Timely results from whole-plant, herbicide-resistant weed screenings are crucial to heighten grower awareness. However, the high degree of physiological dormancy of giant ragweed (Ambrosia trifida L.) seed exacerbates this process. The most effective methods for alleviating dormancy, to date, are either labor-intensive (embryo excision) or require several weeks (soil stratification). This research describes a conditioning process involving clipping and aeration of seed in water that is highly effective at alleviating dormancy and requires less skill and time compared with previous techniques. Ambrosia trifida seeds were collected over 2 yr at two different collection timings (September 25, “early”; October 25, “late”), subjected to various treatments intended to release dormancy, and evaluated for emergence over 18 d in the greenhouse. The use of germination-promoting chemicals (ethephon, gibberellic acid, and thiourea) generally provided no increase in emergence compared with water and occasionally produced seedlings with abnormal growth unsuitable for further experimentation. Conditioning yielded between 30% and 33% emergence for both early and late collections of seeds with no afterripening period compared with 0% emergence for seeds imbibed in water. Following an 8-wk period of dry storage at 4 C, conditioning yielded nearly 80% emergence for both collection timings, while emergence of seeds imbibed in water was 10% and 27% for early and late collections, respectively. Soil stratification in moist soil for 8 wk at 4 C was the second most effective treatment, yielding 46% to 49% emergence across both collections. Parameters of the Weibull function further indicated the conditioning treatment had the fastest rate of emergence and shortest lag phase between planting and first emergence. Methods to germinate A. trifida without an afterripening period have previously been unsuccessful. Therefore, the seed-conditioning method outlined in this work will be useful in expediting the confirmation of herbicide-resistant A. trifida incidences.

In central Asia, Agriophyllum squarrosum is the first species to become established during natural succession on sand dunes. However, low germination percentages and thus poor stand establishment greatly inhibit the use of this key species in the stabilization of dunes. The aim of this review is to critically analyse published information on the seed biology of A. squarrosum with particular reference to identifying the factors limiting germination of seeds sown in the field. A conceptual model is used to illustrate the complexities of factors as well as the unknowns we found about the seed/seedling stage of the life cycle of this sand dune annual. A major result of this review is that we now know that high germination percentages can be obtained by storing freshly collected seeds dry at room temperatures for 2 to 3 months to allow dormancy break to occur via afterripening, and then storing them dry at low (e.g. 4–5°C) temperature to prevent them from entering secondary dormancy. Non-dormant seeds should be sown in the field in late spring when wind-blown sand will cover them, thus ensuring that they are in darkness, which promotes germination, at the time summer rains occur.

The germination of seeds (achenes) of milk thistle [Silybum marianum (L.) Gaertn.] was investigated. One month after harvest, milk thistle seeds had afterripening requirements related to germination temperature that limited germination to 10 to 20 C temperatures. The time required to satisfy afterripening requirements was dependent on germination temperature. Generally the higher the incubation temperature during germination, the longer the afterripening requirement (up to a maximum of 5 months). Once afterripening requirements were satisfied, milk thistle seeds germinated over a temperature range of from 0 to 30 C. Optimum germination occurred with 2 to 15 C 16-h cold periods alternating with 10 to 30 C 8-h warm periods. Emergence of milk thistle seedlings decreased with increased burial depth, but substantial emergence occurred from 8 cm. Germination on the surface of the soil or litter was greatly reduced compared to that with slight soil or litter coverage. Potassium nitrate (KNO3) added to the germination substrate at 1.0 mM enhanced the germination of milk thistle seeds at 2 and 5 C incubation temperatures.

Sorghum-almum (Sorghum almum Parod. # SORAL) is a weakly perennial, rhizomatous grass that in northern climates reproduces mainly by seeds. Environmental factors influencing seed germination and the longevity of buried seeds were studied in growth chamber and field experiments. Alternating temperatures of 20 C for 16 h and 30 C for 8 h were optimum for germination. Light was not critical to germination. Germination varied only slightly across a pH range from 5.0 to 8.8 but decreased sharply below pH 5. Osmotic potentials greater than −0.9 MPa reduced germination substantially, and no germination occurred at −1.5 MPa. Limited germination occurred at NaCl concentrations of 340 mM, and no germination occurred at 510 mM. Seeds that were either mechanically scarified or afterripened for 6 months had a higher percent germination and germination rate than untreated seeds. Sorghum-almum seedling emergence was 11% from seeding depths of 20 cm, but emergence was 67% or higher from seeding depths of 15 cm or less. In field studies, viability of seeds placed on the soil surface or buried 3 or 8 cm was 2% or less at 12 months and 0% at 18 months after burial. Viability of seeds buried 15 and 23 cm was 0.3 and 26%, respectively, at 24 months after burial. Thus, tillage that buried sorghum-almum seeds 20 cm or more could reduce emergence but would also prolong seed persistence. Shallow tillage should favor depletion of sorghum-almum seed reserves.

Storage of intact Texas gourd [Cucurbita texana (A.) Gray] pepos for 21 days after harvest increased germination of seeds from pepos collected 15 to 47 days after flowering. Germination increased as day length decreased and as osmotic potential of germination media increased. Temperatures of 20, 25, and 30C resulted in 72, 93, and 99% germination, respectively. No seeds germinated at 10 or 40C. Seedling emergence decreased as planting depth increased, with no emergence from 12.5 cm. Control of Texas gourd in soybeans [Glycine max (L.) Merr.] was achieved with preemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], metribuzin plus alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide], and oxadiazon [2-tert-butyl-4 (2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], with successful control partially dependent on soil and climatological conditions. Postemergence treatments that resulted in adequate control included applications of acifluorfen {5-[2-chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoic acid}, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene], and metribuzin plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] applied at an early soybean growth stage and repeated.

Most seed of broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. & Rusby] and threadleaf snakeweed [G. microcephala (DC.) Gray] were dormant when collected soon after maturity, requiring 4 to 6 months of storage at room conditions to break dormancy. An alternating temperature regime of 10 C (16 h) and 20 C (8 h) favored snakeweed germination during the afterripening period, but germination was greatest under alternating temperatures of 20 C (16 h) and 30 C (8 h) after 24 months of storage. After 6 months of storage, maximum germination (70% or more) of threadleaf snakeweed seed occurred at continuous temperatures of 15 to 25 C; whereas, broom snakeweed seed germinated best at 15 and 30 C. Germination of both species in darkness was half or less of germination with daily 8-h periods of light. Germination of seed lots containing a high proportion of dormant achenes was enhanced by preimbibition storage at 50 C; after dormancy was naturally broken, exposure to 50 C prior to germination decreased early seedling vigor and growth but not germination.

Rapid biochemical tests developed for measuring viability of nondormant crop seed have been used for measuring dormant weed seed viability. The objective of this experiment was to propose and test a new method for validating one of these assays, the tetrazolium assay, for determining dormant weed seed viability. Subsamples of partially dormant jointed goatgrass seed from the same seed source were periodically subjected to sequential germination and tetrazolium assays as they afterripened until seed were completely nondormant. Changes in percent germinated, percent tetrazolium positive (presumably dormant), and percent tetrazolium negative (presumably dead) seed were graphed versus time, and compared with models of valid and invalid cases. The validation method showed that the tetrazolium assay accurately determined the viability of seed remaining after a 3-wk germination period for jointed goatgrass seed removed from joints at the start, but underestimated the viability for seed afterripened and germinated in joints. The validation method showed that additional research is needed to refine the tetrazolium assay for this latter purpose.

Key metabolic enzymes and germination were studied in developing and mature, dormant and nondormant prickly sida (Sida spinosa L.) seeds. Isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, fructose-1,6-diphosphatase, and phosphofructokinase activities were determined in developing and mature prickly sida seeds. Developing seeds less than 7 days after anthesis and at 17 days or greater after anthesis were unable to germinate. The 7-day-old seeds lacked all but fructose-1,6-diphosphatase activity. The 17-day-old seeds demonstrated all enzyme activities but failed to germinate because dehydration had occurred and seeds were unable to imbibe sufficient water without an afterripening period. Comparison of enzyme activities of dormant and nondormant seeds on incubation showed that only glucose-6-phosphate dehydrogenase was considerably different within the first 8 h of incubation. Nondormant seeds had considerable glucose-6-phosphate dehydrogenase activity before germination (radical protrusion at 8 h), suggesting an active pentose phosphate pathway.

Control of rattail fescue, a winter annual grass, can be difficult in spring or winter wheat. Although rattail fescue is not a new weed species in the Pacific Northwest, occurrences have been increasing in circumstances where soil disturbances are minimized, such as in direct-seed cropping systems. To develop integrated management strategies for rattail fescue, information is needed on the longevity of seed viability in the soil, the presence of seed dormancy, vernalization requirements, and optimal environmental conditions for seed germination and establishment under field conditions. Controlled experiments on the biology of rattail fescue indicated that newly mature seed required an afterripening period of 1 to 12 mo to obtain high levels of seed germination, depending on germination temperature. Maximum seed germination was observed at constant day/night temperatures of approximately 20 C from thermogradient plate studies. Germination tests from seed burial studies indicated that a majority of buried seed was not viable after 2 to 3 yr. Field-grown rattail fescue plants required vernalization to produce panicles and germinable seed. A short afterripening period, cool germination temperature, and vernalization requirements support the classification of rattail fescue as a winter annual. This information will facilitate development of rattail fescue management systems, including crop rotations and various control tactics such as tillage or herbicide application timing during fallow periods.

In the Grande Ronde Valley of eastern Oregon, two perennial grass species in the genus Puccinellia, weeping alkaligrass and Nuttall's alkaligrass, are weeds of Kentucky bluegrass grass-seed production fields. Weeping alkaligrass is introduced from Eurasia, whereas Nuttall's alkaligrass is native to the region. These two species were studied to determine dormancy attributes and optimal temperature conditions for seed germination. Results from the current studies indicate that both species have a high level of embryonic dormancy immediately following seed harvest, which is primarily eliminated through dry storage (afterripening) and an incubation temperature of 20 C. Following adequate afterripening, a prechill treatment of 5 d at 5 C had an inconsistent effect on germination of weeping alkaligrass (P = 0.012 in 2002, 0.156 in 2003) and improved germination of Nuttall's alkaligrass over both years (P < 0.0001). The afterripening requirement for weeping alkaligrass was more than 90 d, whereas Nuttall's alkaligrass required more than 180 d. Following adequate afterripening, both species had rapid and well-synchronized germination at fluctuating day/night temperatures of 30/10 C given unlimited moisture conditions. Given these results, it is unlikely that seeds of either species would germinate in eastern Oregon during the summer months. The data predict a long viability period under dry storage for both species. Weeping alkaligrass and Nuttall's alkaligrass should exhibit a rapid, well-synchronized germination in the spring as observed in the field.

Leafy spurge is a herbaceous perennial weed that reproduces asexually through adventitious vegetative buds and sexually by seeds. Seeds can remain viable in the soil for up to 8 yr. The objectives of this research were to determine whether the seed coat and endosperm restrict germination and to assess whether afterripening treatments affect germinability. Germination of nonafterripened intact seeds was 30% after 28 d of incubation. Afterripening seeds for 12 wk under warm moist conditions provided a twofold stimulation to 58% germination after 21 d compared with the control and three other afterripening treatments. Afterripening under warm moist conditions for an additional 12 wk provided nearly complete germination within 7 to 21 d, but seeds harvested in year 2000 also responded in the same way to cool moist conditions. The removal of seed coat (dehulled) and removal of endosperm surrounding the embryonic axis in dehulled seeds led to rapid germination, approaching 80 to 90% in 5 d. Fructose did not enhance germination of dehulled seeds or embryonic axes. Thus, leafy spurge displays coat-imposed seed dormancy that can be overcome by afterripening under moist conditions.

Germination was investigated in 1-yr and 8-yr-old seed lots of barnyardgrass. Each seed lot was divided into a portion stored dry at 25 C (afterripening) and a portion buried in the field (stratification) in central Europe (latitude 50°N, longitude 14°E). The afterripened seed lost dormancy within 2 yr after dispersal, whereas buried seed passed through annual dormancy/nondormancy cycles. The seed was germinated at five constant temperatures between 17 and 35 C with an 18/6-h light/dark photoperiod. Germination was affected by both seed age and storage conditions. Germination percentage and rate in 8-yr-old afterripened and each of the stratified seed lots varied with temperature. Optimum temperatures for germination were between 27 and 31 C, and the range of adequate temperatures increased with seed age. A common base temperature for germination was 11.7 C. In 1-yr-old afterripened material, the proportion of germinating seed (< 5%) and germination rate were similar at all temperatures. Barnyardgrass thus revealed a plastic strategy of germination. Stratification during the first winter removed dormancy and allowed germination at a narrow range of temperatures. This constraint on optimum germination temperature decreased with increased seed age. Seedling emergence, thus, may vary according to whether seed population originates from the previous year or from old soil seed banks.

Mediterranean characteristics are attributed to the genus Crocus, which is inadequately studied in terms of seed germination. An afterripening requirement is very common in environments with warm and dry periods, and photoinhibition has been detected in many angiosperms inhabiting dry and open areas. The effects of afterripening and light on seed germination were investigated for the first time in 23 native Greek Crocus taxa, collected from various localities with either a Mediterranean or a temperate climate. Germination experiments were conducted in continuous darkness and in light at the optimal temperature for each taxon, with both freshly collected and afterripened seeds; warm stratification (20°C, darkness) was also examined in 22 taxa. A number of selected taxa were additionally investigated with respect to afterripening outdoors, afterripening and warm stratification at higher temperatures (35 and 25°C, respectively), stratification at 20/10°C, dry storage at low temperatures, response to gibberellic acid and phenology of embryo growth. It was postulated that an afterripening requirement is a characteristic of the genus Crocus, and we found that it can be fulfilled in nature during the Mediterranean dry summer. Also, for the vast majority of the taxa, warm stratification and stratification at 20/10°C can both meet the afterripening requirement. Embryos of the taxa studied are underdeveloped and have to grow prior to germination. Intrageneric differences of seed germination were observed only towards light, with photoinhibition being predominant in taxa from drier environments.

The dispersal unit of many species of Brassicaceae is an indehiscent fruit, but relatively few studies have tested the effect of the pericarp on seed germination in this family. Our aim was to determine the effect of the pericarp on seed dormancy in six species of Brassicaceae native to the cold desert of north-west China. Intact dispersal units and isolated seeds of Chorispora sibirica, Euclidium syriacum, Goldbachia laevigata, Spirorrhynchus sabulosus, Sterigmostemum fuhaiense and Tauscheria lasiocarpa were stored dry at ambient laboratory conditions for 0–12 months and tested for germination in light and in dark at 5/2, 15/2 and 30/15°C. The amount of water absorbed by fruits and by seeds within the fruits was determined. For four species, intact fruits, isolated seeds and isolated seeds plus the removed pericarps were used to test for the mechanical versus possible chemical role of the pericarp in seed dormancy. Fresh isolated seeds, which have a fully developed embryo, germinated to lower percentages and rates than afterripened seeds. Thus, seeds have non-deep physiological dormancy. The pericarp significantly reduced germination, but inhibition was not due to lack of water uptake by seeds or to chemical inhibitors. Afterripened seeds of the six species germinated to 0–50% inside the fruits. We conclude that the pericarp plays a dominant role in seed dormancy of the six study species, and it does so by mechanically restricting embryo growth. Thus, the pericarp has the potential to spread germination over an extended period of time.

Knowledge about the hormonal control of grain dormancy and dormancy loss is essential in wheat, because low grain dormancy at maturity is associated with the problem of pre-harvest sprouting (PHS) when cool and rainy conditions occur before harvest. Low GA (gibberellin A) hormone sensitivity and high ABA (abscisic acid) sensitivity were associated with higher wheat grain dormancy and PHS tolerance. Grains of two PHS-tolerant cultivars were very dormant at maturity, and insensitive to GA stimulation of germination. More PHS-susceptible cultivars were less sensitive to ABA inhibition of germination, and were either more GA sensitive or germinated efficiently without GA at maturity. As grain dormancy was lost through dry afterripening or cold imbibition, grains first gained GA sensitivity and then lost ABA sensitivity. These changes in GA and ABA sensitivity can serve as landmarks defining stages of dormancy loss that cannot be discerned without hormone treatment. These dormancy stages can be used to compare different cultivars, seed lots and studies. Previous work showed that wheat afterripening is associated with decreasing ABA levels in imbibing seeds. Wheat grain dormancy loss through cold imbibition also led to decreased endogenous ABA levels, suggesting that reduced ABA signalling is a general mechanism triggering dormancy loss.

Seeds have evolved to be highly efficient environmental sensors that respond not only to their prevailing environment, but also their environmental history, to regulate dormancy and the initiation of germination. In the present work we investigate the combined impact of a number of environmental signals (temperature, nitrate, light) during seed development on the mother plant, during post-shedding imbibition and during prolonged post-shedding exposure in both dry and imbibed states, simulating time in the soil seed bank. The differing response to these environments was observed in contrasting winter (Cvi, Ler) and summer (Bur) annual Arabidopsis ecotypes. Results presented show that environmental signals both pre- and post-shedding determine the depth of physiological dormancy and therefore the germination response to the ambient environment. The ecotype differences in seed response to ambient germination conditions are greatly enhanced by seed maturation in different environments. Further variation in response develops following shedding when seeds do not receive the full complement of environmental signals required for germination and enter the soil seed bank in either dry or imbibed states. Species seed dormancy characteristics cannot therefore be easily defined, as seed dormancy is a dynamic state subject to within-species adaptation to local environments.

The understanding that many aspects of the spatial and temporal patterns of epiphyte communities may be explained by the comportment of early life stages has given rise to a considerable number of germination studies in recent years. Unfortunately, protocols frequently use unproven assumptions and arbitrary experimental conditions. To make future studies as ecologically meaningful as possible we address a number of potential pitfalls with a series of experiments with seeds from a total of 16 species. We show that it is safe to collect capsules for experiments before natural dehiscence – there is afterripening even in the case of very early collections. The application of fluctuating temperatures is not imperative, because there is no consistent difference in the germination response under constant versus fluctuating temperatures. The effects of different osmotic potentials and intermittent drought of varying intensity on germination are qualitatively, but not quantitatively, comparable. Due to the greater ecological realism, we encourage the use of the latter. However, care must be taken to use realistic temperatures – the impact of intermittent drought on germination is modulated by temperature. This highlights the need for data on the in situ temperature regimes during germination as an important prerequisite towards more realistic experiments in the field of germination ecology of vascular epiphytes.

Many studies have compared diaspore dispersal ability and degree of dormancy in the two diaspores of dimorphic plant species. A primary goal of these studies was to determine if germination and dispersal characteristics of the two morphs fit within a high risk–low risk (bet-hedging) life-history strategy, i.e. high dispersal/low dormancy in one morph versus low dispersal/high dormancy in the other one. In a survey of 26 papers on 28 diaspore dimorphic species, we found that in 12 of the studies, which were published between 1978 and 2008, seeds were stored, and thus possibly afterripened, before they were tested for germination. The 14 papers that tested fresh seeds were published between 1963 and 2010. Failure to test fresh seeds likely resulted in misinterpretation of the diaspore dispersal/dormancy strategy in some of the species investigated. We conclude that it is imperative that fresh seeds be tested for germination in order to be certain that the correct relationship between dispersal and dormancy is elucidated, and thus that the correct interpretation is made concerning life-history strategy and bet-hedging, in dimorphic species.

Pre-harvest sprouting (PHS) is a serious risk when adapting quinoa (Chenopodium quinoa) seed production to different temperate environments. Two quinoa accessions, ‘2-Want’ and ‘Chadmo’ were evaluated under field conditions in the Argentinean pampas over 2 years on five different sowing dates, to explore a range of climate conditions under which seed filling is manageable in this region. Both accessions exhibited dormancy during seed development and maturation under the conditions examined; however, dormancy expression was restricted to low temperatures in 2-Want, while seeds of Chadmo, originating from the humid island of Chiloe, southern Chile, expressed a high level of dormancy at all examined temperatures. Dormancy release was observed as a reduction in the lowest temperature permissible for seed germination, which broadened the optimal germination temperature window. Higher storage temperature increased the rate of dormancy release. The environment during seed development on the mother plant affected the levels and patterns of seed dormancy, with higher temperatures and longer photoperiods promoting dormancy. As dormancy was released before the next production period, the levels of dormancy observed in the accession would allow timely planting and uniform germination, while dormancy during seed maturation ensures the prevention of PHS. Chadmo showed deeper dormancy levels in all situations, compared with 2-Want, therefore greater PHS tolerance under various conditions in the pampas region can be expected for Chadmo, which makes this accession a better candidate to be included in adaptive breeding programmes for quinoa.

Among 14 species of herbaceous Fabaceae, all six winter annuals show a marked non-deep physiological dormancy of the embryo in addition to physical dormancy. This physiological dormancy is apparent at 23°C, but not at lower temperatures of 10°C and 5°C and disappears after 3 months of dry storage. These results corroborate the hypothesis that combinational dormancy is a double safety mechanism for delaying germination during summer: physical dormancy postpones germination, and even in early softened seeds germination is prevented by physiological dormancy of the embryo. Softened, swollen seeds of Medicago arabica tolerate a subsequent desiccation and remain viable even after five cycles of dehydration and rehydration. The rate of natural softening of M. arabica seeds increases exponentially at higher temperatures, with a Q10 between 3.4 and 5.1, and obeys the Arrhenius equation. This indicates that a chemical reaction might be involved in breakdown of physical dormancy. Winter annuals with hard seeds show similar properties as winter annuals with permeable seeds: the need for afterripening and requirement of lower temperatures delay germination until autumn. Only one species, Vicia sativa, loses physical dormancy during dry storage. Drying during summer might be a supplementary cue for germination in autumn.