Seed production of Raphanus raphanistrum following herbicide application during reproduction and effects on wheat yield

The influence of weather and agronomic factors on the activity of six selective herbicides applied at reproductive stages of development for the reduction in seed production of Raphanus raphanistrum in wheat was evaluated. The herbicides used in this way generally reduced seed production by between 80% and 100%. Triasulfuron and mixtures of triasulfuron + MCPA consistently provided the greatest reduction in seed production. This was greater when herbicides were applied at the bud and early flowering stages of R. raphanistrum and the efficacy of the herbicides increased as maximum temperature on the day of spraying increased over the range 14–24°C. An applied model developed from these results predicts the reduction in seed production of R. raphanistrum, for each herbicide, given the stage of weed development and maximum temperature on the day of its application. Wheat yield was significantly reduced as densities of R. raphanistrum increased, with predicted losses at low densities being approximately half of those reported in the literature. There was no consistent evidence that the late application of herbicides had any negative effect on wheat yield through crop injury, nor was there any indication of yield improvement. It is concluded that certain herbicides applied during the reproductive phase of development have considerable potential to reduce R. raphanistrum seed production in wheat crops. As part of an integrated strategy, such late post‐emergence application of selective herbicides to regulate seed production has a likely role for managing weed seedbanks, but little or no value for counteracting weed competition.     

Effects of shepherd's purse (Capsella bursa-pastoris L. Medic.) on the growth of radish (Raphanus sativus L.)

Radish (Raphanus sativus L.), a salad vegetable, and shepherd's purse (Capsella bursa-pastoris (L.) Med.), a common annual or biennial weed, are plants of similar height, leaf area and root biomass which often occur together in early summer. To assess the effects of the weed on the crop, plants were grown in well-watered and fertilized monocultures and mixtures in the greenhouse. Growth of both species in monoculture decreased, per plant, as planting density increased, particularly in radish which had a high relative monoculture response. In mixtures, at a range of planting densities, and in different proportions, radish was much the stronger competitor, its total dry matter and tuber production being affected only slightly, and not at all in some experiments, by mixture with C. bursa-pastoris. Thus the relative mixture response of radish ranged from 0.1 to 0.0, and the relative crowding coefficient of radish over Capsella was high, indicating that radish was strongly aggressive in the mixture. Although the two species had similar leaf areas in monoculture, that of C. bursa-pastoris was greatly reduced in mixture. The advantage displayed by radish in intercepting light was further enhanced when it was grown in mixtures because radish increased the height of the greatest part of its leaf area, so increasing its shading of the weed. Withholding water from plants increased dry matter partitioning to the root systems in both species, and slightly increased the competitive advantage of radish over C. bursa-pastoris. It is concluded that the weed poses little threat to the yield of radish crops in the field. Effets de la capselle bourse a pasteur (Capsella bursa-pastoris L. Medic.) sur la croissance du radis (Raphanus sativus L.) Le radis (Raphanus sativus L.) et la capselle bourse à pasteur (Capsella bursa-pastoris L. Medic) mauvaise herbe annuelle ou bisanuelle commune, sont des plantes de hauteur, surface foliaire et système racinaire semblables qui apparaissent souvent ensemble au début de l'été. Pour évaluer les effets de l'adventice sur la culture, les plantes ont été cultivées en monoculture et en culture mixte sous serre avec un bon arrosage et une bonne fertilisation. La croissance des deux espèces en monoculture a diminué par plante parallèlement à l'augmentation de la densité, en particulier chez le radis qui a une réponse à la monoculture relativement élevée. En mélanges, sur un éventail de densités de plantation et dans différentes proportions, le radis a été un compétiteur plus fort avec un poids total en matière sèche et une production tubéreuse peu affectée, et pas dans tous les essais, par le mélange avec la capselle. Ainsi, la réponse au mélange du radis a varié de 0,1 à 0,0 et le coefficient de masse relative du radis par rapport à capselle était élevé, soulignant que le radis était fortement compétiteur dans le mélange. Bien que les 2 espèces aient des surfaces foliaires semblables-en monoculture celle de C. bursa-pastoris a été considérable-ment amoindri en mélange. L'avantage que le adis tire de son interception de la lumière, a été favorisé dans la culture en mélange parce que le radis a accru la hauteur à laquelle se trouvait la majorità de sa surface foliaire, augmentant ainsi son ombrage de l'adventice. En réduisant la source en eau des plantes, on a eu une augmentation de la matière sèche au niveau des racines chez les 2 espèces avec une légère contri-bution à l'augmentation de l'avantage du radis sur la capselle. Il en est conclu que l'adventice représente une faible menace pour le rendement des cultures de radis au champ. Konkurrenz von Hirtentäschel (Capsella bursapastoris (L.) Medic, mit Radieschen (Raphanus sativus L.) Die Gemüsepflanze Radieschen (Raphanus sativus L.) und das verbreitete, ein- bis überjährige Unkraut Hirtentäschel (Capsella bursapastoris (L.) Medic.) haben eine ähnliche Höhe, Blattfläche und Wurzelmasse, sie treten im Frühsommer oft zusammen auf. Um die Wirkung des Unkrauts auf die Kulturpflanze zu untersuchen, wurden die Pflanzen im Gewächshaus in gut gewässerten und gedüngten Rein- und Mischbeständen kultiviert. Bei beiden Arten nahm das Wachstum der Einzelpflanze mit zunehmender Dichte ab, besonders beim Radieschen. In Mischbeständen mit verschiedenen Pflanzendichten und Mischungs-verhältnissen war das Radieschen der stärkere Konkurrent, dessen Gesamttrockenmasse und Rübchenertrag nur wenig und in manchen Versuchen überhaupt nicht durch das Unkraut beeinträchtigt wurden. So variierte die relative Reaktion des Radieschens in den Mischbeständen (mixture response) von 0,1 bis 0,0, und der relative Verdrängungskoeffizient des Radies-chens über Capsella war hoch, worin zum Ausdruck kommt, wie konkurrenzstark das Radieschen in den Mischkulturen war. Obwohl die beiden Arten in Reinbeständen ziemlich ähnliche Blattflächen entwickelten, war diese bei Capsella in Mischbeständen erheblich reduziert. Das Radieschen erlangte in Mischbeständen auch dadurch einen Vorteil bei der Lichtaufnahme, indem der gröte Teil seiner Blattfläche höher lag und so das Unkraut zunehmend beschattete. Bei Wassermangel stieg die Wurzeltrockenmasse bei beiden Arten an, wodurch der Konkurrenzvorteil des Radieschens gegenüber dem Hirteltäschel leicht verstärkt wurde. Diese Unkrautart übt also nur eine kleine Schadwirkung auf den Ertrag von Radieschen aus.     

Drought-induced anatomical changes in radish (Raphanus sativus L.) leaves supplied with trehalose through different modes

Leaf anatomical changes were appraised in exogenously applied trehalose of radish (Raphanus sativus L.) plants grown under nonstress (well-watered) and water stress (60% field capacity) conditions. Two cultivars of radish namely, Manu and 40-Day, were grown in a pot experiment at the Botanical Garden, GCUF, Pakistan. Plants were subjected to 60% field capacity conditions after three weeks of germination. Trehalose (25 mM) was applied to the radish plants through two different modes (foliar and presowing). After 2 weeks of foliar-applied trehalose, the leaves were excised from the plants for studying different anatomical features. Water stress caused a significant reduction in the leaf vascular bundle area, leaf midrib thickness (only in cv. Manu), leaf parenchyma cell area, and the number of vascular bundles in both radish cultivars, while water stress increased leaf epidermis thickness of both radish cultivars. Exogenously applied trehalose through both (presoaking and foliar spray) modes was effective in increasing leaf epidermis thickness, vascular bundle area, midrib thickness, and number of vascular bundles in both radish cultivars under water stress and nonstress conditions. Foliar-applied trehalose was more effective in increasing midrib thickness in both radish cultivars under both water regimes. Of both cultivars, the performance of cv. Manu was better in leaf epidermis thickness, leaf midrib thickness, vascular bundle area, leaf parenchyma cell area, and the number of vascular bundles. Overall, exogenous application of trehalose through both modes was effective in triggering leaf anatomical changes under different water regimes.     

The dormancy of wild oat seed (Avena fatua L.) from plants grown under various temperature and soil moisture conditions

Wild oat plants of types fA, fB and fC were grown at a constant 15 or 20°C during the period of seed maturation. Seed of the three types differed little in dormancy when grown at 15°C, but at 20°C a larger proportion of seeds of type fA were dormant compared with fB or fC. Overall, dormancy of seed produced at 15 and 20°C was 97 and 63% respectively. Plants of another collection of type fB were grown from seed at 15 or 20°C with or without water stress applied only from the time of panicle emergence. Water stress and high temperature reduced viable seed production. Seed dormancy was tested immediately after collection by planting the seed in soil, and by Petri dish tests. Further Petri dish tests were made after 6 months storage. Seedling emergence in the first autumn from seeds of plants matured without water stress at 15°C was 10% compared with 30% for seeds grown at 20°C. Seeds grown with water stress at 15°C gave 47%, and at 20°C 78% emergence. The majority of emergence from seeds formed at 15°C without water stress occurred in the second spring after burial. Petri dish tests support these findings and suggest that seeds produced in hot dry summers are less dormant than those produced in cool moist ones.     

Overcoming seed dormancy in oilseed rape (Brassica napus L.) with exogenous compounds

Dormant seeds of oilseed rape (OSR) can persist in the soil and cause OSR volunteers in subsequent crops. Several approaches were tested in the laboratory and in the field to determine whether dormancy induction and seed persistence can be reduced by using dormancy‐breaking exogenous compounds. In a laboratory experiment, OSR seeds were coated with KNO₃, micronutrients, or gibberellic acid (GA) prior to a secondary dormancy test. In a field experiment, seeds were coated in a manner analogous to the laboratory experiment, and then buried 10 cm deep in the soil for 2.5 months. In a practical demonstration, OSR plants were sprayed with either urea ammonium nitrate (UAN) or a commercial product containing GA prior to seed maturity. Seed coating (laboratory and field experiments) reduced secondary dormancy and seed persistence in the field by up to 99%. The efficiency of the treatments for mitigating secondary dormancy (laboratory and field experiments) in decreasing order was GA > micronutrients > KNO₃ > control. With pre‐maturity spraying (practical demonstration), UAN reduced primary dormancy by up to 77% and the development of secondary dormancy by up to 38%; GA had no effect. Dormancy and seed persistence of OSR seeds may be reduced by a pre‐maturity UAN treatment of OSR mother plants, or by applying appropriate exogenous compounds to OSR seeds.     

Factors affecting seed dormancy and germination of Johnsongrass, Sorghum halepense (L.) Pers.

Seeds of Johnsongrass [Sorghum halepense (L.) Pers.] germinated to higher percentages (20–30% higher) when incubated at 28 and 35° C than at 10 or 22° C. After-ripening was accelerated by dry storage of these seeds at 50°C. Seeds pre-chilled at 6°C for 2–4 weeks followed by incubation at 28°C germinated 40–60%. Light effects on germination were related to incubation temperatures; inhibitory at 22°C; no response at 28°C; and stimulatory at 35°C. Effects of gibberellin A₃ (GA₃) also varied depending on incubation temperature, sodium hypochlorite (NaOCl) immersion and light conditions. Immersion of dry seeds in either 700 mM NaOCl, 900 mM H₂O₂ or concentrated H₂SO₄ before incubation in water was effective in breaking dormancy. This result suggests the modes of action of H₂SO₄ in the termination of dormancy may be similar to those of NaOCl and H₂SO₄ as previously suggested by Hsiao & Quick (1984), that is by modification or scarification of the hull or seed coat membranes, and also by the supply of additional oxygen to the seed.     

Factors affecting threshold levels and seed production of jimsonweed (Datura stramonium L.) in soyabeans (Glycine max (L.) Merr.)

The effects of soyabean Glycine max (L.) Merr. row width, date of planting and year on threshold levels of jimsonweed (Datura stramonium L.) and on jimsonweed seed production were examined over 3 years. Natural infestations of jimsonweed were employed and densities were determined at 3 weeks after planting and also at soyabean harvest. Date of planting affected emergence of both soyabean and jimsonweed seedlings, whereas row width affected weed seedling mortality. Percentage soyabean yield losses attributable to jimsonweed, over all treatments, were greater in the 2 years with above-average rainfall than in the one dry year. Slopes of regression equations and estimates of threshold densities varied significantly among years and between initial and final density counts. The number of jimsonweed seed capsules produced per plant and the number of seeds per capsule declined with jimsonweed density, but the mean number of seeds produced per m² remained fairly constant over a wide density range. Jimsonweed seed production did not decline significantly until well below the threshold densities determined for soyabean yields. Les facteurs du seuil de nuisibilité et de la production de graines chez Datura stramonium L. dans les cultures de soja (Glycine max. (L.) Merr.) L'influence de l'écartement des rangs de soja, Glycine max (L) Merr., de la date de semis, et de l'année, sur le seuil de nuisibilité et la production de graines chez le Datura stramonium L., a étéétudiée durant 3 années. Les études ont été effectuées sur des infestations naturelles de datura, dont les densités ont été déterminées 3 semaines après le semis ainsi qu'à la récolte. La date du semis influence à la fois la levée du soja et celle du datura, alors que l'écartement des rangs influe sur la mortalité des graines de l'adventice. Dans tous les traitements, les pertes de rendement attribuables au datura ont été plus importantes durant les 2 années où les précipitations on été supérieures à la moyenne que durant une année sèche. Les pentes des équations de régression et les estimations de seuils de nuisibilité variaient d'une manière significative selon les années et entre les comptages initiaux et finaux. Le nombre de capsules par plane et le nombre de graines par capsule diminuaient avec la densité des datura, mais le nombre moyen de graines produites par m² est resté assez constant dans une large gamme de densité. La production de graines de datura n'a décliné significativement que pour une densité de plantes située bien en dessous du seuil de nuisibilitéà l'égard des rendements du soja. Faktoren, welche die Schädigungsschwelle und Samenproduktion von Stechapfel (Datura Stramonium L.) in Sojabohnen (Glycine max (L.) Merr.) beeinflussen Während drei Jahren wurde in Sojabohnen der Einfluss von Reihendistanz und Saatzeitpunkt auf die Schädigungsschwelle und Samenproduktion von Stechapfel (Datura stramonium L.) untersucht. Diese Studie basierte auf den natürlichen Stechapfelpopulationen; die Zählungen der Populationsdichten erfolgten drei Wochen nach der Sojasaat und bei der Ernte. Der Saattermin beeinflusste das Auflaufen der Sojabohnen und der Stechapfelsämlinge, während die Reihendistanz die Mortalität der Unkrautsämlinge veränderte. Die Steigung der Regressionsgeraden und die Schätzungen der schädigenden Populationsdichte variierten signifikant in den einzelnen Jahren und zwischen der ersten und letzten Zählung. Die Anzahl der von den Stechapfelindividuen produzierten Samenkapseln pro Pflanze und Samenmenge pro Kapsel nahm mit zunehmender Populationsdichte ab; die pro m² gebildete Samenzahl blieb jedoch über einen weiten Bereich verschiedener Populationsdichten relativ konstant. Die von der Stechapfelpopulation produzierte Samenmenge nahm bis weit unter die für die Sojabohen schädigende Populationsschwelle nicht signifikant ab.     

Physiological basis of dormancy-breaking in wild oat (Arena fatua L.) seed by ammonia

The physiological basis of the dormancy-breaking properties of ammonia gas was investigated. Treatment of dormant, air-dry wild oat (Avena fatua, Montana 73) seed with ammonia did not influence the activity of the pentose phosphate pathway enzymes glucose-6-phosphate dehydro-genase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Ammonia thus does not beak dormancy via increased activity of these enzymes. α-Amylase synthesis in de-embryonated endosperm halves which had been treated with ammonia and subsequently washed under tap water for 48 h increased five-fold. Catalase activity was inhibited by treatment of seed with ammonia but peroxidase activity was stimulated. In the dormant Montana 73 seed both ammonia and GA₃-stimulated germination could be partially inhibited by salicylic hydroxamic acid (SHAM), but SHAM had no effect on the germination of semi-dormant Oxford seeds. Ammonia treatment led to an 81% increase in respiration in incubating seeds. This increase in respiration was also partially inhibited by SHAM. It is postulated that loss of dormancy induced by treatment with ammonia is associated with the induction of increased respiratory activity. There is, however, no conclusive evidence that this increased respiratory activity is via the alternative respiratory pathway. The stimulation of peroxidase activity may also play a role in the loss of dormancy. Les bases physiologiques de la levée de dormance chez les semenees de folles avoines par l'ammoniac Les bases physiologiques des propriétés d'agent de levée de dormance du gaz ammoniac ont étéétudiées. Le traitement de semence de folle avoine en dormance (Avenu fatua Montana 73) avec de l'ammoniac n'a pas eu d'influence sur les enzymes de la chaîne pentosc phosphate, les glucose 6 phosphate deshydrogénase (G6PDH) et 6 phos-phosluconate deshydrogénase (6 PGDH). L'ammoniac ne lève donc pas la dormance par l'augmentation de l'activité de ces enzymes. La synthèse de l'a amylase dans des demi-endo-spermes désembryonnés, traités à l'ammoniac puis lavés sous un robinet d'eau pendant 48 h, a été multipliée cinq. L'activité des cataiases a été inhibée par le traitement de semences à l'ammoniac tandis que celle des peroxydases a été sitmulée. Pour les semences Montana 73, stimulées par NH₃, et GA₃, la germination pourrait être partiellement inhibée par l'acide salicyl-hydroxa-mique (SHAM); en revanche le SHAM n'a pas eu d'effet su la germination des semences Oxford en semi-dormance. Le traitement à l'ammoniac a entraîné une augmentation de 81% de la respiration pour les semences en incubation. Cette augmentation de la respiraiton était également en partie inhibée par le SHAM. Il a été retenu le principe que la levée de dormance induite par le traitement à l'ammoniac était liée à l'induction de l'augmentation de l'activité respiratoire. Cependent. il n'y a pas de preuve décisive que cette activité respiratoire accrue passe par l'autre chaîne respiratoire. La stimulation de l'activité des peroxydases pourrait également jouer un rôle dans la levée de dormance. Physiologiche Ursachen fuür den Verlust der Samenruhe nach Behandlung mit Ammoniak bei Wildhafer (Avena fatua L.) In dieser Arbeit wurden die physiologischen Grundlagen für die, die Samenruhe abbrechende Wirkung von Ammoniakgas untersucht. Eine Behandlung ruhender, lufttrockener Samen von Wildhafer (Avena fatua, Montana 73) mit Ammoniak beeinflusste die Aktivität der den Pentosephosphat Zyklus regulierenden Enzyme Glukose-6-phosphat-Dehydrogenase (G6PDH) und 6-Phosphoglukonat-Dehydrogenase (6PGDH) nicht. Demnach bewirkt Ammoniak den Abbruch der Ruhezeit nicht über eine erhöhte Aktivität dieser Enzyme. In Endosperm-hälften, deren Embryonen entfernt worden waren, stieg die α-Amylasesynthese nach einer Ammoniakbehandlung und darauffolgender, 48 h dauernden Waschung mit Leitungswasser, um das 5-fache. Die Begasung der Samen mit Ammoniak hemmte die Katalasewirkuking, stimulierte hingegen die Peroxydaseaktivität. In ruhenden Samen von Montana 73 konnte die durch Ammoniak und GA₃ stimulierte Keimung teilweise durch Salicylhydroxamsäure (SHAM) gehemmt werden; SHAM hatte jedoch keine Wirkung auf halbdormante Oxford-Samen. In keimenden Samen führte die Ammoniakbehandlung zu einer 81%-eigen Steigerung der Atmung. Diese Atmungserhöhung wurde durch SHAM ebenfalls teilweise gehemmt. Es wird angenommen, dass der durch Ammoniak veranlasste Abbruch der Samenruhe mit der Einleitung einer erhöhten Respirationsaktivität verbunden ist. Es ist allerdings kein schlüssiger Beweis vorhanden, wonach die gesteigerte respiratonsehe Aktivität durch den alternativen respiratorisehen Zyklus verursacht wird. Beim Abbruch der Samenruhe mag eine verstärkte Peroxydaseaktivität ebenfalls eine Rolle spielen.     

The roles of light and pericarp on seed dormancy and germination in feral Raphanus sativus (Brassicaceae)

The timing of seed germination may determine the success of a weed species in an agroecosystem, and its expression is modulated by environmental conditions, but also by seed physiology and anatomy. The aims of this study were to investigate the roles of light, pericarp, dry storage and cold stratification on seed dormancy and germination in feral radish, a troublesome agricultural weed in temperate zones of the Americas that reduces crop yields. To this end, we used isolated intact pods and extracted seeds to test germination over time under contrasting temperature, light and storage conditions. Here, we showed that fresh seeds were non‐dormant, but that light and the presence of the pericarp reduced germination, especially under low temperatures. The pericarp reduced the final water content absorbed by seeds inside pods and decreased absorption/dehydration rates. The pericarp showed several small lignified cell layers in the endocarp, and x‐ray images displayed the lack of space between the partially embedded seed and the endocarp. Dry storage and cold stratification were ineffective in breaking the dormancy imposed by the pericarp. The apparent requirement for darkness and the mechanical restriction of the pericarp may have the potential to induce dormancy, spreading the timing of seed germination over a more extended period and hindering the control of feral radish.     

Seed dormancy and field emergence in Solanum nigrum L.

Solanum nigrum L. showed a consistent seasonal pattern of seedling emergence; it began in early May, reached a peak in late May or June, declined in July and August and ceased in September. Germination tests indicated that a requirement for a temperature approaching 20° C for part of the day probably precludes earlier emergence, while seeds removed from burial in late summer showed evidence of a change in dormancy status which could prevent germination at that time. A strict requirement for diurnally fluctuating temperatures was apparent in fresh, dry-stored, moist-stored and buried seeds: germination of dry-stored seeds at constant temperatures was promoted by gibberellic acid and that of moist-stored seeds by potassium nitrate also. Fresh seeds gave only low percentage germination at fluctuating temperatures in the dark but this increased during moist storage and was also promoted by potassium nitrate and gibberellic acid. Data on seed survival in cultivated soil and on duration of the life cycle are presented and discussed. Dormance des semences et levée au champ de Solanum nigrum L. Solanum nigrumL. a montré un cycle saisonnier bien établi de levée des plantules; ce cycle a commencé au début de mai, a atteint un maximum à la fin de mai ou en juin, a diminué en juillet et en août et s'est arrêté en septembre. Les essais de germination ont révélé la necessité d'une temperature de 20°C environ pendant une partie du jour; cette température empêche probablement une levée plus précoce, alors que les semences déterrées à la fin de l'été ont révélé un changement évident de l'état de dormance qui pourrait prévenir la germination à cette époque. Un besoin strict de fluctuation dans les températures diurnes s'est manifesté chez les semences fraîches, conservés à sec ou à l'humidité, et enterrees. La germination des semences conservées à sec à température constante a été déclenchée par l'acide gibbérellique; celle des semences conservées à l'humidité l'a été aussi par le nitrate de potassium, Les semences fraîches ont donné seulement un faible pourcentage de germination à des températures fluctuantes, à l'obscurité, mais ce pourcentage s'est accru durant le stockage humide et il a été aussi favourisé par le nitrate de potassium et l'acide gibbérellique. Des résultats sur la survie des semences dans un sol cultivé sont présentés et discutés. Dormanz und Feldaufgang bei Solanum nigrum L. Das Auflaufen von Solanum nigrum L. war deutlich von der Jahreszeit abhängig: es begann Anfang Mai, erreichte ein Maximum Ende Mai oder Juni, nahm im Juli und August ab und hörte im September auf. Keimversuche ergaben, dass vermutlich Temperaturen von etwa 20°C zumindest kurzfristig am Tag erreicht werden müssen, wodurch ein Auflaufen früher im Jahr ausgeschlossen wird. Samen, die im Spätsommer geprüft wurden und bis dahin im Boden waren, hatten offensichtlich ein veränderies Dormanzverhalten, das sie am Keimen zu diesem Zeitpunkt hinderte Bei frischen, trocken und feucht gelagerten Samen, sowie bei Samen die im Boden vergraben waren, waren täglich wechselnde Temperaturen eine unbedingte Vorausset-zung für die Keimung, Die Keimung von trocken gelagerten Samen (bei konstanter Temperatur) wurde durch Gibberellin-säure gefördert, und bei feucht gelagerten Samen wirkte Kaliumnitral keimungsfördernd. Frische Samen hatten im Dunkeln bei Wechseltemperaturen eine niedrige Kemrate; die Keimung war aber bei feuchter Lagerung besser und wurde auch durch Kaliumnitral und Gibberellinsäure erhöht. Es werden Angahen zum Überleben in kultiviertem Boden und zur Dauer des Lebenszyklus dieser Art gemacht und diskutiert.     

Seed dormancy and seedling emergence studies in Avena fatua L

Studies were made of seedling emergence of three phenotypes of Avena fatua L. with dif ferent coloured lemmas (fA, fB, fC) originally collected from one site. Each phenotype was grown under the same conditions in 1975 and the resulting seed buried 25 mm deep in soil im mediately after collection. The soil was either left uncultivated (all phenotypes) or cultivated monthly (phenotype fA only). Seedling emergence was assessed weekly and the number of remaining viable seeds was determined at the end of three years. Seeds of different lines of A. fatua (fA phenotypes) obtained from separate locations were grown under the same conditions in 1983, buried and seedling emergence moni tored for 85 months. Without cultivation, overall emergence (mean of three phenotypes) in successive autumns and springs was 9%, 18%, 9%, 33%, < 1%, 14% and <1%. A further 3% of viable seeds were recovered at the end of the experiment. Periodicity of emergence was the same for all phenotypes. Actual numbers of seedlings emerging in each of the periods varied between phenotypes. Total emergence of seed from the inner zone of panicles was significantly less than that from the outer zone, although there was little difference between the two zones in each of the natural emergence periods. Cultivation increased emergence, particularly from secondary seed in the first spring after burial, but did not changes its periodicity. By the second spring seed numbers had declined, and seedling counts were similar from cultivated and non-cultivated soil. No viable seed remained in the cultivated soil after three years. Emergence from the two lines of fA was very different. Seedling emergence occurred after hot dry con ditions, or in warm periods immediately after periods of chilling, particularly those below 4°C.     

Sources of viable seed loss in buried dormant and non-dormant populations of wild oat (Avena fatua L.) seed in Colorado

Buried populations of dormant and non-dormant wild oat (Avena fatua) seed persisted less than 2 years, depth of burial having very little influence on their survival. The mode of seed disappearence, however, was closely related to their depth in the soil. Seed exhaustion through germination in situ increased with increasing depth in the soil, whereas exhaustion through non-viability increased with decreasing depth. Physical and induced dormancies are apparently not capable of supporting prolonged persistence of A. fatua seeds in soil. The lack of prolonged persistence of A. fatua seeds in Colorado derives from a lack of genetically programmed embryonic dormancy in these populations and makes A. fatua easier to control in Colorado than in other cereal-growing regions south of the 43rd parallel because it dramatically reduces the survival of seeds in the soil. The most effective non-chemical control of this grass weed is achieved by means of the shallowest cultivations possible, carried out as late as possible.     

Distribution and seed production of Cirsium arvense (L.) Scop, in Victoria, Australia

In 1971 the net area of Cirsium arvense in Victoria was 1300 ha in permanent pasture, 120 ha in cropping land and 40 ha in non-agricultural land. In ten farms in the most heavily infested parish (approximately 100 km²). C. arvense was present in 35 % of the fields and occurred in some highly productive legume-based pastures. The most common control practice on these farms was pasture slashing. It was considered that the weed had been on the farms for 40–80 years. At a constant temperature of 20°C, but not at alternating temperatures, the germination percentage of seed was enhanced by pre-chilling. At constant temperatures the germination percentage was higher at 30°C than at lower temperatures. Alternating temperatures that included 30°C also increased the germination percentage, but it was depressed at 15°/40°C. The germination percentage of seed from forty sites was 52%-97% and some seed was formed where male and female plants were separated by distances of up to 390 m. However, no seed was found in about a third of the parishes examined. Distribution et production de semences de Cirsium arvense (L.) Scop, dans I'etat de Victoria en Australie. En 1971, la surface nette occupée par Cirsium arvense dans pétat de Victoria était de 1300 ha dans les prairies permanentes, de 120 ha dans les terres cultivées et de 40 ha dans les terres non agricoles. Dans 10 fermes situées dans la partie la plus infestée (approximativement 100 km²) C. arvense était present dans 35% des champs et apparaissait dans quelques pâtures hautement productives â base de 1égumineuses. La méthode de lutte la plus fréquente dans ces fermes était la pâture intensive. 11 était admis que la mauvaise herbe était présente dans les exploitations depuis 40 à 80 ans. A la temperature constante de 20°C, maisnon à des tempértures alternées, le pourcentage de germination des semen-ces fut augmenté par une réfrigération préalable. A température constante, le pourcentage de germination fut plus élevé k 30°C quà des temperatures plus basses. Les températures alternées, qui comprenaient celle de 30°C augmentérent aussi le pourcentage de germination, mats celui-ci diminua à 15°/40°C. Les pourcentages de germination de semences de 40 provenances différences se situa entre 52% et 97%; quelques semences furent formées dans des cas où les plantes mäles et les plantes femelles étaient séparées par des distances atteign-ant 390 m. Toutefois aucune semence ne fut trouvée dans un tiers environ des localities examinées. Verbreitung und Samenproduktion von Cirsium arvense (L.) Scop, in Victoria, Australien Die mit Cirsium arvense verseuchte Flfiche in Victoria im Jahre 1971, gliedert sich auf in: 1 300 ha Daucrweide. 120 ha Ackerland und 40 ha nicht-landwirtschafllich genutzte Fläche. In 10 Betrieben des am stftrksten verseuchten Bezirks (ca. 100 km²), war C. arvense in 35% der Felder vorhanden und kam in einigen hochproduktiven Leguminosenweiden vor. Die gebräuchlichste Bekämpfungsmassnahme in diesen Betrieben war das Abmiihen mit Schlegelhilckslem. Es wird angenommen, dass dieses Unkraut seit 40 bis 80 Jahren in den Betrieben vorhanden ist. Bei einer konstanten Temperatur von 20°C, nicht aber bei Wecheseltemperaturen, wurde durch vorheriges Einfrieren die Keimungsrate erhöht. Bei konstanten Temperaturen war sie bei 30°C hSoUher als bei niedrigeren Temperaturen. Wechseltemperaturen die 30°C einschlossen, erhöhten auch die Keimungsrate; bei 15°C/40°C war sie aher geringer. Die Keimung der Samen von 40 Siandorten betrug 52% bis 97%. Wenn weibliche und mflnnliche Pfianzen his zu 390 m von einander entfernt waren. wurden noch einige Samen gebildet. In etwa einem Drittel der untersuchten Bezirke wurden jedoch keine Samen gefunden.     

Fungal infestation of seeds from seven populations of wild oats (Avena fatua L.) with different dormancy and viability characteristics

Seeds from seven genetically inbred pure lines of wild oats (Avena fatua L.) with different levels of dormancy and viability were analysed for seed-borne fungi. All lines had fungi on the seeds. The predominating fungi were Alternaria alternata and Cladosporium herbarum, of which the latter was non-pathogenic and the former only weakly pathogenic on seedlings of wild oats. Drechslera avenacea, Cochliobulus sativus and Fusarium spp., frequently isolated, were pathogenic on A. fatua. Only D. avenacea was host specific to A. fatua and cultivated oats Avena sativa. Cochliobolus sativus and Fusarium spp, were equal or more pathogenic on seedlings of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oats and rye (Secale cereale L.) than on seedlings of A. fatua. Drechslera avenacea occurred on a significantly higher percentage of seeds from A. fatua lines, AN 51 and AN 474, than from the other lines. Other fungi isolated occurred randomly on all A. fatua lines. There was no relationship between low viability of seeds and fungi carried on the seeds.     

Germination rates of weedy radish populations (Raphanus spp.) altered by crop‐wild hybridisation,not human‐mediated changes to soil moisture

Cultivated plants are known to readily hybridise with their wild relatives, sometimes forming populations with weedier life‐history strategies than their progenitors. Due to altered precipitation patterns from human‐induced global climate change, crop‐wild hybrid populations may have new and unpredictable environmental tolerances relative to parental populations, which would further challenge farming and land‐management weed control strategies. To recognise the role of seed dormancy variation in weed invasion, we compared seedbank dynamics of two cross‐type populations (wild radish, Raphanus raphanistrum, and crop‐wild hybrid radish, R. raphanistrum × R. sativus) across a soil moisture gradient. In a seed‐burial experiment, we assessed relative rates of seed germination, dormancy and seed mortality over two years across cross types (crop‐wild hybrid or wild) and watering treatments (where water was withheld, equal to annual rainfall, or double annual rainfall). Weekly population censuses in 2012 and 2013 assessed the frequency and timing of seedling emergence within a growing season. Generally, germination rates were two times higher and seed dormancy was 58% lower in hybrid versus wild populations. Surprisingly, experimental soil moisture conditions did not determine seedbank dynamics over time. Yet, seed bank dynamics changed between years, potentially related to different amounts of annual rainfall. Thus, variation in seedbank dynamics may be driven by crop‐wild hybridisation rates and, potentially, annual variation in soil moisture conditions.     

Changes in seed bank size and dormancy characteristics of the glyphosate-resistant biotype of goosegrass (Eleusine indica[L.] Gaertn.)

A study on changes in the seed bank size of a glyphosate ( N -(phosphonomethyl)glycine)-resistant (R) Eleusine indica biotype was carried out on a naturally occurring infestation of a young oil palm plantation. The total number of shed seeds collected was 53% of the predicted potential total number of seeds produced by the plants. Ametryn ( N -ethyl- N' -(methylethyl)-6-(methylthio)-1,3,5-triazine-2, 4-diamine) was found to be able to control the R seed population in the soil. The periodicity of seedling emergence was influenced by rainfall subsequent to the 1 month period of seed shedding. Seed burial at 2, 10 and 20 cm depths showed that 39, 33 and 79%, respectively, of viable seed persisted in the soil after 2 years. Seeds in the state of enforced dormancy played an important role in maintaining the seed population throughout the 2 year period of burial in the soil.