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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of temperature and humidity on SO2–induced photosynthetic depression was determined in gas exchange experiments with leaves of Vicia faba, L. Stomatal behaviour was sensitive to humidity resulting in higher uptake rates of SO2 and stronger reductions of photosynthesis at low VPD (vapour pressure deficit). After a fumigation period of 2 h, when the photosynthetic rate had stabilized, photosynthesis of leaves exposed to SO2 at 8°C was reduced much more than at 18°C at the same rate of SO2 uptake. Data analysis with a mechanistic model revealed that this effect was due to the slower rate of S(IV) oxidation at lower temperatures, resulting in higher accumulation of S(IV) and thus stronger reduction of photosynthesis. These results were confirmed by experimental analyses of the S(IV) concentration in leaves following fumigation, which showed that more S(IV) accumulated in leaves exposed at a lower temperature. This may explain the high sensitivity of plants exposed to SO2 under winter conditions, when both VPD and temperature are low.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Weed research 41 (2001), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The impact of uprooting and covering plants on mortality and growth reduction was investigated in the laboratory using Lolium perenne L. and Lepidium sativum L. (harrowed 3–4 days after emergence) and Chenopodium quinoa Willd. (harrowed at emergence) as model weed species. Although the predominant initial effect of harrowing was to cover the plants, only 1–17% of the non-uprooted covered plants were killed because the depth at which they were buried by the harrow was shallow. Uprooting was more effective (47–61% mortality) but strongly dependent on soil moisture content. It accounted for 93 and 95% of L. sativum and C. quinoa mortality, but for only 60% of L. perenne mortality. In L. perenne, the species most sensitive to burying, a strong positive relationship was observed between the percentage of plants covered by harrowing and the fresh weight reduction of the total population 6 days after harrowing. The fresh weight reduction of the total L. sativum population was best related to the percentage of uprooted plants, but the percentage of covered plants also appeared to be a good predictor because of its correlation with uprooting. Most of the uprooted plants were also buried. The fresh weight reduction of the total C. quinoa population was not related to the covering effect of harrowing and only weakly related to the percentage of uprooted plants. The results indicate that the plant recovery process after harrowing needs further study and that field research methods should be refined so that they can better discern initial and final harrowing effects on weeds.
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  • 3
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Destructive measurements to collect input data for models that predict yield loss from relative leaf area of weeds can be laborious. Alternative methods were tested in seven field experiments with sugar beet or spring wheat. Weeds with different morphologies showed the same linear relationships between relative leaf area, meas ured destructively, and cover, assessed by means of a frame, until 3 or 4 weeks after crop emer gence. At later growth stages, differences in weed morphology resulted in different relationships. Visual estimates of weed cover corresponded only roughly with cover assessments with a frame. The possibility of estimating relative leaf area of weeds with a reflectance technique was tested, assuming that for early growth stages the leaf area index of weeds can be considered as additional to that of the crop. In spring wheat, relative leaf areas of Sinapis alba L., sown at different times and densities, correlated well with characteristics based on infra-red reflectance. In sugar beet, these relationships were not as distinct. Techniques d'estimation de la surface foliaire relative et de la couverture des mauvaises herbes dans les cultures, en vue de prédictions de pertes en rendement Des prélèvements destructifs peuvent alimenter en données les modèles qui prédisent les pertes de rendement à partir de la surface foliaire relative des mauvaises herbes, mais ils sont exigeants en temps. Des méthodes alternatives ont été testées lors de sept expériences au champ dans de la betterave ou du blé de printemps. Jusqu'à trois ou quatre semaines après la levée de la culture, des mauvaises herbes possédant différentes morphologies montraient les mêmes relations linéaires entre d'une part la surface foliaire relative mesurée de manière destructive et d'autre part la couverture mesurée grâce à une grille. Aux stades de croissance ultérieurs, du fait des différences morphologiques entre les mauvaises herbes, les relations étaient différentes. Les estimations visuelles de la couverture en mauvaises herbes ne correspondaient qu'approximativement aux mesures de couverture effectuées au moyen de la grille. La possibilité d'estimer la surface foliaire relative des mauvaises herbes avec une technique de réflectance a étéévaluée, en supposant que, aux stades de croissance initiaux, l'indice de surface foliaire des mauvaises herbes peut être considéré comme additif de celui de la culture. Dans le blé de printemps, les surfaces foliaires relatives de Sinapis alba L., semées à différentes époques et à différentes densités, étaient bien corrélées avec des caractéristiques basées sur la réflectance infra-rouge. Dans la betterave à sucre, ces relations n'étaient pas aussi claires. Bestimmung der relativen Blattfläche und des Deckungsgrads von Unkräutern zur Prognose von Ertragsverlusten Die destruktive Gewinnung von Daten der relativen Blattfläche von Unkräutern für Modelle zur Vorhersage von Ertragsverlusten sind arbeitsaufwendig. Alternative Methoden wurden in 7 Versuchen in Zuckerrübe und Sommerweizen untersucht. Morphologisch unterschiedliche Unkräuter zeigten bis zu 3 oder 4 Wochen nach dem Auflaufen der Kulturpflanzen dieselben linearen Beziehungen zwischen der destruktiv gemessenen relativen Blattfläche und dem mittels eines Rahmens bestimmten Deckungsgrad. In späteren Entwicklungsstadien führten die morphologischen Unterschiede zu verschiedenen Verhältnissen. Bonituren des Unkrautdeckungsgrads entsprachen nur grob den mit dem Rahmen ermittelten Deckungswerten. Die Bestimmung der relativen Blattfläche der Unkräuter durch Messung der Lichtreflexion wurde geprüft, wobei angenommen werden kann, daß sich in den frühen Entwicklungsstadien der Blattflächenindex der Unkräuter mit dem der Kulturpflanzen summiert. Im Sommerweizen war die relative Blattfläche von zu verschiedenen Zeiten und in unterschiedlicher Dichte gesätem Sinapis alba L. mit den Daten der Infrarotreflexion gut korreliert, auf den Zuckerrübenflächen nicht so genau.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Weed research 40 (2000), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In this study, the effects of Striga hermonthica (Del.) Benth. on a sensitive and a tolerant sorghum genotype were investigated, and the underlying tolerance mechanisms were distinguished. The sensitive sorghum cv. CK60-B and the tolerant sorghum landrace Tiemarifing were grown in pots with and without seed infestation. Both sorghum genotypes responded to infection by the parasite, but it was evident that CK60-B was more strongly affected than Tiemarifing. Sorghum plant height, final leaf number, green leaf area, kernel yield, number of kernels and 1000-kernel weight were significantly reduced by infection, which also had a marked effect on the phenological development of CK60-B; the majority of the plants remained vegetative and, in the remaining plants, flowering was delayed by about 2 weeks. No effect on the phenological development of Tiemarifing was observed. The tolerant landrace showed significantly lower and delayed emergence of S. hermonthica than the sensitive cultivar, and this could be explained by a delay in the onset of attachment. Significantly higher numbers of reproductive parasitic plants were found in the pots with the sensitive sorghum plants. It is concluded that differences in root architecture and the resulting early infection and higher S. hermonthica numbers are partly responsible for the stronger effects of the parasite on the sensitive cultivar.
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  • 5
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This paper tests the hypothesis that increased soil nitrogen supply reduces the growth of late-emerging weeds in wheat and potato by enhancing canopy leaf area development and thereby reducing the availability of light for weed growth. Two series of experiments were conducted: one in spring wheat (1997, 1999) with sown Stellaria media and one in potato (1998, 1999) with naturally emerged weeds, including S. media. For each crop, two cultivars were grown at three levels of nitrogen supply. In wheat, as in a monoculture of S. media, total dry weight and seed number of the weed increased with soil nitrogen supply, whereas in potato the opposite was found. Increased soil nitrogen supply increased the nitrogen uptake of S. media in wheat, despite the reduced light availability, indicating that S. media in wheat was limited by nitrogen. In potato, on the other hand, growth of S. media was limited by light availability, which decreased with increased soil nitrogen supply. We conclude that the differences in response of S. media in wheat and potato to additional nitrogen supply are attributable to the dual influence of soil nitrogen supply on light and nitrogen availability, which are mediated by the crops.
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  • 6
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Genes contributing to the quantitative variation of a complex crop trait can be numerous. However, using existing approaches, the number of quantitative trait loci (QTL) detected for a trait is limited. Therefore, rather than looking for QTL for a complex trait itself, determining QTL for underlying component traits might give more information. In this study the potential of component analysis in QTL mapping of complex traits was examined using grain yield in spring barley as an example. Grain yield was divided into three components: number of spikes/m2, number of kernels/spike, and 1000-kernel weight. These traits were measured for individuals of a recombinant inbred-line population in field trials conducted over 2 years. By the use of an approximate multiple QTL model, one to eight QTL were detected for each trait in a year. Some QTL were mapped to similar positions in both years. Almost all QTL for yield were found at the position of or in close proximity to QTL for its component traits. A number of QTL for component traits were not detected when yield itself was subjected to QTL analysis. However, relative to the QTL for yield itself, all component-trait QTL did not explain the variation in yield better. The results in relation to the potential of using component analysis in studying complex crop traits are discussed.
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  • 7
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: An eco-physiological simulation model is presented in which competition between crop and weeds is simulated. The procedure is based upon the underlying physiological processes of distribution of the resources light and water over the species and the manner in which the species utilize the amounts taken up for dry matter production. On the basis of the leaf area of the competing species and its distribution over the height of the canopy, the absorbed radiation in relationship to plant height is calculated. Using the CO2 assimilation light response of individual leaves, the profile of CO2 assimilation in the canopy is calculated. The daily rate of CO2 assimilation of the species is obtained by integration over height and daylight period after subtraction of losses for maintenance and growth. Effects of drought are taken into account by a simple water balance in which the available amounts of soil moisture during the growing season are monitored. Soil moisture is allocated to the competing species, in proportion to their demands. The model was parameterized for the crop sugar beet (Beta vulgaris L.) and Chenopodium album L. These parameter values were partly derived from literature data and partly from our own experimental data obtained from monocultures. In a subsequent paper (Kropff et al., 1992), evaluation of the model with experimental data will be presented as well as an evaluation of important species characteristics and strategies for weed control. Un modèle ècophysiologique pour la compétition interspecifique, appliqué a l'influence de Chenopodium album L. sur la betterave sucrière. I. Description du modèle et établissement des paramètresUn modèle éco-physiologique simulant la compétition entre une culture et des adventices est présenté. La procédure est fondée sur le schéma physiologique de distribution des ressources en lumière et en eau entre les espèces et la façpn dont les espèces utilisent les quantités prélevées pour la production de matière sèche. Sur la base de la surface foliaire de l'espèce compétitrice et de sa distribution sur la hauteur de la canopée, la radiation absorbée en relation avec la hauteur de la plante est calculée. En utilisant l'assimilation du CO2 en réponse à la lumière, des feuilles individuelles, le profil de l'assimilation du CO2 dans la canopée est calculé. Le taux journalier de l'assimilation de CO2 des espèces est obtenue par intégration de la hauteur et de la période de lumière du jour après soustraction des pertes pour la vie et la croissance. Les effets de la sécheresse sont pris en compte par une simple pesée de l'eau qui permet de suivre les quantités disponibles d'humidité du sol pendant la saison de croissance. L'humidité du sol est attribuée aux espèces compétitrices en relation avec leursdemandes. La modèle a été paramétré pour la betterave sucrière (Beta vulgaris L.) et Chenopodium album L. Les valeurs des paramètres viennent partiellement de la littérature et partiellement des données expérimentales obtenues dans des monocultures. Dans un article (Kropff et al., 1992) l'évaluation du modèle avec des données expérimentales sera présenté ainsi qu'une évaluation des caractéristiques des espèces importantes et des stratégies de desherbage. Ein ökophysiologisches Modell der interspezifischen Konkurrenz von Chenopodium album aufdie Zuckerrübe. I. Beschreibung des Modells und der ParameterIn einem ökophysiologischem Simulationsmodell zur Konkurrenz zwischen Kulturpflanzen und Unkräutern wurde die Trockenmasseproduktion als physiologisches Prozeß je nach Licht- und Wasserangebot behandelt. Die Lichtabsorption, bezogen auf die Pflanzenhöhe, wurde aufgrund der Blattfläche der konkurrierenden Arten und ihrer Verteilung innerhalb des Bestandes kalkuliert. Die Verteilung der CO2-Asimilation im Bestand wurde anhand der Assimilationsrate einzelner Blätter bestimmt. Die tägliche CO2-Assimilationsrate der Arten wurde aus dem Integral über Höhe und Tageslänge abzüglich der Verluste für den Erhaltungsstoffwechsel und das Wachstum errechnet. Verluste durch Trockenheit wurden durch eine einfache Wasserbilanz unter Einbeziehung der Bodenfeuchte und des spezifischen Bedarfs der konkurrierenden Arten zur Vegetationszeit berechnet. Das Modell wurde für die Zuckerrübe (Beta vulgaris L.) und Weißen Gänsefuß (Chenopodium album L.) parametrisiert. Die Parameterwerte wurden teils aus der Literatur entnommen, teils in eigenen Versuchen mil Reinbeständen gewonnen. In einer Folgeveröffentlichung (Kropff et al., 1992) sollen das Modell mit Versuchsdaten sowie wichtige Charakteristika der Arten und Unkrautbekämpfungsstrategien behandelt werden.
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  • 8
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A simulation model for crop-weed competition, parameterized for sugar beet and Chenopodium album L., was validated with experimental data from five field experiments. Between the experiments, 98% of the variation in yield loss, ranging from –6 to 96%, was explained by the simulation model. After validation, the model was used to analyse the backgrounds of the distinct differences in yield loss between the experiments. The contribution of differences in water shortage appeared to be negligible. The number of days between crop and weed emergence, which ranged from 0–31 days, appeared to be the main factor responsible for the differences in yield loss between the experiments (96%). Further analysis showed that water shortage only influences competitive strength of the weeds when overtopped by the crop. Temperature in the period between crop and weed emergence appeared to be an important factor determining the competitive relationships. It is concluded that the period between crop and weed emergence should be expressed as a developmental measure (i.e. degree days) instead of days. Morphological characteristics such as the relative growth rate of leaf area in early growth phases, specific leaf area and height increase largely determined the competitive strength of a species. The effect of physiological characteristics, such as maximum rate of leaf photosynthesis, was less significant. Un modèle écophysiologique pour la compétition interspécifique appliquéà l'influence de Chenopodium album L. sur la betterave sucrière II. Evaluation du modèleUn modèle de simulation de la compétition culture/adventice, paramétré pour la betterave et Chenopodium album L. a été validé avec des données expérimentales issues de 5 essais de plein champ. Entre les essais, 98% de la variation de perte de rendement, allant de – 6 à 96%étaient expliqués par le modèle de simulation. Après validation, le modèle a été utilisé pour analyser les courbes des différences de pertes de rendement entre les essais. Les différences liées au manque d'eau sont négligeables. Le nombre de jour entre la levée de la culture et de l'adventice qui a varié de 0 à 31 jours, est apparu être le principal facteur responsable des différences entre perte de rendement entre les essais (96%). D'autres analyses ont montré que le manque d'eau influence seulement la vigueur de compétition des adventices quand elles sont recouvertes par la culture. La température de la période entre la levée de la culture et de l'adventice apparaît être un important facteur déterminant les relations de compétition. II estconclu que la période entre la levée de la culture et de l'adventice devrait être exprimée en mesure de développement (par exemple en degrés/jour plutôt qu'en jour). Des caractéristiques morphologiques comme le taux de croissance relative de la surface foliaire dans les premiers stades, la surface spécifique foliaire et l'augmentation de hauteur, déterminent grandement la vigueur de compétition d'une espèce. Les effets des caractéristiques physiologiques comme le taux maximum de la photosynthèse foliaires sont moins significatifs. Ein ökophysiologisches Modell der interspezifischen Konkurrenz von Chenopodium album auf die Zuckerrübe. II. ValidierungEin Simulationsmodell zur Konkurrenz zwischen Kulturpflanze und Unkraut, hier Zuckerrübe (Beta vulgaris L.) und Weißer Gänsefuß (Chenopodium album L.), wurde anhand von Daten aus 5 Freilandversuchen validiert. 98% der Variation der Ertragsverluste, die zwischen –6 und 96% lagen, wurden anhand des Modells erklärt. Nach der Validierung wurden mit dem Modell die Bestimmungsgründe für die jeweiligen Unterschiede der Ertragsverluste analysiert. Der Beitrag von Unterschieden des Wassermangels erschien als vernachlässigbar. Die Konkurrenzkraft der Unkräuter wurde durch Wassermangel nur beeinflußt, wenn sie von der Kulturpflanze überwachsen wurden. Die Anzahl der Tage zwischen dem Auflaufen der Kulturpflanze und der Unkrautart, das 0 bis 31 Tage auseinander lag, erwies sich als größter Faktor für die Ertragsverlustunterschiede (96%). Die Temperatur während der Keimperiode war für die Bestimmung der Konkurrenzbeziehungen wichtig. Deshalb sollte die Keimperiode zwischen Kulturpflanze und Unkraut mit einem Entwicklungsmaß (d.h. Temperatursummen) anstatt in Tagen bemessen werden. Morphologische Kenndaten wie relative Wuchsrate der Blattfläche in frühen Entwicklungsstadien, spezifische Blattfläche und Wuchshöhe bestimmten die Konkurrenzkraft einer Art in hohem Maße. Physiologische Daten wie maximale Photosyntheserate waren weniger signifikant.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 31 (1991), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A new simple empirical model for early prediction of crop losses by weed competition was introduced. This model relates yield loss to relative leaf area of the weeds shortly after crop emergence using the relative damage coefficient q as the single model parameter. The model is derived from the hyperbolic yield density relationship and therefore accounts for the effects of weed density. It is shown that the model also accounts for the effect of different relative times of weed emergence. A strong advantage of the approach is that it can be used when weeds emerge in separate flushes.The regression model described experimental data on sugar-beet – lambsquarters (Beta vulgaris L. –Chenopodium album L.) and maize-barnyard grass (Zea mays L. –Echinochloa crus-galli L.) competition precisely. The model describes a single relationship between crop yield loss and relative leaf area of the weeds over a wide range of weed densities and relative times of weed emergence. Possibilities for scientific and practical application of the model are discussed.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 28 (1988), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In most quantitative studies on interplant competition, static regression models are used to describe experimental data. However, the generality of these models is limited. More mechanistic models for interplant competition, which simulate growth and production of species in mixtures on the basis of the underlying physiological processes, have been developed in the past decade. Recently, simulation models for competition between species for light and water were improved and a detailed version was developed for sugarbeet and fat hen (Chenopodium album L.). The model was validated with data sets of five field experiments, in which the effect of fat hen on sugarbeet production was analysed. About 98% of the variation in yield loss between the experiments (which ranged from –6 to 96%) could be explained with the model. Further analysis with the model showed that the period between crop and weed emergence was the main factor causing differences in yield loss between the experiments. Sensitivity analysis showed a strong interaction between the effect of the variables weed density and the period between crop and weed emergence on yield reduction. Different quantitative approaches to crop-weed competition are discussed in view of their practical applicability. Simulations of experiments, where both the weed density and the period between crop and weed emergence were varied over a wide range, showed a close relation between relative leaf cover of the weeds shortly after crop emergence and yield loss. This relation indicates that relative leaf cover of the weeds accounts for both the effect of weed density and the period between crop and weed emergence. This relation has the potential to be developed into a powerful tool for weed-control advisory systems.
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