Stratified Seeds Research Articles

Growth, pathogenicity and infection behaviour, and genetic diversity of Rhexocercosporidium panicis isolates from ginseng roots in British Columbia

Ginseng roots with reddish-brown to black surface discolourations were collected from eight farms in British Columbia during 2005–2007. Affected tissues predominantly yielded colonies of Fusarium spp. and Rhexocercosporidium panacis when plated onto half-strength PDA. Percentage recovery of these fungi was influenced by root age, with Fusarium species recovered mostly from 1–2-year-old roots and R. panacis from 3- and 4-year-old roots. Roots sampled in July 2007 yielded a higher frequency of Fusarium while those sampled during March and September 2007 yielded a higher frequency of R. panacis. Isolates of R. panacis ranged in pathogenicity from non-pathogenic (29% of total) to weakly aggressive (causing lesions only in the presence of wounds) (54%) to highly aggressive (17%), and infected both ginseng and carrot roots, causing a surface blackening. The optimal temperature range for growth of 10 isolates of R. panacis in culture was 15–20 °C. A nested PCR protocol confirmed the presence of R. panacis in symptomatic ginseng roots as well as in about 20% of non-symptomatic roots. The fungus was also detected by nested PCR in flowers, green and red berries, and non-stratified and stratified seeds. Field applications of propiconazole reduced the frequency of detection by PCR of R. panacis from ginseng berries. Phylogenetic analysis confirmed that most of the isolates recovered in this study were R. panacis, although a few isolates clustered in a separate group.

The contribution of seeds to the recruitment of a Nymphoides peltata population

The Nymphoides peltata population expands quickly in Lake Taihu, China. One question addressed in this study is whether the seeds of N. peltata contribute to this expansion. The buoyancy and germination of N. peltata seeds and the development of N. peltata seedlings were studied, using seeds collected from Lake Taihu. The results indicated that a low wind velocity of 2.4–3.0 m s −1 had a slightly negative effect on seed buoyancy. After 19 and 67 h of gentle stirring, 50% and 90%, respectively, of the N. peltata seeds had sunk. Few seeds floated again after sinking, but these refloating seeds sank soon with the disturbance. The N. peltata seeds did not germinate without stratification, but the stratification of seeds for a two-week period resulted in a high germination rate (63.3%) at a light intensity of 20 μmol photons m −2 s −1 . Both the light and stratification treatments stimulated the seeds germination. The seeds did not germinate in sediment at depths greater than 0.25 cm. A high germination rate (74%) was observed for the seeds that laid on the water–sediment interface; however, nearly all of the germinated seeds floated on the water surface after germination. Only a small fraction (14%) of the buoyant seedlings could re-establish in shallow water (less than 3 cm). In the eighth week of the experiments, the buoyant seedlings that failed to re-establish rotted. When grown in low light intensity conditions, the N. peltata seedlings had smaller cotyledons, shorter primary roots, and weak development of adventitious roots. Sufficient light was important for both seed germination and seedling development. It was found that sexual reproduction is likely to have little direct contribution to the rapid expansion of N. peltata towards the centre of this large shallow lake.

Pre-sowing treatment for breaking dormancy in Acer velutinum Boiss. seed lots

Acer velutinum Boiss is a valuable tree species native to Iran, and its seeds possess physiological dormancy that hampers seedling production in the nursery for large-scale reforestation efforts. The aim of this study was to determine the optimal dormancy breaking treatments for A. velutinum seeds. We conducted a factorial experiment involving six seed lots collected along an elevation gradient from 300 to 1800 m at 300 m interval and four cold-moist stratification periods (0, 4, 8 and 16 weeks) at 4°C and 70% relative humidity. The result shows that the germination of cold-moist stratified seeds was significantly (p < 0.0001) higher than the control for all seed lots. The highest germination capacity was recorded after 16 weeks of cold-moist stratification for all seed lots (68%–88% depending on the seed lot) except those collected from mid altitude sites (600 and 900 m) that germinated equally well (≥ 75%) after 4- and 8-week of clod-moist stratification compared to the other seed lots. The mean germination time was significantly shorter (12 to 19 days, depending on the seed lot) for seeds stratified for 16 weeks than for untreated seeds. It can be concluded that: (1) cold-moist stratification for 16 weeks is the best pre-sowing treatment for breaking dormancy in A. velutinum seeds; and (2) seeds should be collected from mid altitude sites (600 and 900 m) to get more than 80% germination within 15 days, and these seed lots even required shorter cold-moist stratification period (eight weeks) than other seed lots.

The physiological basis for ethylene-induced dormancy release in three Echinacea species with special reference to the influence of the integumentary tapetum

Seeds of Echinacea species have endogenous physiological dormancy. Dormancy release is induced by moist chilling stratification, but seeds treated with ethylene can show increased germination comparable to stratification. The primary aims of this work were to discover whether endogenous ethylene production was required for dormancy release and germination in Echinacea seeds and to investigate the physiological basis for stratification and ethylene-induced dormancy release. There were no significant differences in ethylene production in untreated versus stratified seeds. Seeds subjected to a dormancy release treatment showed reduced sensitivity to exogenous abscisic acid (ABA). Isolated embryos were completely released from dormancy when the outer envelope surrounding the embryo was removed. Isolated embryos with the envelope intact were also induced to germinate when treated with ACC (1-aminocyclopropane-1-carboxylic acid) to increase ethylene production. It was determined that the covering envelope was derived from enlargement of the endothelium layer surrounding the egg sac (integumentary tapetum) plus several crushed layers of the outer integument. Ethylene does not appear to be required for dormancy release and germination in Echinacea seeds. Two possible physiological mechanisms were discovered to explain stratification and ethylene-induced dormancy release. These included a change in seed sensitivity to ABA and changes in the tissues covering the embryo. The data suggests that ethylene-induced dormancy release is independent of stratification and possibly acts by inducing physiological events that are normally downstream of stratification.

Dormancy removal of apple seeds by cold stratification is associated with fluctuation in H2O2, NO production and protein carbonylation level

Reactive oxygen (ROS) and nitrogen (RNS) species play a signaling role in seed dormancy alleviation and germination. Their action may be described by the oxidative/nitrosative “window/door”. ROS accumulation in embryos could lead to oxidative modification of protein through carbonylation. Mature apple (Malus domestica Borkh.) seeds are dormant and do not germinate. Their dormancy may be overcome by 70–90 days long cold stratification. The aim of this work was to analyze the relationship between germinability of embryos isolated from cold (5°C) or warm (25°C) stratified apple seeds and ROS or nitric oxide (NO) production and accumulation of protein carbonyl groups. A biphasic pattern of variation in H2O2 concentration in the embryos during cold stratification was detected. H2O2 content increased markedly after 7 days of seeds imbibition at 5°C. After an additional two months of cold stratification, the H2O2 concentration in embryos reached the maximum. NO production by the embryos was low during entire period of stratification, but increased significantly in germination sensu stricto (i.e. phase II of the germination process). The highest content of protein carbonyl groups was detected after 6 weeks of cold stratification treatment. Fluctuation of H2O2 and protein carbonylation seems to play a pivotal role in seed dormancy alleviation by cold stratification, while NO appears to be necessary for seed germination.

Efficient, Season-Independent Seed Germination in Black Cohosh (&amp;lt;i&amp;gt;Actaea racemosa&amp;lt;/i&amp;gt; L.)

Seed germination in black cohosh was systematically examined in eighteen populations including 15 USDA accessions with an effective protocol for the consistent, season independent germination of this valuable alternative specialty crop. Two in vitro approaches were investigated for breaking the complex double dormancy of black cohosh seeds for yearround germination of plants for increased cultivation and laboratory studies. The first approach was a two-step alternating temperature stratification in which surface sterilized seeds were incubated in darkness at 25?C for two weeks followed by incubation at alternating temperatures of 20?C and 8?C for 12-hour periods with a 16-hour photoperiod for 12 months. The second was a three-step-approach that involved initial stratification of seeds in darkness at 25?C for two weeks, followed by incubation at 4?C in darkness for 3 -4 months and then cultivation at 25?C with a 16-hour photoperiod to generate seedlings. Although both approaches broke double dormancy for black cohosh seed germination, the three-step-stratification technique yielded higher percentage seed germination in less time when compared to the two-step scheme, including for seeds stored over two years. Additional factors of critical importance for efficient germination included the selection of healthy and viable seeds, as well as thorough but non-excessive surface sterilization to control bacterial and fungal contamination. The in vitro approach for black cohosh germination allowed year-round cultivation and culture of a number of different genotypic accessions to enable laboratory based studies on cell culture and transformation approaches to aid in deciphering gene-metabolite relationships in this important medicinal plant.

Effects of cold-stratification, gibberellic acid and potassium nitrate on seed germination of yellow gentian (Gentiana lutea L.)

The purpose of this study was to show the effect of cold-stratification, gibberellic acid and potassium nitrate on seed germination of yellow gentian (Gentiana lutea L.). The seeds of natural yellow gentian populations of the Albanian Alps (Kosovo) were collected in September 2010. Seeds placed in filter paper (plastic bag) and in mixture of sand-soil were cold-stratified (2±1°C) for 72 days. The effect of different concentrations of gibberellic acid (250, 500 and 1000 ppm GA3) and potassium nitrate (0.1, 0.2 and 0.3% KNO 3 ) in final germination percentage (FGP), mean germination time (MGT) and germination index (GI) in non-stratified and stratified seeds were examined. Seeds stratified in filter paper and treated with 1000 ppm GA3 and 0.1% KNO 3 showed significantly higher percentage of germination (FGP and GI), while seeds stratified in mixture of sand-soil showed the highest values of FGP and GI in treatments with 500 ppm GA 3 and different concentrations of KNO 3 . The cold-stratification and GA 3 treatments of yellow gentian seeds are suitable for the higher percentage of germinations. Key words: Gentiana lutea L., cold-stratification, seeds, germination, gibberellic acid (GA 3 ), potassium nitrate (KNO 3 ).

Germination response of threatened African medicinal barberry (Berberis holstii) under light, stratification and temperature treatments

Berberis holstii is the only African representative of the Palearctic genus, Berberis. In Malawi, it is only found on Nyika Plateau where it is intensively and illegally harvested despite legislation banning its collection. Efforts to propagate it by seed have proved futile. This study investigated its germination response under light and stratification treatments. Ripe seeds were germinated under light/dark and chilling conditions, and constant/alternate temperature regimes. Seeds germinated equally well in light and dark conditions except under 20/5°C temperature where stratified seeds exposed to light failed to germinate. Under constant temperature, seeds germinated slightly better in light (about 50%). Seeds that were in dark germinated better under alternating temperatures (up to 80%). Because germination is not restricted by light, the species is unlikely to form a soil seed bank. Key words: Barberry, photoblastism, temperature, stratification.

Outbreaks of Smut Caused by Tilletia maclaganii on Switchgrass in New York and Pennsylvania.

Switchgrass (Panicum virgatum L.) is a native perennial grass with potential as a biofuel crop. The smut fungus, Tilletia maclaganii (Berk.) Clint., is associated with significant biomass reduction in switchgrass in the Midwest (4), but has not been reported in the northeast United States in more than 60 years (New York in 1890 and Pennsylvania in 1946) (2,3). From 2007 to 2010, smutted panicles were observed on the majority of plants in stands of several switchgrass cultivars at the USDA-NRCS Plant Materials Center in Big Flats (Chemung County), NY; in production fields of several switchgrass cultivars near Meadville (Crawford County), PA; and in an ornamental bed of switchgrass in Ithaca (Tompkins County), NY. Smutted panicles emerged 3 to 4 weeks prior to healthy panicles, had a compact, club-shaped appearance, and enlarged florets with swollen ovaries that readily released a powdery mass of odorless, rusty orange-to-dark brown teliospores when pinched. The entire caryopsis of every floret within a panicle was smutted and the infected plants appeared stunted, indicative of systemic infection. The fungus from each location was identified as T. maclaganii based on host, habit, and teliospore morphology (3). Teliospores were pale yellowish brown to reddish brown, varied from globose to slightly irregular in shape, and averaged 21 μm (18 to 25 μm) in diameter. The exospore was thick (2 to 3 μm), finely verrucose, and no sheath was present. True sterile cells, pale yellow and 10 to 18 μm in diameter, were sparsely present. Teliospores germinated and formed large (40 to 60 × 3 to 6 μm), nonconjugating basidiospores within 20 h on 2% water agar (WA). Occasionally, we also found the floret-infecting species T. pulcherrima (1) on switchgrass at very low incidence in Big Flats, NY, but it was easily distinguished from T. maclaganii. Stratified seeds (3 g) of 'Shelter', washed and found to be free of teliospores, were dusted with 0.04 g of teliospores of T. maclaganii isolate Tm001NY09 (Cornell Plant Pathology Herbarium Accession CUP-67931) harvested from infected 'Shelter' in Big Flats, NY in 2009. Inoculated and noninoculated seeds were sown in seedling trays, transplanted, and evaluated at panicle emergence. There were no symptoms on plants from noninoculated seeds. Symptoms on inoculated plants were consistent with field observations and teliospores were reisolated from infected panicles and cultured on 2% WA. Teliospores harvested from a single panicle infected with Tm001NY09 were used for culturing and DNA extraction. The fully annotated sequence of the rDNA internal transcribed spacer and 5.8S regions of this isolate were deposited in GenBank (Accession No. JF745116). Smut outbreaks in New York and Pennsylvania suggest that T. maclaganii must be managed effectively if switchgrass production is to be sustainable in the Northeast.

The Effect of Different Stratification Conditions on the Germination of Fraxinus angustifolia Vahl. and F. ornus L. Seeds

The aim of the paper was to assess the impact of different stratification treatments recommended by the literature on the shortening of manna ash (F. ornus L.) and narrow-leaved ash (F. angustifolia Vahl.) seed germination in order to identify a suitable pre-germination treatment for seedling production. Seeds of three Southern Romanian origins for both species were exposed to four stratification treatments (cold (3oC) and warm (20oC), with and without sand-peat medium). The highest percentage of germination (up to 87% for Fraxinus ornus and up to 71% for F. angustifolia) was recorded in the case of the stratified seeds with cold medium (3oC) and relatively constant seed moisture (between 45% and 65%) throughout the treatment.

Switchgrass (Panicum virgatum L.) Intraspecific Variation and Thermotolerance Classification Using in Vitro Seed Germination Assay

Cardinal temperatures for plant processes have been used for thermotolerance screening of geNotypes, geoclimatic adaptability determination and pheNological prediction. Current simulation models for switchgrass (Panicum virga-tum L.) utilize single cardinal temperatures across geNotypes for both vegetative and reproductive processes although intra-specific variation exists among geNotypes. An experiment was conducted to estimate the cardinal temperatures for seed germination of 14 diverse switchgrass geNotypes and to classify geNotypes for temperature tolerance. Strati-fied seeds of each geNotype were germinated at eight constant temperatures from 10oC to 45oC under a constant light intensity of 35 µmol m-2 s-1 for 12 h d-1. Germination was recorded at 6-h intervals in all treatments. Maximum seed germination (MSG) and germination rate (GR), estimated by fitting Sigmoidal function to germination-time series data, varied among geNotypes. Quadratic and bilinear models best described the MSG and GR responses to temperature, respectively. The mean cardinal temperatures, Tmin, Topt and Tmax, were 8.1, 26.6, and 45.1oC for MSG and 11.1, 33.1, and 46.0oC for GR, respectively. Cardinal temperatures for MSG and GR; however, varied significantly among geNotypes. GeNotypes were classified as sensitive (‘Cave-in-rock’, ‘Dacotah’, ‘Expresso’, ‘Forestburg’, ‘Kanlow’, ‘Sunburst’, ‘Trailblazer’, and ‘Warrior’), intermediate (‘Alamo’, ‘Blackwell’, ‘Carthage’, ‘Shawnee’, and ‘Shelter’) and tolerant (‘Summer’) to high temperature based on cumulative temperature response index (CTRI) estimated by summing individual response indices estimated from the MSG and GR cardinal temperatures. Similarly, geNotypes were also classified as sensitive (Alamo, Blackwell, Carthage, Dacotah, Shawnee, Shelter, and Summer), moderately sensitive (Cave-in-rock, Forestburg, Kanlow, Sunburst, and Warrior), moderately tolerant (Trailblazer), and tolerant (Expresso) to low temperatures. The cardinal temperature estimates would be useful to improve switchgrass models for field applications. Additionally, the identified cold- and heat-tolerant geNotypes can be selected for niche environments and in switchgrass breeding programs to develop new geNotypes for low and high temperature environments.

Effect of osmotic stress and post-stress recovery on the content of phenolics and properties of antioxidants in germinating seeds of grapevine Vitis californica

The tested material consisted of grapevine &lt;em&gt;Vitis californica&lt;/em&gt; stratified seeds germinated under optimum conditions (+25°C in water), under osmotic stress (-0.2 MPa in PEG solution) and submitted to recovery after stress (+25°C in water). The germinating seeds were determined to contain tannins, catechins and the following phenolic acids: gallic, caffeic, &lt;em&gt;p&lt;/em&gt;-coumaric and ferulic. The acids occurred in free, ester- and glycoside-bound forms. The dominant form of phenolic acids was the ester-bound fraction. Gallic acid was the most abundant phenolic acid in germinating seeds, while ferulic acid appeared in the smallest amounts. Our analysis of tannins demonstrated that osmotic stress depressed their concentration. Presence of catechin group compounds such as catechin and epicatechin was also determined. In each sample epicatechin was dominant. The total concentration of catechin increased under stress conditions and declined during post-stress recovery. Catechins are a constituent of tannins and their increase under osmotic stress is most probably caused by the breakdown of some tannins in seeds germinating under stress conditions. Samples submitted to osmotic stress were also found to contain less of total phenolic compounds, whereas in samples which underwent post-stress recovery the total level of phenolic compounds increased. Compared to extracts from seeds germinating under optimum conditions, osmotic stress depressed the capacity of extract to scavenge DPPH&lt;sup&gt;●&lt;/sup&gt; (2,2-diphenyl-1-picrylhydrazyl) and ABTS&lt;sup&gt;●+&lt;/sup&gt; – 2,2-Azino-bis (3-etylbenzothiazoline-6-sulfonic acid) free radicals, but the antioxidant activity rose in seeds submitted to recovery after stress. Positive correlation was therefore demonstrated between the total content of phenolic acids in germinating grapevine seeds and the reducing power of extracts obtained from these seeds and their free radical scavenging activity. The results suggest that osmotic stress inhibits the activity of antioxidizing enzymes in germinating grapevine seeds. Thus, the antioxidative defence system is largely blocked under osmotic stress. It seems that a very high oxidoreductive potential in grapevine tissues prior to occurrence of osmotic stress is essential for maintaining proper homeostasis of oxidation and reduction reactions.

Factors influencing seed germination of Cyperus capitatus, inhabiting the moving sand dunes in southern Europe

Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination.

Dark-mediated dormancy release in stratified Lolium rigidum seeds is associated with higher activities of cell wall-modifying enzymes and an apparent increase in gibberellin sensitivity

Dormancy release in freshly matured, imbibed annual ryegrass ( Lolium rigidum) seeds is inhibited by light and involves a decrease in seed sensitivity to abscisic acid. Other processes involved in dormancy release in the dark were investigated by measuring seed storage compound mobilisation and the activity of cell wall-degrading enzymes. Activities of endo-β-mannanase and total peroxidase were higher in dark-stratified compared to light-stratified seeds, indicating that weakening of the structures constraining the embryo was accelerated in the dark. A dramatic degradation of storage proteins in light-stratified seeds, accompanied by induction of a high molecular mass protease, suggests that maintenance of storage(-like) proteins is also important in dark-mediated dormancy release. α-Amylase activity was induced in dark-stratified seeds at least 48 h prior to radicle emergence upon transfer to conditions permitting germination, or in light-stratified seeds supplied with exogenous gibberellin A 4. This suggests that (a) α-amylase is involved in stimulation of germination of non-dormant L. rigidum seeds, and (b) dark-stratified seeds have an increased sensitivity to gibberellins which permits the rapid induction of α-amylase activity upon exposure to germination conditions. Overall, it appears that a number of processes, although possibly minor in themselves, occur in concert during dark-stratification to contribute to dormancy release.

Germination Ecology of Biennial Wormwood (Artemisia biennis) and Lanceleaf Sage (Salvia reflexa) Seeds

Biennial wormwood and lanceleaf sage have become serious weeds of several crops within the northern Great Plains of the United States and Canada. Both species are prolific seed producers but little is known about their potential for developing persistent seedbanks. Field studies were conducted to determine the influence of duration (7, 8, 11, 19, 20, and 23 mo) and depth of burial (0, 2.5, and 10 cm) on biennial wormwood and lanceleaf sage seed viability and decay. Biennial wormwood and lanceleaf sage seeds were buried in September 2003 (burial 1) and September 2004 (burial 2). In burial 1, biennial wormwood and lanceleaf sage seed viability was 65 and 66%, respectively, after 23 mo of burial. In burial 2, biennial wormwood and lanceleaf sage seed viability was 8 and 3%, respectively, after 23 mo of burial. The difference was likely because of higher soil moisture during burial 2, which promoted seed decay. Controlled-environment studies sought to determine the influence of stratification environments (freezing, chilling, and freeze–thaw) followed by exposure to diurnally fluctuating temperatures on germination of biennial wormwood and lanceleaf sage seeds. Stratified biennial wormwood seed germination was 95% or greater when incubated in fluctuating day/night temperatures of 37/20 or 37/25 C. Stratified lanceleaf sage seeds from freezing and chilling environments did not differ in germination following incubation in fluctuating temperatures and averaged 56 and 55%, respectively. Germination of stratified lanceleaf sage seeds from the freezing and thawing environment was higher than 50% during the thawing cycle, suggesting the possibility of early season emergence of this species. Our study indicates that biennial wormwood and lanceleaf sage have the potential to develop a seedbank that can persist for more than 2 yr. High moisture levels in the soil seedbank can lead to reduced seed survival.

Seed treatment with GA&lt;sub&gt;3&lt;/sub&gt; or stratification enhances emergence of some strawberry tree genotypes: Short communication

The strawberry tree is a valuable ornamental plant because of its attractive red fruits in the fall and winter, and pinkish-white flowers in fall. Additionally, its fruits are processed into various products such as jam, marmalade, wine and alcohol. Since, propagation of the strawberry tree is difficult. This study aimed to examine the influence of stratification and GA&lt;sub&gt;3&lt;/sub&gt;on breaking seed dormancy and enhancing emergence rate of Arbutus unedo. The influence of seed treatment with GA GA&lt;sub&gt;3&lt;/sub&gt; or stratification at 4&amp;deg;C was examined on emergence of five genotypes of strawberry tree (Arbutus unedo L.) near the Black Sea in Turkey. Results indicate that emergence rate increased with increasing GA GA&lt;sub&gt;3&lt;/sub&gt; concentration from 300 to 1,200 ppm and stratification duration from 5 to 15 weeks. In all examined genotypes, the highest emergence rate was obtained using 1,200 ppm GA GA&lt;sub&gt;3&lt;/sub&gt; or 15 weeks of stratification. Regardless of the positive effects of the above treatments, seed emergence rates in all genotypes examined in this study were low. Application of GA GA&lt;sub&gt;3&lt;/sub&gt; or stratification of seeds increased emergence percentage in all Arbutus unedo genotypes examined in the current study.

Seed dormancy dynamics and germination characteristics of Solanum nigrum

SummaryFour experiments were conducted to study seed dormancy and germination requirements in Solanum nigrum. In Expt 1, seeds were stratified at different constant and stepwise rising temperatures and their germinability was tested at three germination regimes at weekly intervals. In Expts 2–4, seeds dry stored at 4°C and stratified at 5 and 15°C were tested at constant temperatures, as well as fluctuating temperatures with constant and increasing amplitudes. Results suggest that the rate of dormancy release increased with increasing temperatures ranging from 4.5 to 18.6°C. However, prolonged stratification at higher temperatures caused subsequent induction of dormancy. When tested at constant temperatures, stratified seeds germinated between 18 and 34°C, with the optimum between 26 and 30°C, while dry‐stored seeds showed no germination. Fluctuating temperatures, with amplitudes ranging from 5 to 15°C, promoted germination of seeds from all treatments. The dormancy dynamics and germination characteristics of the species will have implications for its survival and establishment. This information can be used to predict time of emergence and, thus, improve control of the species in weed management systems.

Seed Germination of Roundleaf Buffaloberry (Shepherdia rotundifolia) and Silver Buffaloberry (Shepherdia argentea) in Three Substrates

Abstract Many western native plant species occur in areas characterized by well-drained soils low in organic matter. Some drought-tolerant native plant species exhibit poor seed germination. It was hypothesized that traditional growing substrates high in organic matter may impede their germination; therefore, stratified seeds of roundleaf buffaloberry (Shepherdia rotundifolia) and silver buffaloberry (Shepherdia argentea) were sown in three substrates differing in organic matter and drainage properties. Seed flats were irrigated twice daily to container capacity, and held on a greenhouse bench for 40 days. Seeds of roundleaf buffaloberry exhibited greatest total germination in a calcined montmorillonite calcined clay substrate (66%); seeds exhibited low germination in a commercial peat-based germination mix (13%) and in a self-prepared, locally popular substrate (22%) that contained sphagnum peat: perlite: calcined clay: sand (2: 2: 1: 1 by vol). Seed germination of silver buffaloberry varied from 42 to 54% and was not different among the three substrates. When substrates are kept consistently moist, a calcined-clay substrate can improve germination of roundleaf buffaloberry, but not silver buffaloberry.

Variation in seed dormancy and light sensitivity in Alopecurus myosuroides and Apera spica‐venti

SummaryVariation in seed dormancy and light sensitivity was studied in Alopecurus myosuroides and Apera spica‐venti. Seeds were collected from different populations, at different dates and from plants emerging in autumn or spring, and used in four experiments. In the first experiment, initial dormancy was investigated in light and darkness. In Expt 2, buried seeds were exhumed on 16 occasions, from September 1997 to March 2000, and germinated in light, in darkness and after a 5‐s light exposure. In Expt 3, emergence was recorded for seeds sown in pots outdoors. In Expt 4, stratified seeds of A. myosuroides only were exposed to photon irradiance ranging from 0.1 to 25 600 μmol m−2. Variation was high among seed collections, but both species showed winter annual dormancy patterns. Apera spica‐venti germinated to high percentages in autumn but negligibly in spring. Alopecurus myosuroides germinated less in spring when tested in darkness and after a short light exposure and emerged poorly in spring, which reflected photo‐desensitisation during cold stratification. We conclude that the peak of emergence in A. myosuroides, and to some extent in A. spica‐venti, is largely regulated by exposure to light interacting with low‐level dormancy. This offers valuable information regarding optimal timing of weed control measures.

Seed flotation and germination of salt marsh plants: The effects of stratification, salinity, and/or inundation regime

We examined the effects of cold stratification and salinity on seed flotation of eight salt marsh species. Four of the eight species were tested for germination success under different stratification, salinity, and flooding conditions. Species were separated into two groups, four species received wet stratification and four dry stratification and fresh seeds of all species were tested for flotation and germination. Fresh seeds of seven out of eight species had flotation times independent of salinity, six of which had average flotation times of at least 50 d. Seeds of Spartina alterniflora and Spartina patens had the shortest flotation times, averaging 24 and 26 d, respectively. Following wet stratification, the flotation time of S. alterniflora seeds in higher salinity water (15 and 36 ppt) was reduced by over 75% and germination declined by more than 90%. Wet stratification reduced the flotation time of Distichlis spicata seeds in fresh water but increased seed germination from 2 to 16% in a fluctuating inundation regime. Fresh seeds of Iva frutescens and S. alternflora were capable of germination and therefore are non-dormant during dispersal. Fresh seeds of I. frutescens had similar germination to dry stratified seeds ranging 25–30%. Salinity reduced seed germination for all species except for S. alterniflora. A fluctuating inundation regime was important for seed germination of the low marsh species and for germination following cold stratification. The conditions that resulted in seeds sinking faster were similar to the conditions that resulted in higher germination for two of four species.