Showing papers on "Germination published in 1975"

Seed and Pod Wall Development in Pisum sativum, L. in Relation to Extracted and Applied Hormones

Abstract: Developing fruits of Pisurn sativum, L., cv. 'Alaska', contain relatively large amounts of hor mones, mainly concentrated in the embryos and liquid endosperm. A close relationship can be demonstrated between changes in extractable amounts of gibberellins (mainly GA20), auxins (methyl 4-chloroindol-3yl acetate and probably 4-chloroindol-3yl acetic acid), and abscisic acid, and changes in growth rates of both the pod wall and seeds. Growth of the pod wall appears to depend largely on hormones supplied by the seeds. Marked changes in the germination capacity of the maturing seeds are closely associated with changes in extractable amounts of methyl-4-chloroindol-3yl acetate and abscisic acid. It is believed that high concentrations of these substances in the embryo, rather than any restriction imposed by the testa, may prevent precocious germination of the seeds.

The influence of gametophytic competition on sporophytic quality in Dianthus chinensis

Abstract: Pollinations were made on either the tip or the basal portions of the stigmatic surface in Dianthus chinensis. These two treatments provided, respectively, either good or modest opportunity for pollen tube competition. The pollen used came from a single clone. Technical and statistical methods were used to reduce greatly the influence of variation in seed weight. Seeds resulting from the two contrasting treatments were planted, and it was found that there were statistically significant differences in germination time and seedling weight between treatments. These results suggest that the quality of the F1 generation can be significantly modified by competition between pollen tubes from a single plant.

Germination Response of Legume Seeds Subjected to Moist and Dry Heat

Abstract: Prescribed burning is used in southeastern USA to promote growth of legu- minous plants which produce seed important as quail food. These seed are characterized by a hard seed coat and the ability to remain dormant but viable for a long time. This study was conducted to determine the effect of heat on germination of seed from several of these legume species. Seeds of 18 species and two varieties were subjected to moist and dry heat treatment. Moist heat increased germination in eight species and two varieties, and dry heat increased germination in seven species and two varieties. agement practice in the southeastern United States, particularly in the Coastal Plain area, where millions of acres of forested land are burned annually for purposes of fuel reduction, slash disposal, seedbed preparation, and improving cattle forage and wild- life habitat. Burning for any of these reasons usually accomplishes some of the others, although vegetative changes which follow forest fire may affect the habi- tat of various species of wildlife either beneficially or detrimentally. Much of the flora and fauna of the Coastal Plains evolved in the presence of frequent burning and their species are referred to as fire species. The under-

Seed Storage and Germination Under Northern Hardwood Forests

Abstract: The species, quantities, and germination of tree seed stored in the forest floor beneath five northern hardwood stands in Pennsylvania were determined by counting seed found in blocks of forest flo...

The Croonian Lecture, 1974: The Physiology of the Pollen Grain Surface

Abstract: Angiosperm pollen grains possess walls of remarkable structural complexity, and the architectural forms encountered are often sufficiently specific and consistent to be useful taxonomically. Lindley, von Mohl and others appreciated this systematic potential almost a century and a half ago, and today a comprehensive pollen taxonomy is taking shape with the publication of the World pollen flora founded by the late Professor Gunnar Erdtman. Surprisingly, until quite recently this interest in the taxonomic aspects of pollen wall morphology has not been matched by any great concern for the functional significance of even the most conspicuous features, such for example as the deep sculpturing so commonly found in the outer layer of the wall. When Erdtman spent a period in my laboratory in Belfast in the mid-1950s we talked at length about pollen and spore morphology and morphogenesis, but I do not recall that we seriously touched upon the adaptive meaning of the wall architecture. We need not have heen so blind, for there were already many suggestive leads. Wodehouse in his distinguished book of 1935 addressed himself not only to the problems of pollen wall morphogenesis, but noted also relations between structure and dispersal agency. German authors had thought along similar lines, and had already pointed to the functional importance of one type of pollen surface material, that which in some species acts as a binding agent ( Polenkitt ), holding grains together in groups and facilitating attachment to pollen vectors. Much earlier had appeared the work of Green (1894), who seems to have been the first to study the nature of pollen emissions. In an early application of substrate film methods, Green showed that intact moistened pollen grains released various hydrolytic enzymes, and surmised that these played some part in the pollen-stigma interaction, perhaps in germination and pollen-tube growth and nutrition. When Green wrote, Blackley’s famous work on the causes of hay fever was already 20 years old; and by the 1950s it was well established that the active constituents released by pollen were non-dialysable and predominantly protein in nature. Various authors commented on the rapidity with which protein exudates are released from pollen grains, and there was speculation on the sources of such mobile fractions; indeed the facts suggested the possibility that these, too, were held like Pollenkitt in sites at or near the surface.

Breaking of seed dormancy by catalase inhibition.

Abstract: Germination of some dormant seeds is promoted by solutions of thiourea, sodium nitrite, and hydroxylamine salts. The promotions are accompanied by irreversible inhibition of catalase (EC 1.11.1.6) in extracts from the seeds. The seeds are also promoted in germination by catechol and pyrogallol solutions. These effects are recorded for lettuce (Lactuca sativa L. cv. Grand Rapids) and pigweed (Amaranthus albus L.) seeds. The results indicae that metabolically derived hydrogen peroxide, spared from decomposition by catalase inhibition, oxidizes reduced NADPH required as the oxidant in the pentose pathway of glucose use. The metabolic system for such use of H2O2 involves the enzymes, peroxidase (EC 1.11.1.7) and pyridine nucleotide quinone oxidoreductase (EC 1.6.99.2), which are present in the dormant seed prior to imbibition of water.

Invasion and ecesis of bird-disseminated woody plants in a temperate forest sere.

Abstract: Dynamics of bird-dispersed woody species as they take part in succession were examined in a Pinus banksiana stand at Argonne National Laboratory with a focus on the function of small openings in promoting community change. Mathematical models were developed for the three first phases of woody species involve- ment in succession: input of seeds, germination and 1st-yr survival, and survival to maturity. All species had a 1st-yr survival rate less than 10% of seed input. Each species demon- strated a different degree of dependence on the various factors determining survival to maturity. For example, Prunus serotina balances a fairly low germination rate and a high rate of seed predation with ability to germinate under a wider range of physical conditions (safe sites) than do other species in the study. Vitis riparia, on the other hand, has a high germination rate. Since most seeds of bird-dispersed species are deposited in shade, each species has adapted ways to survive in shade for a limited number of years which is sometimes sufficient to allow for the occurrence of an opening in the forest or for vegetative growth into an existing opening.

Germination of Seeds in the Shadow of Plants

Abstract: An attempt to prove the ecological significance of red-far red control mechanisms in seed germination was made. The seeds of 30 species were exposed beneath the plant canopies. All the normally light-stimulated seeds, and also seeds of 14 (out of 19) “insensitive’ species and seeds of 1 (out of 4) light-inhibited species, were inhibited or significantly retarded in their germination, as compared with seeds exposed to diffuse light in an artificial construction. Further experiments with “insensitive’ seeds of Lactuca sativa L. cv. Cud Vorburgu showed that after prolonged plant-shadow treatment the seeds became light-sensitive in the usual phytochrome-mediated manner. Seeds exposed under the plant canopies during a few days were extremely sensitive to red or white light, but this sensitivity diminished slowly in the course of treatment. The spectral composition of light filtered through the leaves shows great preponderance of far red radiation. The red-far red reversion can be simply obtained with the natural light and a leaf. In open stands bright weather retards considerably the germination of lettuce, cloudy weather brings about full germination. Some considerations on the ecological significance of seed behaviour, particularly as connected with plant competition, are given.

Relative Importance of Factors Controlling Germination and Seedling Survival in Adenostoma Chaparral

Abstract: Environmental factors affecting germination and growth in the understory of mature stands of Adenostoma fasciculatum H. & A. were examined in the Santa Ynez Mountains near Santa Barbara, California. Nomenclature follows Munz and Keck (1959). Using a multifactor plot design, the effects of animal grazing, soil heating and soil fertility were examined under the shrub cover. Seed germination was greatly stimulated in several species by heat. Seedling growth was enhanced by nutrient enrichment similar to that observed in burned chaparral. Animal grazing had drastic effects on seedling survival. None of the seedlings exposed to animal grazing survived. Growth under the shrub cover was apparently suppressed, even in fertilized plots, by shrubderived toxins and decreased light levels. No single factor can, by itself, account for the entire pattern of germination and growth of all species beneath Adenostoma. The environmental complex under the shrub cover is such that the probability of survival of any single seedling is very low. These selective forces have resulted in the evolution of very efficient seed dormancy mechanisms in several species.

Inhibition of seed germination under leaf canopies in arenaria serpyllifolia, veronica arvensis and cerastum holosteoides*

Abstract: SUMMARY The germination of imbibed seeds of Arenaria serpyllifolia L., Veronica arvensis L. and Cerastium holosteoides Fr. is inhibited under two layers of Tilia×europaea L. leaves. The ecological significance of this phenomenon is discussed.

Genetic Control of Endosperm Amylase Activity and Gibberellic Acid Responses in Standard-Height and Short-Statured Wheats

Abstract: In contrast to standard-height wheat genotypes, short-statured wheats having major genes for dwarfness do not show increased seedling growth after treatment with gibberellic acid. Endogenous gibberellic acid induces synthesis of amylase in the endosperm of germinating seeds, but the amount of amylase synthesized is greatly increased by exogenous gibberellic acid treatment in standard-height and in short-statured wheats that have dwarfing genes from the variety “Norin 10.” “D6899,” which has the “Tom Thumb” gene for height reduction, had about one-fourth of the amylase activity of standard-height and Norin 10-derived, short-statured wheats. This genotype showed little or no increased amylase activity after gibberellic acid treatment. Genetic analyses showed that the amount of amylase synthesized was controlled by a single gene and was dependent on the number of copies of the structural gene present in the endosperm. Dwarfism in wheat may be related to a blockage in gibberellic acid utilization because other workers have found that the amount of endogenous amylase synthesized in Norin 10-derived, short-statured wheats is not growth-limiting, but it is not known if low amylase synthesis is related to dwarfism in the Tom Thumb derivative. No recombinants were recovered in a small population, suggesting that the Tom Thumb gene may pleiotropically affect plant height and the lack of response to gibberellic acid in amylase synthesis and seedling growth.

Factors controlling germination of some dune annuals.

Abstract: Most dune annuals are characterized by autumn germination and spring flowering and consequently are regarded as 'winter annuals' (Salisbury 1952). In a previous paper (Pemadasa & Lovell 1974a) the factors controlling the timing of flowering of a group of annuals in the dune system at Aberffraw, Anglesey, were discussed. This paper is concerned with the factors determining the precise date of germination of these species. The literature suggests that both innate and enforced dormancy mechanisms (Harper 1957) are involved in controlling the timing of germination of winter annuals, and four plausible explanations can be suggested for their germination in autumn but not in spring or summer. (a) The germination capacity of some species is very, or relatively, low owing to innate dormancy. However, by autumn owing to after-ripening (Baskin & Baskin 1971a, b, 1972; Newman 1963; Ratcliffe 1961) and/or softening of the hard seed coat (Williams & Elliott 1960; Quinlivan 1961), which overcome the innate dormancy, rapid germination is possible. (b) Germination of fresh seeds of some species is favoured by temperatures below those prevailing in the field in spring and summer (Hulbert 1955; Newman 1963), but as the seed ages the temperature range for germination is widened thus enabling germination in autumn. (c) The temperatures in spring and summer are above the maximum or optimum for germination; thus seed is subjected to enforced dormancy. The lower temperatures in autumn allow germination (Juhren, Went & Phillips 1956; Went 1948, 1949; Went & Westagaard 1949), although there is no 'change in temperature response' (Newman 1963) with seed ageing. (d) The soil moisture in summer is below the minimum for germination; thus seeds are forced to remain dormant. The increased precipitation in autumn increases the soil moisture regime to a favourable level allowing germination. Although the generalizations made above may be applicable to a wide variety of winter annuals, it must be emphasized that the germination requirements differ widely between species. This paper concentrates mainly on dormancy, temperature regime and soit moisture regime. Other factors, including light and darkness, are given only brief mention. The species examined were Aira caryophylleat, A. praecox, Cerastium atrovirens, Erophila verna, Mibora minima, Saxifraga tridactylites and Vulpia membranacea. A detailed account of the distribution of these species in the dune system at Aberffraw has * Present address: Department of Botany, University of Sri Lanka, Peradeniya, Sri Lanka. t Nomenclature follows Clapham, Tutin & Warburg (1962).

Enzyme to break down lettuce endosperm cell wall during gibberellin-and light-induced germination

Abstract: THE physiology of lettuce seed germination has been a subject of extensive study, but very little is known of the fundamental biochemical events which occur during germination. Here we report that the endosperm cell wall is largely composed of a mannose polymer (that is, a man-nan); and that germinating seeds produce an enzyme capable of its breakdown.

Acidification of the Medium Associated with Normal and Fusicoccin-Induced Seed Germination

Abstract: Fusicoccin, a toxin stimulating cell enlargement and inducing proton extrusion in various plant tissues, has been shown to replace kinetin, gibberellic acid and red light in breaking seed dormancy. It also removes the inhibitory effect of abscisic acid. The present data also show that the stimulating effect of fucicoccin on embryo growth of decoated radish (Raphanus sativus L.) and maize (Zea mays) seeds and on the development of maize embryos is accompanied by an early, significant acidification of the medium. Acidification of the medium is also observed when fusicoccin reverses the abscisic acid-induced inhibition of germination. These results support the hypothesis that the mode of action of fusicoccin in promoting germination involves, as in stimulation of cell enlargement, the activation at the cell membrane level of proton extrusion processes. The physiological significance of fusicoccin-induced release of protons at the onset of germination is discussed in comparison with the results concerning the mechanism of action of fusicoccin on cell enlargement in other plant materials.

Seed production studies on perennial ryegrass, timothy and prairie grass

Abstract: This paper considers the sequence of seed development by measurement and observation of ehanges in seed moisture content, weight, colour, endosperm consistency, germination capacity and yield in perennial ryegrass Grasslands Ruanui, timothy Grasslands Kahu and a New Zealand strain of prairie grass (Bromus unioloides). Seed moisture content was high (60–70%) after anthesis and declined at different rates, depending on the species and the weather. Maximum seed dry weight (maturity) was reached approximately 30 days after peak anthesis in all species and was influenced by N application and grazing. Colour changes in the seedhead and endosperm solidification proved unsatisfactory as measures of maturity. Endosperm solidification was reached 4, 11 and 12 days before maximum seed dry weight in ryegrass, timothy and prairie grass, respectively. Seeds removed from the plant as little as 7, 10 and 4 days after anthesis in ryegrass, timothy, and prairie grass, respectively, germinated, provided that dormancy was broken; but they did not retain viability after 3 months storage. Maximum viability of ryegrass, timothy and prairie grass seed tested immediately after harvest occurred 30, 38 and 16 days after anthesis, compared with 17, 35 and 12 days, respeetively, when germination testing was delayed for 3 months. In ryegrass, grazing caused a significant increase in seed yield in the second year while N application alone did not significantly increase yield. In timothy, grazing and to a lesser extent N, were both detrimental to seed yield in the second year. Highest yields were obtained in treatments not receiving either grazing or N. In prairie grass, grazing depressed and N application increased yields in both years. In all species similar or increased yield could be obtained by mowing the crop at, or slightly prior to, seed maturity and allowing seed development and ripening to continue on the cut straw for up to 10 days. Using this technique higher seed yields were obtained in ryegrass and timothy than when seed was direct-harvested. In prairie grass similar yields were obtained whether the erop was direct-harvested or threshed following drying in the swath for 10 days. The use of ‘drying curves’ for the prediction of correct cutting time of seed crops is suggested for ryegrass, timothy and prairie grass.

Secondary dormancy in light-sensitive lettuce seeds incubated anaerobically or at elevated temperature

Abstract: Light-sensitive lettuce seeds become secondarily dormant within 8–10 days if initial germination is suppressed by far-red light or incubation at elevated temperature (≥30 °C). When germination is suppressed by temperature, induction of dormancy occurs in both red and far-red irradiated seeds and the process is, therefore, independent of the phytochrome system. Dormancy induction requires oxygen, but reversion of phytochrome from the far-red- to the red-absorbing form appears to take place anaerobically.

Ethylene and seed germination

Abstract: Ethylene can break dormancy in a wide range of common weed species. Investigations of the phenomenology of this response have shown that there is a pronounced interaction between ethylene, light and other factors. The implications of these findings will be discussed in relation to the possibility of controlling weed seed germination in cultivated areas.

Effect of stratification temperature and germination temperature on germination and the induction of secondary dormancy in common ragweed seeds.

Abstract: Stratification of common ragweed (Ambrosia artemisiifolia) seeds at 4 C was most successful for breaking dormancy, whereas -5 C was least effective and 10 C was intermediate. Germination in the light exceeded that in the dark at all stratification and germination temperatures. The optimum temperatures for germination in the light were 10/20, 15/25, and 20/30. Maximum germination in the dark occurred at 20/30 C for seeds stratified at 4 and 10 C but the optimum temperatures for seeds stratified at -5 C were 10/20, 15/25, and 20/30. Seeds stratified at -5 and 10 C germinated best after 15 weeks of stratification, whereas 12 weeks of stratification at 4 C resulted in maximum germination. Secondary dormancy was induced in seeds which did not germinate in the dark. This was affected by stratification temperature and duration and germination temperature. The ecological significance of these germination characteristics is discussed.

The role of seed reproduction in the dynamics of established populations of Hieracium floribundum and a comparison with that of vegetative reproduction

Abstract: In the crowded parts of patches of Hieracium floribundum Wimm and Grab, which were established for at least a decade in an ungrazed pasture, 7–10% of the population (3700 individuals/m2) flowered Of the plants that flowered, 94% were alive a year later, but only 5% of these flowered Abortion of flower heads was common; one half of all those which were initiated in early June had aborted by flowering time in early July Freshly dispersed seed had a viability of 57%, which was reduced to 17% a year later, after its storage close to the soil surface Less than 6% of the viable seed was innately dormant Dry, laboratory-stored seed retained its viability for the year but was slower to germinate than soil-stored seed In field conditions, germination was temperature inhibited during most of the growing season Maximum daytime microsite temperatures of less than 32 °C, which is necessary for germination, were found to occur only in early spring and late fall Successful seedling establishment accounts for 1

Growth Regulators and the Phytochrome-Mediated Dormancy of Celery Seeds

Abstract: Seeds of five celery (Apium graveolens L.) cultivars germinated at 15°C in the light or dark but at 22°C only in the light. This light requirement was overcome by treatment with a mixture of the gibberellins GA4 and GA7 (GA4/7) but interactions of cytokinins, daminozide, ethephon, EDTA and N-phenyl-N′-4-pyridylurea (NC5392) with GA4/7 were observed. Varietal differences in response to GA4/7 concentration and the requirement for cytokinins were related to the upper temperature limits for germination of the different cultivars. Seeds of cultivars responding to low concentrations of GA4/7 appeared to contain less natural inhibitor than those requiring either high concentrations of GA4/7 or cytokinin in addition to low GA4/7. The cytokinin requirement for germination was partially removed by leaching the seeds with water. Interaction studies with applied hormones indicated that in seeds incubated in the light inhibition by abscisic acid was partially alleviated by N6-benzyladenine but not by GA4/7 application. The implications of these results are discussed in relation to the involvement of natural plant hormones in the dormancy mechanism of celery seeds.

Detection and location of seed-borne inoculum of Ascochyta rabiei and its transmission in chickpea (Cicer arietinum).

Abstract: A. rabiei infected 70% of C. arietinum samples from C. Anatolia, Turkey. The standard blotter method, using 5 seeds/Petri dish and 12 h NUV 12 h darkness cycles at 22 deg C, proved most suitable for detecting the fungus. The inoculum was spore contamination and mycelium occurred in the seed coat alone or in seed coat and embryo. Pycnidia were observed only in the seed coat of seeds having deep lesions. Inter- and intracellular mycelium was localized to lesions. Pycnidia were subepidermal and contained mature spores. Pycnidiospores obtained from the seed surface and pycnidia from 14-month-old seed stored at 3 plus or minus 2 deg showed 33% germination. The light and temp. responses of the fungus on PDA revealed that opt. colony growth occurred at 19 deg . Pycnidial formation was max. under NUV but failed in darkness. Both superficial and deep infections were equally potent in the transmission of the disease. The fungus was highly pathogenic to seed and 40-day-old plants.This paper was presented at the 17th Int. Seed Testing Congress 1974.

Control of rust diseases by diterpenes from Nicotiana glutinosa

Abstract: AN epimeric mixture of the diterpenes sclareol and 13-epi-sclareol (sclareol) (Fig. 1) has been shown to constitute 10%; of the surface exudate on leaves of Nicotiana glutinosa1. Investigations into its effect on fungal growth showed that it neither inhibits the spore germination of several species of facultative pathogens in vitro nor reduces the weight of mycelium produced in liquid medium. The development of hyphae of certain species of fungi, for example Alternaria brassicicola, is, however, markedly affected by this compound. In the presence of sclareol, increased branching is induced which leads to a substantial reduction in the diameter of colonies growing on agar1. Such morphological effects could be interpreted as the result of alterations in the regulation of natural fungal growth processes. This report describes the effect of sclareol on the germination and growth of rust fungi in vitro, and the protection it can provide to plants against diseases caused by these fungi.

Soil‐plant phytotoxicity and its possible significance in patterning of herbaceous vegetation in a bottomland forest

Abstract: A B S T RA C T Plant growth inhibitors, which are known to exert synergistic effects on herbaceous vegetation, were isolated and quantified from the soils under hackberry trees. Ferulic, caffeic, and p-coumaric acids were isolated from the soils under hackberry trees collected in January, April, and September from 0-15 and 15-30 cm soil depths. Seed germination bioassay indicated considerably higher phytotoxicity levels of individual plant growth inhibitors in January and April soils, and this toxicity level was more drastic when inhibitors were applied accumulatively. Individual phytotoxins extracted from soil in September were not very inhibitory to seed germination of selected test species; however, accumulative effects were still allelopathic to seed germination. Toxicity levels of individual compounds may reduce or disappear in a given time, but the combined action of these chemicals would still be toxic in croplands or in natural communities. Ecological implications of allelopathy in terms of soil-plant interaction are discussed. SOIL-PLANT INTERACTION due to the presence of phytotoxins in the soils of natural plant communities or in croplands is a well-known phenomenon as a soil sickening problem in agricultural fields (Borner, 1960; Patrick, 1955; Patrick and Koch, 1958; Guenzi and McCalla, 1966a; Wang, Yang, and Chuang, 1967). However,

An Introduction to Crop Physiology

Abstract: Prefaces Acknowledgements 1. Prolegomena 2. The environment 3. The supply and use of water 4. The absorption and transport of mineral nutrients 5. Photosynthesis and respiration 6, Germination and seeding emergence 7. vegetative growth 8. Flowering and fruit growth 9. Some aspects of overall growth and its modification 10. The prediction of responses Glossary Appendices Index.

Germination of Botrytis cinerea conidia in vitro in relation to nutrient conditions on leaf surfaces

Abstract: Conidia of different isolates of Botrytis cinerea Pers. ex Fr. varied widely in ability to germinate in water. Sugars and amino acids were added at concentrations similar to natural levels on leaf surfaces. To a limited extent simple sugars promoted germination. Fructose was most effective whilst sucrose was least effective. Amino acids stimulated germination with the exception of taurine and lysine. Lysine reduced the stimulatory effect of a mixture of amino acids. Germination of conidia was only increased by an inorganic nitrogen source, ammonium salts or by a mixture of mineral salts, when glucose was present. Growth factors, yeast extract, gibberellic acid and kinetin had no effect on germination but indole-acetic acid caused a small stimulation. Abscisic acid depressed germination. It is suggested that, like soil fungi, the germination of spores of phylloplane fungi may be nutrient-dependent, or independent with respect to exogenous nutrients. Poor in vivo germination of B. cinerea may be associated with competition.

Effects of Temperature on the Germination and Emergence of Lettuce (Lactuca Sativa, L.) Varieties

Abstract: SummaryThe response of seed germination to temperature, over the range 5-33°C, was studied for 22 varieties of the Crisp, Cos and Butterhead types of lettuce. The overall patterns of response were similar in all varieties, irrespective of the storage conditions or origin of the seed lot. The optimum temperature for germination in all varieties was between 15°C and 22°C, but there was a marked upper temperature limit for germination ranging from 25.7+0.9°C in cv Hilde to 32.8+0.9°C in cv Avoncrisp. In the main, the Crisp types germinated well at 30°C, which inhibited germination in the Butterhead types.In a field experiment where eighteen of these varieties were sown during a period of hot sunny weather, two distinct patterns of emergence were observed, apparently related to the prevailing soil temperatures and the upper temperature limits for germination of each variety. In varieties with a high upper temperature limit for germination, seedling emergence was rapid even during periods of high soil temperat...