ALBERT

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.

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.

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.

Notes: Abstract Relations between leaf rust progress, foliage senescence and yield reduction were studied for seven winter wheat genotypes, differing in their partial resistance to leaf rust. Leaf rust accelerated leaf and ear senescence. Photosynthesis measurements showed, however, that the photosynthetic capacity of the remaining green surface was not affected. Differences between genotypes in yield reduction were largely explained by differences in leaf senescence and, therefore, in cumulative light interception (r=0.83) and crop photosynthesis. Reduction in cumulative light interception was closely related to the area under the disease-progress-curve (r=0.85), which was also closely associated with yield reduction (r=0.88). However, the time taken to reach a 50% reduction of green leaf area and the pustule density on 1 July (i.e. halfway through the epidemic) were just as good predictors of yield reduction as cumulative light interception and area under disease-progress-curve, suggesting that the former are useful criteria in the selection for partial resistance to leaf rust.

Notes: Abstract Differences in yield reduction among seven winter wheat genotypes due to leaf rust, as observed in a field experiment, were analysed using a simulation model. In this model, the effects of the disease on crop growth and yield were described on the basis of light interception, photosynthesis, respiration and assimilate partitioning. The model properly described the observed yield difference between the genotypes, both in the absence and in the presence of leaf rust. According to the model, 66% of total yield reduction was due to an accelerated decrease in green leaf area and 18% was due to light capture by dead leaf tissue at the top of the canopy. Genetic variation in yield reduction was, therefore, mainly explained by variation in leaf senescence. Leaf rust did not affect the photosynthetic rate of the remaining green leaf area. Opportunities of selection for individual damage components were assessed from their simulated effect on grain yield, together with their estimated genetic and environmental variance.

Notes: Summary Mirabilis jalapa plants are very showy through an abundance of reddish, yellowish, white and variegated flowers. The last phenomenon has fascinated various research workers. The authors have studied the inheritance and performed supporting investigations. In this paper a general introduction is given and the colour inheritance of uniformly coloured flowers discussed.

Notes: Summary The somatic chromosome number was found to be 58 for plants with uniformly coloured flowers as well as for plants with variegated flowers. It is concluded that flower variegation is not caused by variation of somatic chromosome number, if any. Yellow pigments occur in all cells of the flower, while violet pigmentation is restricted to the epiderm. Violet pigment is also limited to the epiderm of the hypocotyl and the lower epiderm of the cotyledon. In the epiderm of the flower in ordinary and glandular hairs and in the epiderm of the hypocotyl R can only manifest itself in the presence of Y, whereas in the lower epiderm of the cotyledon R can do so independent of Y. Yellow pigments are composed of several betaxanthins, whereas the violet pigment probably consists of one betacyanin. Y conditions the production of a precursor(s) of betaxanthins while R converts part of this (these) precursor(s) into betacyanin. In the lower epiderm of the cotyledon the production of betaxanthins is hampered. Their precursors are present and can be changed into betacyanin.

Notes: Summary A genetic model for flower variegation in Mirabilis jalapa is given. Two loci effecting pigment production are assumed. The dominant alleles of each of these two loci may be repressed and thus they do not express themselves. In the presence of a dominant variegation gene a repressed allele can become active at some phase of the ontogeny of the plant. Repression and later release of repression results in a pattern of variegation of a dominant colour phenotype on the background of a recessive colour phenotype. Some parallels are drawn between the gene controlling system in M. jalapa and that in maize. In conclusion a practical application for plant breeding is given.

Notes: Summary The inheritance and location of betacyanin production in the cotyledons and hypocotyl have been studied. In the cotyledons these pigments have been located in the lower epidermis. Their production is conditioned by R. In the hypocotyl these pigments have been found in the epidermis. Their production is induced by the complementary alleles Y (or active Yv) and R (or active Rv).