A quantitative analysis of temperature-dependent dormancy changes in Polygonum aviculare seeds

Mathematical models that predict emergence of weed seedbanks could be useful tools for determining the most suitable time for weed seedling control and, consequently, should result in a higher efficacy of applied control methods. To achieve this goal in dormant weed species, functional relationships should be established between environmental factors regulating dormancy and dormancy changes of seed populations. In the present work, we used a simple model and an optimisation procedure to quantify the effect of temperature on Polygonum aviculare seed dormancy release and induction, based on germination data. Dormancy release rate was inversely related to temperature, showing a decreasing logistic trend that results in no dormancy release for seeds exposed to 20 and 25°C. In contrast, dormancy induction rates in absolute values were positively associated with temperature, showing a logistic trend in which dormancy induction was almost zero at low temperatures and maximal at 25°C. Derived model parameters were used to simulate dormancy changes of P. aviculare seeds stored under controlled and field conditions. These results suggest that similar model structures could be used to quantify temperature effects on seed dormancy status of other weed species and to develop predictive models of weed emergence.     

Effects of maternal light environment on germination and morphological characteristics of Sicyos deppei seeds

The effect was studied of sunlight and far-red (FR) light during seed development, on seed quality and germination of Sicyos deppei G. Don. Seeds exposed to FR during development were lighter in colour and their weight, size and water content were significantly lower. Less than 10% of non-scarified freshly harvested seeds germinated. Scarified, freshly harvested seeds developed under sunlight had a partially negative photoblastic response; both red (R) and FR light inhibited germination. The highest and fastest germination occurred in darkness, probably due to the effect of the high photon flux densities on the phytochrome during seed development. Scarified seeds ripened under FR light, germinated well in FR light and in darkness, but R light inhibited germination. After 6 months of storage, the permeability of S. deppei seeds increased, the partially negative photoblastic response was lost and germination of scarified seeds increased. Specifically, in seeds developed under FR, germination in darkness was faster than for the other light treatments, but slow in darkness for seeds developed under sunlight. The physiological and morphological heteroblastic responses in S. deppei probably extend its seed germination and seedling recruitment periods.     

The effects of various temperatures during storage in soil on subsequent germination of sclerotia of Sclerotium cepivorum

The effects of various storage temperatures on germination of sclerotia ofSclerotium cepivorum Berk. were investigated. Sclerotia buried in soil for 10 weeks at temperatures of 5 and 10 °C were conditioned to a fast germination. When germination was performed at 15 °C and induced byAllium extracts, 50% of these sclerotia germinated within 10 days and the total of germination was over 90%. Sclerotia buried at temperatures of 15, 20 and 25 °C were conditioned to a slow germination. About 50% of these sclerotia could be induced to germinate at 15 °C byAllium extracts. The conditioning by high or low temperatures proved to be reversible.The optimum temperature for germination of the cold (5°C) conditioned sclerotia was 10–20 °C. The optimum temperature for germination of sclerotia conditioned at 20 °C was about 10 °C. WithoutAllium extracts 90%, 80%, 50% and 40% of the sclerotia stored at 5 °C, germinated at temperatures of 10, 5, 15 and 20 °C respectively. Sclerotia stored at 20 °C did not germinate withoutAllium extracts at any temperature.Samenvatting Sclerotiën vanSclerotium cepivorum Berk. werden onder niet steriele omstandigheden bewaard bij verschillende temperaturen. Het effect van de bewaring bij verschillende temperaturen op de kieming werd onderzocht. Het bleek dat sclerotiën, die 70 dagen bewaard werden in zakjes met zand in niet steriele grond bij een temperatuur van 5 °C of 10 °C, geconditioneerd werden tot een snelle, vrijwel volledige kieming. Onder invloed van vluchtige stoffen uit gesnipperde ui en knoflook kiemden meer dan 90% van deze sclerotiën bij een temperatuur van 15 °C. Sclerotiën die bij een hogete temperatuur bewaard werden, namelijk bij 15, 20 of 25 °C, kiemden na de bewaarperiode langzaam bij 15 °C. Ongeveer 50% van deze sclerotiën konden tot kieming gebracht worden onder invloed van ui- en knoflookextract. Sclerotiën die door een koude bewaarperiode geconditioneerd waren, namelijk bij 5 of bij 10 °C, kiemden ook zonder ui-en knoflookextract; 78% en 90% van deze sclerotiën kiemden bij temperaturen van respectievelijk 5 en 10 °C. De sclerotiën die een warme bewaarperiode ondergaan hadden, namelijk bij 15, 20 of 25 °C, kiemden niet zonder ui en knoflook. De optimum temperatuur voor de kieming was 15–20 °C voor sclerotiën die bij 5 °C bewaard waren. De optimum temperatuur voor de kieming van sclerotiën die bij 20 °C bewaard waren was lager, en wel ca. 10 °C.De conditionering door een hoge of door een lage bewaartemperatuur bleek reversibel te zijn. Sclerotiën die eerst bij 5 °C bewaard werden en daarna bij 20 °C onderscheidden zich niet van sclerotiën die continu bij 20 °C bewaard werden. Sclerotiën die eerst bij 20 °C bewaard werden en vervolgens bij 5 °C, kiemden als sclerotiën die continu bij 5 °C bewaard waren.     

Effect of fungal toxins on germination of Striga hermonthica seeds

Fourteen fungal toxins were assayed in vitro to evaluate their effect on seed germination of the parasitic weed Striga hermonthica . Among them, T-2 toxin proved to be the most active, being able to inhibit 100% seed germination at 10⁻⁵ M, and being still active when tested at a concentration of 10⁻⁷ M (19% inhibition). Deoxinivalenol was also very active, causing 100% and 69% reduction in germination when assayed at 10⁻⁴ and 10⁻⁵ M respectively. Cytochalasin E, tenuazonic acid, fumonisin B₁, enniatin and nivalenol were shown to have an inhibitory effect of around 50% at 10⁻⁴ M, whereas other toxins had lower or no activity. The high activity shown by some fungal toxins suggests that they may have potential for use as more natural and safe herbicides to suppress parasite seed germination.     

γ射线辐照对3种杂草种子发芽率的影响初报

本文利用60Co-γ射线对芜菁、猪殃殃和反枝苋3种杂草种子进行了50~1000Gy的辐照处理,研究了不同剂量对3种杂草种子萌发的影响,结果表明,发芽7d后,1kGy以下剂量的辐照对3种杂草种子的发芽具有一定的抑制作用,抑制效果因杂草种类的不同而有差异。     

渗透胁迫下氯化胆碱对小麦种子萌发的影响

在15％PEG6000胁迫条件下,研究了氯化胆碱（choline chloride,CC)对小麦种子萌发的影响。研究结果表明,CC对受15％PEG6000胁迫的小麦种子的萌发及根、芽的生长具有明显的促进作用,且以60mg/L CC的效果最好。与对照相比,在该浓度下,平均根长及平均芽长分别可提高14．6％和12．9％,总鲜重可提高17．7％,根／芽比值及萌发率也有所提高,但对生根数无多大影响。同时,CC可使小麦种子α－淀粉酶的活力提高28．0％,使培养介质电导率增长率显著降低,还可使POD活性上升幅度低30．6％。表明,CC促进小麦种子萌发及根、芽生长与提高α－淀粉酶酶活力、降低萌发种子中电解质外渗量及降低POD活性有密切联系。     

Dipropetryn absorption during germination by cucurbit seeds and its influence on seedling growth

The effect of pre-emergence application of dipropetryn on the survival and growth of three watermelon (Citrullus lanatus Thumb.), two cucumber (Cucumis sativus L.), two melon (Cucumis melo L.) and three squash (Cucurbita pepo L.) cultivars was studied in the glasshouse. The tolerance was in the order watermelon > squash > cucumber > melon. After 66 h of germination peeled (with seed coat removed) seeds of ‘Malali’ watermelon, and ‘Michlo-Lavan’ squash accumulated in their cotyledons 119 and three times more ¹⁴C dipropetrym, respectively, than unpeeled (intact) seeds. Three watermelon cultivars accumulated similar concentrations of ¹⁴C in their cotyledons when germinated in soil for 48 h at 26°C or for 120 h at 16°C. Cucumber and squash, however, accumulated significantly higher levels of¹⁴C at the 48 h/26°C regime than at 120 h/16°C. Overall, cucumber and squash accumulated 12 times more ¹⁴C in cotyledons than watermelon, Significant negative correlations were found between seed coal thickness, or the weight ratio of seed coat to total seed, vs dipropetryn accumulation in the cotyledons. The results indicate that the seed coat plays an important role in reducing dipropetryn accumulation within cucurbit seeds during germination and may, at least partially, contribute to the observed tolerance in watermelon. Absorption de la dipropetyrene par des graines de cucurbitacées en germination et influence sur la croissance des plantuies L'effet de traitements de pré-levée par la dipropétryne (2-ethylthio-4,6-di(isopropylamino)-1,3,5-triazine) sur la survie et la croissance de trois cultivars de melon d'eau (Citrullus lanatus Thumb.), deux de concombre (Cucumis sativus L.), deux de melon (Cucumis melo L.) et trois de courge (Cucurbita pepo L.), a étéétudié en serre. Par ordre de tolérance, on a trouvé le classement suivant: melon d'eau > courge > concombre > melon. Après 66 h de germination, des graines pelées (par enlèvement des téguments) de melon d'eau ‘Malali’ et de courge ‘Michlo-Lavan’ accumulaient dans leurs cotylédons respectivement 119 el trois fois plus de ¹⁴C-dipropetryne que des graines non pelées (intactes). Trois cultivars de melon d'eau accumulaient des concentrations similaires de ¹⁴C dans leurs cotylédons lorsqu'ils germaient dans le sol à 26°C pendant 48 h ou à 16°C pendant 120 h. Les concombres et les courges, toutefois, accumulaient significativement plus de ¹⁴C sous le régime 26°C/48 h que sous 16°C/120 h. Globalement, les concombres et les courges accumulaient 12 fois plus de ¹⁴C dans leurs cotylédons que les melons d'eau. Des corrélations négatives significatives ont été trouvées entre l'épaisseur des téguments ou l'importance relative du poids des téguments, d'une part, et l'accumulation de la dipropetryne dans les cotylédons, d'autre part. Les résultats indiquent que les téguments jouent un rôle important en réduisant l'accumulation de dipropétryne à l'intérieur ties graines de cucurbitacées pendant la germination et peuvent, au moins partiellement, contribuer à la tolérance observée chez le melon d'eau. Die Aufnahme von Dipropetryn während der Keimung von Cucurbitaceen-Samen und ihr Einfluss auf das Keimlingswachstum Gegensland dieser Gewächshausuntersuchung war der Effekt von Vorauflaufbehandlungen mit Dipropetryn (2-Aethylthio-4,6-di(isopropylamino)-1,3,5-triazin) auf Ueberleben und Wachstum der Keimlinge von drei Sorten Wassermelonen (Citrullus lanatus Thumb.), zwei Sorten Gurken (Cucumis sativus L.), zwei Melonen-Sorten (Cucumis melo L.) und drei Sorten von Kürbis (Cucurbita pepo L.). Bezüglich Toleranz war die Reihenfolge der Arten: Wassermelone > Kürbis > Gurke > Melone. Nach 66 h Keimungsdauer hatten geschalte Samen von ‘Malali’- Wassermelonen und ‘Michlo-Lavan’-Kürbis in ihren Kotyledonen 119 resp. 3 mal mehr ¹⁴C-Dipropetryn akkumuliert als die ungeschälten, intakten Samen, Drei Sorten von Wassermelonen nahmen ähnliche Mengen ¹⁴C auf, wenn sie in Erde während 48 h bei 26 C oder während 120 h bei 16°C zur Keimung gebracht worden waren. Gurken und Kürbis akkumulierten signifikant höhere Mengen von ¹⁴C währund 48 h bei 26°C, als während 120 h bei 16°C. Im Allgemeinen nahmen Gurken und Kürbis 12 mal mehr ¹⁴C in ihre Kotyledonen auf als Wassermelonen. Es wurden signifikant negative Korrelationen zwischen dem Dicken- resp. Gewichtsverhältnis der Samenschale zum Gesamtsamen und der Anhäufung von Dipropetryn in den Kotyledonen gefunden. Die Resultate weisen darauf hin, dass die Samenschle bei der Reduktion der Dipropetrynakkumulation innerhalb der Samen von Kürbisgewächsen während ihrer Keimung eine wichtige Rolle spielt und, zum mindesten teilweise, zur beobachteten Toleranz der Wassermelone beiträgt.     

红火蚁对8种植物种子的选择性取食及其对种子萌发的影响

在室内研究了红火蚁Solenopsis invicta种群对玉米、绿豆、芥蓝、芝麻、番茄、水稻、藿香蓟及象草等8种植物种子的选择性取食及其对种子萌发的影响,结果表明红火蚁对芝麻种子最为喜好,且刮啃率最高(82.4%),对芝麻、藿香蓟、象草及芥蓝种子具有较高的搬运率(分别为100.0%、72.0%、44.0%及41.6%)和丢弃率(分别为86.4%、50.4%、79.2%及88.9%)。通过观察回收种子的萌发,结果表明红火蚁对芝麻、藿香蓟和象草种子的破坏最为严重,导致其未能正常萌发的种子分别占总数的64.3%、56.0%及49.7%。因此,通过上述指标可以判断红火蚁入侵后对芝麻、藿香蓟和象草种子存在较大潜在威胁。     

The role of arable weed seeds for agroecosystem functioning

A literature study was conducted to gather knowledge on the impact of weed seeds on agroecosystem functioning other than effects related to the production of weed seedlings and plants. The results of the review suggested that a larger and more diverse weed seedbank can contribute to the biodiversity of various groups of macrofauna and microbiota, with a positive or negative impact on the agroecosystem. However, relationships between weed seed availability and functional biodiversity in the field have generally not been established, with the exception of case studies of seeds sustaining populations of granivorous farmland birds or acting as reservoirs and vectors of plant pathogens. To value the contribution of different weed seeds to sustaining populations of functional biota, more detailed information on their relationships with seeds is essential. Hypotheses and related questions that can be used to explore the impact of weed seeds on functional biodiversity have been identified. The identification of weed seed species that are a key to sustaining functional biota may lead to a weed management strategy aiming to minimise the damage of weeds to crops while taking the alternative ecological roles of weed seeds into account.     

Effect of age on the germination of Cassinia arcuata seeds in storage and buried in soil

Seeds of Cassinia arcuata R. Br. (sifton bush), collected annually from near Orange (1987-92) and Boorowa (1987-89). New South Wales. Australia, were stored in a laboratory at a mean temperature of 21°C and a mean relative humidity of 25% and germinated each year for up to 8 years. Seeds from the 1990 and 1992 Orange collections were buried 5 mm and 40 mm deep in the soil for 0.5-2.7 years and the number and germinability of recovered seeds recorded. Germination capacity of seeds stored in the laboratory increased during the first 2 years of storage and then declined slightly in year 3 and markedly in years 4 and 5 to very low levels in year 6 and subsequent years. The seeds collected near Orange had nil germination after 6 years'storage, whereas Boorowa seeds still had 0.2% and 3.5% germination after 7 and 8 years'storage respectively. Seeds that failed to germinate were shown to be non-viable by the tetrazolium test. There was no decline in germination rate during the first 3 years of storage, but, thereafter, there was a substantial annual decline, which would reduce the rate of establishment of seedlings in the field and render them susceptible to competition from improved pastures. The longer and deeper the burial of seeds in the soil and the older the seeds, the fewer seeds that germinated when recovered; meaned for both depths of buriai 23% of 0.9-year-old seeds that had been buried for 0.5 years and 3.4% of 5.1-year-old seeds that had been buried for 2.7 years were recovered in a germinable state. The main causes of loss during burial were germination in the soil and destruction by soil organisms.     

Assessing potential germination period of weeds with base temperatures and base water potentials

Seed germination partly depends on both base temperature (T_b) and base water potential (Ψ_b), which currently are known only for a small number of species. Laboratory experiments were conducted to estimate these parameters for 14 weed species using the ‘x‐intercept’ method. T_b and Ψ_b (°C and MPa) for the 14 weed species were as follows: Amaranthus retroflexus (8.9 and ?0.95), Ambrosia artemisiifolia (3.6 and ?1.28), Avena fatua (2.2 and ?1.02), Capsella bursa‐pastoris (4.5 and ?0.95), Chenopodium album (5.9 and ?0.80), Echinochloa crus‐galli (6.2 and ?1.19), Geranium dissectum (0.6 and ?3.31), Matricaria perforata (2.0 and ?0.75), Picris echioides (5.2 and ?0.79), Polygonum lapathifolium (5.8 and ?1.55), Senecio vulgaris (2.5 and ?1.23), Setaria pumila (8.6 and ?0.75), Solanum nigrum (11.6 and ?0.89) and Veronica hederifolia (0.2 and ?1.67). The two parameters were used to determine potential germination times during expected non‐dormancy periods for three contrasting climatic years in Dijon, France. The number of potential germination days varied little among the tested climatic years, but substantially among species, ranging from 95 ± 9 days for V. hederifolia to 280 ± 7 days for M. perforata. These results may be of value for development of predictive growth models and understanding times when weed control may be most feasible.     

Interrelated effects of temperature, light and oxygen on Amaranthus caudatus L. seed germination

The aim of this study was to investigate the effects of temperature, light and oxygen on the germination of Amaranthus caudatus (var. viridis) seeds. At the highest temperature studied (35°C), seed germination was found to be most rapid and highest in both the dark and the light. Germination was inhibited by continuous white light. The lower the temperature, the greater the inhibitory effect of light. The far-red and blue spectral regions were the most effective in light inhibition. The light effect was also dependent on the percentage of oxygen in the atmosphere around the seeds; it was less marked in O₂-enriched atmospheres. Light/ oxygen dependency resulted from the action of the seed coat and endosperm. Scarified seeds were much less sensitive to light and hypoxia than non-scarified seeds. Effets combinés de la température, de la lumière et de I'oxygène sur la germination des graines d'Amaranthus caudatus L. Le but de ce travail était d'étudier les effets de la température, de la lumiere et de I'oxygène sur la germination des graines d'Amaranthus caudatus (var. viridis). A la temperature la plus élevée utilisée (35°C), la germination était la plus rapide et la plus complète tant à la lumière qu'à 1'obscuritè. La germination était inhibée par la lumière blanche continue. Plus la temperature était basse, plus 1'effet inhibiteur de la lumière était important. Les radiations rouge sombre et bleues du spectre étaient les plus in-hibitrices. L'effet de la lumière dépendait aussi de la teneur de 1'atmosphère en oxygène; il était moins marqué dans des atmosphères enrichies en oxygène. L'interaction lumière/oxygène provenait du tégument et de 1'albumen. Les graines scarifiées étaient beaucoup moins sensibles à la lumière et a 1'hypoxie que les graines non scarifiées. Wechselwirkungen von Temperatur, Licht und Sauerstoff auf die Keimung der Samen von Amaranthus caudatus L. Sowohl im Dunkeln als auch im Licht keimten die Samen von Amaranthus caudatus (var. viridis) bei 35°C, der höchsten Temperatur der Versuche, am schnellsten und meisten. Durch weiβes Dauerlicht wurde die Keimung gehemmt. Je niedriger die Temperatur, desto hölier die Hemmung durch Licht. Im entfernt roten und blauen Spektralbereich war die Lichthemmung am stärksten. Die Wirkung des Lichts hing auch vom Sauerstoffgehalt der die Samen umgebenden Luft ab: Bei O₂₅-Anreiche-rung war sie weniger deutlich. Die Licht/ Sauerstoff-Wechselwirkung wurde von der Samenschale und dem Endosperm beeinfluβt: Geritzte Samen waren gegenüber Licht und O₂-Mangel viel weniger empfindlich als ganze.     

加拿大一枝黄花种子萌发过程中的超弱发光特性研究

加拿大一枝黄花(Solidago canadensis L.)具有较宽的生态域,其种子繁殖能力强,可在多种生境下形成强势种群。用2级变温、7级pH值溶液处理加拿大一枝黄花种子,观察记载其发芽过程中的生物超弱发光值,比较分析其发芽率和发芽速率。结果表明,变温和不同pH处理对种子萌发过程的影响及生物超弱发光强度不同。相对温度较高时,种子的超弱发光值曲线峰值变化较大,在中碱性和酸性条件下曲线分别出现双峰和三峰现象;除pH为5.5外,不同pH处理下种子都具有较高的发芽率和发芽速率;在偏酸或偏碱的逆境条件下,种子表现出较强的生命活力。方差分析表明,不同处理时间和不同pH处理,其种子间的生活力差异显著。     

Factors affecting dormancy and germination of seeds of Eichhornia crassipes (Mart.) Solms from the Nile

E. crassopes requires specific conditions for germination. The best laboratory germination was in clay soil, rich in organic matter, under less than 3 cm depth of water, in light. There are interactions with water depths, soil type, organic deposits, light and temperature. Storage conditions of seeds before germination affect the results. Wetting, drying and re-wetting gave quickest, and complete germination. After 2 years dry-storage, 78% of the seeds were still viable.     

Environmental control of dormancy and germination in the seeds of Cenchrus longispinus (Hack.) Fern.

Seed dormancy and germination in sand burr (Cenchrus longispinus (Hack,) Fern,) were investigated in laboratory and field studies. The burrs contain two types of seeds which differed in their innate dormancy. Primary seeds formed in the upper spikelet usually germinated within a year. Secondary seeds from lower spikelets germinated slowly and remained dormant for longer periods. Dormancy was enforced at low and high temperatures, and secondary seeds apparently developed an induced dormancy when continuously exposed to high temperatures. More than 94 % of the seedlings established during spring. Light suppressed germination, and secondary seeds also developed an induced dormancy when stored in the light. Burrs sown on the soil surface had an extended period of germination lasting for more than 3 years. However, over 96 % of the seeds sown below the surface of bare soil germinated within 2 years. Deep burial did not enforce dormancy, but germination was suppressed by the presence of live vegetation. It is concluded that treatments which disturb the soil and bury the burrs will stimulate the germination of dormant seeds.     

Short soaking in water inhibits germination of Datura ferox L. and D. stramonium L. seeds

Summary. Seed coat structures may play a major role in determining the germination of seeds. The involvement of seed coat characteristics in the inhibition of germination observed when dry seeds of Datura ferox L. and D. stramonium L., were rinsed or soaked in water for 1–5 min ('soaking effect') was investigated. Germination was inhibited by soaking D. ferox seeds even at late stages of the germination process up to one day before root protrusion. Simulation of the 'soaking effect' was achieved by blocking the hilum with lanolin, enamel lacquer or agar during imbibition. Blocking the hilum did not prevent water uptake by the seeds. Seed coat integrity was necessary for the 'soaking effect' since germination inhibition was eliminated by removing or cracking the seed coat. Drying the seeds up to 12 h after soaking reversed the inhibitory effect. SEM observations of both species revealed a loose outer parenchymatous tissue covering the hilum, an inner spongy tissue between the nucellus and the hilum and a space between the seed coat and the nucellus. We concluded that during soaking, water is trapped in the space between the seed coat and the nucellus, and in the intracellular spaces of the spongy tissue within the hilum. This water 'plug' may limit the diffusion of gas(es) to and from the embryo through the hilum, thus inhibiting germination.     

Temperature effects on dormancy release and germination rate in Sorghum halepense (L.) Pers. seeds: a quantitative analysis

Seed dormancy in Sorghum halepense is overcome by exposure to fluctuating temperatures and the effect is determined both by the diurnal amplitude and the maximum temperature. It was found that repeated cycles of particular regimes were additive, each cycle resulting in release from dormancy of a further proportion of the population. The range of regimes having this additive effect was wider in seeds which had after-ripened in the soil during winter than in those which were freshly dispersed. The temperature-dependent germination rate of seeds whose dormancy had been removed by the effect of fluctuating temperatures was analysed using a ‘thermal time’ approach, and estimates obtained of base and optimum temperatures and the required ‘thermal time’ for the germination of different fractions of the population. The results provide a basis for developing a model to predict seedling recruitment in the field using soil temperature data.     

Investigating the effects of temperature on seed germination of cutleaf geranium (Geranium dissectum L.) and determination of its cardinal temperatures

Phytoparasitica - Cutleaf geranium is a weed infesting crop fields in various parts of the world. The present study was conducted to determine the cardinal temperatures of germination for its seeds...