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Showing papers on "Germination published in 1980"


Journal ArticleDOI
TL;DR: A model is developed to consider the interplay between dispersibility and delayed germination in desert annuals and finds that optimal germination fraction is found to be very sensitive to changes in despersibility especially at the limited dispersibilities that are realistic for annual plants.
Abstract: A model is developed to consider the interplay between dispersibility and delayed germination in desert annuals. The model explores the effect of low levels of dispersal, considered realistic for annual plants, on optimal germination fraction. The model also demonstrates the effect of the amount and accuracy of "predictive" (responsive to the environment) dormancy on the optimal innate germination fraction (not responsive to environmental conditions).Optimal germination fraction is found to be very sensitive to changes in despersibility especially at the limited dispersibilities that are realistic for annual plants. As dispersibility increases, optimal germination fraction increases. If plants make two kinds of seeds with differing despersibility, reproduction is maximized if the low dispersal seeds have delayed germination and the high dispersal seeds have quick germination. If dormancy mechanisms permit seeds to germinate when environmental conditions allow successful maturation, and remain dormant when environmental conditions do not permit successful maturation, what fraction of seeds should remain dormant under predicted good conditions as a hedge against inaccurate prediction of the environment? If environmental cues that break dormancy are uncorrelated with environmental conditions that permit successful maturation, predictive dormancy has little or no effect on the optimal innate germination fraction. When predictive dormancy lowers the probability of germinating when environmental conditions preclude successful maturation, the optimal innate germination fraction increases with increasing germination control by predictive dormancy. With a moderate degree of germination control by predictive dormancy, the optimal innate dormancy is still sensitive to changes in dispersal in the low dispersal ranges characteristic of annual plants.Evidence is presented from plant species that have both dispersal and germination dimorphisms to support the predicted correlation of high germination fractions with high dispersal.

522 citations


Book
01 Jan 1980
TL;DR: A Note from the Publisher Objectives Description and Botanical Relationship Contrast of Maydeae and Andropogoneae Origin of Corn The Life Cycle of Corn Development and Structure of Vegetative Parts The Kernel or Seed Seed Germination and Seedling Development The Root System Initials of root tissues Differentiation ofRoot tissues Origin of root branches The Stem Internodes Nodes The Leaf leaves of the embryo Leaves of the seedling and mature plant
Abstract: A Note from the Publisher Objectives Description and Botanical Relationship Contrast of Maydeae and Andropogoneae Origin of Corn The Life Cycle of Corn Development and Structure of Vegetative Parts The Kernel or Seed Seed Germination and Seedling Development The Root System Initials of root tissues Differentiation of root tissues Origin of root branches The Stem Internodes Nodes The Leaf Leaves of the embryo Leaves of the seedling and mature plant Parts of a leaf Development of the sheath and blade of the leaf Arrangement of tissue The epidermis Distribution of stomata Origin and development of stomata Development and Structure of the Reproductive Organs Development of Tassel and Staminate Spikelets Differentiation of tissues Reduction-division Microspores or pollen grains Shedding of pollen Amount of pollen produced Development of the Ear Shoot and Pistillate Inflorescence Differentiation of the tissues Reduction-division Development of the embryo sac Reproduction and Kernel Development Pollination and Germination of Pollen Fertilization Development of the Endosperm The Antipodal Cells in Later Stages of Kernel Development Development of the Embryo The Mature Kernel Inheritance in Corn Genes Xenia Maternal Inheritance Chromosomal Aberrations Inbreeding and Heterosis Corn Breeding Breeding procedure Hybrid seed production Literature Cited Index

462 citations


Journal ArticleDOI
TL;DR: Resuits from this study suggest that prolonged exposure to temperatures above 32 C can reduce pollen germination of many genotypes to levels near zero.
Abstract: High temperatures during maize (Zea mays L.) pollination are known to result in poor kernel set, but little is known of the direct effects of temperature on pollen germination. The purpose of this research was to determine how in vitru pollen germination of different maize genotypes is affected by high temperature stress during anthesis. Tassels from field-grown plants were excised at beginning anthesis, placed in water and transferred to growth chambers maintained at daytime temperatures of 27, 32, and 38 C. Nighttime temperatures were maintained 6 C cooler. In vitro germination was measured after 24 and 48 hours in the growth chamber as well as on pollen collected directly in the field. Genotypes differed in their response to temperature. In some genotypes pollen germ. ination steadily decreased as temperature increased. Others either germinated equally well at 27 and 32 C or germinated better at 32 than at 27 C. All genotypes had a lower germination at 38 C than at 32 or 27 C, and several genotypes exhibited no germination after 48 hours at 38 C. After 24 hours in the 38 C chamber, six inbreds widely used in the 1970’s germinated significantly better as a group than inbred.,; widely used in the 1950’s and 1930’s. Growth environment affected the absolute in vitro germination percentage, but in general genotypes retained similar relative responses to increasing temperature. Resuits from this study suggest that prolonged exposure to temperatures above 32 C can reduce pollen germination of many genotypes to levels near zero

271 citations


Journal ArticleDOI
TL;DR: Soil moisture, temperature, and—to a lesser degree—pH influenced germination of Glomus epigaeus spores, whereas levels of soil fertility and spore density had little or no effect.
Abstract: Soil moisture, temperature, and—to a lesser degree—pH influenced germination of Glomus epigaeus spores, whereas levels of soil fertility and spore density had little or no effect. Maximum germinati...

226 citations


Journal ArticleDOI
TL;DR: Picea mariana predominates in even—aged stands of fire origin at the forest—tundra ecotone near Inuvik, Northwest Territories, Canada and field measurements of water relations suggest no water stress related photosynthetic reduction for mature trees during 1976.
Abstract: Picea mariana predominates in even—aged stands of fire origin at the forest—tundra ecotone near Inuvik, Northwest Territories, Canada. Growth rates of P. mariana decrease with increasing latitude and density although growth rates do not change significantly along the ecotone. Field measurements of water relations, when compared with laboratory determinations of leaf water potentials vs. net photosynthesis, suggest no water stress related photosynthetic reduction for mature trees during 1976. Maximum and minimum leaf water potentials for mature trees were —0.6 and —2.1 MPa on 4 August and 1 July, respectively. Winter measurements of water relations also suggest no water stress. In contrast, 1st—yr seedlings demonstrated sensitivity to water stress with high rates of mortality at low levels of water loss. A macro—mesoclimatic gradient of 4°C was found across the tree line (135—km study transect). Picea mariana seed production and germination are limited by this environmental gradient to °40 km south of modern forest line. Germination and survivorship are also affected by microenvironments within a well—developed soil hummock terrain. The lower cardinal germination temperature of 15°C was the determinant of germination timing and success. Seed production estimates suggested little effect on stand reproduction with burn intervals of 100—200 yr. Shorter or longer burn intervals are believed to reduce stand reproduction. Reduced seed longevity, complete stand destruction by wild—fire, and apparent destruction of seed in the soil restrict establishment to 1—8 yr after fire. This may cause local extermination of the species or out—of—equilibrium tree line positions under conditions of deteriorating environment.

215 citations


Journal ArticleDOI
TL;DR: It is suggested that the co-existence of species at high density in calcareous grasslands may, in part, be explained by differences in germination response to fine-grained variations in the light environment at the soil surface.
Abstract: SUMMARY The germination of 27 species from calcareous grassland was tested in three light treatments in the laboratory: in darkness, under tungsten lamps and under a leaf-canopy. Germination was significantly lower under a leaf-canopy than in the dark in 17 species. The phenomena of leaf-canopy induced dormancy was not associated with the life-span of species, though there was a weak, negative relationship with seed weight amongst 20 perennials in the sample. It is suggested that the co-existence of species at high density in calcareous grasslands may, in part, be explained by differences in germination response to fine-grained variations in the light environment at the soil surface.

204 citations


Journal ArticleDOI
TL;DR: In this article, a study of flowering, germination, and seedling survival was conducted in various stable and unstable soil (surface scraped and surface tilled) sites on King Christian Island, N.W.T., Canada.
Abstract: Studies of flowering, germination, and seedling survival were conducted in various stable and unstable soil (surface scraped and surface tilled) sites on King Christian Island, N.W.T., Canada. Although most species flowered, few set seed in 1973 or 1974. Germination was slow (3 to 6 wk), occurring only after spring snowmelt or summer rains when there were thin films of standing water. Field

195 citations


Journal ArticleDOI
TL;DR: It was found that Parthenium pollen grains contained growth inhibitors which inhibited fruit set in many test species when artificially dusted on the stigmatic surface.
Abstract: SUMMARY White dust spread on the leaves and stigmatic surface of Crotalaria pellida L. and Desmodium heteracarpon (L.) DC var. strigosum Meeuwen growing in the midst of a Parthenium hysterophorus L. stand was found to be clusters of Parthenium pollen. The fruit set in those species was poor. It was found that Parthenium pollen grains contained growth inhibitors which inhibited fruit set in many test species when artificially dusted on the stigmatic surface. In culture conditions the germination and pollen tube growth of the test species were inhibited in the presence of Parthenium pollen or their extract. The plant produces on an average 3375 million pollen grains per square metre areas of the stand. The pollen grains disperse in dusters of 600 to 800 each and are carried great distances by wind. Pollen grains deposited on leaves in large quantity also reduce the chlorophyll content in these species.

173 citations


Journal ArticleDOI
01 Jun 1980-Ecology
TL;DR: Upon exposure to the sequence of natural temperature regimes in spring, induction of secondary dormancy of seeds in darkness occurs in two physiological stages while buried seeds are at low marginal temperatures for germination, and then at higher temperatures they lose the ability to germinate in light.
Abstract: As buried seeds of Ambrosia artemisiifolia came out of primary and secondary dor- mancy, they showed similar germination responses. In early spring at simulated habitat temperatures, seeds germinated well in light but not in darkness, but they germinated well in darkness at temper- atures characteristic of the habitat in late spring and summer. By late spring, seeds had entered secondary dormancy and did not germinate at any temperature in light (14-h daily photoperiod) or darkness. Prolonged exposure to 50C in darkness did not decrease germination in either light or darkness at a 12-h alternating temperature regime of 30'/15'C, but seeds subsequently kept at 151/60C in darkness for 1 mo required light for germination. Seeds then lost the ability to germinate in light as they were exposed sequentially to 20?/10?, 25?/15?, and 30'/15'C in darkness. Thus, upon exposure to the sequence of natural temperature regimes in spring, induction of secondary dormancy of seeds in darkness occurs in two physiological stages. While buried seeds are at low marginal temperatures for germination they lose the ability to germinate in darkness, and then at higher temperatures they lose the ability to germinate in light.

157 citations


Book
01 Jan 1980

155 citations



Journal ArticleDOI
TL;DR: Topsoil samples were collected from two 1 m2 quadrats in six mature forest sites, each representative of a Ghanaian forest type, and regularly watered to promote seed germination to conclude that most seedlings germinated from seeds whose dormancy is broken by exposure.
Abstract: Topsoil samples were collected from two 1 m2 quadrats in six mature forest sites, each representative of a Ghanaian forest type, and regularly watered to promote seed germination. Each sample was subdivided; half the subsamples were exposed to full sunshine, while the other half were shaded until germination ceased and then transferred to full sun. A total of 2028 seedlings belonging to 90 species (of which only 10 species occur in mature forest) were recorded in the sunlit boxes. Only 120 seedlings, of 25 species, germinated in the shade, but a further 41 species were recorded when the shaded boxes were subsequently exposed to sunshine. We conclude that most seedlings germinated from seeds whose dormancy is broken by exposure. WHEN MATURE TROPICAL FOREST is cut and cleared, it is quickly replaced by fast-growing herbs, climbers, and woody plants of species quite different from those present in the original forest. Various opinions have been advanced as to how this happens. One possible explanation is that the seeds from which these colonizing pioneers grow lie dormant in the soil from the time of one gap phase to the next. If this were true, seed longevities of up to several hundred years would be implied. Alternatively, dispersal agents might be responsible for a more-or-less continuous rain onto the forest floor of seed from pioneer species growing in gaps or secondary forest elsewhere. Two possible fates may be envisaged for seeds of pioneer species dispersed onto the floor of intact forest: they might germinate, but the resulting seedlings quickly succumb, or they might lie dormant until the forest is disturbed and the canopy removed. Four main aspects of the problem thus require investigation. Firstly, the size and composition of the pioneer seed stock in soils under mature forest; secondly the distribution and intensity of pioneer seed rain; thirdly the length of viability of pioneer seed; and finally the environmental requirements for germination. Several workers have investigated soil seed stocks by removing samples of topsoil from apparently undisturbed forest, watering the samples under exposed conditions, and assessing the seedlings which come up in them. Symington (1933), one of the first to undertake such experiments, reported that Malaysian forest soils contain abundant dormant pioneer seed, but Whitmore (1978) points out that Symington failed to protect his samples from possible contamination by seed which could have reached them from nearby secondary forest species during the course of the experiment. Other workers have avoided this problem: Liew (1973) and Guevara and GomezPompa (1972) protected their seed boxes from contamination by placing them in greenhouses, while Keay (1960) noted that the species of seedlings recorded in his boxes were not present in the area where the experiments were performed. With respect to the characteristics of the seed rain, Richards (1952: 383) has pointed out that most pioneer species fruit more or less continuously, and that their propagules are provided with efficient dispersal mechanisms. Gomez-Pompa et al. (1976) recently discovered, in an investigation in Mexico, that three of the four commonest seed species to be found in the guts of birds were pioneer species recovered from the soil in nearby primary forest. Although a heavy, widespread rain of poineer seed thus seems probable, direct measurements have not been published. Neither are data available on longevity of dormant seed. So far as the requirements for germination are concerned, all the authors mentioned above concur that seed dormancy is widespread among pioneer species. Ng (1978) states, however, that 'dormancy is not particularly characteristic of pioneer species in the humid tropics,' but by dormancy he implies only mechanical dormancy or the need for after-ripening. Most experiments have, in fact, failed to distinguish between the various possible causes of dormancy. V6azques-Yanes (1976) concludes from an extensive series of experiments, both in the laboratory and the field, that a light requirement is universal for the lPresent address: Department of Botany, The University, Aberdeen AB9 2UD, Scotland, U.K. 256 BIOTROPICA 12(4): 256-263 1980 This content downloaded from 157.55.39.157 on Fri, 08 Jul 2016 05:20:45 UTC All use subject to http://about.jstor.org/terms germination of pioneer species in the Mexican tropical forest where he worked, but he does not seem to have considered temperature as a possible factor.

Journal ArticleDOI
TL;DR: Based on ultrastructure and 14C labeling studies, anaerobically-grown seedlings are highly active metabolically, which may explain, at least for E. crus-galli var.
Abstract: Although rice has long been recognized to be uniquely adapted for growth in low oxygen environments of flooded rice fields, rice weeds of the Echinochloa crus-galli complex appear to be at least as well specialized for germination and growth under such unusual biological conditions. Seeds of two varieties of E. crus-galli germinate and grow for prolonged periods in a totally oxygen-free environment. E. crus-galli germinates as well as rice (Oryza sativa) under a total nitrogen atmosphere and produces as large a seedling in spite of its much smaller seed size. Like rice, the seedlings of E. crus-galli are unpigmented, the primary leaves do not emerge from the coleoptile and no root growth occurs without oxygen. Of particular interest is the ultrastructure of mitochondria from anaerobically-grown seedlings. Mitochondrial profiles from the primary leaf of seedlings grown continuously in nitrogen are very similar to those grown aerobically. The size and shape of the mitochondria are similar and the cristae are numerous and normal in appearance. This is in sharp contrast to previous studies of other species which have reported that mitochondria were vesiculate and tended to lose their normal fine-structure after similar periods without oxygen. Finally, based on ultrastructure and 14C labeling studies, anaerobically-grown seedlings are highly active metabolically, which may explain, at least for E. crus-galli var. oryzicola, its ability to germinate and emerge from flooded rice fields.

Journal ArticleDOI
TL;DR: The pH within the core or central region of dormant spores of Bacillus cereus and B. megaterium is 6.3-6.4 irrespective of the external pH, but the spore's internal pH rises to 7.5 upon germination, suggesting the low internal pH of the dormant spore may be a contributing factor to its metabolic dormancy.
Abstract: The pH within the core or central region of dormant spores of Bacillus cereus and B. megaterium is 6.3-6.4 irrespective of the external pH. However, the spore's internal pH rises to 7.3-7.5 upon germination. The low internal pH of the dormant spore may be a contributing factor to its metabolic dormancy.

Journal ArticleDOI
TL;DR: The wide range in seed vigor observed shortly after harvest maturity emphasizes the importance of timely harvest of seed fields and evaluation of seed viability and vigor soon after harvest.
Abstract: The quality of soybean [Glycine max (L.) Merr.] seed at harvest is dependent on the field production environment during development, maturation, and storage on the plant. These investigations were conducted to evaluate the effects of field weathering after physiological maturity (maximum dry seed weight) on seed viability and vigor. Five production environments were compared for two cultivars (‘Cutler 71’ - 1973, ‘Kent’ and Cutler 71 - 1974 and 1975). Seed was hand-harvested at physiological maturity, harvest maturity (first time the seed dried to less than 14% moisture content), and at regular intervals for up to 3 months after harvest maturity. All seed were evaluated for viability (standard germination test) and vigor (accelerated-aging germination test). Physiological maturity occurred at a seed moisture content of approximately 55% for both cultivars. The time interval from physiological maturity to harvest maturity (desiccation period) ranged from 10 to 20 days and was closely related (R² = 0.88) to the mean open pan evaporation during the period. Seed viability and vigor were highest at physiological maturity and remained high (>80% germination) until harvest maturity for all but one production environment. Viability was maintained at these high levels for 1 to 2 months following harvest maturity for four of five production environments. However, seed vigor declined rapidly, reaching levels that were significantly (α = 0.05) less than those at harvest maturity within 4 to 39 days after harvest maturity. In four of the production environments, seed vigor reached a level of less than 50% germination within 1 month of harvest maturity. The time required for seed vigor to significantly decline following harvest maturity was closely related to mean air temperature (R² = 0.90), mean minimum relative humidity (R² = 0.94), and precipitation per day (R² = 0.75). The wide range in seed vigor observed shortly after harvest maturity emphasizes the importance of timely harvest of seed fields and evaluation of seed viability and vigor soon after harvest.

Journal ArticleDOI
TL;DR: Neutral and polar spore lipids of the vesicular-arbuscular (VA) endophyte Glomus caledonius, were identified and quantitatively determined during spore germination, germ tube growth, and germ tube senescence.

Journal Article
TL;DR: In this paper, eight basic forms of seed structure are described and the seeds of species within each form have been found to have similar dormancy and germination patterns, and various permeability aids are necessary including temperature alternation, KNO(2), light and abrasion.
Abstract: Eight basic forms of seed structure are described. The seeds of species within each form have been found to have similar dormancy and germination patterns. Seed with rudimentary and linear embryos require time for further maturation of the embryo before germination. Miniature seeds require light at the beginning of the germination period. Seeds with peripheral embryos are protected by inhibitors in multiple seed coverings which need to be removed or leached before germination. Non-endospermic seeds or seeds with residual endosperm have mature embryos which are ready to grow but growth is blocked by their seed coverings. Hard seed coats which restrict the imbibition of water require mechanical or chemical abrasion or a release through the hilum, chalaza or strophiole. Seeds having a mucilaginous exudation exclude oxygen and may require light, low temperature or the addition of gibberellic acid. Seeds with multi-layered woody and fibrous seed coats are semi-permeable, allowing water entry but blocking oxygen and retaining strong inhibitors. Extracted embryos grow readily. Various permeability aids are necessary including temperature alternation, KNO(,2), light and abrasion. An understanding of these structural blocks to germination and the modifying effects of environment is directive in establishing methods for germinating flower seeds.

Journal ArticleDOI
TL;DR: It is indicated that the presence of seedlings at high densities inhibits subsequent germination of desert annuals, and this response by seeds is interpreted as an adaptation to avoid an unfavorable competitive climate where growth and survivorship are likely to be low.
Abstract: Field observations and experiments indicate that the presence of seedlings at high densities inhibits subsequent germination of desert annuals. Since plants growing at high densities face severe competition for limited resources, this response by seeds is interpreted as an adaptation to avoid an unfavorable competitive climate where growth and survivorship are likely to be low.

Journal ArticleDOI
TL;DR: Comparisons between ethanolic extractions and soil incorporation of plant residues with presumably non-allelopathic plants revealed that cucumber and barley extracts reduced redroot pigweed radicle growth whereas barley and green foxtail extracts increased greenfoxtail radicles growth.
Abstract: Low species diversity accompanied high populations of Canada thistle [Cirsium arvense (L.) Scop.] . Two perennial grasses and two rushes grew with Canada thistle; annual plants did not. Canada thistle litter, ground roots, and ground foliage added to soil in greenhouse bioassay tests reduced growth of redroot pigweed (Amarantbus retroflexus L.) and green foxtail [Setana viridis (L.) Beauv.] more than cucumber (Cucumis sativis L.) or barley (Hordeum vulgare L.). The addition of nutrients did not mask the toxic effect. Ethanolic extracts of Canada thistle roots and foliage were similar in their ability to reduce radicle growth of barley, cucumber, green foxtail, and redroot pigweed in petri dish studies. There was no significant difference between water controls and controls adjusted to the average pH and osmotic potential of the extracts. Germination of barley and cucumber seed was not affected. Comparisons between ethanolic extractions and soil incorporation of plant residues with presumably non-allelopathic plants revealed that cucumber and barley extracts reduced redroot pigweed radicle growth whereas barley and green foxtail extracts increased green foxtail radicle growth. These effects were not observed when these plant residues were mixed in soil. Additional index words. Plant residue, toxic extracts, weed ecology.

Journal ArticleDOI
TL;DR: It is concluded that tolerance to water stress in growing seedlings can be screened for by using PEG-containing nutrient solutions, and can not be predicted from germination tests in osmotica.
Abstract: A series of experiments was performed in order to evaluate the significance of seed germination and seedling growth in osmotic media as screening methods for drought tolerance. Ten spring wheat (Triticum aestivum L. em Thell.) and one durum wheat (Triticum durum Desf.) were tested under controlled environments, using polyethylene glycol-6000 (PEG) solutions as the moisture stress inducing media. Tolerance in the rate of endosperm utilization, under stress, prior to the onset of germination varied among cultivars. Germination rate or injury to germination at various concentrations of PEG differed significantly among cultivars. Cultivar rating with respect to injury to germination changed with stress levels. Injury to germination did not correlate with endosperm utilization rate in PEG or in water. Germinating seedlings were tolerant to extreme desiccation up to the stage of emergence of the first leaf from the coleoptile. Growth of photosynthesizing seedlings was monitored as they were carried through an increasing concentration gradient of PEG solutions, ranging from −5.9 to −11.3 bars of water potential. Cultivars significantly differed in seedling growth tolerance to increasing levels of water stress. Seedling growth tolerance across cultivars was not correlated with their germination responses under srress. It is concluded that tolerance to water stress in growing seedlings can be screened for by using PEG-containing nutrient solutions. It can not be predicted from germination tests in osmotica. Work was done under a US-Israel Binational Science Foundation (BSF) Grant no. 1654/78.

Journal ArticleDOI
TL;DR: Both seed number and seed dry weight were significantly reduced in the grazed plants of R. obtusifolius and R. crispus and the proportion of lighter seeds germinating was not significantly lower than that of normal seeds.
Abstract: SUMMARY (1) Three experiments were set up to examine the effects of grazing by Gastrophysa viridula on seed production, size and germination rate in Rumex obtusifolius and R. crispus. (2) Two experiments involved established plants in the field. The third experiment used plants grown from seed and subsequently planted out of doors. (3) Both seed number and seed dry weight were significantly reduced in the grazed plants of R. obtusifolius. (4) Seed numbers of R. crispus were not significantly affected, but seed dry weight was significantly reduced in one case. (5) The proportion of lighter seeds germinating was not significantly lower than that of normal seeds.

Journal ArticleDOI
TL;DR: In this paper, dry yellow peas, lentils, and faba beans were germinated under laboratory conditions, and a marked increase in ascorbic acid of the legumes was observed during germination.
Abstract: Dry yellow peas, lentils, and faba beans were germinated under laboratory conditions. Periodic rinsing with water at 2-hr intervals was effective in controlling microbial growth. Marked increase in ascorbic acid of the legumes was observed during germination. Amino acid contents did not change appreciably after 4day germination. Wheat flour blends containing ungerminated and germinated legume flours at 5, 10, and 15% levels were used in baking studies. Addition of 15% legume flours to bread resulted in only small deleterious effects on loaf volume, crumb grain, and flavor. Germination adversely affected the baking properties of peas and lentils, but not faba beans. Blanching of the germinated peas further impaired its baking properties.

Journal ArticleDOI
TL;DR: The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant.
Abstract: Factors controlling the establishment and removal of secondary dormancy in Chenopodium bonus-henricus L. seeds were investigated. Unchilled seeds required light for germination. A moist-chilling treatment at 4 C for 28 to 30 days removed this primary dormancy. Chilled seeds now germinated in the dark. When chilled seeds were held in the dark in −8.6 bars polyethylene glycol 6000 solution at 15 C or in water at 29 C a secondary dormancy was induced which increased progressively with time as determined by subsequent germination. These seeds now failed to germinate under the condition (darkness) which previously allowed their germination. Continuous light or daily brief red light irradiations during prolonged imbibition in polyethylene glycol solution at 15 C or in water at 29 C prevented the establishment of the secondary dormancy and caused an advancement of subsequent germination. Far red irradiations immediately following red irradiation reestablished the secondary dormancy indicating phytochrome participation in “pregerminative” processes. The growth regulator combination, kinetin + ethephon + gibberellin A4+A7 (GA4+7), and to a relatively lesser extent GA4+7, was effective in preventing the establishment of the secondary dormancy and in advancing the germination or emergence time. Following the establishment of the secondary dormancy by osmotic or high temperature treatments the regulator combination was relatively more active than light or GA4+7 in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA4+7 control. The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant. These changes appear to be modulated by light and hormones.

Journal ArticleDOI
TL;DR: Under favourable conditions for sowing, solid and liquid inoculants were generally as good as seed inoculation at similar total rates of application in promoting root nodulation and plant growth, however, when conditions were unfavourable for survival of rhizobia, solid or liquid inocULant gave better nodulations and very often better plant growth and seed yield than Seed inoculation.
Abstract: Ahst~~t Sixteen field experiments were conducted to assess whether inoculant applied as a liquid or in solid form separately from the seed but into the seed bed could be used as a substitute for conventional methods of legume seed inoculation. The experiments were done over a period of 8 years, on several soil types, with both crop and pasture legumes. Criteria used to measure response included success of the applied strain of rhizobia in forming nodules, quality of nodulation, seedling establishment, foliage dry matter production, and seed yield. Under favourable conditions for sowing, solid and liquid inoculants were generally as good as seed inoculation at similar total rates of application in promoting root nodulation and plant growth. However, when conditions were unfavourable for survival of rhizobia, e.g. when seed was dusted with toxic fungicide or when germination was delayed owing to environmental circumstances, solid or liquid inoculant gave better nodulation and very often better plant growth and seed yield than seed inoculation. The implications of these findings on alternatives to conventional seed inoculation and how they might be applied to agricultural practice are discussed.

Journal ArticleDOI
TL;DR: A range of aliphatic, aromatic and amino acids at a concentration of 5 mol m-3 inhibited the extension of roots of barley seedlings and prevented the germination of seeds in atmospheres containing small concentrations of oxygen.
Abstract: A range of aliphatic, aromatic and amino acids at a concentration of 5 mol m-3 inhibited the extension of roots of barley seedlings. Acetic acid is one of the least toxic but its action has the greatest ecological significance because it can be formed in phytotoxic concentrations by micro-organisms in soil. Its uptake and toxicity were greatest at low pH. Of the plant species which were examined, those most affected were barley, wheat and maize, followed by rape and clover. In aerobic conditions, microbial breakdown of the acid decreased its activity, but in atmospheres containing small concentrations of oxygen the acid prevented the germination of seeds. The toxicity could be partially alleviated by calcium carbonate applied as ground chalk to seeds.

Journal ArticleDOI
TL;DR: Both species germinated over a wide range of temperature and emerged from a soil depth of 12.5 cm; however, emergence of sicklepod was more rapid than coffee senna with 63% of the Sicklepod seedlings emerging from 2.5cm after only 3 days.
Abstract: The distribution of sicklepod (Cassia obtusifolia L.) and coffee senna (Cassia occidentalis L.) in the United States is similar and both species are increasing as problems within their range. Sicklepod is a problem in 11 southern states and increasing in 12 while coffee senna is a problem in 7 states and increasing in 8 states. Both species germinated over a wide range of temperature. Germination characteristics were similar in the range of 15 to 36 C. Germination of coffee senna was drastically reduced at 39 C by Rhizopus sp. Seedling growth was similar for both species and was maximum from 30 to 36 C. Both species have a hard seedcoat. Abrasion for 5, 10, or 15 s, puncturing with a needle, and sulfuric acid were all effective in initiating germination. Both species emerged from a soil depth of 12.5 cm; however, emergence of sicklepod was more rapid than coffee senna with 63% of the sicklepod seedlings emerging from 2.5 cm after only 3 days. Additional index words. Weed biology, hard seed, scarification.

Journal ArticleDOI
TL;DR: The response to prechilling fit a mechanism involving homeoviscous adaptation of membrane lipids to temperature, and increased germination responses to subsequent periods of high levels of Pfr which were initiated by red and terminated by far red irradiations.
Abstract: Temperature and kinetic studies were performed to examine the mechanism by which prechilling stimulates phytochrome-dependent seed germination in lettuce, Lactuca sativa, L. cv. Grand Rapids. Imbibed seeds were given a short far red irradiation and one day of dark incubation at 20 C to establish very low levels of the far red-absorbing form of phytochrome—(Pfr). Germination was greatly stimulated by subsequent prechilling treatments when they were followed by a second short far red irradiation. Prechilling therefore increased germination sensitivity to the low, normally inhibitory Pfr levels established by far red irradiation. This sensitivity increased with lowered prechilling temperature to a maximum near 4 C. It was linearly dependent upon duration of prechilling at 4 C up to a near maximal response at 10 hours, and it decayed in a converse manner when seeds were returned to 20 C after 10 hours at 4 C. Prechilling also increased germination responses to subsequent periods of high levels of Pfr which were initiated by red and terminated by far red irradiations. High Pfr periods adequate to promote the germination of unchilled seeds produced sharp inflections at 18 C in the dependence of germination on prechilling temperature. Rates of phytochrome potentiation of germination were not affected by prechilling. The response to prechilling fit a mechanism involving homeoviscous adaptation of membrane lipids to temperature.

Book ChapterDOI
TL;DR: This work has shown that severe dehydration irreversibly switches off production of reserve materials and switches on a controlled senescence program that continues at variable rates until the seed reserve structure is destroyed.
Abstract: Publisher Summary Moisture content plays a role in seed physiology in two ways. First, it may convey information about the expected metabolic activity of the seed—that is, development, resting, or germination. The proportion of structured or vicinal water in the tissue compared to the bulk water, and the change in absolute water content, may play a role here. A dehydration to air dryness would be necessary for the unequivocal switching of the water gradient polarity. This may explain why it is necessary to dry immature seeds below 60% moisture for good viability, even though germination occurs at 60% moisture. Therefore, the absolute moisture content does not dictate a specific physiological activity. Second, the expression of the perceived information is also controlled by moisture status. Severe dehydration irreversibly switches off production of reserve materials and switches on a controlled senescence program that continues at variable rates until the seed reserve structure is destroyed.

Journal ArticleDOI
TL;DR: In bioassays for phytotoxicity of velvetleaf, several dilutions of aqueous extracts from fresh field-collected leaves depressed germination of radish seeds and inhibited growth of soybean seedlings, suggesting interference with water balance and chlorophyll content may be two mechanisms of inhibitory action of toxins present in the leaves of velVEtleaf.
Abstract: Sampling in.a soybean field established that presence of velvetleaf (A. theophrasti) weeds interfered with soybean production. Number of soybean pods and number of pods/stem were significantly lower in transect segments adjacent to velvetleaf plants. In bioassays for phytotoxicity of velvetleaf, several dilutions of aqueous extracts from fresh field-collected leaves depressed germination of radish seeds and inhibited growth of soybean seedlings. Seed germination bioassays from eluates of chromatograms developed in one dimension showed that two of three bands containing phenolic compounds were inhibitory to radish seed germination. Soybeans inhibited by aqueous velvetleaf extracts had increased diffusive resistance, suggesting partial stomatal closure. Inhibited plants also gave evidence of water stress, with leaf water potentials often as low as -20 bars and reduced water content, when compared with controls. Quantification of chlorophyll on a leaf area basis showed that chlorophyll of inhibited plants was below controls. These data demonstrate the allelopathic potential of velvetleaf and suggest that interference with water balance and chlorophyll content may be two mechanisms of inhibitory action of toxins present in the leaves of velvetleaf. SEVERAL INVESTIGATORS have shown that allelopathy may be a part of weed and crop interactions. Bell and Koeppe (1972) reported that allelopathic effects of foxtail (Setaria faberi Herm.) contributed to reduction in corn (Zea mays L.) growth. Curled dock (Rumex crispus L.) and common milkweed (Asclepias syriaca L.) may have inhibitory effects on crop species because of water soluble phytotoxins in the leaves (Einhellig and Rasmussen, 1973; Rasmussen and Einhellig, 1975). Putnam and Duke (1978) hypothesize allelopathy may be a factor in increases in dominance by certain weeds in a variety of crop ecosystems. In addition to investigations implicating the allelopathic potential of several weeds on field crops, a number of weedy species release phytotoxins which influence the vegetational composition of natural communities, both in space and in time (Abdul-Wahab and Rice, 1967; Wilson and Rice, 1968; Parenti and Rice, 1969; Neill and Rice, 1971). Thus, the concept that some plants may adversely affect other plants through biochemical products is a known component of plant interactions. Velvetleaf (Abutilon theophrasti Medic.) is an annual weed of wide distribution in eastern United States and the more mesic regions of the prairie states. It is an introduced species, which is difficult to control in soybean fields because preplant and preemergence herbicide