Showing papers on "Germination published in 1986"

The Influence of Temperature on Seed Germination Rate in Grain Legumes

Abstract: Co veil, S., Ellis, R. H., Roberts, E. H. and Summerfield, R. J. 1986. The influence of temperature on seed germination rate in grain legumes. I. A comparison of chickpea, lentil, soyabean and cowpea at constant temperatures.—J. exp. Bot. 37: 705-715. For a single seed population of each of four species of grain legume positive linear relationships were shown between temperature and rate of germination for different fractions (G) of each population, from a base temperature, Tb(G), at which germination rate is zero, to an optimum temperature, T0(G), at which germination rate is maximal. At constant temperatures warmer than 7i(G) there were negative relations (probably linear) between temperature and rate of germination to the maximum temperature for germination, Tm(G). Within each population Tb(G) did not differ, but it did vary between species, viz. 0 0 °C, 2-5 °C, 4 0 °C and 8-5 °C for chickpea (Cicer arietinum L.), lentil (Lens culinaris Medic.), soyabean (Glycine max [L.] Merr.) and cowpea (Vigna unguiculata [L.] Walp.), respectively. In contrast, T0(G) varied both within each population and also between the four species: 80% of seeds in each population had T„(G) values within the range 31-8 °C to 33 0 °C, 24 0 °C to 24-4 °C, 34 0 °C to 34-5 °C and 33-2 °C to > 40 °C, respectively. Values of Tm(G) were much more variable: the 80% population range was 48 0 °C to 60-8 °C for chickpea, 31 -8 °C to 34-4 °C for lentil and 46-8 °C to 55-2 "C for soyabean; reliable estimates could not be made for cowpea, but the results suggest higher and more variable values of Tm(G) than in the other three species. At sub-optimal temperatures the distribution of thermal time for the different fractions of each population was normal, except for lentil where it was log-normal. A single equation is proposed to describe the influence of sub-optimal temperatures on rates of germination for whole seed populations. At supra-optimal temperatures, variation in thermal time for the different fractions of each population was only slight. The implications of these findings for the adaptation of grain legume crops to different environments, and for the screening of germplasm, are discussed. Key words—Seed germination rate, temperature, grain legumes.

Variable selection on the timing of germination in collinsia verna (scrophulariaceae).

Abstract: Natural selection on the timing of seed germination was investigated in a natural population of the winter annual Collinsia verna (Scrophulariaceae) for two years. The goal was to quantify 1) the importance of the timing of seed germination to life history evolution in this population and 2) variation in selection in time and space. During fall germination, seedlings were assigned to cohorts on the basis of their dates of germination. Growth, survivorship, and reproduction were censused throughout both years. Selection on the timing of germination was quantified using linear and quadratic regressions during three ecologically important periods in the life cycle, using the techniques of Lande and Arnold (1983) and Arnold and Wade (1984a, 1984b). Comparisons were made between years and on two spatial scales within years. Overall, selection favored early-germinating plants in the first year. The primary determinant of the relationship of the timing of germination to fitness was fecundity selection, rather than viability selection on seedlings. Fecundity selection was respondible for from 54% to 80% of the change in the mean time of germination. Significant disruptive selection characterized the second field season, again mediated mainly through fecundity selection. There was also temporal and spatial heterogeneity in selection on this character. Transects and quadrats differed significantly in the direction and magnitude of natural selection. In addition, the direction of selection changed between episodes for the transects. The results illustrate the importance of the timing of germination to life-history evolution in this annual plant and the complex action of natural selection on this character.

The Influence of Temperature on Seed Germination Rate in Grain Legumes I. A COMPARISON OF CHICKPEA, LENTIL, SOYABEAN AND COWPEA AT CONSTANT TEMPERATURES

Abstract: Co veil, S., Ellis, R. H., Roberts, E. H. and Summerfield, R. J. 1986. The influence of temperature on seed germination rate in grain legumes. I. A comparison of chickpea, lentil, soyabean and cowpea at constant temperatures.—J. exp. Bot. 37: 705-715. For a single seed population of each of four species of grain legume positive linear relationships were shown between temperature and rate of germination for different fractions (G) of each population, from a base temperature, Tb(G), at which germination rate is zero, to an optimum temperature, T0(G), at which germination rate is maximal. At constant temperatures warmer than 7i(G) there were negative relations (probably linear) between temperature and rate of germination to the maximum temperature for germination, Tm(G). Within each population Tb(G) did not differ, but it did vary between species, viz. 0 0 °C, 2-5 °C, 4 0 °C and 8-5 °C for chickpea (Cicer arietinum L.), lentil (Lens culinaris Medic.), soyabean (Glycine max [L.] Merr.) and cowpea (Vigna unguiculata [L.] Walp.), respectively. In contrast, T0(G) varied both within each population and also between the four species: 80% of seeds in each population had T„(G) values within the range 31-8 °C to 33 0 °C, 24 0 °C to 24-4 °C, 34 0 °C to 34-5 °C and 33-2 °C to > 40 °C, respectively. Values of Tm(G) were much more variable: the 80% population range was 48 0 °C to 60-8 °C for chickpea, 31 -8 °C to 34-4 °C for lentil and 46-8 °C to 55-2 \"C for soyabean; reliable estimates could not be made for cowpea, but the results suggest higher and more variable values of Tm(G) than in the other three species. At sub-optimal temperatures the distribution of thermal time for the different fractions of each population was normal, except for lentil where it was log-normal. A single equation is proposed to describe the influence of sub-optimal temperatures on rates of germination for whole seed populations. At supra-optimal temperatures, variation in thermal time for the different fractions of each population was only slight. The implications of these findings for the adaptation of grain legume crops to different environments, and for the screening of germplasm, are discussed. Key words—Seed germination rate, temperature, grain legumes.

Effect of Salinity on Grain Yield and Quality, Vegetative Growth, and Germination of Semi‐Dwarf and Durum Wheat1

Abstract: Semi-dwarf bread wheat (Triticum aestivum L.) and durum wheat (Triticum furgidum L., Durum Group) are often grown on saline soils in the western United States. Because of the lack of information on salinity effects on vegetative growth and seed yield of these two species, a 2-yr field plot study was conducted. Six salinity treatments were imposed on a Holtville silty clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCI, (1:l by wt). Electrical conductivities of the irrigation waters were 1.5, 2.5, 5.0, 7.4, 9.9, and 12.4 dS/m the first year, and 1.5, 4.0, 8.0, 12.0, 16.1, and 20.5 dS/m the second year. Grain yield, vegetative growth, and germination were measured. Relative grain yields of one semi-dwarf wheat cultivar and two durum cultivars were unaffected by soil salinity up to 8.6 and 5.9 dS/m (electrical conductivity of the saturatedsoil extract), respectively. Each unit increase in salinity above the thresholds reduced yield of the semi-dwarf cultivar by 3.0% and the two durum cultivars by 3.8%. These results place both species in the salt-tolerant category. Salinity increased the protein content of both grains but only the quality of the durum grain was improved. Vegetative growth of both species was decreased more by soil salinity than was grain yield. Both species were less salt tolerant at germination than they were after the three-leaf stage of growth. Additional index words: Triticum aestivum L., Triticum turgidum L., Durum Group, Salt tolerance, Sodium chloride, Calcium chloride. HEAT (Triticum aestivum L.) continues to be a W predominant crop in the agriculture of the western United States. In 1982,70% of the wheat grown in the United States was produced in the 17 western states (1 7). Much of this wheat is grown on soils where salinity problems already exist or may develop. Considerable research has been conducted on the salt tolerance of various bread wheat cultivars over the past 30 years (1, 2, 12). However, with the development of the Mexican semi-dwarf cultivars, additional research is needed. Although a few preliminary studies on the salt tolerance of the Mexican wheats have been conducted in small pot cultures (1 4, 1 5, 16), salt-tolerance data are not available to predict yield responses in the field. This field plot study was initiated to determine the effect of soil salinity on vegetative growth and grain yield of semi-dwarf bread wheat. In addition, the lack of salt tolerance information on durum wheat (Triticum turgidum L., Durum Group) prompted the authors to include this species in the study. METHODS AND MATERIALS This study was conducted at the Irrigated Desert Research Station, Brawley, CA, on a Holtville silty clay soil [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Tomfluvent]. The crops were grown in 6.0by 6.0-m plots that were enclosed by acrylic fortified fiberglass borders which extended 0.75 m into the soil. The top of the fiberglass borders protruded 0.15 m above the soil level of the plot and was covered with a berm 0.18 m high and 0.60 m wide. Walkways 1.2 m wide between plots and good vertical drainage effectively isolated the treatments in each plot. Prior to planting, triple superphosphate was mixed into the top 0.25 m of soil at the rate of 73 kg P/ha. To assure adequate N fertility throughout the experiment, Ca(N0J2 was added at a rate of (0.14 kg N/ha)/mm of water applied at every imgation. Since the soil contained adequate levels of K, no additional K was added. One bread wheat and one durum wheat cultivar were planted in level plots on 1 Dec. 1981 and 30 Nov. 1983. The bread wheat cultivar for both years was Northrup King Probred. The durum wheat cultivars were Westbred 1000D in 1981 and Northrup King Aldura in 1983. The cultural practices used at planting were identical for both experiments. Each plot contained 17 rows of Probred and 17 rows of the durum cultivar. The rows were planted 0.15 m apart with the seed placed approximately 25 mm apart within the row. The experimental design consisted of six treatments replicated three times in a randomized split-plot design, with salinky as main plots and species as subplots. At the time of planting, the soil profiles were still salinized from previous experiments. The initial K , (electrical conductivity of the saturated-soil extract) averaged to a depth of 1.2 m for the six treatments in 1981 were 3.0,4.9, 7.3, 9.5, 11.4, and 12.4 dS/ m, while in 1983 they were 3.7, 4.6, 7.1, 8.2, 9.6, and 11.6 dS/m. To assure good germination, 70 mm of nonsaline water (1.5 dS/m) was applied prior to planting to leach salts from the top 0.15 m of soil; another 50-mm nonsaline irrigation was applied after planting. Thirty days after planting, when the plants were approximately 60 mm tall, differential salination was initiated. Irrigation water salinities were increased stepwise in one-third increments over a 2-week period by adding equal weights of NaCl and CaCl, until desired salt concentrations were achieved. In 1981-1982, the electrical conductivity of the six imgation waters ( K , J was 1.5 (Control), 2.5, 5.0, 7.4, 9.9, and 12.4 dS/m. The salinity of the imgation waters was increased to 1.5, 4.0, 8.0, 12.0, 16.1, and 20.5 dS/m in the 1983-1 984 season to obtain greater yield reductions. During both growing seasons, all plots were irrigated approximately every 2 to 3 weeks to keep the matric potential of the control treatments above 85 J/kg in the 0.15to 0.3-m zone. The total amounts of imgation water applied after planting were 680 mm in 1981-1982 and 480 mm in 1983-1984. Soil samples were collected from each plot approximately 2, 4, and 6 months after planting. Two soil cores per plot were taken in 0.3-m increments to a depth of 0.9 m. The average K, for each of the three depths for both years is presented in Table 1. The monthly mean daytime-high temperatures ranged from 22°C in December, 1983, to 29.5\"C in April, 1984; monthly mean nighttime-low temperatures for the same period ranged from 5 to 10.5\"C. In 1982, the monthly mean daytime-high temperatures ranged from 20.5\"C for January to 29.5\"C for April, and the monthly mean nighttime-low temperatures ranged from 4 to 1 1 \"C. In December, 198 1, the mean high and low temperatures were 24 and 5\"C, respectively. The mean Class A pan evaporation ranged from 3 mm/day in December to 11 mm/day in May. The accumulative pan evaporation during the 1981-1982 and 1983-1984 growing seasons were 805 mm and 680 mm for Probred, and 910 mm and 760 mm for 1000-D and Aldura, respectively. I Contribution from the USDA-ARS, U.S. Salinity Laboratory, Riyerside, CA 92501. Received 27 Jan. 1986. Research agronomist, supervisory plant physiologist, and agronomist, respectively, USDA-ARS, U.S. Salinity Laboratory, Riverside, CA, and research food technologist, USDA-ARS, Wheat Quality Laboratory, Fargo, ND 58105. Published in Agron. J. 78:1053-1058 (1986). 1053 Published November, 1986

Evidence for Allelopathy by Residues and Aqueous Extracts of Rye (Secale cereale)

Abstract: Under simulated no-till conditions in the green- house, rye (Secale cereale L. 'Wheeler') residues reduced emergence of lettuce (Lactuca sativa L. 'Ithaca') and proso millet (Panicum miliaceum L. #3 PANMI) by 58 and 35%, respectively, over that obtained with a wood shaving control mulch. Rye shoot tissue inhibited lettuce germination 52% more than root tissue. Petri dish bioassays of residue in soil confirmed phytotoxicity on cress (Lepidium sativum L. 'Curly'), lettuce, barnyardgrass (Ecbinocbloa crus-galli L. Beauv. # ECHCG), and proso millet. Radicle elongation was a more senstive measure of phytotoxicity than germi- nation per se. Phytotoxicity increased as the distance from seeds to rye residues decreased. While rye shoot residues caused 40% greater inhibition of cress radicle elongation in sterile soil than nonsterile soil, bamyardgrass was equally inhibited in both soil regimes. Phytotoxicity decreased in nonsterile soil, indicating that the compounds were degraded by microorganisms. Phytotoxic compounds in shoots were water extractable. Cress and barnyardgrass responded simi- larly to both aqueous rye extracts and to residues added to soil.

Microsite requirements for germination and establishment of three grass species

Abstract: The safe sites, i. e., microsite requirements for germination and establishment, were partially characterized for three of the dominant grass species of the Edwards Plateau of central Texas, Aristida longiseta, Bouteloua rigidiseta and Stipa leucotricha. Seeds were germinated and grown in field-collected soil in a greenhouse under different watering regimes and in soil-filled benches with various soil surfaces and with adult plants. Both watering regime and microsite type strongly affected germination and establishment. Litter and rocks, but not the proximity of an adult plant, increased germination, survival and growth. A safe site for these species appears to be a microsite that prevents desiccation. Differences among the species in the relative favorableness of different types of microsites were slight. Species differed more in the timing of germination. Since the timing of rainfall and of temperature fluctuations varies considerably between years in central Texas, different cohorts of seedlings, and hence different species, may be successful in different years.

Development and function ofAzospirillum-inoculated roots

Abstract: The surface distribution ofAzospirillum on inoculated roots of maize and wheat is generally similar to that of other members of the rhizoplane microflora. During the first three days, colonization takes place mainly on the root elongation zone, on the base of root hairs and, to a lesser extent, on the surface of young root hairs.Azospirillum has been found in cortical tissues, in regions of lateral root emergence, along the inner cortex, inside xylem vessels and between pith cells. Inoculation of several cultivars of wheat, corn, sorghum and setaria with several strains ofAzospirillum caused morphological changes in root starting immediately after germination. Root length and surface area were differentially affected according to bacterial age and inoculum level. During the first three weeks after germination, the number of root hairs, root hair branches and lateral roots was increased by inoculation, but there was no change in root weight. Root biomass increased at later stages. Cross-sections of inoculated corn and wheat root showed an irregular arrangement of cells in the outer layers of the cortex. These effects on plant morphology may be due to the production of plant growth-promoting substances by the colonizing bacteria or by the plant as a reaction to colonization. Pectic enzymes may also be involved. Morphological changes had a physiological effect on inoculated roots. Specific activities of oxidative enzymes, and lipid and suberin content, were lower in extracts of inoculated roots than in uninoculated controls. This suggests that inoculated roots have a larger proportion of younger roots. The rate of NO− 3, K+ and H2PO− 4 uptake was greater in inoculated seedlinds. In the field, dry matter, N, P and K accumulated at faster rates, and water content was higher inAzospirillum-inoculated corn, sorghum, wheat and setaria. The above improvements in root development and function lead in many cases to higher crop yield.

In vitro germination of some Western European orchids

Abstract: Several germination factors were studied in 23 Western European orchids in order to obtain a germination percentage which approximates the maximum percentage of coloured embryos after an adaptation of the tetrazolium test. The duration of seed pretreatment with Ca(OCl)2+ Tween-80 was one of the most important factors controlling the germination of Western European orchids. Best germination occurred in continuous darkness at 23°C on dilute media. The nitrogen source had a species related influence. The best results were obtained with casein hydrolysate, although it could nearly be replaced by one amino acid, L-glutamine. A cytokinin was required by Cypripedium calceolus and Epipactis hellborine but was not necessary for Lisiera ovata and Dactylorhiza maculata. Experiments with 3 species have shown that the objective, to obtain a germination percentage, which approximated the maximum percentage of coloured embryos, was achieved. This has led to the elaboration of a basic sowing method for European orchids. The application of this method gave good germination responses with 21 of the 23 species tested.

A revision of the hormone balance theory of seed dormancy: studies on gibberellin and/or abscisic acid-deficient mutants of Arabidopsis thaliana.

Abstract: The basic framework of the hormone theory of seed dormancy originates from Luckwill [9], who suggested that the dormancy of apple seeds depends on the interaction between naturally occurring growth-inhibiting and growth-promoting substances. In later years, the interaction has often been described as a balance between simultaneously occurring promotive hormones, such as gibberellins (GAs) and cytokinins, and the inhibitory hormone, abscisic acid (ABA). It has been pointed out that the theory is mainly based on the effects of exogenous growth regulators on germination and dormancy, in which dormancy can be maintained, imposed and released by these chemicals singly or in combination [2]. Such effects are considered to reflect the action of naturally occurring hormones within seeds. Environmental factors, such as light and temperature conditions, are thought to operate on dormancy by causing changes in the balance between promotors and inhibitors.

Effect of seed size on seedling success in three species of sesbania (fabaceae)

Abstract: Variation in seed size may produce variation in seedling fitness, but the relationship is not simple. Differences in seed size within and among species may not have the same effects. We examined effects of differences in seed size within and among three species of Sesbania, S. macrocarpa, S. drummondii, and S. vesicaria, on seedling emergence and growth in the greenhouse and the field. Of the three species, the largest-seeded species, S. vesicaria, produced the largest, longest-lived seedlings in both the greenhouse and the field. Even though plant size differed, annual S. macrocarpa produced the same seed mass as annual S. vesicaria in the greenhouse. Within-species effects were less clear. In the greenhouse, S. vesicaria seedlings grown from large seeds remained largest until maturity, but the other species did not exhibit this effect. Some persistent within-species effects of seed size differences on height were observed in the field in 1981, but not in 1980, suggesting that field conditions increase the importance of seed size differences. Unscarified S. drummondii seeds germinated before seeds of the two annual species. Within species, larger seeds of the annuals and smaller seeds of the perennial germinated first. Differences among the species in the importance of seed size to seedling fitness may allow the species to have different patterns of regulation of reproduction in response to stress. Sesbania vesicaria showed the largest within-species effects of seed size and has the lowest plasticity in seed size, suggesting that patterns of plasticity have been selected such that the most important component of yield varies least. WHILE THEORETICAL CONSIDERATIONS predict that the production of larger seeds will yield larger, more competitive seedlings (Salisbury, 1942; Harper, Lovell, and Moore, 1970; Stebbins, 1971; Smith and Fretwell, 1974), studies of the relationship between seed size and seedling growth and survivorship have given mixed results (e.g., Twamley, 1967; Carelton and Cooper, 1972). Seed size may affect initial seedling growth, but not final seed yield (Black, 1959; but see Gross and Soule, 1981). Furthermore, the effects of seed size may be apparent only under competitive conditions (Black, 1958; Stanton, 1984) and earlier germination of small seeds may compensate for initial differences in seed size (Black and Wilkinson, 1963). Thus, although a number of studies of the effect of seed size on seedling success have been performed, our understanding of this relationship remains incomplete. ' Received for publication 30 July 1985; revision accepted 21 October 1985. David Braun weighed plant parts, Scott Shapiro sorted roots, and Kevin Ford and Mary Jean Hattrup assisted in the germination experiment. Tim Holtsford, Norm Ellstrand, Norma Fowler, and Don Levin provided helpful comments on an earlier draft of this manuscript. Financial support was provided by a research grant and a fellowship awarded to DLM from the graduate school of The University of Texas, Austin. Permission to work at Lake Somerville was provided by the U.S. Army Corps of Engineers, Ft. Worth District. 2 Present address: Department of Biology, Univ. of New Mex., Albuquerque, NM 87131. A number of factors may make the relationship between seed size and seedling fitness complex. First, the relationship between seed size and seedling quality may not be linear (Marshall, Fowler, and Levin, 1985a), so that all differences in seed size may not have uniform effects. For example, growth rates may differ among seedlings of varying size (Stebbins, 1976). Second, differences in seed size among species may represent physiological differences in addition to differences in size and, thus, have different effects than variation in size within species. Third, the nature of the size differences in seedlings-whether differences in leaf area, stem length or root length are involved-may determine the conditions under which increased seed size will have an impact on fitness. Fourth, the most important effect of seed size may be its influence on the kind of microsite in which germination and seedling establishment is possible (e.g., Gross and Werner, 1982; Gross, 1984) rather than its influence on seedling growth. Fifth, field conditions, which may involve microhabitat variation and competition, could either mask or exaggerate seed size effects seen in the greenhouse (Fenner, 1978; Gross, 1984). Finally, even if seed size and seedling size are correlated, plasticity in offspring size, rather than a constant size, may be adaptive in a variable habitat (Bradshaw, 1965; Capinera, 1979). Attempts to understand the importance of

Allelopathic research of subtropical vegetation in Taiwan : III. Allelopathic exclusion of understory byLeucaena leucocephala (Lam.) de Wit.

Abstract: Leucaena leucocephala plantations in Kaoshu, southern Taiwan, exhibit, after several years of growth, a unique pattern of weed exclusion beneathLeucaena canopy. The pattern has been observed in manyLeucaena plantations in Taiwan and is particularly pronounced in the area where a substantial amount ofLeucaena litter has accumulated on the ground. Field data showed that the phenomenon was primarily not due to physical competition involving light, soil moisture, pH, and nutrients. Instead, aqueous extracts ofLeucaena fresh leaves, litter, soil, and seed exudate showed significantly phytotoxic effects on many test species, including rice, lettuce,Acacia confusa, Alnus formosana, Casuarina glauca, Liquidambar formosana, andMimosa pudica. However, the extracts were not toxic to the growth ofLeucaena seedlings. The decomposing leaves ofLeucaena also suppressed the growth of the aforementioned plants grown in pots but did not inhibit that ofLeucaena plants. By means of paper and thin-layer chromatography, UV-visible spectrophotometry, and high-performance liquid chromatography, 10 phytotoxins were identified. They included mimosine, quercetin, and gallic, protocatechuic,p-hydroxybenzoic,p-hydroxyphenylacetic, vanillic, ferulic, caffeic, andp-coumaric acids. The mature leaves ofLeucaena possess about 5% dry weight of mimosine, the amount varying with varieties. The seed germination and radicle growth of lettuce, rice, and rye grass were significantly inhibited by aqueous mimosine solution at a concentration of 20 ppm, while that of the forest species mentioned was suppressed by the mimosine solution at 50 ppm or above. However, the growth ofMiscanthus floridulus andPinus taiwanensis was not suppressed by the mimosine solution at 200 ppm. The seedlings ofAgeratum conzoides died in mimosine solution at 50 ppm within seven days and wilted at 300 ppm within three days. It was concluded that the exclusion of understory plants was evidently due to the allelopathic effect of compounds produced byLeucaena. The allelopathic pattern was clearly shown in the area with a heavy accumulation ofLeucaena leaf litter, which was a result of drought and heavy wind influence.

The relationship of host and endophyte during flowering, seed formation, and germination of Lolium perenne

Abstract: The development of a fungal endophyte in the tissue of Lolium perenne during flowering, seed set, and germination is described. The endophyte progresses intercellularly from the vegatative apex into the inflorescence primordium and floral apices, from where it penetrates the tissues of ovary and ovule. At megagametophyte maturity, hyphae are concentrated outside its wall adjacent to the large lateral antipodal cells and subsequently gain entry to the embryo sac, probably soon after fertilisation. During early embryogenesis, hyphae occur on the surface of the embryo, and penetrate it at the ‘notched’ stage. At seed maturity, hyphae are widespread within the embryo, including the plumule apex, as well as below the testa, between cells of the aleurone layer, and between scutellum and endosperm. At germination, hyphae outside the embryo appear to play no further part in invasion of the already infected embryo. The endophyte of Festuca arundinacea has a similar relationship with its host and appears t...

Stimulation of germination of spores of glomus versiforme by spore-associated bacteria

Abstract: Germination of spores of Glomus versiforme (Karsten) Berch (=Glomus epigaeum Daniels and Trappe) was greatly reduced by surface disinfestation to remove naturally associated microbial flora. Spores which remained contaminated with bacteria after surface disinfestation germinated at a much higher rate than did spores with no evident bacterial contamination. Germination of non-surface disinfested spores was minimal on Nobel agar, a medium which did not support visible growth of spore-associated bacteria. On Bacto agar, a medium which did support growth of spore-associated bacteria and fungi, spore germination was minimal when bacterial growth was inhibited by antibiotics, but was significantly greater when spore-associated bacterial growth was not inhibited by antibiotics. Germination of surface disinfested spores was increased 1.5- to 2.2-fold by addition of bacteria previously isolated in pure culture from non-surface disinfested spores. Hyphae emerging from spores in the presence ofthe bacteria were smooth, developed small vesicles, and were substantially longer and more extensively branched than those from surface disinfested spores without bacteria. The latter hyphae were characterized by meager growth, an abnormal knobbed appearance, and a lack of vesicle formation. Spore-associated bacteria capable of stimulating germination of spores of G. versiforme were found to belong to several different genera, including Pseudomonas and Corynebacterium.

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Fire and the transition to seedlings

Abstract: Fire, through soil heating effects, causes flushes of seed germination in Acacia suaveolens. Optimal temperatures for germination are between 60 and 80°C for any duration, or up to 100°C for durations less than 1 h. Exposure to temperatures less than 60°C leaves seeds dormant and viable, whilst seed death occurs in increasing proportions with increasing exposure to temperatures greater than 80°C. A field study of temperatures in the soil under simulated burns showed that the innate seed dormancy in A. suaveolens would only be broken for seeds up to a depth of 1 cm in ‘cool’ or 4 cm in ‘hot’ burns. In the hot burns some of the seeds in the top 1 cm of the soil were killed by excessive heating. These simulated burns most resemble cool and moderate/high intensity wildfires, respectively. Seeds can emerge from depths up to 8 cm and, for any seeds buried deeper than this, the probability of emergence is progressively reduced down to nil at 14 cm. Seeds buried between 5 and 10 cm will be heated sufficiently to break their dormancy only in a very high intensity wildfire. Seeds buried between 5 and 10 cm deep mostly occur in nests of an ant, Pheidole sp. Field observations of emergent seedlings confirm that post-fire emergence is concentrated over a small range of soil depths directly related to the intensity and duration of heating that occurs, whilst occasional seedlings may appear from greater or lesser depths largely dependent upon the spatial heterogeneity of soil heating in natural fires.

Role of ethylene in Lactuca sativa cv Grand Rapids seed germination

Abstract: Promotion of thermoinhibited (30 degrees C) lettuce (Lactuca sativa cv ;Grand Rapids') seed germination by ethylene is similar to the action of the gas in other hormonal systems. Ethylene was more active than propylene and ethane was inactive. An inhibitor of ethylene production, aminoethoxy-vinylglycine, reduced ethylene evolution and germination. Inhibitors of ethylene action such as, 5-methyl-7-chloro-4-ethoxycarbonylmethoxy-2,1,3-benzothiadiazole, 2,5-norbornadiene, and silver thiosulfate inhibited germination and the effect was reversed by the addition of ethylene to the gas phase. The action of ethylene appears to be due to the promotion of radial cell expansion in the embryonic hypocotyl. The action of N6-benzyladenine and fusiccocin, which also overcome thermoinhibition, appears to be due to a promotion of hypocotyl elongation. None of the germination promoters studied appeared to function by lowering the mechanical resistance of the endosperm to embryonic growth. Data presented here are consistent with the view that ethylene plays a role in lettuce seed germination under thermoinhibited and normal conditions.

Effect of germination time, temperature and moisture on malting of sorghum

Abstract: The effect of germination conditions on sorghum malt quality and malting loss was studied by germinating sorghum for different periods of time up to 6 days over a range of temperatures (24 to approximately 36°C) and moisture conditions. The moisture conditions varied from that sufficient to maintain green malt weight to that where surface moisture remained on the malt throughout germination. Germination time, temperature, moisture and the three possible pairwise interactions all had a highly significant effect on malt diastatic power, free α-amino nitrogen and extract. Malting loss was highly significantly affected by germination time and moisture and their pair-wise interaction. However, over the range examined, germination temperature had no significant effect on malting loss. In general diastatic power, free α-amino nitrogen, extract, and malting loss all increased with germination time. Germination temperatures of 24° and 28°C were both equally good for the development of diastatic power, free α-amino nitrogen and extract but higher temperatures were progressively worse. Distatic power, free α-amino nitrogen, extract and malting loss were, in general, all increased by high moisture during germination. However, high moisture and a negative effect on diastatic power towards the end of the germination period.

Factors influencing seed germination in salicornia pacifica var. utahensis

Abstract: The halophyte, Salicornia pacifica var. utahensis (Tiderstorm) Munz produces seed under high salinity conditions, and deposits its seed on saline soil. Experiments were conducted to determine the effect of salinity, temperature and growth regulators on germination. Results indicate that the seeds can germinate at very high salt concentration (5% NaCl). Germination was sensitive to the changes in temperature regimes. At higher 30-20 C, light-dark sequence, no germination occurred at 3, 4 and 5% NaCl treatments. On the other hand, 30% germination did occur at 5% NaCl treatment at a temperature regime of 15-5 C. These seeds required light for germination. Only 50% germination occurred in the non-saline control in the dark and the addition of NaCl further reduced germination. The GA3 partially alleviated the inhibitory effect of NaCl and darkness. Kinetin did not promote germination.

An experimental study of seed ingestion and germination in a plant-animal assemblage in Ghana

Abstract: Fleshy fruits collected from abundant woody plants on the Accra Plains, Ghana, were fed to frugivorous species common in the area. Seeds of each plant species were retrieved from each frugivore species for germination trials, and ingested seeds compared to fresh seeds in germination percentage and rapidity. Altogether 85 plant X animal feeding combinations were attempted. In 73% of trials, ingestion did not affect germination percentage; the remain-ing trials were about equally divided between significant increases and decreases. Ingested seeds had significantly faster germination in 12%, and significantly slower germination in 8%, of the trials. Germination percentages in all samples of fresh seeds ( = 37%) did not differ signifi-cantly from those ingested seeds ( = 31%).There was a significant association between the effect of ingestion on both germination rapidity and percentage (significantly increased, decreased, or neither) and the plant species involved; there was no such association between the effect of ingestion and the animal species. Animals had inconsistent and frequently negligible effects on germination. Two-way analyses of variance (plants X animals) of germination percentage and of germination improvement showed that plant species were a significant source of variation and animal species were not. The fleshy-fruited plants of this assemblage are not generally dependent upon animals for successful germination of their seeds.

Experimental studies of the evolutionary significance of sexual reproduction. iii. maternal and paternal effects during seedling establishment

Abstract: To determine whether genetic differences in fitness components exist among seeds and seedlings in a natural population, weighed propagules of six parents of Anthoxanthum odoratum from a reciprocal diallel cross were planted into the parental source population, a mown field. Seed families of maternal genotypes differed in germination success, while paternal families showed no detectable differences. Differential germination success could not be attributed to propagule weight. Seed families ranked differently in germination percentage in different blocks. No survivorship differences among parental seed families could be detected. There were significant cross × block × germination and cross × block × survivorship interactions; different crosses performed better or worse in different blocks. In some cases, crosses sired by different fathers within a maternal seed family differed in germination or survivorship, suggesting that natural selection may be capable of discriminating among juvenile genotypes within a maternal family despite the presence of large overall maternal effects. These results indicate that seedling establishment may differ according to genotype and that microsite heterogeneity may maintain genetic variation in juvenile traits in natural plant populations.

High salt tolerance potential in Lycopersicon species during germination

Abstract: The potential to improve seed germination responses to salinity was evaluated for 13 accessions representing six wild Lycopersicon species and 20 accessions of L. esculentum. Germination response times increased in all accessions at 100 mM NaCl. Analysis indicated that one accession of L. peruvianum (PI126435) germinated faster under high salinity than all other accessions and was closely followed by L. pennellii (LA716). The fastest germinating L. esculentum accession, PI174263, ranked third. Additional wild ecotypes exhibiting rapid germination at 100 mM NaCl were identified among L. pimpinellifolium and L. peruvianum.