Showing papers on "Germination published in 1984"

Seed variation in wild radish: effect of seed size on components of seedling and adult fitness

Abstract: Seed mass in wild radish (Raphanus raphanistrum) varies up to sixfold within single fruits. The impact of such variation on subsequent growth and fecundity was studied. Seeds from single fruits were used to minimize genetic differences among individuals. Weighed seeds were planted close together in a disturbed area typical of Raphanus habitats. Large seeds (> 6 mg) were more likely to emerge as seedlings than were small seeds (<4 mg). Seed size had no effect on emergence time. Seedlings from large seeds grew more rapidly and produced more flowers than did those from related smaller seeds. Results from the field experiment contrasted with those obtained in greenhouse growth studies, where seed size had no significant effect on final plant size. This study points out two factors that have led to inconsistent results in previous studies of seed size and seedling success: (1) differences in the timing of growth measurements, and (2) the presence or absence of competitive inequities among neighbors within the experimental design.

Review of data analysis methods for seed germination

Abstract: Numerous procedures for data analysis of seed germination responses are scattered throughout the literature. Here an attempt has been made to summarize the existing methods, to compare the information they provide and to examine their strengths and weaknesses. The methods reviewed include the percent germination, germination index, coefficient of velocity, median response time, probit analysis, curve-fitting of cumulative germination, heat sums, survival analysis with life tables, logistic regression, proportional hazards regression and accelerated failure time analysis. Comparisons among these method are discussed and illustrated with data from germination responses in tomato (Lycopersicon eseulentum Mill.). Seed germination involves not only qualitative responses of individuals, but also population responses which are distributed over time. Standard analysis of variance or regression methods are appropriate for a data analysis where germination of all viable seed is observed, but they are inappropriate when some viable seeds fail to germinate. Such missing (censored) data complicates statistical analysis and subsequent interpretation. Germinations tests should be designed to determine the nature of censored responses, which can be subsequently accommodated by several statistical procedures referred to as survival analysis.

Light requirements of neotropical tree seedlings: a comparative study of growth and survival

Abstract: (1) Eighteen species of wind-dispersed trees on Barro Colorado Island, Panama, are compared with respect to germination, survival, and growth of seedlings during 1 year under sun and shade conditions in a screened enclosure. The species vary in their mean dry weight of seed from 1.9 mg to 686 mg. (2) High and synchronous germination occurs in both sun and shade for sixteen of the eighteen species. Most species have epigeal germination with leafy green cotyledons. (3) Seedlings of fifteen species survive better in sun than shade; none survive better in shade than sun. Survival in shade and in sun are positively correlated. Shade tolerance varies widely and continuously among the species; it correlates with adult wood density, an indicator of growth rate and successional status, but not with the dry weight of seed reserves. The more shade-tolerant species have a lower proportion of seedlings dying from disease in the shade. (4) Seedling height after 1 year is greater in sun than in shade for all species. In both sun and shade, growth rate and height at 1 year are not correlated with adult wood density or shade tolerance. Seed dry weight correlates with seedling height in both sun and shade at 4 weeks, but with height in shade only at 1 year. Seedlings in shade show no or slow growth after the initial growth has used the seed reserves. (5) In the shade, number and length of leaves show little or no change with time; leaf turnover is negligible. In the sun, leaf number increases and successively younger leaves mature at larger sizes. Leaf size is greater in the sun than in the shade Senescence of the leafy cotyledons is more rapid in sun than shade for all species. (6) This experimental study predicts that all species examined benefit from seed dispersal to light-gaps. Some species are restricted as seedlings to gaps, while others persist, but do not grow appreciably, in the shaded understorey. The implications of these differences in light requirements for the size-age structure and for the spatial pattern of the populations are discussed.

The effect of salinity and temperature on the germination of polymorphic seeds and growth of atriplex triangularis willd.

Abstract: Polymorphic seeds of Atriplex triangularis were germinated at various temperatures (5-15 C, 5-25 C, 10-20 C, 20-30 C) and salinity regimes (0 to 1.5% NaCl) in order to determine their germinability and early seedling growth under these conditions. Larger seeds generally had a higher germination percentage in saline medium. The rate and percentage of germination decreased with increased salinity stress. A thermoperiod of 25 C day and 5 C night, 12 hr/12 hr, temperature enhanced germination of seeds. Early seedling growth is promoted in larger seeds at lower salinity, and at high-day and low-night temperatures. Polymorphic seeds have different physiological requirements which provide alternative situations for seed germination in natural habitats. ATRIPLEX TRIANGULARIS WILLD. (Chenopodiaceae) is an annual species of halophyte which is widely distnbuted in coastal and inland salt marshes of North America (Chapman, 1974; Ungar, 1974; Osmond, Bjorkman and Anderson, 1980).

The Effects of Seed Burial and Soil Disturbance on Emergence and Survival of Arable Weeds in Relation to Minimal Cultivation

Abstract: (1) Seeds of sixteen weed species (six grasses and ten herbs) were collected from arable field margins during 1977. Species included were Agrostis gigantea, Alopecurus myosuroides, Arrhenatherum elatius, Avena fatua, Bromus sterilis, Poa trivialis, Capsella bursa-pastoris, Galium aparine, Papaver rhoeas, Plantago major, Polygonum aviculare, Stellaria media, Tripleurospermum inodorum, Veronica arvensis, Veronica persica, and Viola arvensis. Seeds were sown in soil in pots or boxes at various depths, and either disturbed periodically or left undisturbed. Periodicity of emergence was recorded for each species. (2) Four patterns of emergence were recorded: (i) emergence in spring alone; (ii) predominantly in autumn; (iii) in both spring and autumn; (iv) emergence indifferent to season. Most of the grasses emerged predominantly in autumn whereas the main period of emergence for many of the dicotyledonous species was in spring. (3) Burial of small-seeded species both delayed and reduced seedling emergence as compared to surface-sown seed. In contrast germination and emergence of the larger-seeded species was increased by burial. Soil disturbance increased the total number of seedlings which emerged, but in general it did not alter the relative periodicity of germination, nor was emergence promoted by cultivation at times outside the period of natural emergence. (4) The number of viable but ungerminated seeds which remained after 2 years varied between species. It was least for surface sown seed and greatest for buried undisturbed seed. Most frequent were A. myosuroides, Viola arvensis, P. rhoeas and P. aviculare. No seeds of A. elatius, B. sterilis or G. aparine remained after 12 months. (5) Relatively few species emerged from below 50 mm with the exception of several large-seeded species. These species generally failed to establish from seed on the soil surface. (6) The results are discussed in relation to the use of minimal cultivations for cereal production. It is concluded that the majority of annual grass-weeds, despite having little innate dormancy, will continue to be encouraged by current agronomic practices. In contrast, many annual dicotyledonous species will decline in importance, partly as a result of their susceptibility to herbicides and partly because their periodicity of germination does not coincide with the establishment phase of autumn-sown cereals.

Effect of temperature and pH on water relations of field and storage fungi

Abstract: The effects of temperature and pH on the water relations of groups of field fungi, Aspergillus and Penicillium spp., were studied in vitro using wheat extract agar. The minimum water activity ( a w ) necessary for germination, growth and sporulation varied considerably within and between the three groups. For spore germination field fungi required from 0.85 a w ( Alternaria alternata, Cladosporium herbarum ) to 0.90 a w ( Verticillium lecanii ); Aspergillus spp. 0.71 a w A. amstelodami ) to 086 a w ( A. fumigatus ); and Penicillium spp. from 079 a w ( P. piceum ) to 0.83 a w ( P. roquefortii ). The minimum water activity tolerated close to the optimum temperature for growth was usually lower than that tolerated under sub-optimal conditions. Altering the pH from 6.5 to 4 increased the minimum a w for germination by about 0.02 a w at optimum temperatures and 0.05 a w at marginal temperatures. The change in pH also increased the number of days before germination occurred. In general, germination occurred at a lower a w than linear growth which in turn occurred at a lower a w than asexual sporulation.

The Seed: Germination

Abstract: Knowledge of the mature seed and its germination is of importance in the study of seed formation Indeed, embryogeny and germination are extensions of each other separated by a period of relative metabolic inactivity called quiescence, and are essentially different phases of the continuing process of embryo growth and development Obviously, the nature of the pre-quiescence embryo bears very heavily on early germination behaviour and its control, and answers to questions relating to germination behaviour are increasingly being sought during the period of seed development

The Seed: Structure

Abstract: The seed functions as the reproductive unit of the Spermatophyta (seed plants), and links the successive generations. Other important seed functions concern dispersal and survival under cold, dry or other inclement conditions. There is an immense diversity in the internal and external structure of seeds. These differences are, to an appreciable extent, related to dispersal and germination strategies, and may involve the size and position of endosperm and embryo, structure, texture, and color of seed-coat, and the shape and dimensions of the seed as a whole. The minute seeds of orchids may weigh as little as 0,000002 g each. The seeds of the legume Mora oleifera are possibly the heaviest, and the weight of each exceeds 1,000 g, whereas a one-seeded fruit of the palm Lodoicea maldivica weighs more than 20,000 g. The seed consists of three components: embryo, endosperm (sometimes perisperm), and seed-coat. Both endosperm and embryo are the products of double fertilization, whereas the seed-coat develops from the maternal, ovular tissues. The seed habit is a significant advancement in the evolution of higher plants. Seed plants show several evolutionary advantages over spore-producing plants. Fertilization takes place within the protective tissues of the mother plant, and during its development the embryo is nourished by the mother plant. Besides, the embryo is covered by the protective seed-coat and often provided with storage material. These factors made the seed plants so successful that they became the dominant component in the terrestrial environments of the earth.

Fire survival of Cape Proteaceae - influence of fire season and seed predators

Abstract: Many Cape Proteaceae store seed reserves in closed cones on the plant and rely entirely on these reserves for episodic recruitment after fires. Population size is sensitive to intervals between fires but also to fire season. Populations can be nearly eliminated by successive winter or spring fires. Three hypotheses explaining seasonal variation in recruitment were tested: (a) seeds germinate immediately after fire but seedlings die from summer drought; (b) seeds remain dormant over summer but the longer the delay between seed release after fire and germination 1) the greater the competition between seedlings and resprouts, or 2) the greater the seed losses to predators and/or decay before germination. Drought-avoiding dormancy occurred in 9 of 11 Cape Proteaceae studied, all of which delayed germination to autumn or winter. Seedling emergence and survival was not significantly increased after removal of competitors by methyl bromide poisoning. Seed predation, measured by exclosures, however, significantly reduced seed reserves before germination and also number of seedlings emerging. Post emergence seedling predation was negligible in the burn in contrast to adjacent mature vegetation where seedling predation was very heavy. The role of germination cues and rodent behaviour in controlling population recruitment is discussed and it is concluded that a knowledge of both is essential for predicting vegetation dynamics in this system.

Phenotypic Variety in Seed Germination Behavior: The Ontogeny and Evolution of Somatic Polymorphism in Seeds

Abstract: Germination polymorphism is commonly found among seeds in bulked samples. When the source of this variation in behavior has been investigated it often has been found to derive from differences between seeds produced within the same clutch (i.e., from the same mother). The ontogeny of these somatic polymorphisms is discussed with particular reference to the Leguminosae. Five generalizations emerge. (1) Differences in germination behavior are frequently associated with differences in the rate of seed development. (2) Polymorphism in seed size is frequently correlated with polymorphic behavior. (3) Polymorphism within a clutch may occur between or within fruit. (4) The type or ratio of types of seed produced may vary with time and season. (5) The degree of somatic polymorphism present in a clutch may be heritable. A general model of seed development is described which can account for these five features of within-clutch diversity in germination behavior. The term somatic heterochrony is suggested for the pro...

The effect of seed size and maternal source on individual size in a population of ludwigia leptocarpa (onagraceae)

Abstract: Seed size is normally distributed for many annual species, while mature plant size is frequently positively skewed. A study was conducted to determine the influence of seed size and the role of genetic differences in determining relative seedling size for Ludwigia leptocarpa. Seed size had a significant effect on percentage germination and time of seed germination but no effiect on dry weight or leaf area of seedlings. Seed size and spacing had a significant effiect on seedling dry weight for plants grown under competition, while relative day of emergence had no effect. Familial (genetic) diffierences were found in average seed weight between maternal plants, but not in average number of days to germination, average weight of seeds which germinated, or shoot dry weight. It is concluded that neither seed size alone nor genetic differences between plants are directly responsible for the development of size hierarchies in L>dwigia leptocarpa populations. Large seed size does convey an advantage in growth when plants from seeds of differing initial size interact.

Control of Seed Germination by Abscisic Acid : II. Effect on Embryo Water Uptake in Brassica napus L.

Abstract: Germination of rape (Brassica napus L.) seeds proceeds in two phases, an initial imbibition phase and a subsequent growth phase. The time courses of water uptake, O2 uptake, and ATP accumulation demonstrate that exogenous abscisic acid (ABA, 0.1 millimoles per liter) specifically prevents the embryo from entering the growth phase. The inhibition of water uptake by ABA is a rapid (lag-phase about 1 hour) and fully reversible process which appears to be the cause rather than the result of changes of the energy metabolism. In untreated seeds, an osmotic pressure (polyethylene glycol 6000) of 11 bars is required for a simulation of the ABA effect on water uptake. However, in ABA-treated seeds an osmotic pressure of only 3 bars is sufficient to suppress water uptake. Thus, ABA lowers the ability of the embryo to absorb water under osmotic stress. In a two-factor analysis of the simultaneous action of ABA and osmoticum on germination, a complete synergistic interaction between these factors was found while ABA and cycloheximide exhibit independent (multiplicative) coaction. These results are interpreted in terms of a common controlling point of ABA and osmotic stress in the water relations of germinating seeds.

Salinity Effects on Seed Yield, Growth, and Germination of Grain Sorghum

Abstract: In field trials at Brawley, California, sorghum cv. Asgrow Double TX and Northrup King NK-265 were sown on silty clay in mid-May 1982, given adequate N and P fertilizer and irrigated with saline water (1:1 NaCl and CaCl2) of electrical conductivity 1.5-12.1 dS/m. Grain yield was unaffected by soil salinity up to 6.8 dS/m, but each subsequent increase in salinity of 1 dS/m reduced yield by 16%. Yield reduction was due primarily to a decrease in grain weight/ear rather than to a reduction in ear formation. Grain yield of Double TX was significantly higher than that of NK-265. Vegetative growth was less affected by soil salinity than was grain yield. Salinity up to 8.2 dS/m did not affect germination. Higher salt levels delayed germination but did not affect the final germination percentage. Sorghum was more salt tolerant at germination than at later growth stages

Abscisic Acid and Precocious Germination in Soybeans

Abstract: Immature embryos ot soybeans (Olycine max L. Merr.J can be induced to germinate precociously by depleting the endogenous pool of abscisic acid (ABA). Washing the embryos or allowing the embryos to dry slowly within or out of detached pods causes a gradual decline in ABA content. The extent of germination is correlated with the length of washing or drying treatments, which in turn, affects the level of endogenous ABA. Providing embryos are three weeks of age or older, maturation and precocious germination can be induced by treating embryos in a way that causes a reduction in embryo ABA content. Drying is not an obligatory requirement for soybean seed maturation or germination.

Longevity of Witchweed (Striga asiatica) Seed

Abstract: Witchweed (Striga asiatica Lour. ♯4 STRLU) seed remained viable for 6 yr under open-shelf laboratory conditions and for 14 yr when deep buried under field conditions. Seed kept in normal atmosphere of the laboratory for < 1 through 6 yr had the following germination percentages: 2, 95, 95, 94, 83, 38, and 7. Newly harvested seed will not germinate because of postmaturity ripening requirements. There were no viable seed after 7 yr of shelf storage in the laboratory. Seed buried in the field gave 60 to 90% germination the first season after production. Annual recovery and testing showed a gradual reduction in viability to 10% at year 14 for the deepest buried seed; shallower buried seed expired sooner. No germination occurred thereafter.

Seed dynamics in Calluna-Arctostaphylos heath in north-eastern Scotland.

Abstract: (1) Estimates were made of seed production, dispersal and storage in the soil in Calluna-Arctostaphylos heath in N.E. Scotland. Germination and seedling establishment in recently burned areas were also studied. (2) Seed production and dispersal by individual species were found to follow the abundance of the species in each stand, though the performance of some species declined as the Calluna canopy closed. Little seed input occurred from surrounding areas into closed or recently burned stands. (3) The amount of seed stored in the soil varied according to stand age. Seeds of Calluna vulgaris and Carexpilulifera increased in abundance with stand age. Stored seed of most other species decreased in numbers though in some there was a slight increase in the degenerate Calluna vulgaris phase. (4) The number of seedlings establishing after fire was far fewer than would be expected from the soil seed store, and is correlated with the type of substrate left by the fire. (5) Seed budgets are estimated for a 15 year fire rotation for the major species studied.

The effect of seed dimorphism on the germination and survival of Salicornia europaea L. populations

Abstract: Seed dimorphism influenced the germination behavior of Salicornia europaea L., with small seeds being more dormant and less salt tolerant than large seeds. All of the large less dormant seeds of S. europaea germinated prior to May, and all seedlings produced after this time were from small seeds. A persistent seed bank was maintained by the small dormant seeds. Survivorship was relatively constant during the normal germination season, but increasing salinity stress at any time during the spring reduces the chance of seedling survival. Little germination occurred from July through September because of the high surface soil salinities during this period. SALICORNIA EUROPAEA L. is an annual halophyte in the family Chenopodiaceae (Fernald, 1950). The plant has an erect habit, with an articulated and apparently leafless stem. Branching is decussate and in the mature plant all of the branches terminate in a spike-like inflorescence of 3-flowered cymules. The central flower of a cymule always produces a larger seed than the two lateral flowers (Konig, 1960; Dalby, 1962; Ungar, 1979). Seeds from the lateral flowers are less salt tolerant and more dormant than the larger seeds of the central flowers (Ungar, 1979). Small seeds have a light and a stratification requirement, similar to the condition found in S. patula studied by Grouzis, Berger and Heim (1976). Ungar (1979) concluded from his germination studies that S. europaea exhibited a somatic seed dimorphism. Somatic seed polymorphism is defined as the production of seeds of different morphologies and behavior on different parts of the same plant (Harper, 1977). The phenomenon has been reported in a number of weedy annuals that occupy unpredictable environments, and seems to be the rule in several genera of the family Chenopodiaceae (Harper, Lovell and Moore, 1 9 70). The diffierential germination behavior of different seed morphs has been discussed by several authors (Harper, 1965; Williams and Harper, 1965; Harper et al., 1970; Baskin and Baskin, 1976; Harper, 1977; Flint

The effect of seed dimorphism on the germination and survival of salicornia europaea

Abstract: Seed dimorphism influenced the germination behavior of Salicornia europaea L., with small seeds being more dormant and less salt tolerant than large seeds. All of the large less dormant seeds of S. europaea germinated prior to May, and all seedlings produced after this time were from small seeds. A persistent seed bank was maintained by the small dormant seeds. Survivorship was relatively constant during the normal germination season, but increasing salinity stress at any time during the spring reduces the chance of seedling survival. Little germination occurred from July through September because of the high surface soil salinities during this period. SALICORNIA EUROPAEA L. is an annual halophyte in the family Chenopodiaceae (Fernald, 1950). The plant has an erect habit, with an articulated and apparently leafless stem. Branching is decussate and in the mature plant all of the branches terminate in a spike-like inflorescence of 3-flowered cymules. The central flower of a cymule always produces a larger seed than the two lateral flowers (Konig, 1960; Dalby, 1962; Ungar, 1979). Seeds from the lateral flowers are less salt tolerant and more dormant than the larger seeds of the central flowers (Ungar, 1979). Small seeds have a light and a stratification requirement, similar to the condition found in S. patula studied by Grouzis, Berger and Heim (1976). Ungar (1979) concluded from his germination studies that S. europaea exhibited a somatic seed dimorphism. Somatic seed polymorphism is defined as the production of seeds of different morphologies and behavior on different parts of the same plant (Harper, 1977). The phenomenon has been reported in a number of weedy annuals that occupy unpredictable environments, and seems to be the rule in several genera of the family Chenopodiaceae (Harper, Lovell and Moore, 1 9 70). The diffierential germination behavior of different seed morphs has been discussed by several authors (Harper, 1965; Williams and Harper, 1965; Harper et al., 1970; Baskin and Baskin, 1976; Harper, 1977; Flint

Ecophysiology of Seed Germination in the Tropical Humid Forests of the World: A Review

Abstract: Most forest tree seeds from the humid tropics germinate soon after dispersal forming carpets of semi-dormant seedlings. Delayed germination and enforced dormancy is frequent among light- gap adapted species, some emergent trees and species with hard-coated seeds. Dormancy is more important as an adaptative trait in marked seasonal forests.

Early Events in Germination

Abstract: Publisher Summary This chapter discusses the early events in germination of seeds that have lost viability through prolonged storage or artificial aging and those seeds that remain moist when mature, the so-called recalcitrant seeds. Three phases of metabolism of development of seeds can be recognized: imbibition, the lag phase, and germination. The seeds of some species can be induced to germinate only if they have first become air dry and then rehydrated during imbibition. This applies also to immature seeds of certain species. The seeds of soybean can be induced to germinate at unusually early stages of development by first air-drying. Desiccation and rehydration terminate the synthesis of proteins normally accumulated during development and initiate the synthesis of different proteins: a germination pattern. Although the seed shows no obvious and outward sign of change during the lag phase, the effect of temperature on the duration of this phase can be taken as evidence that preparations are being made at the metabolic level for the eventual act of germination. The data on seed leakage and on maturation of mitochondria in pea suggest that there is a change in membrane architecture at water contents below 20%–30%. Such a change might possibly mediate the observed effects of desiccation and inhibition on seed development.

Structural Aspects of Dormancy

Abstract: Publisher Summary This chapter discusses different structural aspects of coat-imposed dormancy. Dormancy in seeds provides a means by which germination is delayed until favorable conditions for growth and establishment in the field are met. The water-impermeable coat protects the embryo from adverse storage and environmental conditions and actively promotes seed longevity. However, it is still unknown whether impermeability is due to mechanical processes (for example, shrinkage and closer packing of the cells in the seed coat as the seed matures) or to chemical effects (for example, impregnation of the cell walls with hydrophobic substances). A combination of both may exist and the operative mechanisms may differ among various species. The strength and other mechanical properties of the coat need to be measured for many more species to determine if mechanical constraints to embryo expansion or radicle extension prevent germination. From a small number of studies, it is evident that the lens in mimosoid seeds and an area near the chalazal discontinuity in malvaceous seeds are underlain by a single or double layer of thin-walled, sub-palisade cells, whose walls break readily under stress. In papilionoid seeds, the hilum functions as a hygroscopically activated, one-way valve that permits drying out of the seed during maturation. The mechanism(s) of natural breakdown of the seed coat and the effects of passage through birds and animals are two virtually unexplored areas. The available reports of the effects of artificial treatments on the seed coat are sometimes vague and frequently contradictory. There is a need for co-operative research between workers in various fields to understand these problems and to minimize unnecessary proliferation of speculation and hypotheses.

Seed Polymorphism and Germination Responses to Salinity Stress in Atriplex triangularis Willd.

Abstract: Seeds of Atriplex triangularis exhibited a very pronounced morphological and physiological seed polymorphism. Seed size varied from 1.0 to 2.8 mm and predicted the likelihood of successful establishment through its effect on germination and seedling vigor. Large seeds had a mean dry weight of 2.44 ± 0.16 mg and a mean length of 2.45 ± 0.24 mm; medium seeds, mean dry weight of 1.21 ± 0.10 mg and mean length of 1.78 ± 0.19 mm; small seeds, mean dry weight of 0.64 ± 0.04 mg and mean length of 1.27 ± 0.10 mm. The degree of salt tolerance increased progressively with increasing seed size. Seeds from all size classes that were initially treated with 2%-5% NaCl had from 85% to 100% germination after being immersed in distilled water for 6 days, indicating a transitory adverse effect of salt stress on germination. The amount of water absorbed by all seeds is influenced by change in media salinity but not by hormonal treatments. Small seeds contain more Na+ and Cl- than medium and large seeds. Seedling dry weight ...

Desiccation studies in relation to the storage of Araucaria seed

Abstract: SUMMARY Relationships between seed moisture content (fresh weight basis) and germination were examined for nine Araucaria species by desiccation under mild environmental conditions. The lowest safe moisture content, below which germination percentage begins to decline, was estimated in each case. Seeds can be grouped into three moisture content categories: the first group (including A. araucana, A. angustifolia, A. hunsteinii and A. bidwillii) cannot be safely dried to below 25–40%; the second group (including A. columnaris, A. rulei, A. nemorosa and A. scopulorum) cannot be dried to below about 12% without damage; the third category contains A. cunninghamii, which can be dried to 2% without damage. Seeds in the first group should be stored at 0–5 °C with moisture contents above the lowest-safe value. Provided freezing damage does not exceed 10%, seeds in the second group should be kept at - 18°C or lower with about 7% moisture content for long-term storage and at 0–5 °C with about 12% moisture content in the short term. Seed of A. cunninghamii is best retained at near 5% moisture content and in -18°C or lower. The lowest-safe moisture content was found to be associated with seed size and weight, higher moisture content values coinciding with greater size and weight of seed. Food reserve materials also differed among the groups; seeds of the first group were mainly starchy, whilst those in the other categories possessed a high lipid content.

The influence of burial and dry-storage upon cyclic changes in dormancy, germination and response to light in seeds of various arable weeds

Abstract: In general, shallow burial (25 mm) reduced seedling emergence except in the case of B. sterilis, which also germinated at a depth of 150 mm but failed to emerge. Cyclic changes in dormancy of buried seeds were observed. Although sensitivity to light was enchanced by burial, germination and response to light quality varied between seasons. Dormancy of most species, including the winter annuals A. myosuroides, Veronica persica and Viola arvensis, was least in autumn and most in summer. Papaver rhoeas was least dormant in spring and S. media was least dormant in summer. Generally, red light promoted germination whereas far-red light or darkness was not stimulatory. However, A. myosuroides was more sensitive to far-red light in autumn than at other times of the year. Natural day-light promoted germination of A. myosuroides, S. media and Veronica arvensis. Germination of B. sterilis was delayed in natural daylight. Transfer of A. myosuroides, Papaver rhoeas, Veronica arvensis and Viola arvensis from darkness to daylight increased germination above that obtained under natural daylight. Germination of freshly collected seeds of Alopecurus myosuroides, Arrhenatherum elatius, Poa annua, Poa trivialis, Plantago major and Viola arvensis was promoted by short irradiations of red light. Dry-storage did not affect germination of Alopecurus myosuroides, Poa annua, Plantago major or Viola arvensis, but did affect dormancy and light requirement of Poa trivialis. Burial of seeds of Alopecurus myosuroides, Poa trivialis and Plantago major increased their sensitivity to far-red light. It is concluded that cyclic changes in seed dormancy and associated light sensitivity are determined seasonally and result from changing environmental factors and that they are of adaptive importance for survival.