Embryo Development in Ripe Seeds of Eranthis hiemalis and its Relation to Gibberellic Acid

The ripe seeds of Eranthis hiemalis (L.) Salisb., the winter aconite, contain undeveloped embryos. At 20–25°C the embryos grow only little, and the seeds do not germinate. Rapid embryo development starts if the seeds, after 3 weeks of “after-ripening” at 20–25°C, are placed at low temperature, 3–4°C; germination then takes place after 2–3 months, Embryo development without germination occurs when the seeds are placed in gibberellic acid solutions at 20–25°C. Embryo development is inhibited at low temperature by the specific inhibitor of gibberellin biosynthesis, 2-chlorethyl cholin chloride, but is restored by the simultaneous addition of gibberellic acid. It is suggested that one early effect of the cold is to bring about a synthesis of gibberellin.     

Influence of an abscisic acid (ABA) seed coating on seed germination rate and timing of Bluebunch Wheatgrass

Semi‐arid rangeland degradation is a reoccurring issue throughout the world. In the Great Basin of North America, seeds sown in the fall to restore degraded sagebrush (Artemisia spp.) steppe plant communities may experience high mortality in winter due to exposure of seedlings to freezing temperatures and other stressors. Delaying germination until early spring when conditions are more suitable for growth may increase survival. We evaluated the use of BioNik? (Valent BioSciences LLC) abscisic acid (ABA) to delay germination of bluebunch wheatgrass (Pseudoroegneria spicata). Seed was either left untreated or coated at five separate rates of ABA ranging from 0.25 to 6.0 g 100 g^?1 of seed. Seeds were incubated at five separate constant temperatures from 5 to 25°C. From the resultant germination data, we developed quadratic thermal accumulation models for each treatment and applied them to 4 years of historic soil moisture and temperature data across six sagebrush steppe sites to predict germination timing. Total germination percentage remained similar across all temperatures except at 25°C, where high ABA rates had slightly lower values. All ABA doses delayed germination, with the greatest delays at 5–10°C. For example, the time required for 50% of the seeds to germinate at 5°C was increased by 16–46 d, depending on the amount of ABA applied. Seed germination models predicted that the majority of untreated seed would germinate 5–11 weeks after a 15 October simulated planting date. In contrast, seeds treated with ABA were predicted to delay germination to late winter or early spring. These results indicate that ABA coatings may delay germination of fall planted seed until conditions are more suitable for plant survival and growth.     

The ecology of germination and reproduction of less frequent and vanishing species of the Czechoslovak flora III.Hesperis tristis L.

The ecology of seed germination was examined in air-conditioned boxes in the laboratory, and the sprouting conditions of seeds were investigated in an experimental plot at Pr?honice. It was found that the seeds showed no marked dormancy, but that by stratification or putting of seeds into cool soil the speed and abundance of germination was enlarged, especially at low temperatures. The optimum temperatures for germinating are 10/25–30 °C and 15°C (see the table). At the temperature of 3 °C the seeds did not germinate. The sprouting of seeds which got into the soil at the end of summer or at the beginning of autumn goes off mostly from October to November and again in spring, about the middle of April. The young plants with one pair of true leaves for the most part hibernate. In natural conditions this species reproduced only in the generative way, by seeds, in laboratory conditions the possibility of vegetative propagation by cuttings is also reported. The main way of spreading is by anemochory (steppe runners).     

Seed germination at different temperatures and seedling emergence at different depths of Rhamnus spp

Rhamnus alaternus and R. ludovici-salvatoris, two Mediterranean shrubs with different geographic distributions, have shown important differences in seedling recruitment capacity. The objectives of this work were to determine the ability of these species to germinate seeds under different temperature ranges, as well as the capacity of seedlings to emerge from different burial depths, in order to better understand their regeneration processes. Two different experiments were performed. In the first one, seed germination was studied in Petri dishes and in the dark at different temperature regimes: a) 5–15°C, b) 10–20°C and c) 15–25°C (12h/12h). In the second experiment, seedling emergence capacity from different burial depths (0.5, 2 and 5 cm) was tested. R. ludovici-salvatoris showed a significantly higher final germination rates, a lower dormancy period, and average time response at 10–20°C than at other temperature ranges, although differences were much greater when seeds were subjected to the 5–15°C temperature regime. By contrast, R. alaternus did not show significant differences between treatments (5–15°C and 10–20°C) in germination behavior. Seedling emergence of both species was lower and slower when seeds were buried at 5 cm. However, R. ludovici-salvatoris always showed a lower seedling emergence capacity than R. alaternus at any burial depth. The low ability of R. ludovici-salvatoris to germinate seeds and emerge between 5–15°C, even from shallow depths, is discussed in relation to its low regeneration capacity and declining geographic distribution.     

Seed dormancy-breaking and germination requirements ofDrosera anglica,an insectivorous species of the Northern Hemisphere

Seeds of Drosera anglica collected in Sweden were dormant at maturity in late summer, and dormancy break occurred during cold stratification. Stratified seeds required light for germination, but light had to be given after temperatures were high enough to be favorable for germination. Seeds stratified in darkness at 5/1 °C and incubated in light at 12/12 h daily temperature regimes of 15/6, 20/10 and 25/15 °C germinated slower and to a significantly lower percentage at each temperature regime than those stratified in light and incubated in light. Length of the stratification period required before seeds would germinate to high percentages depended on (1) whether seeds were in light or in darkness during stratification and during the subsequent incubation period, and (2) the temperature regime during incubation. Seeds collected in 1999 germinated to 4, 24 and 92 % in light at 15/6, 20/10 and 25/15 °C, respectively, after 2 weeks of stratification in light. Seeds stratified in light for 18 weeks and incubated in light at 15/6, 20/10 and 25/15 °C germinated to 87, 95 and 100 %, respectively, while those stratified in darkness for 18 weeks and incubated in light germinated to 6, 82 and 91 %, respectively. Seeds collected from the same site in 1998 and 1999, stratified in light at 5/1 °C and incubated in light at 15/6 °C germinated to 22 and 87 %, respectively, indicating year-to-year variation in degree of dormancy. As dormancy break occurred, the minimum temperature for germination decreased. Thus, seed dormancy is broken in nature by cold stratification during winter, and by spring, seeds are capable of germinating at low habitat temperatures, if they are exposed to light.     

The germination characteristics of <Emphasis Type="Italic">Scrophularia marilandica</Emphasis> L. (Scrophulariaceae) seeds

Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA₃ and KNO₃). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO_3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10⁻⁴ M GA₃ caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.     

Effects of temperature, light, storage conditions, sowing time, and burial depth on the seed germination of Cardiocrinum cordatum var. glehnii (Liliaceae)

In this study, we conducted experiments to accumulate practical information on the propagation and establishment of a population of Cardiocrinum cordatum var. glehnii by seed sowing. C. cordatum var. glehnii seeds require approximately 19 months from seed dispersal to cotyledon emergence in the field. However, the period from seed dispersal to radicle emergence was shortened to approximately 7–8 months by the temperature transition of 25/15°C (60 days) → 15/5°C (30 days) → 0°C (120 days) → 15/5°C (i.e., 15/5°C represents alternating temperature treatment wherein the seeds were placed at 15°C for 12 h during the day and then at 5°C for 12 h during the night). More than 90% of the seeds, which were stored dry at 5°C for 12 months and sown in pots in the field, showed cotyledon emergence, whereas in seeds stored dry at 25°C, dry at room temperature, and non-dry at room temperature, cotyledon emergence was decreased by less than 1%. More than 88% of the seeds that were stored dry at 5°C and sown in the field in October 2002 immediately after collecting, November, and from April to July 2003 showed cotyledon emergence in spring 2004. However, seeds sown in August, September, and October 2003 showed cotyledon emergences of 57.6%, 0%, and 0% in spring 2004, respectively. Seeds collected in October 2002 and sown until July 2003 in the field received adequate high temperature in summer, moderate temperature in autumn, and cold temperature in winter; therefore, the percentage of cotyledon emergence was high in spring 2004. On the other hand, seeds sown in August 2003 or later could not receive enough high temperature; thus, cotyledons emerged from only a few seeds.     

Response of Amaranthus retroflexus L. seeds to gibberellic acid, ethylene and abscisic acid depending on duration of stratification and burial

Freshly harvested, dormant seeds of Amaranthus retroflexus were unable to germinate at 25 and 35 °C. To release their dormancy at the above temperatures, the seeds were stratified at a constant temperature (4 °C) under laboratory conditions or at fluctuating temperatures in soil or by outdoor burial in soil. Fully dormant, or seeds stratified or buried (2006/2007 and 2007/2008) for various periods were treated with exogenous gibberellic acid (GA₃), ethephon and abscisic acid (ABA). Likewise, the effects of these regulators, applied during stratification, on seed germination were determined. The results indicate that A. retroflexus seed dormancy can be released either by stratification or by autumn–winter burial. The effect of GA₃ and ethylene, liberated from ethephon, applied after various periods of stratification or during stratification, depends on dormancy level. GA₃ did not affect or only slightly stimulated the germination of non-stratified, fully dormant seeds at 25 and 35 °C respectively. Ethylene increased germination at both temperatures. Seed response to GA₃ and ethylene at 25 °C was increased when dormancy was partially removed by stratification at constant or fluctuating temperatures or autumn–winter burial. The response to GA₃ and ethylene increased with increasing time of stratification. The presence of GA₃ and ethephon during stratification may stimulate germination at 35 °C. Thus, both GA₃ and ethylene can partially substitute the requirement for stratification or autumn–winter burial. Both hormones may also stimulate germination of secondary dormant seeds, exhumed in September. The response to ABA decreased in parallel with an increasing time of stratification and burial up to May 2007 or March 2008. Endogenous GA_n, ethylene and ABA may be involved in the control of dormancy state and germination of A. retroflexus. It is possible that releasing dormancy by stratification or partial burial is associated with changes in ABA/GA and ethylene balance and/or sensitivity to these hormones.     

PHYSIOLOGICAL ECOLOGY OF GERMINATION OF VIOLA RAFINESQUII

Seeds of the winter annual Viola rafinesquii Greene exhibit true dormancy at the time of maturity and dispersal in mid to late spring. During the summer rest period the seeds pass from a state of true dormancy to one of relative dormancy and finally to what may be called a state of complete nondormancy. As the seeds enter relative dormancy they will germinate mostly at relatively low temperatures (10, 15, 15/6, and 20/10 C), but as after-ripening continues they gain the ability also to germinate at higher temperatures (20, 25, and 30/15 C). During June, July, and August seeds will not germinate at field temperatures even if kept continuously moist. But by September and October seeds may germinate to high percentages over a wide range of temperatures, including September and October field temperatures. This pattern of germination responses, involving breaking of true dormancy and widening of the temperature range for germination during relative dormancy, appears to be an adaptation of the species to a hot, dry season. Seeds of V. rafinesquii stored on continuously wet soil (field capacity) or on soil that was alternately wet and dried during the summer did not after-ripen at low temperatures (10, 15, 15/6, and 20/10 C) but did after-ripen fully at high temperatures (20, 25, 30/15, and 35/20 C). Thus, the high temperatures that V. rafinesquii “avoids” by passing the summer in the dormant seed stage actually are required to break seed dormancy and, therefore, are essential for completion of its life cycle.     

Physiological dormancy in seeds of tropical montane woody species in Hawai`i

Worldwide, there is relatively little information on seed dormancy and germination of tropical montane species. Our aim was to help fill this knowledge gap by conducting seed dormancy/germination studies on woody species from this vegetation zone in Hawai`i. All species had water-permeable seeds with a fully developed embryo. Seeds of 29 species (23 genera) were incubated in light/dark at 15/6, 20/10 and 25/15°C and germination monitored at 2-week intervals for 16–128 weeks. Seeds of Chenopodium oahuense, Dubautia menziesii and Silene lanceolata were non-dormant (ND) and those of 26 other species had physiological dormancy (PD); 10 of the 26 species had conditional PD. The optimum germination temperature regime(s) was (were) 25/15°C, 17 species; 25/10 and 20/10°C, 2; 20/10°C, 6; 20/10 and 15/6°C, 2; and 15/6°C, 2. Worldwide, PD in the woody genera included in our study is more common than ND. In addition to its contribution to the world biogeography of seed dormancy/germination, this study will be useful to conservation biologists who need to germinate seeds of tropical montane species.     

Seed maturation time influences the germination requirements of perennial grasses in desert climate of Arabian Gulf

Qatar has a dry, subtropical desert climate, with minimum annual rainfall and intensely hot and humid summers. Using indigenous grass, those adapted to local conditions have the potential to be used for fodder and can also be used for restoration or rehabilitation of degraded rangelands. Chloris virgata, Coelachyrum brevifolium and Cenchrus ciliaris bloom twice a year from April to May (summer) and September to October (winter) under the nursery condition. Therefore, it is important to understand, how seeds produced in different seasons affect the dormancy as well as germination of these species. Seeds of C. virgata, C. brevifolium and C. ciliaris, three desert grasses, were collected from the plants growing on Shahniya nursery in two different seasons, summer (May) and winter (October). The seeds collected in May (summer) were stored up to winter. However seeds collected in October (winter) were immediately used for experiment. We compared the germination potential of seeds that matured in different season at different alternating temperatures at 15/25, 20/30 and 25/35 °C. Lower temperatures correspond to the dark period, while higher temperatures reflect the light period. Seeds collected in summer season (old seeds) were heavier as compared to seeds collected in winter season (new seeds). Winter seeds of C. virgata seem to be dormant, while summer seeds, germinated well in all the tested temperature regimes. However, C. ciliaris seeds showed opposite trends.     

THE GERMINATION STRATEGY OF OLDFIELD ASTER (ASTER PILOSUS)

At maturity in November, a high percentage of Aster pilosus Willd. seeds germinated in light at high temperatures (30/15, 35/20 and 40/25 C). Stratification during winter lowered the temperature requirement for germination, and high percentages of germination were obtained in light at 15/6 and 20/10 C., as well as at 30/15, 35/20 and 40/25 C. Stratification in darkness was completely ineffective, but stratification in light was partially effective in overcoming the light requirement for germination. Inability of seeds to germinate at low temperatures prevents germination after dispersal in late autumn and winter, when freezing temperatures could kill the seedlings. The lowering of the temperature requirement for germination during winter stratification allows the seeds to germinate and the resulting vegetative rosettes to become well established before the onset of the periodic summer droughts that occur in habitats occupied by A. pilosus.     

GERMINATION ECOLOGY OF PHACELIA DUBIA VAR. DUBIA IN TENNESSEE GLADES

The germination characteristics of a population of the winter annual Phacelia dubia (L.) Trel. var. dubia from the middle Tennessee cedar glades were investigated in an attempt to define the factor(s) regulating germination in nature. Factors considered were changes in physiological response of the seeds (after-ripening), temperature, age, light and darkness, and soil moisture. At seed dispersal (late May to early June), approximately 50 % of the seeds were non-dormant but, would germinate only at low temperatures (10–15 C). As the seeds aged from June to September, there was an increase in rate and total percent of germination at 10, 15, and 20 C, and the maximum temperature for germination increased to 25 C. Little or no germination occurred at the June, July, and August temperatures in 0- to 2-month-old seeds, even in seeds on soil that was kept continuously moist during this 3-month period. At the September, October, and November temperatures 3- to 5-month-old seeds germinated to high percentages. In all experiments seeds germinated better at a 14-hr photoperiod than in constant darkness. Inability of 0- to 2-month-old seeds to germinate at high summer temperatures allows P. dubia dubia to pass the dry summer in the seed stage, while increase in optimum and maximum temperatures for germination during the summer permits seeds to germinate in late summer and early fall when conditions are favorable for seedling survival and eventual maturation.     

Effects of temperature and light on germination and early seedling development of the pine pink orchid (Bletia purpurea)

Orchid seed physiology is a poorly understood phenomenon owing to an emphasis on production and the challenges associated with propagating orchids from minute seed. We investigated the role of simulated south Florida temperatures and illumination (dark and 12 h photoperiod) in regulating germination and seedling development using asymbiotic seed germination assays of Bletia purpurea. Our objectives were to determine whether in situ germination is limited by seasonal temperatures and to determine whether temperature alters responses to illumination. Bletia purpurea seeds were able to germinate to > 90% under all treatments. The greatest germination after 3 weeks was observed at 29/19°C under continual darkness and at 25°C under dark and illuminated conditions. The slowest germination was observed at simulated winter temperatures (22/11°C). Illumination initially inhibited germination and development, but resulted in equal or greater development by week six. Germination under 22/11°C was strongly inhibited by illumination, indicating an interaction between temperature and light sensing systems.     

Morphophysiological dormancy in seeds of the ANA grade angiosperm Schisandra arisanensis (Schisandraceae)

We determined the kind of seed dormancy in Schisandra arisanensis, an ANA grade ([A]mborellales [N]ymphaeales [A]ustrobaileyales) angiosperm with medicinal value. Seeds have small underdeveloped embryos, and following seed maturity their length increased approximately 360% before radicle emergence. Germination was delayed 6–8 weeks, and the percentage and rate were much higher at 15/6, 20/10 and 25/15°C than at 30/20°C. For seeds incubated at 5/5°C (8 weeks) → 15/6°C (4 weeks) → 20/10°C (8 weeks) → 25/15°C (12 weeks) → 20/10°C (5 weeks), embryos grew at 15/6°C → 20/10°C, and almost all seeds that germinated (89%) did so at 20/10°C → 25/15°C. When seeds were incubated in a complementary temperature sequence, 25/15°C (12 weeks) → 20/10°C (8 weeks) → 15/6°C (4 weeks) → 5/5°C (9 weeks) → 15/6°C (4 weeks), embryos grew at 25/15°C → 20/10°C. Nearly all seeds that germinated (93%) did so at 25/15°C → 20/10°C and at 15/6°C following 9 weeks at 5/5°C. Based on the temperature requirements for embryo growth and seed germination, seeds of this species have non‐deep simple morphophysiological dormancy (C_1bB).     

Effect of maturation conditions on light and temperature requirements during seed germination of Citrullus colocynthis from the Arabian Desert

• Seed germination of Citrullus colocynthis, as in many other species of Cucurbitaceae, is inhibited by light, particularly at low temperatures. Germination response to light and temperature has been attributed to day length and temperature during seed maturation. This study assessed the effects of these factors on the germination response of C. colocynthis to temperature and light quality.
• Ripe fruits were collected from natural habitats during December and February and germinated at three temperatures (15/25, 20/30 and 25/35 °C) in five light treatments (dark, white light and Red:Far Red (R:FR) ratios of 0.30, 0.87 and 1.19). Additionally, unripe fruits were also collected from natural habitats and completed their maturation in growth chambers under different day lengths (6, 16 and 24 h of darkness) at 10/20 °C, and in darkness at both 10/20 °C and 25/35 °C. Mature seeds of the different treatments were germinated in the same five light treatments at 15/25 °C.
• Germination was significantly higher in the dark than that in any light treatment. Seeds matured at higher temperatures (i.e. seeds from the December collection and those matured at 25/35 °C) had significantly higher germination than those matured at lower temperatures (i.e. seeds from the February collection and those matured at 10/20 °C). Dark germination was significantly higher for the December collection than for the February collection. Seeds of the two collections germinated in the dark only at 15/25 °C. However, seeds matured in a growth chamber at 10/20 °C in darkness germinated at 15/25 °C in all light treatments, except for the R:FR ratio 0.30. Seeds of the different treatments failed to germinate in FR‐rich light.
• This study demonstrates that both temperature and day length during seed maturation play significant roles in the germination response of C. colocynthis. Additionally, the dark requirement for germination is likely beneficial for species with the larger seeds, such as C. colocynthis, which produce bigger seedlings that are able to emerge from deep soils and are competitively superior under dense vegetation and resource‐limited conditions.

     

Common Leafspot of Alfalfa: Ascospore Germination and Disease Development in Relation to Moisture and Temperature

In a moist chamber Pseudopeziza medicaginis ascospores infected alfalfa (Medi sativa L.) moderately to abundantly within 6–10 h at 10–20 °C and within a longer time-span outside this temperature range. Approximate limits of the range were 2.5 and 28 °C; no infection took place at 30 °C. At 14°C ascospores infected alfalfa abundantly at 98 %relative humidity (RH) and above, moderately at 97%, sparsely at 95 and 96%, but not at 94% and below. Ascospores were hydrophilic, germinating best at or near 100%, RH but did not germinate at or below 93 % RH. After infection was established, tiny leafspots became visible within 6–7 days at constant temperatures of 15–25°, 10 days of 10°C, 13 days of 5 °C, and 25 days of 2.5 °C. They failed to develop into normal size spots within 4 weeks at constant temperatures near 30 °C, or near 10 °C and lower. Temporary exposure of incipiently diseased plants 1–6 days to 30–38 °C adversely affected subsequent leafspot development at 20–24°C. Inhibition depended on temperature and on the extent of post-infection disease development.     

Seed germination ecology of Viola calaminaria,an endangered metallophyte with a narrow distribution

Viola calaminaria is an endangered metallophyte endemic to a small area close to the border between Belgium, Germany and the Netherlands, where it grows on rock outcrops rich in heavy metals (zinc, lead and cadmium). Because V. calaminaria reproduces mainly by seeds, it is of crucial importance to understand its germination requirements. Germination percentage and speed at constant (11–25°C) and alternating (23/09°C) temperatures were investigated in five large populations. Germination percentage was positively correlated to seed weight. Germination was low (<25%) at 11 and 16°C, intermediate (around 65%) between 20 and 25°C and the highest (93%) at the alternating temperature regime (23/09°C). V. calaminaria is a slow germinator requiring 41 days on average to germinate at 23/09°C and considerably more at 20 to 25°C (105 days on average). Our results also highlighted that the species is desiccation tolerant and can therefore be safely conserved under standard seed bank conditions.