Competition between sugarbeet and Sinapis arvensis and Chenopodium album, as affected by timing of nitrogen fertilization

The effects of timing of N fertilization (early, standard or late) on competition between two sugarbeet cultivars (Ritmo, semi-prostrate; and Rizor, erect) and two weeds ( Sinapis arvensis and Chenopodium album ) were studied over 2 years at Viterbo. In both years, time of N fertilization did not influence biomass, yield and yield quality of the weed-free crop, but early N fertilization gave higher crop biomass reduction in the presence of S. arvensis and lower crop biomass reduction in the presence of C. album . Root and sucrose yield responded to competition in the same way as biomass. However, percentage reductions were higher, as both weeds affected harvest index. The two cultivars showed the same response to competition. At the weed densities studied, crop competitive ability was favoured by late N fertilization in the presence of S. arvensis and by early N fertilization in the presence of C. album . Crop competition only reduced seed production by C. album but lowered seed germination of both weeds.     

Metabolic effects in rapeseed (Brassica napus L.) seedlings after root exposure to glyphosate

Metabolic effects in rapeseed (Brassica napus L.) seedlings after root exposure to sublethal concentrations of glyphosate were examined in order to evaluate the possibilities of using a response pattern in plants as a measure of exposure to glyphosate through the growth media, more sensitive than the well-known biomarker shikimate. Rapeseed seedlings were grown in hydroponic nutrient solutions containing varying sublethal concentrations of glyphosate (1–50 μM). After 9 days of glyphosate exposure, the shoots of the seedlings were analysed with respect to the effects on selected metabolites downstream from the primary affected metabolite shikimate, which accumulated linearly in response to glyphosate exposure (from 0 to ∼126 μmol/g DW). The selected metabolites analysed, comprising the free amino acids, and the glucosinolates derived therefrom, showed complex patterns in response to glyphosate exposure. Most noteworthy was though that they responded at the lowest concentrations of exposure to glyphosate (1 μM), where no visual effects, decrease in shoot DW or shikimate could be detected, indicating that a biomarker response more sensitive than that of shikimate can be established for plants exposed to glyphosate.     

Inter- and intraspecific competition of fat-hen (Chenopodium album L.) and groundsel (Senecio vulgaris L.)

The responses of Chenopodium album L. and Senecio vulgaris L. to inter- and intra-specific competition were investigated in both additive and replacement series experiments under glasshouse conditions. When grown with tomato the two weed species had similar effects on shoot dry weight at low densities but 5. vulgaris showed more competitive effect at higher densities. Weed density did not affect the concentrations of N, P, K, Ca or Mg in tomato shoots but dry matter and total amounts of nutrients were reduced increasingly with the increase in density of both weeds. The concentration of nutrients in the shoots of the weeds was not affected by density but dry matter yield and total nutrient accumulation per plant fell as the density increased. The concentrations of N, P, K and Mg in the shoots were higher in C. album than S. vulgaris but that of Ca was lower. In a replacement series experiment the two weed species behaved differently. With C. album, both dry matter yield and total nutrient per plant were reduced as its proportion in the mixture increased but, with S. vulgaris, dry matter per plant increased with its proportion in the mixture. One plant of C. album grown with five S. vulgaris gave a higher shoot dry weight than when present in higher proportions or in a pure stand. In a pure stand of six plants the shoot dry weight per plant of C. album was 26% of that of one plant grown with five S. vulgaris. In comparison, the shoot dry weight of one S. vulgaris in pure stand was 120% of that of one plant grown with five C. album. The reduction in growth of C. album was associated with a greater reduction in its ability to accumulate K than other elements. The competition index (CI) of C. album in terms of dry weight decreased with its proportion in the mixture but the reverse was true for S. vulgaris. The relative competitive ability index (RCAI) of C. album was almost 3–5 times that of S. vulgaris. The results showed that differences between the weeds in inter- and intraspecific competition were closely related to the growth of their root systems. Compétition inter- et intraspécifique du chénopode (Chenopodium album L.) et du senecon (Senecio vulgaris L.) Les réponses du chénopode (Chenopodium album L.) et du sénecon (Senecio vulgaris L.) à la compétition inter- et intra-spécifique ont étéétudiées en serre lors d'expériences à séries additives ainsi qu'à séries de remplacement. Quand elles étaient cultivées avec des tomates, les deux mauvaises herbes avaient des effets similaires sur la matière sèche des parties aériennes à faibles densités, mais S. vulgaris se montrait plus compétitif à fortes densités. La densité des mauvaises herbes n'affectait pas les concentrations en N, P, K, Ca et Mg dans les parties aériennes de la to-mate. Par contre, la matière séche et les quantités totales de nutriments étaient d'autant plus réduites que la densité des deux mauvaises herbes était élevée. La concentration en nutriments dans les parties aeriennes des mauvaises herbes n'était pas affectée par leur densité mais le rendement en matière sèche et l'accumulation totale de nutriments par plante décroissaient lorsque la densité augmentait. Les concentrations en N, P, K et Mg dans les parties aériennes étaient plus élevées chez C. album que chez S. vulgaris mais celle de Ca était plus basse. Dans une expérience à séries de remplacement, les deux espèces de mauvaises herbes se comportaient différemment. Chez C. album, le rendement en matière sèche ainsi que la quantité totale de nutriments par plante diminuaient lorsque sa proportion dans le mélange augmentait mais, chez S. vulgaris, la matière sèche par plante augmentait avec sa proportion dans le mélange. Un pied de C. album cultivé avec 5 pieds de S. vulgaris produisait davantage de matière sèche aérienne que lorsqu'il était présent en proportions plus importantes ou en culture pure. Dans une culture pure de 6 plantes, la matière sèche aérienne par pied de C. album représentait 26% de celle d'une plante cultivée avec 5 pieds de S. vulgaris. En comparaison, la matière sèche aérienne par pied de S. vulgaris en culture pure représentait 120% de celle d'une plante cultivée avec 5 pieds de C. album. La réduction de croissance de C. albumétait associée à une réduction de sa capacitéà accumuler K, qui était plus marquée que pour les autres éléments. L'Indice de Compétition de C. album en terme de matière sèche diminuait avec sa proportion dans le mélange, mais l'inverse était vrai pour S. vulgaris. L'Indice Relatif d'Aptitude à la Compétion de C albumétait presque 3,5 fois plus élevé que celui de S. vulgaris. Les résultats montraient que les différences entre les mauvaises herbes en ce qui concerne la compétition inter- et intra-spécifique étaient étroitement liées à la croissance de leur système racinaire. Inter- und intraspezifische Konkurrenz des Weißen Gänsefußes (Chenopodium album L.) und des Gemeinen Greiskrauls (Senecio vulgaris L.) Die inter- und intraspezifische Konkurrenz von Chenopodium album und Senecio vulgaris wurde sowohl in additivem als auch substitutivem Versuchsansatz im Gewächshaus untersucht. In Mischbeständen mit Tomate hatten beide Unkrautarten bei geringer Pflanzendichte eine ähnliche Wirkung auf die Sproß-Trockenmasse, doch Senecio vulgaris war bei hohen Dichten konkurrenzstärker. Die Unkrautdichte hatte keinen Einfluß auf den N-, P-, K-, Ca- oder Mg-Gehalt der Tomatensprosse, aber die Trockenmasse und der gesamte Nährstoffgehalt nahm mit zunehmender Dichte der beiden Unkräuter ab. Der Nährstoffgehalt in den Sprossen der Unkräuter wurde durch die Pflanzendichte nicht beeinflußt, aber die Trockenmasse und der gesamte Nährstoffgehalt nahm mit zunehmender Dichte der beiden Unkräuter ab. Der N-, P-, K-und Mg-Gehalt war bei Chenopodium album höher als bei Senecio vulgaris, doch der Ca-Gehalt war niedriger. In einem substitutiven Versuchsansatz verhielten sich die beiden Unkrautarten verschieden. Bei Chenopodium album wurden sowohl die Trockenmasse als auch der gesamte Nährstoffgehalt pro Pflanze im selben Maße reduziert, wie sein Verhältnis im Mischbestand zunahm; bei Senecio vulgaris stieg die Trockenmasse pro Pflanze mit seinem Anteil im Mischbestand an. Chenopodium album entwickelte bei einem Mischungsverhältnis von l Pflanze zu 5 Senecio-vulgaris-Pflanzen eine höhere Sproß-Trockenmasse als bei höheren Verhältnissen oder im Reinbestand. In einem Reinbestand von 6 Pflanzen war bei Chenopodium album die Sproß-Trockenmasse pro Pflanze 26 % der Masse einer Pflanze, die mit 5 Senecio-vulgaris-Pflanzen wuchs. Bei Senecio vulgaris dagegen war die Sproß-Trockenmasse pro Pflanze im Reinbestand 120 % der Masse einer Pflanze, die mit 5 Chenopodium-album-Pflanzen wuchs. Mit der Wuchshemmung ging bei Chenopodium album eine Abnahme seiner Fähigkeit, K und andere Nährstoffe aufzunehmen, einher. Der Konkurrenzindex von Chenopodium album, bezogen auf die Trocken-masse, nahm mit seinem Anteil in den Mischbeständen ab, während bei Senecio vulgaris das Gegenteil der Fall war. Die relative Konkurrenzfähigkeit von Chenopodium album war fast 3.5mal so groß wie die von Senecio vulgaris. Die Unterschiede der inter- und intraspezifischen Konkurrenz der beiden Unkrautarten stand in enger Beziehung zur Entwicklung ihres Wurzelsystems.     

Environmental conditions and isozyme polymorphism in Chenopodium album L.

Electrophoretic variations within four enzyme systems (α-esterase, acid phosphatase, malate dehydrogenase and leucine amino peptidase), were studied for various garden and field populations of Chenopodium album. A correlation was found between the degree of polymorphism for the electrophoretic traits and environmental conditions. The amount of phenotypic polymorphism is very high in gardens, intermediate in an untreated and, low in herbicide-treated fields and nil for a triazine resistant population in a maize (Zea mats L.) monoculture. Furthermore, the tetraploid versus hexaploid ratio is higher within garden populations. Higher variability in garden populations is due, in part, to a high proportion of polymorphic phenotypes, and in part to a low effect of selection pressure in such types of habitat. Although there is a difference between phenotypes of populations from acid soils and those from more basic ones, we cannot be sure that the variation of polymorphism is due only to selection.     

Chloroplastic resistance to triazine herbicides in Sinapis arvensis L. (wild mustard)

Leaf chlorophyll fluorescence (LCF) of atrazine-susceptible Sinapis arvensis L. (wild mustard) biotype was greatly increased (119–181%)and the Hill reaction activity of isolated chloroplasts was inhibited by 10⁴ M of either atrazine, metribuzin or diuron. In contrast the LCF as well as photochemical activity of the chloroplasts of resistant biotype remained unaffected by 10⁴ M atrazine. However, in response to 10⁴ M metribuzin, LCF of the resistant biotype increased by 43% and Hill reaction activity of the chloroplasts was partially blocked. Complete inhibition of the Hill reaction and a 96% LCF increase in response to diuron indicated that the atrazine-resistant S. arvensis biotype had no tolerance to diuron. Similar chloroplast photoreaction responses were observed when the known atrazine-susceptible and resistant Brassica campestris L. (bird's rape) biotypes and B. napus L. cv. Laurentian (rutabaga) genotypes were subjected to the triazine and urea herbicides. These results indicate that resistance to atrazine, in the resistant S. arvensis biotype, is based in the chloroplasts and could involve a selective modification of the PS II complex with respect to the triazine herbicides. Résistance chloroplastique aux herbicides de la famille des triazines chez Sinapsis arvensis L. (moutarde des champs) Chez un biotype de Sinapis arvensis L. (Moutarde des champs) sensible à l'atrazinc. la fluorescence chlorphyllienne des feuilles était fortement augmentée (de 119 à 181%), et la réaction de Hill des chioroplastes isolés, fortement diminuée, par des traitements à l'atrazinc. la métribuzine ou le diuron 10⁴ M. Par contre, ni la fluorescence chlorophyllienne ni la réaction de Hill n'étaient affectées par de l'atrazine 10⁴ M chez un biotype résistant. Toutefois, en réponse à de la métribuzine 10⁴ M, la fluorescence chlorophyllienne du biotype résistant était augmentée de 43%, et la réaction de Hill chez les chioroplastes était partiellement bloquée. L'inhibition complète de la réaction de Hill et une augmentation de 96% de la fluorescence chlorophyllienne après traitement au diuron indiquaient que le biotype de S. arvensis résistant à l'atrazine ne manifestait pas de tolérance à l'égard du diuron. Par comparaison, des réponses chloroplasliques similaires ont été obtenues lorsque des biotypes de Brassica campestris L. (navette des oiseaux) et des génotypes de B. napus L. cv Laurentian (rutabaga) sensibles ou résistants à l'atrazinc ont été traités par des herbicides de la famille des triazines et des urées substituées. Ces résultats montrent que la résistance à l'atrazine, chez le biotype S. arvensisétudié, est un caractère chloroplastique et implique probablement une modification sélective du complexe PS II à l'égard des triazines. Chlaraplastenresistenz gegen Triazinherbizide bei Sinapis arvensis L. (Ackersenf) Bei atrazinempfindlichen Biotypen von Sinapis arvensis L. wurde die Blattchlorophyll-Fluores-zenz (LCF) in isolierten Chloroplasten durch 10⁴m Atrazin, Metribuzin oder Diuron stark gesteigert (119–181%), die Hillreaktion aber gehemmt. In resistenten Biotypen hingegen blieben LCF und die photochemische Aktivität durch 10^?4m Atrazin unbeeinflusst. Resistente Biotypen reagierten auf 10^?4m Metribuzin mit einer Erhöhung der LCF um 43% während die Hillreaktion in den Chloroplasten teilweise blockiert wurde. Eine komplette Hemmung der Hillreaktion und eine um 96% gesteigerte LCF durch Diuron weisen darauf hin, dass atrazinresistente Biotypen von S. arvensis gegenüber Diuron nicht resestent sind. Aehnliche Veränderungen der Photoreaktionen in Chloroplasten konnten beobachtet werden, wenn atrazinemp-findliche und -resistente Brassica campestris L., Biotypen (Ackerkohl) und B. napus L. cv. Laurentian, Genotypen (Kohlrübe) Triazin- und Harnstoffherbiziden exponiert wurden. Diese Ergebnisse weisen darauf hin, dass die Ursache der Unempfindlichkeit gegenüber Atrazin bei den resistenten S. arvensis-Biotypen in den Chloroplasten liegt und dass eine selektive Veränderung des PS II Komplexes in Bezug auf die Triazinherbizide eingeleitet werden kann.     

Studies on competition between wheat and Chenopodium album L.

Interspecific competition between wheat (Triticum aestivum L.) and Chenopodium album L., was studied in pots using the replacement series design of de Wit. Competitive interference for phosphorus, and to some extent for nitrogen, between the two species was noted. This played a major part in limitation of growth of wheat plants by C. album, whereas wheat exhibited greater non-competitive interference in restricting potassium uptake by the weed. Increasing interference from the weed resulted in significant reductions in wheat grain size and yield.     

Morphophysiological traits and atrazine sensitivity in Chenopodium album L

BACKGROUND: A Chenopodium album L. biotype surviving in atrazine-treated Serbian corn fields (VC) was compared against atrazine-susceptible (S) and atrazine-resistant (R) standards.RESULTS: Atrazine (2 kg ha(-1)) killed S and VC shoot biomass 15 days after treatment (DAT), but R was only suppressed by 42% and survived 8 kg ha(-1). Atrazine at 2 kg ha(-1) only inhibited VC height by 60% as against 100 and 0% for S and R respectively. Chlorophyll fluorescence (Fv/Fm) and transpiration were insensitive to atrazine in R, but were inhibited by 90 and 100% in S and by 50 and 60% in VC respectively. Decline of Fv/Fm after 2 kg ha(-1) atrazine was stabilized at 3 DAT for the VC biotype.CONCLUSION: A toxicity mitigation mechanism could have facilitated VC survival in an atrazine-treated field. Further knowledge on this mechanism is needed to establish if surviving VC plants are indicators of atrazine resistance evolution in these Serbian corn fields. Variables related to foliar function provided better detection of weed mechanisms to survive herbicide action than the usual shoot biomass measurements.     

Physiological investigations into the resistance of a wild mustard (Sinapis arvensis L.) biotype to auxinic herbicides

Possible mechanism(s) of resistance to auxinic herbicides in wild mustard (Sinapis arvensis L.) were investigated by characterizing responses of susceptible and resistant biotypes to 2,4-D, di-camba or picloram. No differences between bio-types were observed in absorption, translocation, or metabolism of foliar-applied radiolabelled herbicides. In contrast, the levels of ethylene production varied between biotypes. The susceptible biotype produced twofold and sixfold more ethylene than the resistant biotype within 4 h and 44 h of herbicide application, respectively. These results suggest that the mechanism of resistance in wild mustard is not due to differences in absorption, translocation, or metabolism. Ethylene production studies imply that resistance to auxinic herbicides may be attributed to altered target site(s) of action. Bases physiologiques de la résistance aux herbicides auxiniques d'un biotype de moutarde des champs (Sinapis arvensis L.) Les mécanismes possibles de la résistance aux herbicides auxiniques chez la moutarde des champs (Sinapis arvensis L.) ont été recherchés en caractérisant les réponses de biotypes résis-tants et sensibles au 2,4-D, au dicamba et au pi-clorame. Aprés application des herbicides radioactifs sur le feuillage, aucune différence d'absorption, de migration ou de métabolisme n'a été observée. Par contre, la production d'éthylene différait entre les biotypes. Le biotype sensible produisait 2 et 6 fois plus d'éthylène que le biotype sensible, respectivement 4 et 44 heures après l'application d'herbicide. Ces résultats sug-gèrent que la résistance aux herbicides auxiniques chez la moutarde des champs n'est pas due à des différences d'absorption, de migration ou de métabolisme mais pourrait provenir d'une altération du site d'action. Physiologische Untersuchung der Resistenz eines Acker-Senf-(Sinapis arvensis-) Biotyps gegenüber Wuchsstoffherbiziden Der mögliche Mechanismus der Resistenz gegenüber Wuchsstoffherbiziden beim Acker-Senf (Sinapis arvensis L.) wurde unhand der Reaktion von empfindlichen und resistenten Biotypen gegenüber 2,4-D, Dicamba oder Picloram untersucht. Hinsichtlich Absorption, Translokation oder Metabolismus der auf die Blätter applizierten, radioaktiv markierten Her-bizide wurden keine Unterschiede beobachtet. Die Ethylenbildung variierte jedoch zwischen den Biotypen. Der empfindliche produzierte in-nerhalb 4 oder 44 Stunden nach der Herbizid-applikation 2-bzw. 6mal mehr Ethylen als der resistente. Aus den Ergebnissen läßt sich schließen, daß beim Acker-Senf der Resisten-zmechanismus nicht in der Absorption, der Translokation oder dem Metabolismus liegt, sondern die Ethylenbildung daran beteiligt ist, wo die Wirkorte fur die Wuchsstoffherbizide liegen.     

Growth, development and nutrient accumulation in Senecio vulgaris L. and Chenopodium album L.

Growth, development and nutrient accumula tion in Chenopodium album and Senecio vulgaris grown in pure and mixed stands were investi gated through several experiments conducted under glasshouse conditions. Results showed that the two weeds were different in their growth, development and tissue concentration and accu mulation of mineral elements. The mean concen trations of nitrogen, phosphorus, potassium, calcium and magnesium in shoots of C. album were higher than those of S. vulgaris, while root concentrations of nitrogen, potassium and mag nesium were lower for C. album. Marked dif ferences between the two weed species in their responses to different potassium levels were found. C. album had a high specific requirement for potassium while the reverse was true for S. vulgaris. The competitive ability and accumula tion of nutrients by C. album appeared to be greatly dependent on the availability of high potassium levels in the media.     

Modelling population dynamics of Sinapis arvensis in organically grown spring wheat production systems

Although we know that alterations in crop density, crop spatial pattern and inclusion of more selective weed control can improve weed suppression for organic growers, it is unknown whether these result in changes to the weed seedbank that increase cropping system profitability over time. Data collected from field trials conducted in 2009 and 2010 in Maine, USA, comparing regional grower practices (Standard) with management that aimed to (i) facilitate better physical weed control through the use of wide row spacing and inter‐row cultivation (Wide) or (ii) enhance crop–weed competition through increased seeding rate and narrow inter‐row spacing (Narrow HD), were used to construct a matrix population model with an economic sub‐model. Using field measurements of grain yield and weed survival and fecundity, we investigated the lasting implications of employing alternative organic spring wheat (Triticum aestivum) production practices on Sinapis arvensis population dynamics. In most scenarios, the model indicated that regional production practices were not sufficient to prevent an increase in the weed seedbank, even with excellent weed control. The two alternative methods, on the other hand, were able to limit weed population growth when initial densities were low or cultivation efficacy was >80%. Due to higher seed costs in the Narrow HD system, net returns were still lower after 10 years of simulation in this system compared with wide rows with cultivation, despite a lower weed seedbank.     

Influence of corn density and planting pattern on the growth of common lambsquarters (Chenopodium album L.)

Crop density and spatial arrangement affect the potential of intraspecific and interspecific competition as they increase the canopy light absorption. The effects of the corn density and planting pattern on the growth of common lambsquarters ( Chenopodium album L.) was studied in a randomized, complete block design with three replications and factorial arrangement at University College, Aburaihan, Iran, in 2003. The plant density was the recommended density and 1.5-fold the recommended density. The planting pattern treatment also was performed at two levels: one- and two-row planting. The common lambsquarters density was 0, 5, 10, and 15 plants m⁻¹ per row. The results showed that the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters were decreased by increasing the corn density. But, the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters under the two-row planting pattern were less than under the one-row planting pattern, although these differences were not significant.     

Development of near-isogenic lines and identification of markers linked to auxinic herbicide resistance in wild mustard (Sinapis arvensis L.)

BACKGROUND: Auxinic herbicides are widely used for selective control of many broadleaf weeds, e.g. wild mustard. An auxinic‐herbicide‐resistant wild mustard biotype may offer an excellent model system to elucidate the mechanism of action of these herbicides. Classical genetic analyses demonstrate that the wild mustard auxinic herbicide resistance is determined by a single dominant gene. Availability of near‐isogenic lines (NILs) of wild mustard with auxinic herbicide resistance (R) and herbicide susceptibility (S) will help to study the fitness penalty as well as the precise characterization of this gene. RESULTS: Eight generations of backcrosses were performed, and homozygous auxinic‐herbicide‐resistant and auxinic‐herbicide‐susceptible NILs were identified from BC₈F₃ families. S plants produced significantly more biomass and seed compared with R plants, suggesting that wild mustard auxinic herbicide resistance may result in fitness reduction. It was also found that the serrated margin of the first true leaf was closely linked to auxinic herbicide resistance. Using the introgressed progeny, molecular markers linked to auxinic herbicide resistance were identified, and a genetic map was constructed. CONCLUSION: The fitness penalty associated with the auxinic herbicide resistance gene may explain the relatively slow occurrence and spread of auxinic‐herbicide‐resistant weeds. The detection of the closely linked markers should hasten the identification and characterization of this gene. Copyright © 2012 Society of Chemical Industry     

Die infraspezifische Struktur von Chenopodium album L. in Beziehung zur Herbizidresistenz

Herbicide resistance in relation to the infra-specific structure of Chenopodium album Chenopodium album is one of the weeds in which herbicide resistance has developed, especially to triazines. In order to identify herbicide-resistant populations at an early stage, the relationships between subtaxa of this polymorphic species and their response to her bicides was investigated. Using the infra-specific systematics of Aellen (1960) as a basis, a new structure was developed from observations over several years. The genetic stability of several anatomical characteristics was evaluated and as a result, the shape of the inflorescence was taken as the basic characteristic. Tests of her bicide susceptibility showed that the taxon with a pseudo-umbelliferous inflorescence had a higher resistance to triazines. C. album biotypes identified to be triazine resistant in the GDR since 1985 all belonged to this taxon. C. suecicum, which closely resembles C. album and often grows together with it, is highly sus ceptible to triazines. In general there was cross-resistance to triazines and chloridazon. Pyridate, bentazon, metobromuron and bromuron were fully effective against these biotypes. The activity of metribizin and combinations of bromuron or fenuron with triazines was some what reduced. Triazine-resistant biotypes of C. album responded more slowly to bromuron than susceptible plants.     

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.     

Differential nitrogen response to atrazine of susceptible and resistant populations of lamb's-quarters (Chenopodium album L.)

Populations of lamb's-quarters (Chenopodium album L.) susceptible and resistant to atrazine exhibited a differential response in regard to the concentration of individual and total amino acids (soluble and protein) in the leaf tissue following atrazine treatment of young plants. The two northern- and two southern-susceptible populations from southern Ontario showed a consistent increase in amino acid levels 1 week after treatment with atrazine at 0.5 kg/ha whereas this did not occur with the corresponding resistant populations. Leaf dry weight was decreased by atrazine in the susceptible populations only but the parallel enhancement of amino acid levels in these populations resulted in no significant decrease in the leaf amino acids per plant except for one southern population. Ammonia increased in concentration in the treated susceptible populations, but not in the resistant. Under the experimental conditions examined a degree of inhibition of photosynthesis by atrazine in lamb's-quarters appeared necessary to bring about the “nitrogen effect” resulting in increases in nitrogen compounds.     

Absorption, translocation and metabolism of pyridate in a tolerant crop (Zea mays) and two susceptible weeds (Polygonum lapathifolium L. and Chenopodium album L.)

Absorption, translocation and metabolism of ¹⁴C-pyridate were compared in tolerant maize. moderately susceptible Polygonum lapathifolium and susceptible Chenopodium album. Foliar absorption was limited in all species, but comparatively higher penetration levels were observed in younger leaves of dicotyledonous species. The absorbed radioactivity was not very mobile and translocation appeared mainly sym-plastic. Herbicide selectivity could not be explained on the basis of absorption and transport. Chenopodium and P. lapathifolium degraded pyridate and formed unstable water-soluble conjugates that easily released a phytotoxic metabolite. By contrast, more stable unidentified water-soluble metabolites were found in maize. That metabolic difference could explain the selectivity of pyridate.     

Interference between triazine-resistant Brassica napus and Panicum miliaceum

Atrazine carryover often limits growers to production of atrazine-tolerant crops the year following application, and allows the increase of triazine-tolerant weed species such as Panicum miliaceum L. (wild proso millet). Tiriazine-resistant Brassica napus L. cv. ‘Triton’ (oilseed rape) was tested to characterize the nature of interspecific interference with P. miliaceum. In a greenhouse study, atrazine at 2.2 kg ha^?1 depressed oilseed rape fruit (siliqua) number and fruit dry weight, and delayed flowering, but did not significantly affect height or weight of shoots, Oilseed rape fruit weight was reduced at 200 P. miliaceum plants m^?2. fruit number and shoot weight were inhibited at 400 weeds m^?2. and height was reduced and flowering delayed at 600 weeds m^?2. Number and weight of fruits were reduced by one-third after 8 weeks of interference as compared to oilseed rape grown with the weed for 4 weeks. Oilseed rape height was reduced by 29% and shoot weight by 55% by 600 weeds m^?2 and 2–2 kg ha^?1 atrazine, while fruit number and weight were reduced by 72%. Oilseed rape shoot weight was reduced by 74% by 600 weeds m^?2 for 12 weeks of interference, while fruit number and weight were reduced by 85% and 82%. respectively. In a field study, fluazifop reduced early season P. miliaceum cover by 72%, but did not increase oilseed rape cover. Mid-season P. miliaceum shoot weight was decreased by 97% by fluazifop and oilseed rape shoot weight was increased by 34%. P. miliaceum control increased oilseed rape biomass by 38% at 89 days, but biomass of oilseed rape sown at 11.2 kg ha^?1 with 2.2 kg atrazine ha^?1 was not decreased by P. miliaceum interference at 89 days.     

多效唑在油菜生产上的应用效果

培育壮苗是目前油菜生产上提高产量的关键措施之一，植物生长调节剂多效唑对油菜壮苗有一定的促进作用。笔者探讨不同浓度多效唑对培育油菜壮苗及其产量的影响，旨在为多效唑在油菜上应用提供依据。     

干旱胁迫对藜叶片干旱诱导蛋白的影响

采用SDS-PA GE(十二烷基硫酸钠-聚丙烯酰胺)凝胶电泳法进行蛋白质的分离,研究干旱胁迫对藜叶片干旱诱导蛋白的影响.结果表明:干旱胁迫10 d,中度干旱藜的叶片110.3 KD和103.9 KD及24.8 KD,22.7KD,21.0 KD蛋白谱带明显加强,重度干旱胁迫下22.7 KD,21.0 KD蛋白谱带增强,但弱于中度干旱胁迫;干旱胁迫15 d,中度干旱胁迫下蛋白谱带与第10 d中度干旱胁迫下的蛋白谱带相比,26.4 KD和19.2 KD蛋白谱带增强.这说明干旱诱导了藜一些适应水分胁迫相关基因的表达,或使一些基因的表达量增强,导致一些新蛋白质的出现或某些蛋白质量的增加而增强其对干旱胁迫的抵抗能力.     

Influence of light intensity on growth of triazine-resistant rapeseed (Brassica napus)

Growth and biomass allocation of nearly isonuclear lines of triazine-resistant and susceptible rapeseed (Brassica napus L.) were compared. Resistant and susceptible lines produced by reciprocal crossing were grown in a greenhouse and in growth chambers under high and low photon flux densities (PFD). Thirty to forty per cent greater average dry weight accumulation was observed in susceptible lines grown under high PFD. Higher leaf area ratio, lower root-shoot ratio and lower specific leaf weight were observed in resistant lines grown in high PFD. These morphological modifications are consistent with a mechanism of compensation of lower photosynthetic performance. Little difference in dry weight and biomass allocation was seen in resistant and susceptible plants grown under low PFD. The similarity in growth response observed in susceptible and resistant plants grown under low PFD indicates the inefficient photochemistry in resistant plants does not necessarily result in lower productivity. Influence de l'intensite lumineuse sur la croissance de colza (Brassica napus L.) resistant aux triazines La croissance et la répartition de la biomasse de 2 lignées isonucléaires voisines de colza résistant et sensible aux triazines ont été comparées. Des lignées sensibles et résistantes produites par fertilisation croisée ont été cultivées dans une serre et en chambres climatiques sous des densités de flux de photon (PFD) hautes et faibles. Trente à quarante pour cent de plus dans 1'accumulation de la matière sèche ont été observées chez les lignées sensibles cultivées sous hauts PFD. Un ratio plus important de la surface foliaire, un ratio plus bas racine/tige et un poids spécifique foliaire plus faible ont été observées chez les lignées résistantes cultivées sous hauts PFD. Ces modifications morphologiques sont liées avec un mécanisme de compensation du rendement photosynthétique plus faible. Une faible différence dans le poids sec, et la répartition de la biomasse a été observed entre les plantes sensibles et résistantes cultivées sous faibles PFD. La similitude de la croissance observée chez les plantes sensibles cultivées sous faibles PFD montre que la déficience photochimique chez les plantes résistantes ne résulte pas nécessairement en une productivité plus faible. Einfluß der Lichtintensität auf das Wachstum von Triazin-resistentem Raps (Brassica napus L.) Das Wachstum und die Biomassebildung von fast reinen Linien von Triazin-resistentem und von -empfindlichem Raps wurden vergleichen. Durch Kreuzbefruchtung wurden resistente und empfindliche Linien gewonnen, die im Gewächshaus und Phytotron unter hoher und niedriger Lichtintensität gezogen wurden. 30–40% höhere mittlere Trockenmasse wurden bei hoher Lichtintensität bei den empfindlichen Linien festgestellt. Ein höherer Blattflächenindex, ein kleineres Wurzel/Sproß-Verhältnis und ein geringeres spezifisches Blattgewicht wurden bei hoher Lichtintensitaät bei den resistenten Linien gefunden. Diese morpholo-gischen Veränderungen stimmen mit einem Mechanismus zur Kompensation geringerer Photosynthese überein. Bei niedriger Lichtintensität gab es nur kleine Unterschiede in der Trockenmasse- und Biomassebildung zwischen den resistenten und den empfindlichen Pflanzen, worin sich zeigt, daß der ineffiziente Photochemismus der resistenten Pflanzen nicht notwendigerweise zu einer geringeren Produktivität führen muß.