is synthesized in leaves from betaine aldehyde, and this process is catabolized by betaine aldehyde dehydrogenase (BADH). When the seedlings were cultivated on the medium without NaCl, relatively high level of BADH activity was found. The activity increased 5-fold in the seedlings grown under 0.5 M NaCl stress. Increases in betaine content and BADH activity were found during seed germination. InS. japonica, the salt stress promoted BADH activity, subsequently endogenous betaine contents were increased, and increased betaine seemed to secure seed germination under salt stress.     

Seed germination,seedling inoculation and establishment ofAlnus spp. in containers in greenhouse trials

Methods for production of containerized seedlings ofAlnus species were developed which permit nitrogen-fixing nodules to form on the root systems prior to outplanting, in order to provide an early nitrogen input during seedling establishment. The methods are based on procedures for inoculating root systems with suspensions ofFrankia (Actinomycetales), applied either directly in the container cell as a soil drench at the time of seeding, or as a root dip for seedlings transplanted into the containers. Germination of dried, stored seed was enhanced by light and by presoaking for 16 h in water. Pretreatments to overcome seed dormancy or to eliminate fungal pathogens did not further enhance germination. Some loss of seedlings was recorded in the early stages of growth shortly after germination, which is a factor in calculating projected seedling yield. Nodulation and seedling growth were evaluated in terms of growth media characteristics. Seedlings performed well in peat-vermiculite, at soil pH between 5.5 and 8.0.     

Seed oil fatty acid patterns of theAconitum-Delphinium-Helleborus complex (Ranunculaceae)

Many members ofRanunculaceae contain unusual fatty acids in their seed oils. This leads to rather typical genus-specific fatty acid patterns or fingerprints in these seed oils. The members of theDelphinioideae and/orHelleboroideae, however, do not contain highly unusual fatty acids. Nevertheless, their seed oil fatty acid fingerprints are also fairly typical and genus-specific, and the patterns found are rather consistent throughout several species of one genus. It was found that species ofAconitum do not contain fatty acids with 20 carbon atoms.Delphinium, Consolida, Helleborus, Nigella and others do contain C₂₀ fatty acids. In allHelleborus species, for example, there was a consistent C₂₀ fatty acid pattern of 20:020:120:2>20:3. Species ofNigella andGaridella contain high levels,Helleborus low levels, of 20:2n-6 in their seed oils.Delphinium andAconitum both contain low levels of 18:3n-3, whereasHelleborus spp. consistently show high levels of this fatty acid. The genus-specific fatty acid patterns found are discussed, and a correlation with the subfamily and tribe affiliation of the genera investigated here is attempted.     

Comparative population ecology of dune slack species: the relation between population stability and germination behaviour in brackish environments

Populations of short-lived pioneer species from brackish primary dune slacks and beach plains usually have to cope with unpredictably fluctuating abiotic conditions. Life history parameters play a major role in adaptation to temporal environmental heterogeneity. A population's susceptibility to fluctuating salinity levels may be largely determined by seed dormancy characteristics (e.g. seed variability, degree of enforced dormancy imposed by salinity) and juvenile salt resistance rather than by adult salt resistance.Nomenclature follows Hegi (1966).     

Genetic analysis of field germination in soybean (Glycine max. (L) merill.)

Summary Genetic analysis for germination percentage was carried out in the F₃ and F₄ generations of a diallel cross involving six promising genotypes of soybean. Results indicated a high amount of genetic variability and a moderately high heritability together with genetic advance, suggesting a possible improvement for this character through hybridization and selection. Correlations at different levels revealed a strong negative association of germination with only one seed character: seed weight. This observation was further confirmed from path coefficient analysis. These findings strongly suggest that to base selection on seed weight which may not influence the seed quality of soybean.     

Juggling carbon: allocation patterns of a dominant tree in a fire-prone savanna

In frequently burnt mesic savannas, trees can get trapped into a cycle of surviving fire-induced stem death (i.e. topkill) by resprouting, only to be topkilled again a year or two later. The ability of savanna saplings to resprout repeatedly after fire is a key component of recent models of tree–grass coexistence in savannas. This study investigated the carbon allocation and biomass partitioning patterns that enable a dominant savanna tree, Acacia karroo, to survive frequent and repeated topkill. Root starch depletion and replenishment, foliage recovery and photosynthesis of burnt and unburnt plants were compared over the first year after a burn. The concentration of starch in the roots of the burnt plants (0.08 ± 0.01 g g⁻¹) was half that of the unburnt plant (0.16 ± 0.01 g g⁻¹) at the end of the first growing season after topkill. However, root starch reserves of the burnt plants were replenished over the dry season and matched that of unburnt plants within 1 year after topkill. The leaf area of resprouting plants recovered to match that of unburnt plants within 4–5 months after topkill. Shoot growth of resprouting plants was restricted to the first few months of the wet season, whereas photosynthetic rates remained high into the dry season, allowing replenishment of root starch reserves. ¹⁴C labeling showed that reserves were initially utilized for shoot growth after topkill. The rapid foliage recovery and the replenishment of reserves within a single year after topkill implies that A. karroo is well adapted to survive recurrent topkill and is poised to take advantage of unusually long fire-free intervals to grow into adults. This paper provides some of the first empirical evidence to explain how savanna trees in frequently burnt savannas are able to withstand frequent burning as juveniles and survive to become adults. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

授粉方式对铁皮石斛种质座果及种子萌发的影响

为进行铁皮石斛(Dendrobium officinale)的良种选育和种苗生产,对46个铁皮石斛种质进行人工授粉试验,研究了不同授粉方式的授粉成功率、座果率和种子的萌发能力。结果表明,4种授粉方式的授粉成功率明显不同,不同种质间的授粉成功率可达100%,且座果率普遍较高。只有31.3%的种质可以成功自花授粉,且座果率相差较大。同株异花授粉和种质内异株授粉的成功率和座果率均介于上述二者之间。授粉后所得种子的萌发率和萌发速度在4种授粉方式间也呈现与授粉成功率和座果率一致的趋势。这表明在铁皮石斛种质中存在自交不亲和现象,因此以不同产地来源的铁皮石斛种质为亲本进行人工授粉,可大大提高授粉的成功率和座果率,以及后代种子的萌发能力。     

Seed mass and emergence time effects on performance of Panicum dichotomiflorum Michx. across environments

Summary The effects of seed mass and emergence time on growth and reproduction of the annual, C₄ grass, Panicum dichotomiflorum Michx., were investigated in an experimental field study. Individual seeds of P. dichotomiflorum of known mass were sown into marked plots in four newly-abandoned fields that differed in soil nutrient availability, soil moisture and the time of the year in which they were abandoned. Seedling emergence was monitored daily for four weeks following sowing. In none of these fields was there any relationship between seed mass and emergence time. Analyses of covariance indicated that the effects of seed mass and emergence date on plant performance varied among fields. Seed mass affected performance in one field (SOUTH EARLY) where abiotic stress after emergence was high. In contrast, later emergence significantly reduced performance in all four fields. We used a path analysis to decompose the direct and indirect effects of seed mass and emergence time on plant performance in each field. The path analysis revealed that in all four fields, final weight had a significant positive effect on seed production. The effect of seed mass and emergence time had variable (and often opposite effects) on these traits. Seed mass only had a significant positive, direct effect on seed production in the most abiotically stressful field (SOUTH LATE). In the other fields, the effects of seed mass on fecundity were mediated by the effect on final weight. Thus, the effects of seed mass and emergence time on growth and reproduction in P. dichotomiflorum vary across environments.     

Ribosomal RNA integrity and rate of seed germination

The integrity of ribosomal RNA (the percentage of complete, un-nicked molecules) in seeds was studied by electrophoresis under denaturing conditions. Two batches of carrot seed, harvested at different stages of maturity, and four batches ofNicotiana seed stored for various times were used. Within each species, there was a correlation between the integrity of the rRNA of the dry seed and the rate of germination of that seed. In carrot seed, there was extensive degradation of existing rRNA in both the embryo and endosperm during the first two days of imbibition.     

Effects of parentage,prior fruit set and pollen load on fruit and seed production in Campanula americana L

Summary We conducted a controlled crossing experiment to examine the effects of maternal and paternal parentage, the size of the pollen load, and prior fruit production on the proportion of flowers that set fruit, seed number per fruit and seed weight in a natural population of Campanula americana. Effects due to the maternal parent were large for all measures of fruit and seed production, while the paternal parent had a significant effect only upon mean seed weight. As the number of prior fruits on the maternal plant increased the probability that a flower would produce a mature fruit, the number of seeds per fruit, and total seed weight per fruit all decreased. We found no effect of the size of the pollen loads used in this study on fruit or seed production. These results are consistent with those of other studies that suggest in natural plant populations maternal effects, especially environmental maternal effects, can have an overwhelming effect on fruit and seed production and on seed characteristics.     

Halophyte and glycophyte salt tolerance at germination and the establishment of halophyte shrubs in saline environments

Saline sites suffer variations in surface salinity, available soil water, temperature, soil crust strength and other factors which can influence germination and establishment. For establishment to occur the germinating seed must capitalise on a window of opportunity. This window can be widened by placing seeds in a low-salt niche, covering the seeds with a mulch (such as vermiculite), spraying the seed and mulch placement with a coating which may stabilise the favourable situation and raise soil temperature. In this paper it is shown that using seeds collected from plants of Atriplex amnicola which produce many volunteer seedlings in their vicinity can assist establishment from direct seeding. These seeds had the ability to germinate under saltier and cooler conditions than seeds from A. amnicola bushes which did not produce volunteers. Seeds of a halophyte (Atriplex lentiformis) and a non-halophyte (Medicago sativa) are able to imbibe water from a saline substrate in a similar manner. The water enables the seeds of both species to mobilise stored growth materials and produce and elongate radicles. When the seedlings try to erect a hypocotyl and spread their cotyledons, the non-halophyte, in a saline medium, becomes flaccid, distorted and dies. The halophyte seedling shows evidence of high salt tolerance in the form of succulence of cotyledons and trichomes on true leaves even before they are visible and goes on to successfully develop a functioning plant. Nevertheless, germination of halophyte seeds is inhibited or severely reduced at salinity levels above 250 mM NaCl and slowed and reduced progressively up to those levels.     

Effect of salinity on composition, viability and germination of seeds of Chenopodium quinoa Willd

Salinity influences plant growth, seed yield and seed quality even of halophytic crops such as Chenopodium quinoa. Plant growth, total seed yield, number of seeds, fresh weight and dry weight of seeds, were all significantly reduced in the presence of salinity. Only at high salinity did the content of proteins (as well as total N) increase significantly in the seeds whereas the content of total carbohydrates (as well as total C) decrease. Aside from that the capacity for germination was diminished by a reduced seed size and a disproportionate reduction of the volume of the perisperm. However, the reduced capacity seemed to be compensated by an accelerated germination owing to high Na and Cl concentrations leading to a low water potential in the walls of the plant ovary. At high salinity the passage of NaCl to the seed interior was hindered by the seed cover. There was an obvious gradient between potentially toxic (Na and Cl) and essentially needed elements (K, Mg, Ca, P and S) across the seed coat of salt treated plants and also a significant change of the distribution of elements in the embryo. The results indicate a highly protected seed interior leading to a high salinity resistance of quinoa seeds.     

Effect of temperature on the in vitro radial growth of Zoophthora radicans and Pandora blunckii, two co-occurring fungal pathogens of the diamondback moth Plutella xylostella

The effect of four different temperatures (15, 20, 25 and 30°C) on the in vitro growth of 19 isolates of Pandora blunckii and 14 isolates of Zoophthora radicans from Plutella xylostella larvae was investigated. Both species grew more at 20 and 25°C than the other two temperatures. However, Z. radicans grew more than P. blunckii at 20 and 25°C. Within each species there were differences amongst: all isolates regardless of geographical origin, isolates from different countries and isolates from Mexico. No relationship was found between optimal growth temperature and geographical origin. This represents the first report of the relationship between temperature and the in vitro growth of P. blunckii. The ecological role of this large variability amongst isolates within each species is discussed.     

Facultative ripening in Hamelia patens (Rubiaceae): effects of fruit removal and rotting

Summary In Costa Rica individual Hamelia patens trees produce fruit throughout the year and experience dramatic changes in rates of fruit removal and rotting. During some moths, most fruits rot because they are not removed. Rotting fruits increase the probability that other fruits on the same infructescence will rot. When removal rates are high, fruits are taken as soon as their seeds become viable but before the fruit is completely ripe. Experimental removal of fruits produced significantly higher ripening rates than on control infructescences. This response allows Hamelia to ripen more fruit and increase the number of fruits taken when dispersers are abundant (e.g., during migration). The proximate mechanism of this response probably includes reallocation of energy conserved when partially ripe fruits are removed. Responding to fluctuating disperser populations likely increases dispersal success and may function as the ultimate cause.     

Irrigation and fertilization effects on seed number,size, germination and seedling growth: implications for desert shrub establishment

Plants with limited resources adjust partitioning among growth, survival, and reproduction. We tested the effects of water and nutrient amendments on seed production, size, and quality in Sarcobatus vermiculatus (greasewood) to assess the magnitude and importance of changes in reproductive partitioning. In addition, we assessed interactions among the environment of seed-producing plants (adult plant scale), seed size, and seedling microenvironment (seedling scale) on successful seedling establishment. Interactions of these factors determine the scale of resource heterogeneity that affects seedling establishment in deserts. Both total number of seeds produced per plant and seed quality (weight and germination) increased significantly in the enriched treatment in a 3-year field experiment. Seedling length 3 days after germination and seed N concentration, other measures of seed quality, were higher for seed from both irrigated and enriched plants than for seed from control plants. Field S. vermiculatus seed production and quality can be substantially increased with irrigation and nutrient enrichment at the adult plant scale and this allows management of seed availability for restoration. However, based on a greenhouse study, seedling environment, not the environment of the seed-producing plant or seed size, was the most important factor affecting seedling germination, survival, and growth. Thus it appears that production of more seed may be more important than improved seed quality, because higher quality seed did not compensate for a low-resource seedling environment. For both natural establishment and restoration this suggests that heterogeneity at the scale of seedling microsites, perhaps combined with fertilization of adult shrubs (or multi-plant patches), would produce the greatest benefit for establishing seedlings in the field.     

藏药多刺绿绒蒿种子萌发特性研究

多刺绿绒蒿(Meconopsis horridula)为罂粟科绿绒蒿属一年生草本植物,是一种极具观赏价值和药用价值的高山植物,目前处于濒危状态,因此研究多刺绿绒蒿种子的萌发特性对其种子育苗及人工栽培具有重要意义。为了提高多刺绿绒蒿的种子发芽率,该研究以多刺绿绒蒿的种子为材料,分析了不同消毒剂、浸种时间、温度和外源植物激素对种子萌发特性的影响。结果表明:(1)最适消毒方法为75%乙醇1 min+3%H2O25 min,最适浸种时间为24 h,最适温度和光照条件为20℃/10℃(光照12 h/黑暗12 h),用无菌水浸种后的种子发芽率为49.67%。(2) GA_3100～600 mg·L~(-1)和NAA 5～30 mg·L~(-1)可以提高种子的发芽率、发芽势和发芽指数,缩短发芽启动时间和发芽持续时间,对种子的萌发有促进作用。(3) 6-BA 5 mg·L~(-1)和10 mg·L~(-1)对种子的萌发有一定的促进作用,但不显著,6-BA浓度≥15 mg·L~(-1)则抑制种子的萌发。(4)用GA3500 mg·L~(-1)浸种后的种子发芽指标最好,发芽率、发芽势和发芽指数分别为69.67%、33.00%、4.51,种子的发芽起始时间和发芽持续时间分别为10.67 d、11.67 d。     

The impact of temperature regimes on development,dormancy breaking and germination of dwarf shrub seeds from arctic,alpine and boreal sites

It has been suggested that the infrequent sexual reproduction of arctic dwarf shrubs might be related to the harsh environmental conditions in which they live. If this is the case, then increases in temperature resulting from global climate change might drastically affect regeneration of arctic species. We examined whether recruitment of Empetrum nigrum ssp. hermaphroditum and Vaccinium uliginosum (hereafter E. nigrum and V. uliginosum) was affected by temperature during three reproductive stages: seed development, dormancy breakage and germination. Seeds were collected from an arctic, an alpine (only E. nigrum) and a boreal site with different climates; stored at different winter temperatures and incubated for germination at different temperatures. Seeds of V. uliginosum developed in the boreal region had a higher percentage germination than did seeds developed in the Arctic. In contrast, seeds of E. nigrum from the arctic site had a higher or similar percentage germination than did seeds from the alpine and boreal sites. Increased winter temperatures had no significant effect on resulting germination percentage of E. nigrum. However, V. uliginosum seeds from the arctic site suffered increased fungal attack (and thus decreased germination) when they were stratified under high winter temperatures. Seeds of both species increased germination with increased incubation temperatures. Our results suggest that both species would increase their germination in response to warmer summers. Longer summers might also favour the slow-germinating E. nigrum. However, increased winter temperatures might increase mortality due to fungal attack in V. uliginosum ecotypes that are not adapted to mild winters.