Seed germination requirements of Trembleya laniflora (Melastomataceae), an endemic species from neotropical montane rocky savannas

Trembleya laniflora is an endemic shrub from neotropical montane rocky savannas of southeastern Brazil. It has been indicated as a potential candidate for ecological restoration of abandoned iron‐ore mines due to heavy metal accumulation. Here, we evaluated the seed germination requirements of T. laniflora. Seeds collected in 2005 and 2008 were set to germinate under a broad range of temperature and light conditions. Seed viability was estimated by dissecting seeds under a dissecting microscope for embryo presence/absence. Seeds were photoblastic and optimum temperature range was 20–25°C, coinciding with the onset of the rainy season. Seeds were viable after 42 months of storage, which together with small seeds that easily get buried and light requirement for germination suggest formation of soil seed banks. Except the large fraction of embryoless seeds, almost all tested seeds germinated when incubated under light conditions; therefore, T. laniflora should be regarded to have nondormant seeds. Easiness of burial resulting from small seed size and positive photoblastism may both contribute to incorporation into soil seed banks. Our data suggest that the long‐term storage of T. laniflora seeds provides a useful strategy for plant reintroduction.     

Germination Response Patterns during Dormancy Loss in Achenes of Six Perennial Asteraceae from Texas, USA

Abstract When subjected to simulated habitat temperatures, achenes of six perennial Asteraceae from southcentral Texas came out of dormancy during summer. In the early stages of dormancy loss, achenes of Erigeron modestus, Gaillardia suavis and Hymenoxys scaposa germinated (to ≥ 10%) in light at 12/12 hr daily thermoperiods of 15/6, 20/10 and 25/15°C and those of Pinaropappus roseus at 15/6 and 20/10°C. After additional dormancy loss, achenes of these four species also germinated at 30/15 and 35/20°C. Achenes of these four species had a Type 1 germination response pattern, which heretofore has not been reported in perennial Asteraceae. Achenes of Chaptalia nutans first germinated (to ≥ 10%) at 20/10 and 25/15°C and those of Hymenopappus scabiosaeus at 20/10°C, but with further loss of dormancy achenes of both species also germinated at 15/6, 30/15 and 35/20°C. Thus, achenes of these two species had a Type 3 pattern. This is the first report of perennials in any family with a Type 3 response pattern whose seeds come out of dormancy during summer. Presence of annual and perennial Asteraceae with Type 2 in temperate eastern North America and annual and perennial Asteraceae with Type 1 in southcentral Texas causes us to conclude that climate is more important than the type of life cycle in determining the type of germination response pattern.     

Restoring the Victorian Western (Basalt) Plains grassland. 1. Laboratory trials of viability and germination, and the implications for direct seeding

Summary   The Victorian Western (Basalt) Plains grassland is one of Australia's most threatened plant communities. Practitioners using seed for its restoration need to know whether seed can be sown fresh or whether it requires an after-ripening period. This study assessed the viability and germination of freshly harvested wild seed from 64 grassland species indigenous to the Basalt Plains of western Victoria. The seed was collected as part of a broader experiment that examined the potential of direct-sown complex seed mixes for the restoration of grassland communities. The germination of fresh seed at 25°C varied widely between species. Comparisons with tetrazolium viability tests for each species indicated varying levels of dormancy within the species pool. Germination separated into three broad responses at day 28. One-third of the species failed to germinate, one-third germinated at 1% to 50% and the remaining species germinated between 51% and 100%. Therefore, if the aim of a sowing was the rapid and synchronous establishment of most of the sown species, the use of fresh seed in restoration could be problematic. After 3 months of dry storage, eight species were re-tested for germination. Each of the selected species had shown high viability but low initial germination. Only two species significantly increased their total germination at 25°C. The annual species, Triptilodiscus pygmaeus , increased its total germination from 6% as fresh seed to 99% after dry storage. Testing the viability and germination capacity of freshly harvested seed from a large and diverse sample of native grassland species demonstrated that many of the species were unlikely to germinate rapidly or synchronously when sown in complex seed mixes soon after harvest. This finding has implications for the scheduling and management of restoration projects that rely on the use of such seed.     

The effect of parent plant nutrition on seed size, viability and vigour and on germination of wheat and triticale at different temperatures

Seed was obtained from two adjacent trials of wheat (cv. Avalon) and triticale (cv. Lasko) harvested in 1990. The treatments consisted of factorial combinations of five levels of spring nitrogen (50, 100, 150, 200 and 250 kg N ha^-1) with fungicide treatments designed to control foliar diseases. Seed was graded by size into different fractions. Application of foliar fungicides to the parent plant increased the proportion of large seed in wheat but not in triticale. Fungicide application had no effect on seed vigour (quantified as the value of K; after controlled deterioration), final germination, median germination time (t₅₀) or rate of germination. Parent plant nutrition altered the proportions of seed in different size categories in triticale and wheat. In laboratory germination tests, final germination of wheat increased with seed size. Large (> 3.0 mm diameter) wheat seed from plots receiving 50 kg N ha“¹ had a lower final germination than large seed from plots which had received greater amounts of nitrogen, but t₅₀ and K; were similar for all nitrogen levels. In triticale, the higher the seed weight, the higher the final germination, the faster the rate and the higher the Ki. Final germination, t₅₀ and K;, were all positively correlated with the amount of nitrogen received by the parent plants. Parent plant nutrition had no effect on the response to temperature of final germination, t₅₀, or rate of germination for large or small seeds of both wheat and triticale.     

The effect of temperature on sex ratio in the isopod Porcellionides pruinosus: Environmental sex determination or a by-product of cytoplasmic sex determination?

The sex ratios of the progenies of woodlice Porcellionides pruinosus (Crustacea, Isopoda) raised at different temperatures were studied. Females from three French populations sampled in the wild produced highly female-biased broods at 20°C and male-biased broods above 30°C. The effect of high temperature was not due to selective mortality of females. Sex determination was thus sensitive to temperature in P. pruinosus. We also found an interpopulation variability of sex ratio thermosensitivity and a weak inheritance of male-biased sex ratios at high temperatures. Samples taken from a wild population throughout the year showed that while the thermal conditions required for changes in the sex ratio occurred, there was no significant variation in the sex ratio. On the other hand, almost all the females and many males in the four populations studied harboured intracytoplasmic bacteria. These maternally inherited symbionts belong to the genus Wolbachia and are known to possess a feminizing effect. While in other arthropods Wolbachia are destroyed at high temperatures, the symbionts of P. pruinosus were detected by a PCR procedure whatever the rearing temperatures. In light of these results, we propose that the thermosensitivity of sex determination in P. pruinosus could reflect the removal of the cytoplasmic effect on sex determination rather than environmental sex determination sensu stricto. The reduction in the amount of bacteria (but not their entire elimination), or the inhibition of bacterial metabolism, may be responsible for sex ratio variations relating to temperature. The incomplete inheritance of male-biased sex ratios at high temperatures might reflect a selection of thermo-tolerant bacterial strains.     

度胁迫对罂粟种子萌发影响及其活力变化规律的研究

为妥善保存罂粟种质资源及防止种子老化,研究了温度对罂粟种子萌发及种子活力的影响。结果表明:罂粟为高温敏感低温萌发型种子,发芽的适宜温度为10～20℃,最适温度为18℃左右,低于5℃和高于20℃的温度,种子萌发受到抑制;在对其进行丸化包衣时,加热温度应控制在60℃以内,时间应控制在60min以内;在常温库存条件下,罂粟种子活力随贮藏年限的增加而下降,贮藏时间超过五年后,发芽率低于50%,不宜作种用,在作为种质资源保存时,须每隔五年繁殖一次。     

Germination responses of a seed population of Taraxacum officinale Weber to constant temperatures including the supra-optimal range

Abstract The germination responses of a nondormant fraction of a seed population of Taraxacum officinale Weber at constant temperatures in the range 7–34°C were analysed through a time-course study. Maximal percentage germination (approximately 90%) was attained at temperatures 10–18°C, where simple linear relationships were observed between the temperature and the germination rates, i.e. the reciprocals of the time taken to germinate by subpopulations with 20–80% germination. There was a variation in the required ‘thermal times’ (θ) which characterized the linear relationships, the distribution of which could be approximated for the seed population by the following distribution function: where m is the median of the distribution, and A is a shape parameter characterizing the pattern of the distribution. Final percentage germination decreased with increasing temperature from 20 to 32°C, where the final percentage germination vs. temperature plotted on a normal probability scale yielded a straight line, indicating the normality of the distribution of the upper limit temperature in the seed population. The estimated mean and standard deviation were 27.25 ± 3.75°C. The rate of germination for the subpopulation with 20–80% germination also decreased with increases in the temperature from 22 to 30°C. If the relationships between the temperature within this range and the rate for the subpopulations with 20–80% germination were approximated by the regression lines, the negative ‘thermal time’ characterizing the yielded linear relationship would have a distribution which could be approximated by the same function with the required thermal time for the relationship of suboptimal range. The parameters m and A for the negative ‘thermal time’ were determined to be 2870 K h and 1.7 × 10^-10 K^-3 h^-3.     

Geographic variation in the flood-induced fluctuating temperature requirement for germination in Setaria parviflora seeds

Our aim was to search for specific seed germinative strategies related to flooding escape in Setaria parviflora, a common species across the Americas. For this purpose, we investigated induction after floods, in relation to fluctuating temperature requirements for germination in seeds from mountain, floodplain and successional grasslands. A laboratory experiment was conducted in which seeds were imbibed or immersed in water at 5°C. Seeds were also buried in flood-prone and upland grasslands and exhumed during the flooding season. Additionally, seeds were buried in flooded or drained grassland mesocosms. Germination of exhumed seeds was assayed at 25°C or at 20°C/30°C in the dark or in the presence of red light pulses. After submergence or soil flooding, a high fraction (>32%) of seeds from the floodplain required fluctuating temperatures to germinate. In contrast, seeds from the mountains showed maximum differences in germination between fluctuating and constant temperature treatment only after imbibition (35%) or in non-flooded soil conditions (40%). The fluctuating temperature requirement was not clearly related to the foregoing conditions in the successional grassland seeds. Maximum germination could also be attained with red light pulses to seeds from mountain and successional grasslands. Results show that the fluctuating temperature requirement might help floodplain seeds to germinate after floods, indicating a unique feature of the dormancy of S. parviflora seeds from floodplains, which suggests an adaptive advantage aimed at postponing emergence during inundation periods. In contrast, the fluctuating temperature required for germination among seeds from mountain and successional grasslands show its importance for gap detection.     

华北平原11种植物种子萌发的生物学零点与积温探究

研究分析了华北平原11种植物种子萌发所需要的生物学零度和积温,结果表明:与其原产地年均气温比较,由于长期的适应,各植物的生物学零点和原产地的平均气温存在明显的正相关关系;种子萌发的积温和种子萌发的生物学零度之间存在显著地负相关关系。     

不同温度下四川金川县岷江柏种子的发芽特征

岷江柏(Capressus chenggiana S．Y．Hu)是我国川甘地区特有的濒危乔木。通过对不同温度下岷江柏种子的发芽特征研究,分析了种子的发芽周期和最适发芽温度,以及温度对种子发芽的影响,并讨论了岷江柏的发芽特征与环境温度的关系,从而为岷江柏的人工繁育和物种保护提供了理论依据。结果表明：种子发芽周期为20d,其中0～5d为萌动期,5～15d为高峰期。种子发芽温度为5℃～30℃,适宜发芽温度为10℃～25℃,5℃和30℃不利于种子发芽。在贮藏过程中,贮藏开始阶段10℃不利于种子发芽,贮藏4～10个月后10℃～25℃种子发芽的差别不明显。种子最适发芽温度在2003年1月、4月、7月和10月分别为：20℃、15℃、20℃、25℃。在贮藏过程．不同温度下种子的发芽率、发芽势和T50都有显著影响。岷江柏种子的发芽周期和最适发芽温度．以及贮藏过程中的发芽特征与环境温度有着密切的关系．这是植物对自然环境的一种适应。     

The influence of temperature during seed development on the germination characteristics of millet seeds

Abstract. The cardinal temperatures, rate of germination and final percentage germination of pearl millet seeds were measured for seeds raised in greenhouses maintained at mean air temperatures of 19, 22, 25, 28 and 31°C. The results showed that cardinal temperatures for germination are unaffected by the temperature during seed development and growth. However, the conditions during seed growth did affect seed size and, subsequently, germination rate and seed viability.     

Phytochrome control of skotodormancy release in Grand Rapids lettuce achenes

Light-requiring Grand Rapids lettuce ( Lactuca sativa L.) achenes develop skotodormancy when imbibed in darkness for 7 days at 25°C. Redried skotodormant achenes maintain this type of dormancy upon subsequent rehydration. At 25°C full germination of skotodormant achenes can be induced by continuous and intermittent red light illumination as well as by several brief red irradiations given daily. One brief (10 min) red light irradiation can partly break skotodormancy at 20°C, while at lower temperatures the same treatment results in full induction of germination. Phytochrome control of the release from skotodormancy is proven by a) the dependence of the germination response on the relative sequence of red and far-red light in cyclic irradiations, and b) the reversion of red action by subsequent far-red irradiation. The time course of germination of skotodormant achenes treated with intermittent red light depends upon the length of dark interval between the light pulses. Germination is considerably delayed compared to that of non-skotodormant ones, induced by a single brief red light treatment. This fact in combination with the requirement, over a long period of time, of P_fr action for full manifestation of germination, indicates that skotodormancy is a deeper form of dormancy. It is concluded that the germination of lettuce achenes may always be subjected to phytochrome control.     

苜蓿种子萌发和幼苗生长对温度、光照和埋深的响应

紫花苜蓿(Medicagosativa)是世界人工草地重要的优良牧草.研究其种子萌发和幼苗生长对温度、光照及埋深等环境因子的响应,对苜蓿草地的种植及管理具有重要的实践指导意义.采用室内控制实验,分析了紫花苜蓿种子萌发和幼苗生长对恒温(10、15、20、25、30℃)、变温(6/15、10/20、15/25、15/30、...     

Changes in sensitivity of Amaranthus retrof/exus L. seeds to ethylene during preincubation. I. Constant temperatures

Abstract. Germination responses of redroot pigweed ( Amaranthus retroflexus L.) seeds to ethylene were determined at 25, 30, 35, or 40° C after preincubation at various temperatures (15–35° C) for different periods (0.5–32 d). After 7 d preincubation, seeds showed a log-linear germination response to ethylene concentration in most of the temperature treatments. Sensitivity to ethylene increased with longer preincubation; response thresholds of 0.03−0.09 cm³ m⁻³ were observed after 32 d, compared to 0.18−1.6 cm³ m⁻³ after 7 d of preincubation. Preincubation at 15 or 20° C generally enhanced germinability, whereas 25 or 30° C produced secondary dormancy, which was readily broken with ethylene. Temperature during preincubation also significantly influenced the slope of the dose-response curve. The responses of preincubated redroot pigweed seeds to ethylene suggested that, in the field, seeds would probably not lose their sensitivity to this gas during prolonged burial in soil.