Germination Of Achenes Research Articles

Germination-Temperature Profiles for Achenes of Yellow Starthistle (Centaurea solstitialis)1

Yellow starthistle is an annual that is dependent on achene production, dispersal, and germination for stand renewal. Our purpose in this study was to determine the temperature relations for germination of achenes of this species. Germination temperature profiles were developed for achenes of yellow starthistle collected from 15 sites in California, Nevada, and Oregon. Each profile consisted of achene germination at 55 constant or alternating temperatures from 0 through 40 C. A total of 85 germination temperature profiles were developed by using the germination data to construct quadratic response surfaces through regression analysis. For most profiles, germination occurred at all the temperature regimes except a constant 40 C. This includes a constant 0 C and 0 alternating with 40 C. Rarely, there was no germination at 35 C and 35 C alternating with 40 C. The only evidence of afterripening requirements for achenes of yellow starthistle that we noted occurred at very cold temperature regimes. At those temperatures, the germination of dark-colored achenes without pappus increased 3 mo after harvest, and decreased for light-colored achenes with a pappus. No single temperature regime always supported optimum germination when all the profiles were combined. The most frequent optima was 2/20 C. Comparing all profiles for the Davis, CA, accession, there were 5 regimes (5 and 10 C cold periods alternating with 15 through 25 C warm periods) that always supported optimum germination. Light-colored achenes with pappus tended to have optimal germination at colder temperatures, and the dark-colored achenes at higher temperatures when seeds were tested immediately after harvest.Nomenclature: Alfalfa, Medicago sativa L. #3 MEDSA; tocalote, Centaurea melitensis L.; yellow starthistle, Centaurea solstitialis L. # CENSO.Additional index words: Seedbed ecology, seedbed temperatures, optimum germination, invasive species.

Germination characteristics of Artemisia ordosica (Asteraceae) in relation to ecological restoration in northern China

Artemisia ordosica Krasch. (Asteraceae) is the dominant psammophytic shrub species on the Ordos Plateau of northern China and is used for revegetation of semi-arid areas. Experiments were conducted to determine the effects of light intensity, constant temperature, alternating temperatures, and water potential on germination to determine why air-dispersed achenes fail to germinate well in the field. Achenes germinated within a wide alternating temperature window, except under the 5:15 °C (night:day) temperature regime in darkness. Final percent germination (FPG) was higher in darkness than in light at alternating temperature regimes, except under the 20:30 °C (night:day) temperature regime. Achenes subjected to a range of constant temperatures in the dark had high FPG over 76.8% except at 30 °C (8%). Photosynthetic photon flux densities (PPFD) of 100 and 400 µmol·m–2·s–1 significantly lowered FPG under a 10:20 °C (night:day) regime, while at 0–25 µmol·m–2·s–1 PPFD, the FPG was over 92%. Few achenes germinated at –1.4 MPa. The most suitable temperature for germination of achenes placed under water stress was 20 °C. The best timing for air dispersal is mid-May, so seeds would become covered with sand at a time when temperature and soil moisture conditions were optimal for germination.Key words: air dispersal, Artemisia ordosica, hydrothermal time, psammophytes, semi-arid regions, temperature.

Effect of temperature on dormancy and germination of Eupatorium cannabinum L. achenes

This study investigated the effects of various temperature regimes on dormancy and germination inEupatorium cannabinum, a common wetland species in Central Europe. Germination of dry-stored achenes was tested at increasing amplitudes of temperature fluctuations, and stratified achenes were germinated at constant temperatures. Dormancy release was examined in the laboratory at constant temperatures of 3, 8, 12, 15 and 18°C. The effect of an increase in temperature during stratification from 5°C to 15, 18 or 20/10°C on dormancy was tested. Moreover, achenes were exposed to yearly seasonal temperature cycles in the soil in an experimental garden. Germination of dry-stored achenes was not promoted by fluctuating temperatures, while stratified achenes germinated (>5%) over a range of constant temperatures between 9 and 36°C. Dormancy was relieved at all stratification temperatures, but temperatures ≤12°C were more effective than higher temperatures, since germination occurred over a wider range of test conditions after these pretreatments. An induction of secondary dormancy occurred only if the temperature was increased during stratification. Annual dormancy cycles were apparent when achenes were germinated at 15°C, while at 25 and 15/5°C germination was always >60%. The germination behaviour ofEupatoriumis that of a typical wetland species. Thus, non-dormant achenes germinated at relatively high temperatures, and germination was promoted by fluctuating temperatures. The annual course of dormancy revealed that achenes can germinate throughout the growing season under favourable conditions. Achenes sown in an experimental garden germinated in spring, when daily mean temperatures were around 14°C. A decline in viability of achenes after 19 months' burial indicated thatEupatoriumdoes not form a long-term persistent seed bank.

Biological characteristics of an invasive south African species

Senecio inaequidens, a south African species that has recently invaded parts of Europe, especially human disturbed habitats, was examined under laboratory and glasshouse conditions to assess the germination of achenes, soil seed banks, growth of seedlings and its breeding system. These observations allowed identification of ecological characteristics that may contribute to the invasiveness of the species. Achenes derived from three populations of S. inaequidens were germinated over a wide temperature range (from 14/6 °C day/night temperatures to a constant temperature of 30 °C). They exhibited a rapid achene germination especially when temperatures reached 20 °C. Germination of seeds from soil samples also exhibited a prolonged germination over time suggesting therefore different types of dormancy. Growth response was studied along a nitrogen gradient from 0.33 to 16.0 mmol l−1 and data were interpreted using growth analysis. Seedlings of S. inaequidens exhibited a slow growth in low nutrient availability and a rapid growth rate when exposed to high nutrient availability, which contributed to producing a large leaf area and biomass. Four types of pollination were studied in S. inaequidens. Hand-pollinations showed that S. inaequidens was mostly self-incompatible. Self-pollinated capitula only showed 7.6% viable achenes, significantly lower than insect-pollinated and cross-pollinated capitula. Some individuals were more self-fertile than others ensuring the production of some offspring in a situation of colonisation. Natural pollination occurred with generalist insects. Most of these results confirm the invasive ability of S. inaequidens.

Dormancy and germination of heteromorphic achenes of Bidens frondosa

Summary Bidens frondosa is an annual weed occurring on mudflats with heteromorphic achenes. Central achenes are brown and elongated, and peripheral achenes are black and thicker. To identify differences in dormancy between the two morphs, germination of dry-stored achenes, and achenes stratified for 2, 4 and 13 weeks at 5°C, were tested at 15, 25 and 20/10°C in light for two populations. None of the achenes germinated after dry storage or when stratified for 2 or 4 weeks. Significant differences in dormancy between the two morphs were obvious at 20/10°C and 25°C after 13 weeks of stratification. Periphery achenes were less dormant as they germinated to 75% (Furst-Puckler-Park population, FPP) and 65% (Spreewald population, SPR) at 25°C, while only 18% (SPR) and 45% (FPP) of the central achenes germinated. Germination was completed within 3 days. At 20/10°C, the germination rate of periphery achenes was higher than those of central achenes, but nearly all achenes of both morphs had germinated after 21 days. No germination occurred at 15°C. Central achenes are morphologically better-adapted for dispersal by animals. Their deeper dormancy and slower germination might be a strategy to reduce the risk of germination in new, unfavourable habitats. In contrast, less dormant and fast-germinating peripheral achenes with a lower dispersal capability remain near the mother plant and thus can replace it in the following spring.

Survival, germinability and fungal colonization of dimorphic achenes of the annual weedGalinsoga parvifloraburied in the soil

SummaryGalinsoga parviflora(Asteraceae) is a widespread annual weed that produces capitula containing both disc achenes with pappus and ray achenes without pappus. The latter are dispersed within a winged structure formed by capitulum bracts. We buried both achene types in an agricultural soil to be exhumed regularly to investigate whether they differed in survival, germinability and fungal colonization in the soil seedbank. Ray achenes remained viable longer than disc achenes, with different loss rates for the achene types. In both cases, loss rate was very high for the first 10 months, and then loss rates for the achene types tended to level off and even converge by the end of the observation period. The percentage of remaining viable disc achenes was alwaysc.10–15% lower than that of the ray achenes, except on the first and last sampling dates. Germination percentages for viable ray and disc achenes before burial and after exhumation were not statistically different during most of the observation period, except for that between 100 and 200 days of burial (mid‐autumn–winter). There, germination of disc achenes reached 26.4% after 126 days of burial, whereas germination of ray achenes was close to zero. In addition, after 779 days, the germinability of ray achenes was 21.3%, whereas it was 0% for disc achenes. Surface‐disinfected viable disc and ray achenes had low infection rates (0–15%) for both fungi and bacteria during the observation period. The fungal and bacterial infection peaks for both achene types were asynchronous. In general, the expected difference (lower infection rate for ray achenes) was not observed for fungal or bacterial infection.

The achene pappi and elaisomes of Centaurea L.: Dispersal and germination in some Italian species

The presence/absence of pappi and elaiosomes, types of elaiosome reserves, and germination were studied in 38 Italian taxa belonging to different sections of the genus Centaurea L. Achenes with pappus, with elaiosome, with pappus and elaiosome, and without pappus and elaiosome were found. Many species had elaiosomes containing lipids, which were sometimes associated with proteins and/or starch; in sporadic cases, only proteins were found. Subspecies of the same genus and specimens of the same species from different localities were sometimes diversified with regard to pappus and elaiosome. Germination experiments were carried out in 16 taxa using intact achenes and achenes with elaiosomes removed. In eight taxa, no statistically significant difference was found between germination of achenes with and without elaiosomes. Seeds of C. aeolica, C. aplolepa subsp. ligustica, C. leucophaea, and C. veneris without elaiosome germinated, sometimes in a low percentage, but better than seeds with elaiosome intact.

Soluble sugars in light-sensitive Grand Rapids lettuce seeds treated with red light, gibberellic acid and a plant-derived smoke extract

The escape time for far-red light reversal of red light induced germination of light-sensitive Grand Rapids lettuce seeds was determined to be 5h. Levels of soluble sugars were determined during the first 8 h of imbibition in seeds treated with red light, gibberellic acid and an aqueous smoke extract all of which stimulate germination of the photoblastic achenes in the dark. Sucrose was the main reserve sugar in the dry seeds; glucose, fructose and rhamnose were also detected. An increase in sucrose was detected 2 h after the start of imbibition, lasting 13h. This increase occurred in all treatments, including dark-imbibed control seeds. This suggests that breaking of dormancy is not totally dependent on utilisation of soluble sugars.

The role of dimorphic achenes in the biology of the annual weed Leontodon longirrostris

Various aspects of the reproductive biology and dimorphism of achenes from the annual heterocarpic weed Leontodon longirrostris (Finch & PD Sell) Talavera were studied in the laboratory and field. The species is self‐incompatible, pollinated by generalist insects and produces two different types of achene in the capitula: peripheral and central achenes. Peripheral achenes are heavier (1.63 mg) and exhibit virtually no pappus and short‐range dispersal, whereas central achenes are lighter (0.45 mg), possess a well‐developed pappus and are produced in greater numbers. The morphological differences between the two types of achene result in differences not only in dispersal, but also in germination, seedling vigour and the ability of seedlings to emerge from different achene burial depths. Central achenes germinate more rapidly and in higher proportions under a broad spectrum of conditions. On the other hand, germination in peripheral achenes is much more restricted, partly as a result of their thick pericarp; a high proportion of this type of achene does not germinate and remains in a dormant state on the ground, forming a temporary seedbank. Because of the increased size of the embryo, seedlings from peripheral achenes can emerge from greater depths and are initially more vigorous than those from central achenes. Central achenes represent a strategy that facilitates settling in new areas; peripheral achenes represent a strategy that ensures in situ persistence. These biological characteristics are advantageous for colonizing species.

Phytochrome controls achene germination in Bidens pilosa L. (Asteraceae) by very low fluence response

Achene without ornament of the tegument were light insensitive with germination under all tested light conditions. Achene with verrucose ornament of the tegument presented low germination under darkness and high germination under light conditions. By pre-incubation at 36° C for remotion of pre-existing Pfr and by comparison of results of counting of dark germinating achenes at the end of experiment and daily under dim green safe light (0.001mumol m-2 s-1 nm-1) we concluded that germination was controlled by phytochrome through very low fluence response.

WATER ABSORPTION BY MUCILAGINOUS ACHENES OF ARTEMISIA MONOSPERMA: FLOATING AND GERMINATION AS AFFECTED BY SALT CONCENTRATIONS

Artemisia monospermais a dominant perennial desert shrub occurring in active sand dunes and stabilized sand fields. A cyanobacterial crust develops on stabilized sand and, as a result, runoff water may occur after rains. The mucilaginous achenes may float on the runoff water and disperse into depressions or cracks.In these experiments, almost half of the achenes remained afloat on distilled water for 3 days and on different concentrations of salt solutions, more achenes remained afloat for longer. High concentrations of salt inhibit germination. NO,” may influence achene germination on cyanobacterial sand crust. Mucilaginous achenes absorb water within about 60 min, and after 120 min reach their water capacity. The achenes from which the mucilage has been removed can float for a longer period and germinate earlier than intact ones. Seedlings that developed from achenes with mucilage had greater vigor than those without.The ecological significances of mucilaginous achenes is discussed.

バラの種子（痩果）の発芽に対する温度の影響

バラの種子（痩果）の発芽に対する温度の影響

Role of Temperature in Dormancy Break and/or Germination of Autumn‐maturing Achenes of Eight Perennial Asteraceae from Texas, U.S.A.

Abstract Achenes of Aster ericoides, Baccharis neglecta, Brickellia dentata, Eupatorium havavense, Gymnosperma glutinosum, Helianthus maximilianii, Verbesina virginica and Viguiera dentata were collected at maturity in autumn in southcentral Texas and tested for germination over a range of thermoperiods (15/6, 20/10, 25/15, 30/15 and 35/20°C)simulating those in the habitat from September to May. Achenes of Aster, Baccharis, Brickellia, Eupatorium and Gymnosperma were nondormant, thus cold stratification did not change the range of thermoperiods over which they germinated. However, cold stratification increased the percentage of Brickellia achenes germinating at 15/6 and 20/10°C. Achenes of Helianthus, Verbesina and Viguiera were conditionally dormant at maturity, and cold stratification decreased the minimum thermoperiod for germination of Helianthus, Verbesina and Viguiera achenes to 15/6°C and increased the maximum thermoperiod for germination of Verbesina achenes to 35/20°C.Thus, achenes of Helianthus and Viguiera exhibited a type 2 germination response pattern during dormancy break and those of Verbesina a type 3. Germination percentages of Helianthus, Verbesina and Viguiera achenes increased during 6–8 wk of incubation at 20/10 and 15/60°C, which simulate habitat temperatures from November to February. Therefore, winter field temperatures are favorable for dormancy loss as well as for germination. If the soil is too dry for germination of conditionally‐dormant achenes in autumn, a reduction of the minimum temperature for germination during winter would allow them to germinate in midto late winter, several months before the onset of the high temperature and drought conditions of early summer.

Achene dimorphism in Bidens pilosa L. (Asteraceae) as determined by germination test

The germination of achenes of Bidens pilosa L. was analyzed during the life span of the mother plant. Decrease in the range of achene size was monitored until the senescence of the mother plant when the shortest achenes were harvested. The analysis of the germination percentage confirmed the presence of two distinct classes, formerly defined as short and long ones. Because length can not be used for the separation of those classes, the morphological characteristics of the tegument, specially of the ornament must be used for separation of the achenes with verrucose tegument (formerly named as short achenes) and achenes without ornament of the tegument (formerly named as long achenes). The achenes with verrucose tegument presented dormancy and light sensitivity, and the achenes without ornament of the tegument presented no dormancy and no light sensitivity for the germination process.

Seed Maturity, Storage Time and Temperature, and Media Treatment Effects on Germination of Two Wild Sunflowers

AbstractDormancy in achenes (seeds) of wild sunflower (Helianthus) species ensures that they do not germinate in temperate climates until conditions are optimal for seedling survival. However, high achene dormancy results in low germination of achenes, precluding utilization of many wild species for domestic purposes. Interest in the use of native Helianthus species for domestic purpose such as low‐maintenance ornamentals, revegetation, cut flowers, and genetic improvement of cultivated sunflower has recently increased. The objectives of this study were to evaluate germination media to overcome dormancy and enhance germination of two annual species, H. annuus L. and H. petiolaris Nutt., and to evaluate the influence of achene maturity and storage time and temperature on germination. A 1 mM gibberellic acid (GA3) medium was the most effective stimulant in laboratory tests for enhancing germination of H. annuus. Germination of treated achenes was 81%, compared with 38% for the control. Germination of H. petiolaris achenes was 60% with the 1 mM GA3 medium, compared with 9% for the water control. This GA3 medium enhanced germination regardless of achene maturity, storage time, or storage temperature. When averaged over all media, achene maturities, and storage times and temperatures, H. annuus had a germination of 41%, compared with only 21% for H. petiolaris. The age of the achenes at harvest influenced germination. Achenes harvested 20 d after flowering generally had greater germination than those harvested 40 d after flowering, especially for H. petiolaris. Storage time and temperature could not overcome the dormancy imposed prior to germination in either species. Utilization of germination media to enhance germination of wild Helianthus species will facilitate their use for domestic purposes.

Effect of light and temperature on germination of dimorphic achenes of Centautea solstitialis in California

Centciurea solstitialis L. is a winter annual weed of Eurasian origin that is widespread in the western United States. Capitula produce dimorphic achenes that are dispersed at different times. Factors investigated in the laboratory that affected germination were light, temperature, achene type (plumed and nonplumed), collection date, dormancy, and storage. The presence of large interactions among the factors affecting germination was constant throughout these studies. Although some germination occurred in the dark, a daily (8 h light: 16 h dark) photoperiod of white light produced higher germination percentages in both fresh and stored achenes. Even a single brief (10-min) exposure to light was almost comparable with a daily 8-h photoperiod. Maximum germination of nearly 100% was achieved in light under constant temperatures of 10, 15, and 20 °C and alternating temperatures of 15:5 and 20:10 °C. Broadening of temperature optima related to afterripening occurred for July achenes stored for 2 months and August-fresh achenes under alternating temperatures. Germination differences between achene types were more prevalent under dark than under light conditions. In general, germination of plumed achenes was higher than that of nonplumed achenes. In darkness, nonplumed achenes showed a shift in optimum germination temperature (from 15 to 20 °C) from July to September. Germination of nonplumed achenes in intact capitula was never greater than 21%, regardless of time of collection, because of the presence of the involucral bracts. Key words: yellow starthistle, germination, light, temperature, dimorphic achenes.

Optimization of the Colchicine Dropper Technique for Use in Vitro with Fragaria vesca

Previous research has optimized the colchicine dropper technique for chromosome doubling under greenhouse conditions. In recent years, in vitro germination of cut strawberry achenes has greatly increased germination rates. Combining the two techniques would be especially useful when chromosome doubling is desired for interspecific hybridization. Fragaria vesca was chosen for initial study. Treatments included colchicine levels of 0%, 1%, 2%, 3%, 4%, or 5% (w/v); exposure time to colchicine was from 6 to 16 to 26 hours; application was at the cotyledon stage or after the first true leaf formed; presence or absence of 3 g activated charcoal/liter; and presence or absence of DMSO. Media consisted of MS salts and vitamins, 30 g sucrose/liter, and 2.5 g phytogel/liter. Charcoal enhanced upward growth of seedlings, thus allowing better placement of colchicine droplets. Reduced exposure time and application at the first true-leaf stage allowed higher levels of colchicine to be used without greatly reducing the vigor of treated seedlings.

Intra-specific variation in the inhibitory effects of Thymus vulgaris (Labiatae) monoterpenes on seed germination.

The ecological role of plant secondary compounds has received a great deal of attention yet little is known regarding variation in the ecological significance of different compounds produced by a single species. This is particularly pertinent to species where variation in compound presence is under genetic control. In this study we have quantified variation in the inhibitory effects of the six dominant monoterpene oils produced by different genotypes (or chemotypes) of Thymus vulgaris on achene germination of an associated species (Brachypodium phoenicoides), and seeds of T. vulgaris itself, in controlled experimental conditions. The experiments involved the germination of seeds of the two species with crushed leaves or pure essences of the six chemotypes, i.e. four experimental trials. A significant inhibitory effect against B. phoenicoides was found for both crushed leaves and the range of concentrations of pure oils used in the trial. The two phenolic compounds had a greater effect than the non-phenolic leaves and pure oils. The significant differences between non-phenols and the controls declined faster over time for crushed leaves and low concentrations of the pure essences than did that between the phenolics and the controls. There was a significant inhibitory effect against the germination of T. vulgaris seeds for the crushed leaves and the pure oils, although the contrast between the non-phenols and the phenols was not significant. The effect of the different oils varied depending on the seed source of the thyme seeds used in the trial. This is suggested to be due to differences in the rates of outcrossing among the sampled populations. The effects of the oils on the associated species, B. phoenicoides, were not found to be greater than their effects on the germination of thyme seeds. The results are discussed in the context of a potential role for such inhibitory effects in relation to the onset of rainfall and suitable germination conditions.

Germination Ecology of Bidens laevis (Asteraceae) from a Tidal Freshwater Wetland

LECK, M. A. (Department of Biology, Rider College, Lawrenceville, NJ 08648-3599), C. C. BASKIN AND J. M. BAsKiN (School of Biological Sciences, University of Kentucky, Lexington, KY 40506-0225). Germination ecology of Bidens laevis (Asteraceae) from a tidal freshwater wetland. Bull. Torrey Bot. Club 121: 230-239. 1994.-Eight or more weeks of cold stratification (5?C) were required to break dormancy in achenes of Bidens laevis (L.) BSP from a tidal freshwater wetland. When achenes began to come out of dormancy, they germinated to 50% first at 35/20?C, and then with additional stratification the minimum temperature for 50% germination decreased to 1 5/6?C. Germination of stratified achenes was inhibited by darkness and was completely prevented by hypoxia (inundation in closedjars). Seeds inundated in openjars and those in Petri dishes, however, germinated to > 80%. Germination declined sharply with depth of burial (0, 1, and 5 cm). Moisture regime (drained, saturated, and inundated) also significantly affected germination, but afterripening condition (cold greenhouse or 5?C) altered the effect. Interaction between depth of burial and moisture regime was significant (P 1 yr) following winter afterripening of achenes in the field.

Studies on achene germination, transplantability, salinity tolerance, and cultivation of gumweed ( Grindelia camporum) in hot and semi-arid conditions

The study reports achene germination under varying laboratory conditions, transplantability, survival of seedlings in saline soils, and a field cultivation trial of Grindelia camporum (gumweed) in a semi-arid and hot climate. Achenes placed under a thin layer of soil, on wet filter paper, or in water, at ambient temperature and a diffuse daylight/night cycle germinated at 75%, 69% and 65% respectively. In total dark at ambient temperature compared with 8°C, the achene germination in water was 41% and 48%, respectively. During the 2-step procedure of a cool pretreatment at 8°C in the dark for 4 days followed by a shift to ambient temperature and diffuse daylight/night cycle, however, germination rose to 74%. Achenes germinated in water or on wet filter paper survived well when transplanted to soil whereas those germinated under a thin layer of soil, when uprooted, did not withstand transplantation. Survival of seedlings in saline soils having electrical conductivity of 4, 8, 12 and 16 mmho/cm was, respectively, 31%, 18%, 7% and zero as compared with 91% in the normal soil (3 mmho/cm). During the growing season of 363 days, two crops were harvested yielding 1.36 kg m −2 year −1 biomass and 128 g m −2 year −1 crude resin.