Showing papers on "Germination published in 1990"

A comparison of methods for estimating seed numbers in the soil

Abstract: (1) Seed-bank species composition and seed density were determined in an annually ploughed field at the Kellogg Biological Station in south-western Michigan, U.S.A. using three different methods: direct germination, germination following cold-stratification, and washing using a modified elutriation system. A fourth method, flotation on a salt-density gradient was abandoned after preliminary trials showed it was inefficient and inaccurate. (2) Twenty soil cores (2 5 cm in diameter, 15 cm deep) were taken from each of twentyfive sampling points in the field. Cores were divided into three depth intervals (0-2 cm, 2-5 cm and 5-15 cm) and five cores from each quarter of a sampling quadrat were combined and randomly assigned to one of the four methods for estimating the seed bank. (3) A total of fifty species was detected in the seed bank of this community. Overall, more species were detected with cold-stratification (forty-two species) than with direct germination (thirty-seven) or elutriation (thirty-five). Plots of species-sampling-area curves showed that fifteen to twenty sampling locations were sufficient to determine the number of species present in the seed bank with any of these methods. (4) Seed-density estimates were significantly higher in the elutriated samples. This was due primarily to the inclusion of inviable seeds in the counts from the elutriated samples. (5) There were significant differences in seed viability among species recovered in the elutriated samples. Both Ambrosia artemisiifolia and Chenopodium album, seeds of which were common in the samples, had low viability (25% and 3%, respectively). (6) Germination methods (particularly when more than one pre-treatment method is used) provide a more complete listing of species present in the soil seed bank of a community than elutriation. However, elutriation methods may be more useful for documenting variation in seed distributions on a large spatial scale or in quantifying the distribution of species with unique, easily identifiable seeds. Elutriation seems particularly well-suited for quantifying the distribution of plants that are considered weeds in agricultural systems, because many of these species have seeds that are easily identified and retain viability when dried.

A water relations analysis of seed germination rates.

Abstract: Seed germination culminates in the initiation of embryo growth and the resumption of water uptake after imbibition. Previous applications of cell growth models to describe seed germination have focused on the inhibition of radicle growth rates at reduced water potential (Psi). An alternative approach is presented, based upon the timing of radicle emergence, to characterize the relationship of seed germination rates to Psi. Using only three parameters, a ;hydrotime constant' and the mean and standard deviation in minimum or base Psi among seeds in the population, germination time courses can be predicted at any Psi, or normalized to a common time scale equal to that of seeds germinating in water. The rate of germination of lettuce (Lactuca sativa L. cv Empire) seeds, either intact or with the endosperm envelope cut, increased linearly with embryo turgor. The endosperm presented little physical resistance to radicle growth at the time of radicle emergence, but its presence markedly delayed germination. The length of the lag period after imbibition before radicle emergence is related to the time required for weakening of the endosperm, and not to the generation of additional turgor in the embryo. The rate of endosperm weakening is sensitive to Psi or turgor.

An Intermediate Category of Seed Storage Behaviour? I. COFFEE

Abstract: Seeds of four cultivars of arabica coifee (Coffea arabica L.) were tested for germination following hermetic storage for up to 12 months at several different combinations of temperatures between —20 °C and 15 °C and moisture contents between 5% and 10% (wet basis). Most of the seeds from one cultivar withstood desiccation to between 5% and 6% moisture content, a seed water potential of approximately 250 MPa, but those of the remaining three cultivars were much more sensitive to desiccation damage. Moreover, in all four cultivars, seed longevity at cool and sub-zero temperatures, and at low moisture contents did not conform with orthodox seed storage behaviour: viability was lost more rapidly under these conditions than at either warmer temperatures or higher moisture contents. The results confirm that coffee seeds fail to satisfy the definitions of either typical orthodox or recalcitrant seed storage behaviour. These results, therefore, point to the possibility of a third category of storage behaviour intermediate between those of orthodox and recalcitrant seeds. One of the main features of this category is that dry seeds are injured by low temperatures.

Concepts and Technologies of Selected Seed Treatments

Abstract: Seed treatments are used on many crop seeds for a variety of purposes. The greatest use of seed treatments has been to provide an inexpensive insurance against rotting of planted seeds by soil fungi such as Pythium spp. and Rhizoctonia solani. Seed treatments for many other purposes are being de­ veloped and used. Increasingly, commercial seed treaters are beginning to view seed treatments as a means to substantially increase the value of the seed and to improve plant growth and productivity. Examples of other types of seed treatments are: (a) treatment with systemic chemicals that can translocate into the seed to control deep-seated plant pathogens. Several chemicals also translocate to the above-ground portions of the seedling and protect against foliar diseases; (b) treatment with microor­ ganisms that can proliferate on the seed, transfer to the root and fix N2, enhance uptake of nutrients, protect the subterranean plant portions against attack by soil-inhabiting fungi, and/or increase plant growth; (c) physical treatments that control seedbome pathogens; (d) seed coatings or pellets that can improve seed shape for planting or provide other benefits; (e) physiolog­ ical seed treatments that enhance germination rate and plant performance; and (j) various treatments that affect seed moistUre relationships and result in improved seed storability or performance.

An intermediate category of seed storage behaviour

Abstract: The effects of endocarp removal either before or after dessication and storage, and of humidification prior to testing the seeds for germination were investigated to determine whether these factors might help to explain the contradictions in the literature regarding the survival of coffee seeds in storage

Regulatory mechanisms involved in the transition from seed development to germination.

Abstract: (1990). Regulatory mechanisms involved in the transition from seed development to germination. Critical Reviews in Plant Sciences: Vol. 9, No. 2, pp. 155-195.

The Genetics of Bacterial Spore Germination

Abstract: INTRODUCTION 531 SPORE FOR/elATION AND STRUCTURE 532 SPORE GERMINATION 535 GERMINATION GENES AND THEIR ANALYSIS 538 Characteriization of Mutants 538 Genes Involved in the L-alanine Germination Pathway 540 Genes Involved in the Alternative (AGFK) Pathway 542 Genes Common to Both Germination Pathways 543 Genes lnvolved in Spore Structure 544 Spore Mum’ants Constructed by Reverse Genetics 545 MODELS O1:’ SPORE GERMINATION 546 CONCLUSIONS 548

Annual Variation in Seedfall, Postdispersal Predation, and Recruitment of a Neotropical Tree

Abstract: Knowledge of the dynamics of seed production and seedling recruitment of individual tree species is crucial for a complete understanding of tropical forest dynamics, yet multiyear studies on the seed and young seedling stages of tropical trees are virtually nonexistent. In a 4-yr study of the understory tree Faramea occidentalis on Barro Colorado Island, Panama, the author quantified natural levels of viable seedfall, seedling emergence, and seedling establishment, and experimentally estimated postdispersal seed predation. The levels of viable seedfall, seed predation, seedling emergence, early seedling survival, and seedling recruitment all differed significantly among years. The proportion of fallen seeds destroyed by predators before germination was not related to the quantity of F. occidentalis seedfall. Within a year, however, F. occidentalis seed predation appeared to be influenced by community-wide seedfall, with high predation rates during times of low seed abundance and very low predation during the late dry season peak in seedfall by the community. Most of the annual variation in recruitment can be explained by the combination of seedfall and seed predation; in 3 of the 4 yr seedling emergence could be predicted from a knowledge of viable seedfall and the probability of a seed surviving until the peak ofmore » germination. The 4th yr, however, demonstrated that environmental conditions provide a sporadic, though important, limitation to recruitment. In comparison to many tree species, early seedling survival was relatively high, as was the ratio of seedlings recruited per seed falling. The highly successful recruitment of F. occidentalis is associated with a high population density of both saplings and adults in the study area.« less

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) : III. Sensitivity of Germination to Water Potential and Abscisic Acid during Development.

Abstract: Muskmelon (Cucumis melo L.) seeds are germinable 15 to 20 days before fruit maturity and are held at relatively high water content within the fruit, yet little precocious germination is observed. To investigate two possible factors preventing precocious germination, the inhibitory effects of abscisic acid and osmoticum on muskmelon seed germination were determined throughout development. Seeds were harvested at 5-day intervals from 30 to 65 days after anthesis (DAA) and incubated either fresh or after drying on factorial combinations of 0, 1, 3.3, 10, or 33 micromolar abscisic acid (ABA) and 0, −0.2, −0.4, −0.6, or −0.8 megapascals polyethylene glycol 8000 solutions at 30°C. Radicle emergence was scored at 12-hour intervals for 10 days. In the absence of ABA, the water potential (Ψ) required to inhibit fresh seed germination by 50% decreased from −0.3 to −0.8 megapascals between 30 and 60 DAA. The Ψ inside developing fruits was from 0.4 to 1.4 megapascals lower than that required for germination at all stages of development, indicating that the fruit Ψ is sufficiently low to prevent precocious germination. At 0 megapascal, the ABA concentration required to inhibit germination by 50% was approximately 10 micromolar up to 50 DAA and increased to >33 micromolar thereafter. Dehydration improved subsequent germination of immature seeds in ABA or low Ψ. There was a linear additive interaction between ABA and Ψ such that 10 micromolar ABA or −0.5 megapascal osmotic potential resulted in equivalent, and additive, reductions in germination rate and percentage of mature seeds. Abscisic acid had no effect on embryo solute potential or water content, but increased the apparent minimum turgor required for germination. ABA and osmoticum appear to influence germination rates and percentages by reducing the embryo growth potential (turgor in excess of a minimum threshold turgor) but via different mechanisms. Abscisic acid apparently increases the minimum turgor threshold, while low Ψ reduces turgor by reducing seed water content.

Light Beneath the Litter in a Tropical Forest: Effect on Seed Germination

Abstract: The spectral composition of the light transmitted through the forest canopy, through dry and moist litter leaves, and through intact forest litter was measured in a tropical rain forest in Mexico. Germination of photoblastic seeds of some pioneer trees and shrubs was studied over a light quality gradient, and in field germination experiments on the surface of the forest floor and beneath the litter layer. There is a shift to longer wavelengths inside the forest that is even greater beneath the litter. Light filtered through dead leaves strongly inhibits germination as demonstrated with field and laboratory germination experiments. The role of litter as a light filter might be important in maintaining a reserve of dormant seeds in the soil in tropical rain forests. See full-text article at JSTOR

Effects of seed weight and microsite characteristics on germination and seedling fitness in two species of quercus in a subtropical wet Hill forest

Abstract: Tripathi, R. S. and Khan, M. L. 1990. Effects of seed weight and micro site characteristics on germination and seedling fitness in two species of Quercus in a subtropical wet hill forest. - Oikos 57: 289-296. There is large variation in seed weight within the two species of Quercus (Q. dealbata L. and Q. griffithii Hk. f. & Th.) selected for the present study. Effects on germination and survival of oak seedlings were studied in relation to variation in seed weight and microsite characteristics. Germination showed a strong correlation with seed weight. Heavy seeds germinated earlier and showed better germination than light seeds and seedlings produced from the former survived and grew better. The differences in growth of the seedlings emerged from the seeds having different weights persisted in the second year also. Emergence, survival and growth of the seedlings were highest in the plots devoid of litter and herbaceous cover and lowest in the control plots which were not cleared. Seedling emergence, survival and growth were more adversely affected by herbaceous cover than litter.

The effect of soil water potential on seed germination of some British plants

Abstract: SUMMARY ‘Seeds’ of 15 species collected from a range of habitats contrasting in soil water status were germinated in soils of known matric potentials ranging from near field capacity to the permanent wilting potential (– 0.05, –0.5, –1.0 and –1.5 MPa). Germination was very sensitive to soil water potential and species responded in various ways. Some showed germination responses which correlated with the soil water status of their native habitat: none of the wetland species studied could germinate to any great extent at low soil water potentials; in contrast some species associated with drier habitats achieved high levels of germination in soils as dry as –1.0 MPa (and –1.5 MPa for one ruderal species). However, other species from drier habitats failed to germinate at low soil water potentials, and it is suggested that this may be a mechanism to avoid exposing the seedling to an unfavourable environment.

Synchronous and high frequency germination of interior spruce somatic embryos following partial drying at high relative humidity

Abstract: The germination of mature somatic embryos of interior spruce was limited by the low frequency of root emergence. In addition, development was abnormal, since elongation and greening of the hypocotyl and cotyledons preceded root emergence by 1–2 weeks. Pretreatment of the embryos on water-saturated Kim-paks increased the frequency of root emergence but did not alter the abnormal pattern of germination. Somatic embryos do not survive desiccation at room humidity, but partial drying at high humidity promoted germination up to 90%. Furthermore, this treatment decreased the time required for root emergence such that elongation of the root and hypocotyl–cotyledon was synchronized over a period of 5–6 days. This germination closely resembled that of excised zygotic embryos. Drying over a range of humidities indicated that humidities of 81% and lower were lethal to the embryos, whereas germination was enhanced following treatment at humidities greater than 95% relative to untreated controls. The best germination ...

Exudate molecules initiating fungal responses to seeds and roots

Abstract: Plant pathogenic fungi survive in soils in a quiescent state. In order for many root-pathogen interactions to be initiated, dormant propagules must be activated by molecules present in seed and root exudates. Without the release of such stimulatory molecules, the majority of root infections do not occur. Currently, little is known about the specific molecules involved in stimulating propagule germination and initiating root-pathogen interactions. Although certain molecules can be shown to elicit germination responses in vitro, responses of propagules reared on conventional culture media do not always reflect the responses of those formed on plant tissues in soil. Consequently, it is not possible to extend conclusions from laboratory determinations of the role of specific exudate molecules in stimulating fungal propagule germination to soil systems. The interaction of Pythium species with germinating seeds has served as a model system to answer questions about propagule behavior and the role of exudate stimulant molecules in establishing root-fungus interactions. The potential role of both volatile and water-soluble molecules in stimulating propagule germination are discussed.

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes II. GERMINATION AT REDUCED WATER POTENTIAL

Abstract: Seed germination rates (GR = inverse of time to germination) are sensitive to genetic, environmental, and physiological factors. We have compared the GR of tomato (Lycopersicon esculentum Mill.) seeds of cultivar T5 to those of rapidly germinating L. esculentum genotypes PI 341988 and PI 120256 over a range of water potential ( were also assessed. Germination time-courses at different 0's were analysed according to a model that identified a base, or minimum, \j> allowing germination of a specific percentage (g) of the seed population (ifib(g)), and a 'hydrotime constant' (9H) indicating the rate of progress toward germination per MPa.h. The distribution of if>b(g) determined by probit analysis was characterized by a mean base b) and the standard deviation in b among seeds ( . A normalized time-scale for comparing germination responses to reduced ij> is introduced. The time to germination at any tp (t g(tfi)) can be normalized to be equivalent to that observed in water (/g(0)) according to the equation fg(0) = (l -^(ip/Ms)))^^)- PI 341988 seeds were more tolerant of reduced > b(g), but did not lower the minimum b between intact and cut seeds incubated at high 0 was much less («0-l MPa), indicating that at the time of radicle protrusion, the endosperm had weakened to the point where it constituted only a small mechanical barrier. In the intact seed, endosperm weakening and the downward adjustment in embryo ifib ceased at

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes

Abstract: The bases of differences in germination rates (GRg = inverse of time to germination [/g] of percentage g) among three cold/salt tolerant tomato (Lycopersicon esculentum Mill.) accessions (PI 341988, PI 120256, and PI 174263) and one cold/salt-sensitive tomato cultivar (T5) were investigated. The effects of seed priming (6 d imbibition in aerated - 1-2 MPa polyethylene glycol solution at 20 °C followed by redrying) and of removing the endosperm/testa cap covering the radicle on the temperature sensitivity of GRg, and the interaction of these treatments with genotypes, were also examined. GRg decreased linearly with decreasing temperature for all genotypes and seed treatments. The minimum or base temperatures for germination (Th) varied by Tb, but did not lower the minimum temperature at which germination could occur. Priming increased the GRg of T5 seeds to equal or exceed those of control (non-primed) seeds of the cold/salt-tolerant genotypes at any T> Tb, but the PI lines exhibited an even greater response to priming. Times to germination within each seed lot were normally distributed on a logarithmic scale. Priming increased the variance in tg within a seed lot when compared to control seeds. However, the variation in thermal time for germination between the 10th and 90th percentiles of the seed population (0r(lO-9O)) was relatively unaffected_by priming due to the reduction in 0r in primed seeds. Removing the endosperm cap and testa opposite the radicle tip decreased dT almost 6-fold and and reduced Tb by 5 °C in T5 and PI 341988, implicating processes in the endosperm/testa as the limiting factors in germination at suboptimal temperatures.

A comparison of maturation drying, germination, and desiccation tolerance between developing seeds of Acer pseudoplatanus L. and Acer platanoides L

Abstract: SUMMARY Differences in maturation drying and desiccation tolerance during seed development were detected between the two contrasting Acer spp., Norway maple (Acer platanoides L.), which shows orthodox seed storage behaviour, and sycamore (A. pseudoplatanus L.), which shows recalcitrant seed storage behaviour. In both species, the onset of germinability (150 d tests at 5 °C) occurred after percentage seed moisture content had begun to decline, but before net loss in seed moisture. The onset of germinability in Norway maple occurred 4 wk before physiological maturity (i.e. 4 wk before the end of the increase in seed dry matter), whereas in sycamore it occurred some ten weeks before physiological maturity when the seeds were only 60 % filled. Seeds of Norway maple were able to tolerate enforced rapid desiccation to 10% moisture content (f. wt) at physiological maturity, when maturation-drying had reduced seed moisture content to 54 %. Between 2 and 4 wk later seed moisture content rapidly declined naturally to 25 %, at which value the fruits were shed. In contrast, a constant rate of maturation-drying was observed in sycamore. The seeds were shed at 58 % moisture content and, in almost all cases, the seeds were intolerant of rapid desiccation to c. 10 % moisture content throughout seed development. A very small proportion of sycamore seeds did survive rapid desiccation when harvested between 6 September and 4 October, but no seeds survived desiccation to 5 % moisture content or below. A comparison of the germination of sycamore seeds harvested on four dates and dried to various moisture contents showed that the seeds tolerated greater desiccation as they matured between 12 July and 20 September, but there was no further change thereafter. The results are therefore compatible with previous classifications of seed storage behaviour in each species, and with the view that the initial decline in seed moisture content stimulates the developmental switch which results in the onset of germinability in both orthodox and recalcitrant seeds.

The effect of some mediterranean scrubland frugivores upon germination patterns

Abstract: SUMMARY (1) The probabilty of germination, the length of seed dormancy, and the temporal pattern of germination of five bird-dispersed plant species of an eastern Mediterranean scrubland community varied depending on the plant species, on which of seven bird species they were experimentally fed to, on whether or not they remained covered by pulp, and on whether or not the pulp was experimentally removed before sowing. (2) It is proposed that, in order to withstand the passage through the gut, seeds are protected in a way that may delay their germination after defecation and alter the inherent dormancy, depending on the amount of wear the seeds go through while in the gut. The experimental results suggest that frugivory modifies the length of this dormancy so that the evenness of seedling emergence over time increases as more dispersers, each of which treats the seed in its gut differently, ingest the fruit. This may help to spread the risks encountered during germination, as an adaptation to a relatively mesic environment with an unpredictable rain pattern. (3) Rhamnus palaestinus seeds are encased in a sheath with unique features. It fully protects the seeds during passage through the gut of a disperser, and is shed immediately after defecation. Thus protection does not wear out in the gut, yet germination is not impaired and remains totally independent of gut characteristics of the various dispersers.

Intrinsic GUS-like activities in seed plants.

Abstract: Fifty-two plant species, covering some Gymnosperms and all the key groups of Angiosperms, were chosen for surveying their intrinsic beta-glucuronidase-like activities. Histochemical (overnight incubation) and qualitative fluorometric (24 h incubation) assays indicated that, with few exceptions, such activities were detected in certain part(s) of the fruit walls, seed coats, endosperms or, especially, the embryos of the tested plants. Most of such activities in the excised immature embryos of soybean and string bean disappeared after one to a few days' in vitro culturing. Such activities in the intact mature seeds of these two species diminished also during germination process. The vegetative organs of seedlings/mature plants usually lack such activities. The enzyme(s) responsible for such activities was antigenically dissimilar to E. coli beta-glucuronidase.

Effects of sand burial on seed germination, seedling emergence, survival, and growth of Agropyron psammophilum

Abstract: Studies were conducted to determine the effects of sand burial on seed germination, seedling emergence, survival, and growth of Agropyron psammophilum In the field, seedlings of A psammophilum em

Influence of seed size and quality on seedling development under low nutrient conditions in five Australian and South African members of the Proteaceae.

Abstract: (1) Seedling development under nutrient-deficient conditions was investigated for five bradysporous members of the Proteaceae to test the hypothesis that large seed size and high embryo nutritional quality reflect the outcome of selection favouring propagules suited for establishment in infertile soils characteristic of those natural environments dominated by members of the Proteaceae. (2) Seeds of Protea lorifolia, Protea cynaroides, Leucadendron laureolum, Hakea sericea and Banksia laricina were germinated and grown on nutrient-deficient sand for 200 days. Every forty days ten seedlings of each species were harvested to determine growth, allocation patterns and nutrient use. Seedling parts were dried, weighed and analysed for N, P, K, Ca and Mg. . (3) Seedlings of all Proteaceae species were able to survive prolonged periods of nutrient scarcity irrespective of seed size. (4) Rapid germination of Proteaceae seeds does not appear to be a significant means of increasing seedling fitness. (5) Seed mass was positively correlated with seedling size. (6) No correlation between relative growth rates and seed size was found. (7) Seeds of members of the Proteaceae show selective storage of specific nutrients (N and P) such that seed chemical composition is unbalanced for optimum seedling growth. These elements complement the rich sources of cations Ca,Mg and K found in soils of post-fire environments when maximal recruitment of proteoid species occurs.

Abscisic acid and osmoticum prevent germination of developing alfalfa embryos, but only osmoticum maintains the synthesis of developmental proteins

Abstract: Developing seeds of alfalfa (Medicago sativa L.) acquire the ability to germinate during the latter stages of development, the maturation drying phase. Isolated embryos placed on Murashige and Skoog medium germinate well during early and late development, but poorly during mid-development; however, when placed on water they germinate well only during the latter stage of development. Germination of isolated embryos is very slow and poor when they are incubated in the presence of surrounding seed structures (the endosperm or seed coat) taken from the mid-development stages. This inhibitory effect is also achieved by incubating embryos in 10−5 M abscisic acid (ABA). Endogenous ABA attains a high level during mid-development, especially in the endosperm. Seeds developing in pods treated with fluridone (1-methyl-3-phenyl-5[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone) contain low levels of ABA during mid-development, and the endosperm and seed coat only weakly inhibit the germination of isolated embryos. However, intact seeds from fluridone-treated pods do not germinate viviparously, which is indicative that ABA alone is not responsible for maintaining seeds in a developing state. Application of osmoticum (e.g. 0.35 M sucrose) to isolated developing embryos prevents their germination. Also, in the developing seed in situ the osmotic potential is high. Thus internal levels of osmoticum may play a role in preventing germination of the embryo and maintaining development. Abscisic acid and osmoticum impart distinctly different metabolic responses on developing embryos, as demonstrated by their protein-synthetic capacity. Only in the presence of osmoticum do embryos synthesize proteins which are distinctly recognizable as those synthesized by developing embryos in situ, i.e. when inside the pod. Abscisic acid induces the synthesis of a few unique proteins, but these arise even in mature embryos treated with ABA. Thus while both osmoticum and ABA prevent precocious germination, their effects on the synthetic capacity of the developing embryo are quite distinct. Since seeds with low endogenous ABA do not germinate, osmotic regulation may be the more important of these two factors in controlling seed development.

Effects of canopy openings on tree seed germination in a Malaysian dipterocarp forest

Abstract: The germination of 43 tree species native to the lowland forests of Malaysia was monitored on forest soil in trays placed in closed-canopy forest, an artificial forest gap, and a large clearing. Germination varied significantly among habitats, with only seven species germinating well in all three sites. Seed germination of most species demonstrated clear patterns of shade tolerance or intolerance identical to those long recognized for tree seedlings. Favoured locations for germination were similar to known distributional patterns of adult individuals in mature and secondary forests. Most forest canopy species germinated in the gap, but germination in the large clearing was dramatically reduced or nil; the regeneration of these species in large clearings will be severely retarded even when seeds are present. Canopy-induced inhibition of germination was apparent in several pioneer species; seeds moved from the forest into the gap or clearing germinated rapidly. Results indicate that natural treefall gaps do not inhibit the germination of most species, but do allow pioneer species to germinate, and therefore regenerate. Although germination occurred in all three locations, the level of germination for particular species varied greatly among habitats. We conclude that germination requirements play a very important role in controlling the species composition of regeneration in forest understorey, gap, and large clearing habitats.

Differential germination of two closely related species of Solanum in response to bird ingestion

Abstract: This study evaluated the effect which ingestion of seeds of Solanum nigrum and S. luteum by bulbuls (Pycnonotus xanthopygos) and blackbirds (Turdus merula) had on their germination, and tried to reveal the ecological implications of such endozoochory. Those closely related plant species are often sympatrical but whereas S. nigrum is a noxious weed invariably associated with human disturbed habitats, S. luteum may also occur in natural plant associations. Our data indicated that germination of seeds of S. nigrum was not affected by ingestion by either bulbuls or blackbirds. On the contrary, germination of the seeds of S. luteum was significantly (p < 0.01) improved by their ingestion by either bird species. Comparative scanning electron micrographs of the seeds showed that seed coat sculpture of S. nigrum was not affected by ingestion. In contrast, in ingested seeds of S. luteum, the sculpture of the seed coat was abraded compared with the uningested seeds; here, also, in the seeds ingested by the bulbuls, the intracellular contents disappeared, and in most of those ingested by blackbirds, there was destruction of the cell wall as well. Assumedly abrasion of the seed coat sculpture of S. luteum increases the seed coat permeability and consequently germination. It would seem that germination and dispersal of this more arid species which grows in unstable habitats is mediated largely by birds, whereas the germination of S. nigrum seeds is not affected by avian ingestion; for this weed, birds serve only as dispersal agents.

Allelopathy and autotoxicity in alfalfa: characterization and effects of preceding crops and residue incorporation.

Abstract: Alfalfa (Medicago sativa L.) is known to be both autotoxic and allelopathic. Greenhouse and laboratory experiments were conducted to determine if WL-316 alfalfa exhibits short-term autotoxicity and long-term autotoxicity and allelopathy. Long-term autotoxicity and allelopathy of alfalfa were verified at Urbana, IL, by comparing the germination and growth of alfalfa and sorghum [Sorghum bicolor (L.) Moench] on Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) previously cropped to alfalfa (alfalfa-soil) and sorghum (sorghum-soil). Short-term autotoxicity of alfalfa was investigated by studying the effect of incorporating its roots only and both roots and shoots on the germination and growth of alfalfa in alfalfa-soil and sorghum-soil. The data were further supported by a laboratory bioassay of seedling exudate and shoot leachate of alfalfa and sorghum. Plant height and fresh weight per plant of alfalfa and fresh weight per plant of sorghum were lower on alfalfa-soil than on sorghum-soil. Germination percentages of both alfalfa and sorghum and plant height of sorghum were unaffected by the preceding crop. The two soils differed in nutrient content, but fertility was high and should not have been limiting to the growth of either crop. As a result, allelopathic/autotoxic compounds in alfalfa-soil were implicated in the growth inhibition of the two crops. Soil incorporation of fresh alfalfa roots only or both roots and shoots reduced alfalfa emergence, plant height, and dry weight per plant. Primary effects of water-soluble inhibitory compounds from alfalfa shoot appeared to be on germination and radicle elongation, the latter being apparently more sensitive than the former. Alfalfa allelopathy seems to be more severe than autotoxicity. A flow diagram describes different kinds of allelopathy and autotoxicity and various situations that verify the existence of a particular kind of allelopathy or autotoxicity

Role of carbohydrates in desiccation tolerance and membrane behavior in maturing maize seed

Abstract: Seed corn (Zea mays L.) ears harvested at seed moisture contents greater than 400 g H₂O kg⁻¹ fresh wt. (fw) are sensitive to rapid, high-temperature (45–50 °C) drying, but tolerant to low-temperature drying. A preconditioning process that precludes this injury without major moisture loss was used to study the nature of the drying damage and the role of soluble sugars in membrane stabilization during drying of two seed corn hybrids. Ears were harvested at moisture contents of 550, 450, and 400 g H₂O kg⁻¹ fw, and preconditioned at 35 °C for 6 to 48 h before drying at 50 °C. Seed germination was correlated with leachate conductivity (r = −0.79) and sugar leakage (r = −0.80) after different times of preconditioning indicating the involvement of membrane function in the damage caused by high temperature drying. Total soluble-sugar concentration decreased during preconditioning with no significant change individual monosaccharide content. The percentage composition of sucrose and a larger oligosaccharide, raffinose, increased significantly during preconditioning. The high correlations between raffinose/sucrose and warm germination, conductivity, and sugar leakage (r = 0.83, −0.80, and −0.71 for A632, and 0.89, −0.78, and −0.79 for B73, respectively) indicates the added effect of raffinose on induced protection. These results suggest that soluble-sugar compositional relationships rather than absolute content may play an important role in membrane stabilization. The presence of raffinose at certain levels also may be a key factor in protecting maturing seeds from high temperature drying damage. The results also indicate that the transition from desiccation intolerance to tolerance is metabolic and not necessarily related to moisture loss. Journal Paper no. J-13479 of the Iowa Agric. and Home Economics Exp. Stn., Ames Project no. 2526.

A Comparative Study of the Germination Characteristics of Seeds from a Moist Tall Grassland Community

Abstract: To account for observed patterns of emergence in the warm temperate grasslands of Japan the seed germination of several dozen species was tested following various types of thermal pre-treatment. An enormous variety of responses was observed among the species, especially in the capacity for immediate germination and the responses to moist storage with chilling. The extent of chilling requirement for the breakage of primary dormancy was largely correlated with the timing of seed dispersal, spring-summer dispersers tending to have a larger chilling requirement. On the other hand, the seedling emergence phenology of the species was closely related to the temperature dependency of the germination of non-dormant seeds. Key-words: Germination, phenology, seedling emergence, seed dispersal, thermal responses

Allelopathic and herbicidal effects of extracts from tree of heaven (Ailanthus altissima).

Abstract: Mature trees of Ailanthus altissima produce one or more potent inhibitors of seed germination and seedling growth. Inhibitor activity is highest in bark, especially of roots, intermediate in leaflets, and low in wood. Crude extracts of Ailanthus root bark and leaflets corresponding to 34 and 1 9 mg water extractable material/L, respectively, caused 50% inhibition of cress radicle growth. Ailanthus seeds also contain one or more inhibitors. These are bound within the seed by the pericarp but diffuse into water agar when the pericarp is removed. The inhibitor(s) could readily be extracted from Ailanthus tissues with methanol, but not dichloromethane, indicating polar characteristics. Ailanthus leaflets had highest inhibitory activity during expansion in spring, whereas activity of trunk bark peaked just before emergence of leaves. This pattern suggests transport of allelochemicals from bark into new leaves. A comparison of seven plant species for sensitivity to the inhibitor(s) from Ailanthus root bark showed little selectivity, although velvetleaf was somewhat more resistant. The inhibitor(s) from Ailanthus root bark exhibited strong herbicidal effects when sprayed pre- and postemergence on plants in soil in the greenhouse. Postemergence effects were striking, with nearly complete mortality of all species, except velvetleaf, at even the lowest doses tested. The results suggest the allelochemical(s) from Ailanthus may have potential for development as natural-product herbicides. PLANTS PRODUCE many compounds that have no apparent metabolic, physiologic, or struc