Temperature Dependence of Viability and Dormancy of Zizania palustris var. interior Seeds Stored at High Moisture Contents

Seeds (caryopses) of North American wild rice (Zizania palustrisvar. interior), a temperate aquatic grass, have been thoughtto require storage at low temperatures and high moisture contentsto preserve viability. The seeds are also deeply dormant atmaturity and require up to 6 months of stratification to breakdormancy. We report here that wild rice seeds can retain viabilityat moisture contents 30% (f. wt. basis) for up to 6 monthsat temperatures as high as 30 °C, and for at least 1 yearat temperatures below 20 °C. Dormancy is not broken at temperaturesabove 10 °C, but subsequent stratification requirementsare unaffected by prior warm storage. Cold storage is thereforenot required to maintain viability of wild rice seeds, but isnecessary to break dormancy. Hydrated wild rice seeds can befrozen to –10 °C without damage, but dormancy is notlost at subfreezing temperatures. These results provide newoptions for long-term storage of wild rice seeds. Zizania palustris var. interior (Fassett) Dore, wild rice, seed, germination, dormancy, storage, moisture content     

Seed Longevity of Rice Cultivars and Strategies for their Conservation in Genebanks

Changes in seed quality during ripening were studied in sixteencultivars of rice, representing the three ecogeographic racesofOryza sativa, and one cultivar ofO. glaberrima, grown duringone dry season (Nov. –May) 1992 –1993 at Los Baños, Philippines. Mass maturity (defined as the end ofseed filling period) among the cultivars was attained between18.5 and 21.6d after anthesis (DAA). The seed moisture contentat mass maturity varied between 24 and 40%. Germination abilityof seeds in the early stages of development varied significantly,but as mass maturity approached, germination increased to themaximum and no significant differences were found among cultivars.The seeds were stored hermetically at 35 °C with 15±0.2%moisture content and the resultant seed survival data were analysedby probit analysis. Potential longevity (quantified by the valueof seed lot constantK_iof the seed viability equation) was greatestbetween 33 and 37 DAA, i.e. about 2 weeks after mass maturity.The stage during development at which seeds achieve maximumpotential longevity is described by the term storage maturity.Lowlandjaponicacultivars, large seeded accessions (seed mass40mg) andO. glaberrimahad shorter storage longevity ( , standarddeviation of the frequency of seed deaths in time=1.47 weeks)while cultivars with purple pericarp survived longer than othercultivars ( =2.33 weeks). The initial germination of thejaponicacultivarsat storage maturity was high (99 –100%) and the estimatesof maximum potential longevity (K_i) which ranged between 3.3(Shuang cheng nuo) and 4.4 (Minehikare) were close to thoseof theindicacultivars. This research suggests that seed production environment betweenNov. and May at Los Ba ños is benign for the temperatejaponicacultivars.The implications of these results on management of rice geneticresources are discussed. Oryza sativaL.; rice; germplasm conservation; seed production environment; seed development; seed longevity     

Predicting the Growth Interactions between Plants in Mixed Species Stands using a Simple Mechanistic Model

The Conductance model is a simple mechanistic model used topredict the growth of species in monoculture or mixtures fromparameter values derived from plants grown in isolation. Incontrast to many mechanistic models that require extensive parameterization,the Conductance model is able to capture the growth of a broadrange of species using a few simplified assumptions regardingplant growth and easily derived species-specific parameter values.We examine the assumptions within the Conductance model thattotal leaf area per plant is proportional to total plant weight,and that an isolated plant has a projected crown zone area thatis proportional to the 2/3 power of its weight. Power ratherthan linear relations were found between weight and leaf areafor Brassica oleracea, Daucus carota, Matricaria inodora, Solanumnigrum,Stellaria media , Trifolium repens and Veronica persica.For all seven species, the value of the power was less thanunity. All species also exhibited a power relation between crownzone area and weight, with the slope of this relation beingless than 2/3 for B. oleracea, D. carota and S. media. Althoughmorphology type accounted for some of the variation in the parametervalues relating to light interception, there were considerabledifferences between species within upright or prostrate foliagespecies groups. The Conductance model was used to predict yieldsof B. oleracea, S. nigrum and V. persica grown in both monocultureand binary weed-crop mixtures over a range of temporal and spatialscales. After calibrating the model to non-competing plants,the model was used to predict growth of the weed and crop speciesin contrasting densities and stand types. In some crop-weedcombinations, predicted crop and weed weights were within 17%of observed values, with no systematic deviations. In others,systematic and large deviations occurred.Copyright 2001 Annalsof Botany Company Brassica oleracea L., Daucus carota L., Matricaria inodora L., Solanum nigrum L.,Stellaria media L., Trifolium repens L., Veronica persica L., competition, growth, leaf area, crown zone area, light, shoot morphology, canopy architecture     

Mimicking a semi-arid tropical environment achieves dormancy alleviation for seeds of Australian native Goodeniaceae and Asteraceae

Background and Aims: Seed physiological dormancy (PD) limits the use and conservationof some of Queensland's (Qld) native forb species. It was hypothesisedthat optimum dormancy-alleviating treatments would reflect environmentalconditions that seeds experience in situ, and this premise wastested for PD seeds of four species native to south-west Qld. Methods: High temperatures and increased rainfall during summer are characteristicof this semi-arid tropical environment. Ex situ treatments weredesigned to mimic conditions that seeds dispersed in springexperience during the summer months before germinating in coolerautumn temperatures. Seeds received between 4 and 20 weeks ofa dry after-ripening (DAR), warm stratification or dry/wet cyclingtreatment (DAR interspersed with short periods of warm stratification),in darkness, before being transferred to germination test conditions.In addition, natural dormancy alleviation of one of the Goodeniaceaespecies was investigated in situ. Key Results: Dry/wet cycling resulted in higher levels of germination ofActinobole uliginosum (Asteraceae), Goodenia cycloptera andVelleia glabrata (Goodeniaceae) when compared with constantDAR or stratification, while Goodenia fascicularis (Goodeniaceae)responded better to short durations of warm stratification.Long durations of DAR partially alleviated PD of A. uliginosum;however, stratification induced and maintained dormancy of thisspecies. Modifications to the dry/wet cycling treatment andgermination test conditions based on data collected in situenabled germination of G. cycloptera and V. glabrata to be furtherimproved. Conclusions: Treatments designed using temperature, relative humidity andrainfall data for the period between natural seed dispersaland germination can successfully alleviate PD. Differences betweenthe four species in conditions that resulted in maximum germinationindicate that, in addition to responding to broad-scale climatepatterns, species may be adapted to particular microsites and/orseasonal conditions.     

Variation and Allometry of Seed Weight inAeschynomene americana

One hundred and fifty seeds from each of 72Aeschynomene americanapopulationswith world-wide origin were weighed individually and the meanand distribution of seed weight were calculated and comparedbetween populations. Mean seed weight varied less than five-foldbetween populations with about 80% having a mean seed weightbetween 2–3 mg. However, differences between the largestand smallest seeds (2–8 mg) ranged two-17-fold withinpopulations. Populations that had larger mean seed weights alsohad larger maximum and minimum seed weights but not larger standarddeviations than those with smaller mean seed weights. Seed distributionsfor populations with a mean seed weight2 mg were positivelyskewed while those for all populations with a mean seed weight4mg were negatively skewed. Populations that flowered later producedsmaller seeds than those that flowered earlier.Copyright 1998Annals of Botany Company. Seed weight, weight distribution, inter-population variation, correlation among traits,Aeschynomene americana.     

Seed germination ecology of the threatened endemic Iberian <Emphasis Type="Italic">Delphinium fissum</Emphasis> subsp. <Emphasis Type="Italic">sordidum</Emphasis> (Ranunculaceae)

Seeds of Delphinium fissum subsp. sordidum are physiologically dormant at maturity, with underdeveloped embryos; thus they have morphophysiological dormancy (MPD). The aims of this study were to determine the requirements for embryo growth, dormancy break and germination, to characterise the type of seed dormancy and to evaluate the effects of light, seed age, pollination mechanism, and inter-annual and inter-population variability on germinative ability. After 3 months of incubation at 5°C (cold stratification) in darkness conditions, the mean embryo length increased from 5.6 to 2.07 mm, with 76% of seeds germinating. Conversely, embryos of seeds incubated during 3 months at 20/7 or 28/14°C hardly grew and no germination was recorded. Since cold stratification was the only requirement for the loss of MPD, and both dry storage in laboratory conditions and warm stratification prior to cold stratification shortened the cold stratification period required for germination, it could be concluded that D. fissum subsp. sordidum seeds have intermediate complex MPD. Cold stratification and incubation in darkness conditions promoted higher germination percentages than those in light. In addition, germinative ability increased with seed age up to 8 months (reaching 96% at 5°C in darkness), showed a pronounced inter-annual and inter-population variability, as well as a significant decrease in seeds coming from pollination by geitonogamy. High temperatures (25/10 or 28/14°C) induced seeds to secondary dormancy, so seedling emergence in the greenhouse was restricted to February–March. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter. This study is the first one to document a gradual increase in germination percentage with seed age for plant species with intermediate complex MPD.     

Changes in Ultrastructure and Abscisic Acid Level, and Response to Applied Gibberellins inTaxus maireiSeeds Treated With Warm and Cold Stratification

Seeds ofTaxus maireiare known for their deep dormancy whichcan only be broken by a procedure involving warm stratificationfollowed by cold stratification. Treatments with alternatingtemperatures of 25/15 or 23/11 °C (12 h light) for 6 monthsfollowed by 5 °C for 3 months were successful in overcomingseed dormancy. After 6 months of warm stratification, cytologicalchanges observed included: enlargement of the embryo; a decreasein the number of lipid bodies; appearance of ER; and increasesin mitochondria, plastids, dictyosomes, vacuoles and microbodiesin the shoot apical meristem. Cold stratification followingthe warm treatment induced cell division, and one or two distinctnucleoli in the shoot apical meristem cells were observed. Bothwarm and cold stratification reduced endogenous ABA concentrationsfrom the original 8888 pg per freshly harvested seed to 392and 536 pg, respectively. Treatment with exogenous gibberellinsafter seeds had been warm-stratified showed that GA₄and GA₇wereeffective at promoting seed germination, but GA₃was not. Theseresults suggest that the strong seed dormancy ofT. maireicouldbe caused by a high ABA content and underdevelopment of theembryos in freshly shed seeds. We conclude that warm stratificationwith alternating temperatures increases the growth of embryosby cell expansion and enlargement and decreases ABA content,but seeds still remain ungerminated. Cold stratification mayinduce the response to GAs and initiate cell division resultingin release from physiological dormancy and subsequent germinationofT. maireiseeds.Copyright 1998 Annals of Botany Company Taxus mairei; ultrastructure; abscisic acid; gibberellin; seed dormancy; stratification; germination.     

Differences in Seed Production Between Stellaria media Populations from Different Habitat Types

Seed production in several populations of Stellaria media fromdifferent types of habitat was examined. Two populations, onefrom a flower garden and the other from a herring gull colonywere compared in detail by growing them at three soil fertilitylevels under similar conditions in a greenhouse. Three important differences between the two populations independentof soil fertility emerged: the garden plants flowered on averageeleven weeks earlier, they produced much smaller seeds, andthey produced more seeds per capsule. Other differences were influenced by soil fertility: at highfertility the garden plants produced about 50 per cent moreseeds than the gull colony plants, but on a seed weight basis,the gull colony plants were the more productive. However forboth populations at high fertility the proportion of shoot biomassallocated to seed production was similar. Some of these differences can be accounted for in terms of conditionsoccurring in the two habitats, in particular the relative importanceof disturbance and competition at the sites. Chickweed, Stellaria media (L.) Vill., ecotypic differentiation, time to flowering, seed production, resource allocation     

Reproductive performance of native and alien colonizing phanerogams on a glacier foreland,Iles Kerguelen

The retreat of the Ampère Glacier, on Kerguelen, has left wide ice-free areas where five native and two alien vascular plant species are involved in primary colonization. The number of seeds produced by individual fertile plants has been determined for each species and germination capacity has been tested under different temperature and light conditions. Colobanthus kerguelensis and Cerastium fontanum produced the highest number of seeds per plant. No dormancy mechanism occurred in either species and they appeared to be the most successful colonizers during the early stages following the deglaciation. No seeds of Azorella selago and Agrostis magellanica had germinated after 2 months. Dormancy was demonstrated only in Poa kerguelensis. Festuca contracta was the only species which exhibited a negative photo-sensitivity. Germination of indigenous seeds required relatively high temperatures, whereas the optimum temperature for germination in the introduced Poa annua was 10°C. These results are compared with the few data available in the subantarctic literature and ecological implications are discussed.     

Are Seasonal Dormancy Patterns in Arabidopsis thaliana Regulated by Changes in Seed Sensitivity to Light, Nitrate and Gibberellin?

Imbibed seeds of Arabidopsis thaliana (L.) Heynh., passed annuallythrough a pattern of changes in dormancy. Dormancy was brokenin summer and re-induced in autumn-winter. A second small germinationflush occurred in early spring. The role of sensitivity to light,nitrate and gibberellins (GAs) in regulating annual dormancypatterns and germination was studied with the use of GA-deficient(gal-2) and wild-type seeds. Dark-incubated seeds were exposedto a natural temperature regime for periods up to 18 monthsand at regular intervals germination capacity of portions ofseeds was tested at laboratory conditions. Germination datafitted as logistic dose response curves showed that sensitivityto light varied with the seasons in both genotypes. From interpretationof curve parameters, it is proposed that the observed sensitivitychanges involve alterations in the number of receptors, in thebinding characteristics of the receptors and/or in the responsechain initiated by ligand-receptor interaction. In this responsechain GA biosynthesis is stimulated (wild type) and sensitivityto GAs is enhanced (wild type, gal -2). GA sensitivity is alsodirectly influenced by temperature, thus without the interferenceof light. However, the significance of direct regulation ofGA requirement seemed to diminish with prolonged incubationoutdoors, whereas reversible changes in light sensitivity remainedclear. Therefore, we propose that seasonal dormancy patternsare mainly regulated by changes in sensitivity to light. GAsensitivity contributes to this pattern but is not primarilycontrolling dormancy. The GA requirement for germination isobvious as gal-2 seeds did not germinate at any time of theyear when deprived of applied GAs. However, GA biosynthesisis not required for dormancy control, as a dormancy patternwas also observed in the absence of the capacity to synthesizeGAs. Nitrate or sensitivity to nitrate did not contribute tothe regulation of dormancy and germination of this species.Copyright1994, 1999 Academic Press Arabidopsis thaliana (L.) Heynh., curve fitting, dormancy, fluence response curve, germination, gibberellin, gibberellin dose response curve, hormone mutant, light, mouse-ear-cress, nitrate, phytochrome, receptor, seasonal dormancy pattern, sensitivity     

Does cold stratification level out differences in seed germinability between populations?

Populations of seeds can vary greatly in their dormancy-breaking and germination characteristics. The purpose of this study was to determine if such dormancy differences are levelled out by cold stratification. Seeds of 33 annual weed species, each represented by three populations, were tested in light and darkness 7 weeks after harvest and after two stratification treatments: 18 weeks at 3 °C in the laboratory and 19 weeks outdoors in soil during winter. Cold stratification removed population differences in some species, but in several species such differences became apparent only after stratification. This happened either because dormancy became stronger in weakly dormant seeds (winter annuals) or weaker in strongly dormant seeds (summer annuals). In several species, the light requirement for germination increased after stratification. These results clearly indicate that germination tests performed on fresh seeds from a single population may not adequately predict germination percentages in the field.     

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.     

PHOTOCONTROL AND TEMPERATURE DEPENDENCE OF GERMINATION OF RUMEX SEEDS

1. Light is not obligatory for the germination of the seed ofRumex obtusifolius L. subsp.agrestis DANSER, which has beenregarded as being a typical light sensitive seed. Even in continuousdarkness, a short period of high (30°) or low temperature(5°) treatment evokes germination very readily. 2. Germination is markedly promoted by 1 min exposure to a redlight and this red light effect is completely removed by 1-hrexposure to a far-red light. Alternations of the red and far-redradiation bring about an alternate promotion and inhihibitionof germination. 3. When a dark interval is inserted between the red and thefar-red treatments, inhibition of germination becomes less distinctas the duration of darkness increases. When the seeds are irradiatedwith far-red prior to red, with an inserted darkness, germinationpromotion due to the red light also decreases with the durationof inserted darkness. 4. Complicated interdependence between the light and temperatureeffects are demonstrated. This suggests a participation of somereactants besides pigments in the photoreaction. 5. The observed interdependence between the light and temperatureeffects on the germination of Rumex seeds implies that, if,as BORTHWICK has assumed, two forms of pigment, viz., a far-red-absorbingform and a red-absorbing one, are participating in the photoreaction,they should be presumed to coexist from the start of imbibition. (Received September 27, 1960; )     

Seed dormancy and germination of the rare,high elevation Balkan endemic <Emphasis Type="Italic">Cerastium dinaricum</Emphasis> (Caryophyllaceae)

Short or long-term ex situ conservation is becoming increasingly important in conservation of plants in today’s changing environments. One of the important steps in ex situ conservation is the collection and storage of seeds and the consequent establishment of seed germination protocols. Cerastium dinaricum (Caryophyllaceae) is an endemic, high elevation and rare species of European conservation concern. Because of its severely fragmented distribution along the Dinaric Alps, the populations are likely to undergo further shrinkage in the future, which addresses the need of a long-term effective conservation management. From the potential ex situ population management perspective, we focused our study on germination ecology of C. dinaricum. The study revealed that temperature considerably affected the germination of seeds, which germinate better at 20 °C rather than 10 °C. A period of cold-wet stratification also significantly improved the final germination percentage with more pronounced increase at 20 °C, while addition of GA3 increased the final germination percentage by breaking the dormancy of non-stratified seeds. Mechanical scarification did not improve germination; on the contrary, it resulted in the lowest germination success. Seeds grown in complete darkness germinated significantly better compared to control when they were exposed to cold-wet stratification. Contrary to previous studies on some alpine species, which germinate better when exposed to light, dark treatment resulted in the highest germination percentages with 70 and 90% germination success after 4 and 8 weeks of stratification, respectively.     

Dormancy Release,Germination, and Electrolyte Leakage from Apple Embryos during Stratification in the Presence of Sucrose

The dynamics of dormancy release during the stratification of apple (Malus domestica Borkh.) seeds was quantitatively described by three characteristics of seeds germination: the percentage of seeds that germinated by the tenth day, mean germination time, and the sum of seeds germinated in each of ten days (Timson's parameter), which allowed the assessment of the viability, the rate of dormancy release, and seed heterogeneity. We showed that apple seeds were characterized by a combined (physical and physiological) type of dormancy, with the seed coat and the embryo envelope being involved in the maintenance of physical dormancy. The addition of sucrose to the stratification medium accelerated the release of seed dormancy and improved all characteristics that determine seed germinability. Electrolyte leakage from embryos hardly changed during stratification, which agrees with the fact that all seeds remained viable throughout the entire period of dormancy. We assume that the release of seed dormancy is not a single-stage process.     

The ecological distribution of C4 and C3 grasses in the Hawaiian Islands

Summary Isoenzyme analyses were carried out on the hypotetraploid Stellaria media and the diploid Stellaria pallida occurring on abandoned sandy fields in the coastal dunes of the Netherlands. Amylase isoenzymes in germinating seeds of Stellaria media showed a striking intrapopulational variability, which is in accordance with the germination behaviour of the different subpopulations. In contrast to these findings no intrapopulational variation nor developmental change in isoenzyme pattern could be detected on basis of 14 other analysed leaf enzymes. For five enzymes there was a difference in isoenzyme pattern between the species Stellaria media and Stellaria pallida. Of these five enzymes two showed an interpopulational variation in Stellaria media. The fact that there was almost no variability of the isoenzyme pattern in Stellaria pallida could be explained by the permanent autogamous (cleistogamous) state of the species. Effects of polyploidy on the isoenzyme pattern and its activity could not be demonstrated. Consequences of the extreme difference between the monomorphic pattern of the leaf enzymes as opposed to the polymorphism of the amylase are discussed in view of the difference in germination ecology and lifecycle strategy of Stellaria media subpopulations.     

Studies on the seed transmission of cucumber mosaic virus in chickweed (Stellaria media) in relation to the ecology of the virus

Cucumber mosaic virus (CMV) was transmitted in the seed of infected Stellaria media plants. The rate of seed transmission varied both in manually infected plants (3–21%) and in plants grown from infected seed (21–40%). In naturally infected plants the rates of transmission found were 4–29%. Seeds recovered from field soil carried 4–5% infection and in infected seed placed in the soil the virus persisted for at least 5 months. Seed transmission of CMV also occurred in infected Lamium purpureum (4%), Cerastium holosteoides (2%) and Spergula arvensis (2%) but it could not be demonstrated in six other more common weed species in five botanical families. Seed transmission in Stellaria media occurred with a British (W) and an American (Y) strain of CMV. The virus was shown to occur in S. media pollen. The importance of CMV-infected S. media seed in the soil in relation to the epidemiology of the virus is discussed.     

Tree Competition and Species Coexistence in a Sub-boreal Forest, Northern Japan

The growth and mortality patterns and the mode of competitionof six tree species forming a sub-boreal climax forest in Hokkaido,northern Japan, were investigated based on the diffusion modelat the level of the individual tree 2 m height in a 2·3-hastudy site. Picea jezoensis, Picea glehnii, Betula ermanii andAbies sachalinensis were dominant species, occupying approx.94% of the total basal area. Sorbus commixta and Acer ukurunduensewere subordinate species occupying approx. 6% of the total basalarea. A model for individual growth was developed, consideringboth intra- and inter-specific competition and the degree ofcompetitive asymmetry. Asymmetry was found in intraspecificcompetition of Sorbus commixta and Acer ukurunduense. Piceajezoensis, Betula ermanii and Abies sachalinensis showed symmetricintraspecific competition. There was little interspecific competitionamongst Picea jezoensis, Picea glehnii and Betula ermanii. Abiessachalinensis competed symmetrically with Picea jezoensis (onlyvery weakly, P < 0·1) and Betula ermanii (P < 0·01).Picea glehnii gave no indication of inter- or intra-specificcompetition. The growth of the four dominant species was neveraffected by the two subordinate species; the growth of the twosubordinate species was governed by the abundances of the fourdominant species, the sum of which almost amounted to standcrowdedness (i.e. symmetric competitive effect and one-sidedcompetitive direction). On the scale of 2·3 ha of thesub-boreal forest, symmetric competition prevailed over one-sidedor asymmetric competition although statistical evidence forany competitive effects was rather weak. This was probably dueto the relatively low tree density and stand crowdedness ofthis climax forest. Little competition between the dominantspecies suggested by relatively low proportions of r²-valuesattributable to competitive effects indicates weak organizationamongst the component species (i.e. species were more or lessindependent of each other) at the level of the individual tree 2 m height on the 2·3-ha scale.Copyright 1995, 1999Academic Press Climax forest, diffusion model, individual growth, one-sided competition, size structure, symmetric competition     

Amylase Activity and Loss of Viability in Wheat

Changes in total and -amylase synthesis were compared in twowheat samples aged up to 70% viability level. The results showedthat differences in amylase levels can be detectable betweenunaged and aged wheats and also between the two aged samples.Thus seed viability loss is characterized by decreases in amylaseproduction. However, these changes appear to affect the germinationrate, but not the final germinability. Trticum durum L. cv. Appulo, wheat, seed ageing, amylase, -amylase     

Analysis of the Effect of Cold Stratification on the Germination Response to Light and Alternating Temperatures using Selected Seed Populations of Ranunculus sceleratus L.

From a single population of achenes (seeds) of Ranunculus sceleratusL. sub-populations were selected on the basis of the sensitivityof individuals to an increasing number of daily light/temperatureshift cycles. Each cycle comprised a 4 h pulse of red lightfollowed by a 4 h temperature shift from 16 to 31 ?C. Selectionfor low dormancy (NND and ND) and high dormancy (D and DD) populationsresulted in a > 5-fold difference in the number of cyclesrequired for 50% germination. Despite a shift in the mean levelof dormancy the distributions of sensitivity (slopes of dose-responsecurves) were similar in all four selected populations. Differentialeffects of cold stratification on the germination response tolight and alternating temperatures were related to the depthof primary dormancy. The proportion of individuals that respondedpositively to the dormancy breaking effects of cold stratificationfollowed the trend DD < D < ND < NND. In high dormancypopulations (D and DD) the rate and uniformity of germinationof some individuals was reduced by cold stratification, indicatinga dormancy inducing effect. Over the range 2 to 11 ?C the effectivenessof dormancy release or dormancy induction was inversely relatedto temperature. The effects of cold stratification on the expressionof dormancy in R. sceleratus are discussed in relation to areproductive strategy involving winter and summer annual behaviour. Key words: Cold stratification, selection, dormancy, light, alternating temperatures, germination