Differential growth and response to atrazine between and within susceptible and resistant biotypes of Chenopodium album L.

Differential growth and response to atrazine were examined in greenhouse experiment with three populations of Chenopodium album from southwestern Ontario: two known susceptible (SI. SII) and one resistant (R). Germination of the resistant biotype was less than SII but the same as SI. R seedlings were not as mature at 16 days and weighed less at 23 days than seedlings of SI and SII. Within SI. early-(ESI) and late-flowering (LSI) variants were recognized. Older plants of R (37 and 44 days) had a greater growth rate than two of the susceptible populations (LSI and SII). In terms of vegetalive, floral, and total biomass. mature individuals of ESI were less productive than the other populations, but devoted a greater percentage of dry weight to floral production. Young plants (37 days old) were sprayed with atrazine at 00125, 0.25, 0.5, 1.25, 2.5 and 5 kg/ha. Population ESI was most sensitive to at razine; height and weight of stems and production of new leaves showed decreases at 0.25 and 0.125 kg/ha. respectively, compared to the untreated. Populations LSI and SII showed greater tolerance and decreases in these characters occurred at a higher rate of atrazine. Leaf weight per plant decreased at 0.25 kg/ha as a result of decreases in weight per unit area of leaf for all susceptible population. Growth of R as measured by the above criteria was not affected by atrazine treatments but leaf weight per unit area was slightly reduced at 2.5 and 5.0 kg/ha Single leaves of 48 day old plants were infused with at razine concentrations of 0.5, 2.0, 3.0 and 20.0 ppm. Leaf chlorosis increased with concentration and injury was greater in populations LSI and SII than in ESI. A small amount of chlorosis occurred in R.     

Genetic variation and phylogenetic relationships of triazine-resistant and triazine-susceptible biotypes of Solanum nigrum– analysis using RAPD markers

The expansion of weed species is a major problem in agriculture, especially when the number of herbicide-resistant biotypes is rising continuously. The major ecological questions associated with the evolution of herbicide resistance involve an intricate understanding of the interplay between gene frequency, fitness, inheritance and gene flow. In this study, the RAPD (Random Amplified Polymorphic DNA) technique, which facilitates detection of variability at DNA level, was used to examine the spread of Solanum nigrum L. populations. Twenty-five populations, from Poland, France and the UK, were analysed. Six populations from Poland and one from France showed target site-based triazine resistance. The genetic relationship between individuals was studied using the RAPD technique. It was found that some resistant populations from the Gabin and Grojec areas show very high affinity levels compared with individuals from France. Three groups of populations in which resistance had developed independently were distinguished. The results of the present investigation suggest that migratory birds, such as Turdus pilaris L. and Sturnus vulgaris L., play an important in spreading S. nigrum seeds.     

Establishment and growth of Senecio jacobaea L. and Senecio erucifolius L. in grassland

Senecio erucifolius L. (hoary ragwort) has become conspicuous on roadside verges in southern England. Like Senecio jacobaea L. it is poisonous, so it might be a threat to animal production. In boxed swards the growth of S. jacobaea was less adversely affected by the greater competition from grass with a high level of nitrogen fertilizer than was the growth of S. erucifolius. Also, young S. jacobaea plants showed a much greater ability to regrow after their shoots had been cut at ground level. In a range of grassland managements S. jacobaea established better from seed than did S. erucifolius. Establishment of both species on molehills was poor because of the likelihood that the seedlings would be disturbed or even buried by fresh mole activity. Ten months after sowing, seedlings of S. jacobaea had persisted well in the higher nitrogen environment of ex-cow-dung patches, whereas S. erucifolius had not. Under intensive sheep grazing, in the absence of fertilizer, transplants of S. erucifolius had much greater root dry weights than did those of S. jacobaea. Also, in regrowth after cattle grazing on a fertilized sward, S. jacobaea plants had greater shoot dry weights than did S. erucifolius. Thus, although S. erucifolius can establish from seed in bare patches in an intensively grazed sward it is likely to be less persistent than S. jacobaea if the gaps are ex-dung patches or if nitrogen fertilizer is applied.     

Growth and fitness of triazine-susceptible and triazine-resistant common waterhemp (Amaranthus tuberculatus var. rudis)

Two greenhouse trials were conducted over a 2 year period (2004 and 2005) to compare the relative growth potential and fitness of triazine-susceptible (TS) and triazine-resistant (TR) waterhemp biotypes. Waterhemp plants from each biotype were grown in 6 L pots in the greenhouse in a completely randomized design. There was no difference in leaf number, plant height, plant biomass, time to bud or time to flower between the two biotypes. The TR female waterhemp plants produced 30% less reproductive biomass and 39% less seed than the TS biotype. The fitness penalty associated with triazine resistance was related to reproductive capability, not to vegetative growth.     

Evolution of resistance to simazine in Senecio vulgaris L.

Fruits were collected from populations of S. vulgaris growing on commercial fruit farms and progenies were tested for susceptibility to simazine. The five least susceptible populations, which originated from sites where simazine had been applied annually for periods ranging from six to ten years, were subjected to two generations of artificial selection for simazine resistance. Two control populations which originated from unsprayed sites were treated similarly. One population originating from Malpas, Cheshire showed a significant response to selection. The simazine resistance of the other six populations was not improved by artificial selection. Selected progenies of the Malpas population were completely unaffected by simazine at 2.8 kg ha^?1. The potential for evolution of resistance to simazine in S. vulgaris is discussed and the effects of ecological and genetic factors on the rate of evolution are assessed.     

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.     

Possible rôle of allelopathy in the competition between tomato, Senecio vulgaris L. and Chenopodium album L.

Summary. The allelopathic effect of Chenopodium album L. (fat-hen) and Senecio vulgaris L. (groundsel) on tomato ( Lycopersicon esculentum Mill cv. Ailsa Craig) plants was investigated under glasshouse conditions. A new technology was used to separate competitive from allelopathic effects. These experiments suggested that C. album had an effect on tomato through allelopathy. C. album leach-ates significantly reduced shoot fresh and dry weights and the accumulation of N, P, K, Ca and Mg of tomato shoots. No effect was found on the quantities of these elements in tomato roots. Leachate of five plants of C. album per pot was sufficient to reduce tomato growth. Addition of 10 or 20 g kg⁻¹ of C. album dried shoots to the soil mixture significantly decreased the fresh and dry weights of tomato plants. S. vulgaris leachates did not show significant effects on the growth or nutrient accumulation of tomato plants.     

Tolerance of triazine-resistant and susceptible biotypes of three weeds to heat stress: a fluorescence study

The photosynthetic performance of Solarium nigrum L., Poa annua L. and Chenopodium album L. resistant to triazines was investigated in order to determine whether the alteration of the 32-kD protein of photosystem (PS) II changed the ability to oxidize the PSII primary quinone acceptor Q_A. The effect of heat stress on the photochemistry of the resistant biotypes and the susceptible biotypes was also compared. The weeds were screened with the in-vivo modulated chlorophyll fluorescence device to measure the photochemical component of fluorescence quenching (q_Q), which provided semi-quantitative information on the redox state of Q_A. At 25°C, an increase in the amplitude of the parameter 1-q_Q, which reflected the reduced state of Q_A, was observed in all resistant biotypes, compared to the susceptible wild biotypes. This was attributable to a shift in the equilibrium between Q_A^? and Q_B (the PSII secondary quinone acceptor) in favour of Q_A. A heat stress of 35°C did not increase the level of reduced Q_A, except in the resistant biotypes of Poa annua. The photochemical activity of the two types of leaves exposed to increasingly high temperatures (25–65°C) indicated that quinone oxidation was more affected by heat stress in mutant resistant biotypes than in the susceptible biotypes. The quinone reoxidation was nullified at 60, 56 and 60°C, respectively, for susceptible biotypes of Solatium nigrum, Poa annua and Chenopodium album, and at 56, 48 and 54°C, respectively, for the three resistant biotypes. Heat also induced changes in the dark fluorescence F₀, an indicator of the heat sensitivity of the light-harvesting chlorophyll protein complex of PSII (LHCPII). The temperature dependence (25–70°C) of this fluorescence parameter confirmed the higher susceptibility of heat-treated resistant leaves. Indeed, the temperatures of the peak of F₀ (Tp) were 60, 55 and 62°C for susceptible Solanum nigrum, Poa annua and Chenopodium album, respectively. The Tp values for the three resistant biotypes were 55, 48 and 57°C, respectively. It is concluded that heat tolerance is related to differences in the organization of the chlorophyll antennae (LHCPII) between the two biotypes. Tolerance de biotypes sensibles et resistants aux triazines de 3 adventices au stress de la chaleur: une étude de fluorescence Les rendements photosynthétiques de Solanum nigrum L., Poa annua L. et Chenopodium album L. resistant aux triazines ont étéétudiés en vue de déterminer dans quelle mesure l'altération de la protéïne 32 kD du photosystème (PS) II, affecte la capacité d'oxyder l'accepteur quinonique primaire de PS II. Q_A L'influence d'un stress de chaleur sur la photochimie de biotypes résistants et de biotypes sensibles a été comparée. Les mauvaises herbes ont été triées au moyen de la fluorescence de la chlorophylle in vivo, pour mesurer la composante photochimique de réduction de la fluorescence (q_Q) qui donne une information semi quantitative de l'état redox de Q_A. A 25 °C, une augmentation dans l'amplitude du paramètre 1-qQ, qui reflète l'état réduit de Q_A a été observée chez les biotypes resistants encomparaison des biotypes sauvages sensibles. Ceci a été attribuéà une modification dans l'équilibre entre Q^?_A et Q_B (l'accepteur quinonique secondaire PS II), en faveur de Q_A. Un stress thermique de 35°C n'a pas augmenté le niveau de Q_A réduit, sauf chez le biotype résistant de Poa annua. L'activité photochimique des feuilles des 2 types exposées à des hautes températures croissantes (25 à 65°C) a montré que l'oxydation de la quinone était plus affectée par le stress thermique chez les biotypes mutants résistants que chez les biotypes sensibles. La réoxydation de la quinone était annulée à 60, 56 et 60°C respectivement pour les biotypes sensibles de Solatium nigrum, Poa annua et Chenopodium album et à 56, 48 et 54°C respectivement pour les 3 biotypes résistants. La chaleur a également entrainé des changements dans la fluorescence F₀, un indicateur de la sensibilitéà la chaleur du complexe collecteur de lumière du PS II (LHCP II). La dépendance avec la température (25–70°C) de ce paramètre de fluorescence a confirmé la plus grande sensibilité des feuilles résistantes soumises à la chaleur. En effet, les températures du pic de F_o (Tp) étaient de 60, 55 et 62°C respectivement, pour les biotypes sensibles de Solanum nigrum, Poa annua et Chenopodium album. Les valeurs Tp pour les 3 biotypes résistants étaient respectivement de 55, 48 et 57°C. Il est conclu que la tolérance à la chaleur est liée aux différences dans l'organisation des antennes chlorophylliennes (LHC P II) entre les 2 biotypes. Hitzetoleranz Triazin-resistenter und -empfindlicher Biotypen von drei Unkrautarten Die photosynthetische Leistung Triazin-resistenter Biotypen von Solanum nigrum L., Poa annua L. und Chenopodium album L. wurde dahingehend untersucht, ob eine Veränderung des 32-kD-Eiweisses des Pigmentsystems II (PII) die Fähigkeit änderte, den primären Quinon-Akzeptor Q_A des PII zu oxidieren. Auch die Wirkung einer Hitzebehandlung auf die photochemischen Reaktionen resistenter und empfindlicher Biotypen wurde verglichen. Die Unkräuter wurden in vivo mit einem Chlorophyll-Fluorimeter gescreent, um die photochemische Komponente der Fluoreszenz-Auslösung (q_Q) zu messen, die eine semiquantitative Information über den Redox-Zustand des Q_A lieferte. Die Amplitude des Parameters l-q_Q, der den reduzierten Zustand des Q_A widerspiegelte, nahm bei 25°C bei allen resistenten Biotypen im Vergleich zu den empfindlichen zu. Dies konnte einer Verschiebung des Gleichgewichts zwischen Q^?_A und Q_B (dem sekundären Quinon-Akzeptor Q_A des PII) zugunsten des Q_A zugeordnet werden. Eine Hitzebehandlung mit 35°C erhöhte den reduzierten Q_A nicht, außer bei resistenten Biotypen von Poa annua. Die photochemische Aktivität von Blättern der beiden Typen, die steigenden Temperaturen von 25 bis 65°C unterworden wurden, zeigte, daß die Quinon-Oxidation bei den resitenten Biotypen durch den Hitzestreß stärker beeinflußt wurde als bei den empfindlichen. Die Quinon-Reoxidation wurde bei den empfindlichen Biotypen von Solanum nigrum, Poa annua und Chenopodium album bei 60, 56 bzw. 60°C aufgehoben, bei den resistenten bei 56, 48 bzw. 54°C. Hitze führte auch zu Änderungen der Dunkel-Fluoreszenz F_o, einem Indikator der Hitzeempfindlichkeit des lichtabsorbierenden Chlorophyll-Eiweißkomplexes des PII (LHCPII). Die Temperaturabhängigkeit dieses Fluoreszenz-Parameters bei 25 bis 70°C bestätigte die höhere Empfindlichkeit hitzebehandelter Blätter resistenter Pflanzen. So waren F_o-Peaks bei empfindlichen Solanum nigrum, Poa annua und Chenopodium album bei 60, 55 bzw. 62°C, bei resistenten bei 55, 48 bzw. 57°C festzustellen. Daraus wurde geschlossen, daß die Hitzetoleranz auf Unterschieden im Aufbau des lichtabsorbierenden Pigmentsystems LHCPII der beiden Biotypen beruht.     

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.     

Differential atrazine interference with the Hill reaction of isolated chloroplasts from Chenopodium album L. biotypes

Atrazine [2-chloro-4-(ethylaminol-6-(isopropyl-amino)-s-triazine] resistant biotypes of lamb's quarters (Chenopodium athum L) were reported in the maize growing areas of Ontario, where the herbicide had been used fur a number of years. Field samples from four locations proved tolerant to higber than recommended rates of atrazine in controlled environment screening trials. A resistant biotype was not killed with up to 40 kg/ha atrazine. Diuron at 5 x10-5 M inhibited the Hill reaction with isolated chloroplasts of resisiant and susceptible biotypes of lamb's-quarters. However, with 10-4 M atrazine, the photochemical activity was inhibited in chloroplasts isolated from the susceptible biotype but not in chloroplasts from the resisiant biotype. With maize chloroplasts, inhibition with 10-4 M atrazine was the same as with the susceptible biotype of lamb's-quarters. These studies suggested that a new mechanism of intraspecific resistance in lamb's quarters to atrazine was involved, other than differences in uptake, translocation and metabolism reported with interspecific comparisons involving the s-triazines and other herbicides, It was also concluded that atrazine and diuron did not have precisely the same mechanism of action as photosynthetic inhibitors with lamb's-quarters, and that external and or internal structure or function of chloroplasts in relation to atrazine inhibition can vary significantly even in biotypes of the same species.     

An association between triazine resistance and powdery mildew resistance in Epilobium ciliatum and Senecio vulgaris

The response of four naturally occurring biotypes of Epilobium ciliatum and four sources of Senecio vulgaris to the herbicide atrazine were compared with their susceptibility to the powdery mildews Sphaerotheca epilobii and Erysiphe cichoracearum. Biotypes that were resistant to atrazine were also resistant to mildew. Mechanisms that might explain the association between atrazine resistance and mildew resistance are discussed, along with possible implications of these findings for farmland ecology and for the production of herbicide- and mildew-resistant crop plants.     

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.     

psbA mutation (Asn266 to Thr) in Senecio vulgaris L. confers resistance to several PS II-inhibiting herbicides

DNA sequence analysis of the psbA gene encoding the D1 protein of photosystem II (PS II), the target site of PS II-inhibiting herbicides, identified a point mutation (Asn266 to Thr) in a bromoxynil-resistant Senecio vulgaris L. population collected from peppermint fields in Oregon. Although this mutation has been previously reported in Synechocystis, this is the first report of this particular point mutation in a higher plant exhibiting resistance to PS II-inhibiting herbicides. The resistant population displayed high-level resistance to bromoxynil and terbacil (R/S ratio 10.1 and 9.3, respectively) and low-level resistance to metribuzin and hexazinone (R/S ratio 4.2 and 2.6, respectively) when compared with the susceptible population. However, the population was not resistant to the triazine herbicides atrazine and simazine or to the urea herbicide diuron. A chlorophyll fluorescence assay confirmed the resistance levels and patterns of cross-resistance of the whole-plant studies. The resistant S. vulgaris plants produced fewer seeds. Differences in cross-resistance patterns to PS II-inhibiting herbicides and the difference in fitness cost could be exploited in a weed management program.     

Wintering of the biotrophic fungus Puccinia lagenophorae within the annual plant Senecio vulgaris: implications for biological weed control

Epidemics of the obligate biotrophic fungus Puccinia lagenophorae might be used to control populations of the annual plant, groundsel, Senecio vulgaris . Insight into the mechanisms of survival of P. lagenophorae over winter may help to explain the number of inoculum sources, and their strength (assessed by number and size of pustules), present in an S. vulgaris population in spring, indicating the probability and rate of progress of a subsequent epidemic. Results of the study indicated survival of the rust as mycelium within the host over winter. Survival outside the host is unlikely, because aecidiospores lost their capacity to germinate over winter and teliospores have not been reported to be infectious. Survival of S. vulgaris plants over winter was reduced by rust infection in autumn. The mortality of S. vulgaris was 30–100% depending on the date of infection. All plants infected early in autumn died but those infected late in autumn were more likely to survive. In turn, poor survival of the host impacted on the survival of P. lagenophorae over winter. Consequently, the results of the study suggest that no inoculum sources, or only a few weak ones, are present in vulgaris populations in spring. This suggestion was supported by observations of an S. vulgaris population at a ruderal site. Therefore, research on biological weed control should focus on increasing the negative impact of P. lagenophorae on S. vulgaris populations while augmenting the probability of survival of the rust over winter to start new epidemics in spring.     

Resistance to Erysiphe fischeri in two populations of Senecio vulgaris

The frequency and distribution of different specific phenotypes for resistance to Erysiphe fischeri was studied in two populations of the annual weed Senecio vulgaris (groundsel) one located in Glasgow, Scotland the other located about 480 km south at Wellesbourne, England. Progeny of individual plants from the two host populations were tested for their response to up to 10 different isolates of E. fischeri , five from each location; each isolate had a different specific virulence phenotype. Most plants in each sample were susceptible to all 10 isolates. The proportion of plants whose progeny were resistant to a particular isolate ranged from 1% to 10% with the exception of resistance to one isolate that occurred with a frequency of 37% at Wellesbourne. Overall, resistance to one or more of the 10 isolates appeared to be more common in the plant population sampled at Wellesbourne than at Glasgow. Of the total number of groundsel line/isolate combinations tested, 10% involving Wellesbourne plants and 2% involving Glasgow plants were incompatible, i.e. resistant/avirulent. Both groundsel populations tended to be dominated by one or two resistance phenotypes but they were nevertheless highly heterogeneous when less frequent resistance phenotypes were considered. This was particularly evident at Wellesbourne where 10 different resistance phenotypes were recorded amongst a total of 75 plants growing within an area of 1 m².     

Effects of rust infection of Senecio vulgaris on competition with lettuce

The effects of rust (Puccinia lagenophorae) on competition between groundsel (Senecio vulgaris L.) and lettuce were investigated. In small tubs in a glasshouse environment, rust infection reduced the dry weight yield of groundsel both in monocultures and mixtures with lettuce at total densities from 35 to c. 1100 plants m^-2. While rust did not affect the relative mixture response of groundsel it resulted in a significant decrease in the relative mixture response of lettuce. Indeed, the yield-density relationship of lettuce in mixture with rusted groundsel was not significantly different from that of lettuce in monoculture. At 1120 groundsel plants m^-2, lettuce yield in mixture with uninoculated groundsel was inhibited by c. 50% when the ratio of lettuce: groundsel (L:G) was 1:3. By contrast, in mixture with rusted groundsel, lettuce yield per tub was not changed by varying L:G, eight lettuce with 24 groundsel yielding no less than 32 in monoculture. Although the severity of rust did not appear to differ, infection inhibited groundsel yield and modified competitive interactions only when L:G was low. In a field experiment the fresh weight yield of lettuce was significantly inhibited by interference from uninoculated groundsel at all sowing densities from 250 to 65 000 seed m^-2. Conversely, lettuce yield was not significantly reduced by rust-infected groundsel until weed density exceeded c. 4000 m^-2. Even at greater sowing densities, lettuce yield in plots with rusted groundsel was two to three limes greater than in plots with uninoculated groundsel. Inoculation with rust reduced the impact of groundsel upon lettuce yield without causing any significant increase in groundsel mortality. The effects of rust were consistent in both glasshouse and field and were attributed to the decreased competitive ability of infected groundsel plants, especially at high density. The implications of the results for the use of rusts in biocontrol are discussed. Effets d'une infection par la rouille de Senecio vulgaris L. sur la competition en culture de laitue Les effets de la rouille (Puccinia lagenophorae) sur la compétition entre le séneçon vulgaire (Senecio vulgaris L.) et la lailue ont étéétudiés. Dans des petits containers sous serre, une infestation de rouille a réduit le poids sec du seneçon tant seul qu'en mélange avec des laitues, à des densités de 35 à 1100 plantes m^-2). Bien que la rouille n'ait pas affecté le comportement relatif du seneçon en mélange, on a abouti à une réduction significative de la réponse de la laitue en mélange. En effet, la relation poids-densité de la laitue en mélange avec des seneçons ‘rouilles’, n'était pas significativement différente de celle de la laitue seule. A 1120 pieds de seneçons m^-2 le poids de lailue en mélange avec des pieds sains était réduit de 50% pour un ratio laitue/seneçon de 1/3. Par opposition, en mélange avec le seneçon ‘rouillé’, le poids de laitue par container n'a pas changé même en faisant varier le rapport L/S. 8 laitues avec 24 seneçons ne pèsent pas moins que 32 laitues seules. Bien que la sévérité de l'attaque de rouille ne semble pas entraîner de différence, l'infection a contrarié le poids des seneçons et modifié la compétition inter espèces seulement quand le rapport L/S était bas. Au champ, le poids frais de laitue a été significativement réduit par l'interférence de seneçons sains à toutes les densités de semis (de 250 à 65000 graines m^-2). Au contraire, le poids de laitue n'a pas été signifieativement réduit par des seneçons attaqués par lu rouille jusqu’à des densités supérieures à 4000 m^-2. Même à des densités de semis plus importantes, le poids des laitues dans les parcelles avec des seneçons attaqués était 2 à 3 fois plus grand que dans les parcelles sans inoculation de seneçon. L'inoculation avec la rouille a réduit l'impact du seneçon sur le poids de la laitue sans engendrer d'augmentation sensible de la mortalité du seneçon. Les effets de la rouille ont été conséquents à la fois en serre et en plein champs et on leur a attribué la baisse de compétitivité des plantes de seneçon infestées, spécialement aux fortes densités. Les implications de ces résultats sur l'utilisation possible des rouilles en lutte biologique fait l'objet d'une discussion. Die Beeinflussung der Konkurrenzkraft von Senecio vulgaris auf Salat durch Rostinfektionen In der vorliegendcn Arbeit wurde der Einfluss von Rost (Puccinia lagenophorae) auf die Konkurrenzkraft des Gemeinen Kreuzkrauts (Senecio vulgaris L.) gegenüber Salat (Lactuca sativa cv. ‘Avon Defiance’) untersucht. Unter Gcwächshausbedingungen reduzierten Rostinfektionen das Trockengewicht von S. vulgaris, sowohl in Monokultur als auch in Mischung mit L. sativa, bei einer totalen Pflanzendichte von 35 bis 1100 Pflanzen m^-2. Während die Rostinfektionen die relative Wachstumsreaktion von S. vulgaris, wenn in Mischung mit L. sativa wachsend, nicht beinflusste, hatte die Infektion eine signifikante Reduktion der Konkurrenzwirkung auf Salat zur Folge. Tatsächlich war die Beziehung zwischen Ernie und Pflanzendichte von in Mischkultur mit rostinfiziertem Kreuzkraut wachsendem Salat nicht signifikant verschieden von dem in Monokultur gewachsenem Salat. In Gegenwart von 1120 nicht infizierten Kreuzkrautpfianzen m^-2 war die Salaternte um 50% verringert, wenn das Zahlenverhältnis Salat/Kreuzkraut (S:K) 1:3 war. Demgegenüber wurde in Mischung mit infizieriem Kreuzkraut die Salaternte pro Kulturbehälter durch die Veränderung des Verhältnisses S:K nicht beeinflusst; 8 Salatpflanzen, mit 24 Kreuzkrautexemplaren zusammen kultiviert, ergaben nicht weniger Ernteertrag als 32 in Monokultur gewachsene Salatpflanzen. Obwohl die Schwere der Infektionen nicht verschieden zu sein schien, reduzierten sie die Krautgewichte der Kreuzkrautpflanzen und ihre Konkurrenzkraft nur, wenn das Verhältnis S: K klein war. In einem Feldversuch wurden die Erntefrischgewichte des Salats durch die Konkurrenz nicht infizierter Kreuzkrautpfianzcn, bei Saatdichten von 250–65 000 Samen m^-2, signifikant gehemmt, Im Gegensatz dazu vermochte rostinfizierles Kreuzkraut, bis zu einer Unkrautdichte von 4000 Pflanzen m^-2, die Erntegewichte des Salats nicht signifikant herabzusetzen. Sogar bei höheren Unkrautdichten war die Salaternte in Parzellen mit infiziertem Kreuzkraul 2–3 mal höher als in Gegenwart von nicht befallenem Unkraut. Die Infektion von S. vulgaris durch Rost verringerte die Beeintächtigung der Salaternte durch das Unkraut, ohne dass eine signifikante Erhöhung der Mortalität des letzteren feststellbar war. Die durch Rostinfektioen bedingten Effekte waren in Gewächshaus und Freiland übereinstimmend und wurden der verminderten Konkurrenzkraft befallener Kreuzkrautpflanzen zugeschrieben; dies war speziell manifest in Gegenwart hoher Unkrautdichten. Die Ergebnisse dieser Untersuchung werden im Lichte der Möglichkeit diskutiert, Rostinfektionen als biologischcs Bekämpfungsmittel einzusetzen.     

Diversity and variation in expression of resistance to Erysiphe fischeri in Senecio vulgaris

The reactions of 20 inbred lines of Senecio vulgaris (groundsel) to inoculation with up to 10 isolates of Erysiphe fischeri (powdery mildew) were investigated in a number of repeat experiments. There was considerable variation among isolate/plant line reaction phenotypes with examples of both isolate-specific complete resistance and isolate-specific partial resistance. Some plant lines possessed high levels of partial resistance to all isolates tested. Incubation temperature and plant age influenced the infection types of some isolate/plant line combinations. In this pathosystem, complete and partial resistance, together with age-dependent and temperature-dependent resistance, appear to have evolved to facilitate a defence strategy based on a complex mosaic of interacting factors.     

A fresh view on the control of the annual plant Senecio vulgaris

The life historyof the annual weed Senecio vulgaris is described, as are theeffects of pathogens and insects on the plant. Using this basicknowledge, the use of the rust fungus Puccinia lagenophorae andthe moth Tyria jacobaeae for control of S. vulgaris following thesystem management approach is discussed. The successfulapplication of the system management approach of biological weedcontrol requires a thorough knowledge of the interactions ofplant--natural enemies--environment--man. The available knowledgeabout this kind of interaction is discussed with respect to thebiological control of S. vulgaris     

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.