Use of fluorescence induction to diagnose resistance of Alopecurus myosuroides Huds. (black-grass) to chlorotoluron

The inhibition of photosynthesis of detached black-grass leaves by chlorotoluron could be quantified by measuring the fluorescence induction using a sensor that almost fully suppressed the reflection component. The induction curve was measured twice on the same leaf spots, first after putting the leaves in the herbicide solution for 16 h, and again after placing the leaves in water for 1 day. Leaves from resistant plants showed partial to full recovery from the inhibition, while susceptible plants did not. These results for fluorescence induction were compared with the inhibition of photosynthesis rate in intact black-grass plants by chlorotoluron in the nutrient solution, and the recovery that occurred when the roots were placed again in herbicide-free nutrient solution. The similarity of the results indicates that the procedure for fluorescence induction can replace the more labour-intensive and complicated demonstration of inactivation by measuring photosynthesis rate. Each plant must be measured separately to avoid suppressing the differences between plants within a population. The method was used for samples from 22 fields in The Netherlands in which resistance of black-grass to chlorotoluron was suspected. The results indicate that substantial resistance was present in only two populations, but that weak resistance occurred in all fields. Utilisation de l'induction de fluorescence pour diagnostiquer la résistance au chlorotoluron chez le vulpin, Alopecurus myosuroides Huds. L'inhibition de la photosynthèse de feuilles de vulpin par le chorotoluron pourrait être quantifiee par la mesure de l'induction de fluorescence en utilisant un récepteur qui supprime quasiment la reflexion. La courbe d'induction était mesuree 2 fois, sur les memes fragments de feuille, la première après avoir mise pendant 16 h les feuilles dans la solution herbicide, et de nouveau après avoir placé les feuilles dans l'eau pendant un jour, Les feuilles des plantes resistantes se recuperaient partiellement à totalement de l'inhibition, tandis que les plantes sensibles ne le faisaient pas. Ces résultats sur l'induction de fluorescence ont été comparés avec le taux d'inhibition de la photosynthèse dans des plantes intactes de vulpin par le chlorotoluron dans la solution nutritive et avec la récupération qui apparaissait quand les racines étaient de nouveau placées dans une solution exempte d'herbicide, Les résultats similaires montrent que le procédé de I'induction de fluorescence peut remplacer la démonstration de l'inactivation, beaucoup plus laborieuse et compliquée par la mesure du taux de photosynthèse, Chaque plante doit être mesurée séparément pour éviter la suppression des différences entre piantes dans une population. La méthode a été utilisée pour les échantillons venant de 22 champs aux Pays-Bas dans lesquels on suspectait une résistance du vulpin au chlorotoluron. Les résultats montrent qu'une resistance réelle était seulement présente dans deux populations, mais qu'une faible résistance existait dans tous les champs. Fluorimetrische Diagnose der Resistenz von Alopecurus myosuroides Huds. (Acker-Fuchsschwanz) gegenüber Chlortoluron Die Hemmung der Photosynthese in isolierten Blättern von Acker-Fuchsschwanz durch Chlortoluron konnte durch Messung der Fluoreszenz-induktion bestimmt werden, wobei ein Sensor benutzt wurde, der die Reflektion fast vollständig ehminierte. Die Induktionskurve wurde zweimal gemessen, zum einen nach dem Einstetzen der Blätter für 16 h in die Herbizidlösung und zum andern nochmals nach einem Tag auf Wasser, Blätter resistenter Pflanzen erholten sich teilweise oder ganz von der Hemmung, solche empfindlicher Pflanzen nicht. Die Ergebnisse der Fluoreszenzinduktion wurden mit der Hemmung der Photosyntheserate intakter Pflanzen durch Chlortoluron in der Nährlösung und der Erholung nach Überführen der Wurzeln in herbizidfreie Nährlösung verglichen. Die Ähnlichkeit der Ergebnisse zeigt, daß man die arbeitsintensivere und komplizierte Bestimmung der Inaktivierung mittels Messung der Photosyntheserate durch die Fluoreszenzinduktion ersetzen kann. Jede Pflanze muß für sich gemessen werden, um ein Verwischen der Unterschiede zwischen den Pflanzen einer Population zu vermeiden. Die Methode wurde zur Untersuchung von Proben aus 22 Feldern in den Niederlanden angewandt, wo Resistenz von Acker-Fuchsschwanz gegenüber Chlortoluron vermutet wurde. Nur in 2 Populationen wurde eine volle Resistenz festgestellt, aber eine schwache Resistenz lag bei allen Fällen vor.     

Impact of drilling date on Apera spica-venti L. and Alopecurus myosuroides Huds, in winter cereals

The impact of drilling date on Apera spica-venti and Alopecurus myosuroides in winter cereals was investigated in field trials in 1991 and 1992. Two drilling dates were considered with an inter val of 14 to 16 days between dates. Generally, drilling date had an inconsistent effect on weed plant populations in spring, but seedling emerg ence of both species appeared to be delayed at the later drilling compared with the earlier date. This delay may partly explain the reduced com petitive ability of A. myosuroides in wheat in 1991 and 1992 and of A. spica-venti in wheat in 1991 at the later drilling date. The seed popula tion per plant of both species was lower at the later date in some instances, whereas in others drilling date had no effect. Reduced seed produc tion was mainly caused by a reduction of the number of inflorescences per plant. The poten tial of utilizing drilling dates as a cultural control measure against grass weeds is discussed.     

The production and shedding of Alopecurus myosuroides Huds. seeds in winter cereals crops

Seed shedding from heads of Alopecurus myosuroides occurred from late June to late August at most locations. Most seeds were shed before winter wheat (Triticum-aestivum L.) was harvested hut at two winter barley (Hordeum sativum L.) sites, only 50% of seed was shed prior to harvest. The viability of seeds shed at the start and end of the shedding period tended to be lower than that at peak shedding time in late July and early August. There were large differences between sites in the viability of the total amount of seed shed. The results of viability tests based on the presence of full caryopses and germination in pots of sterile soil were similar. Assessments of head numbers and head length were significantly correlated with total seed production. Head length, but not head number assessments, were also significantly correlated with viable seed production.     

Influence of tillage, straw disposal system and seed return on the population dynamics of Alopecurus myosuroides Huds. in winter wheat

Alopecurus myosuroides Huds. was studied over a 2-year period in winter wheat established after tine cultivations or direct drilling. Straw was removed by baling or spread and burnt. Seed production was either allowed or prevented by cutting and removing all vegetation at the end of the first year. Cultivation differences had no consistent effect on plant or seed populations. Straw burning destroyed about 50% of seeds and encouraged the germination of surviving seeds. Weed populations in the crop were lower on burnt than on baled areas. Where seed shedding was allowed, populations of seeds in soil and plants increased by up to nine-fold per year. Straw burning resulted in smaller population increases. Seed decline in the soil averaged about 80% per year, so that less than 6% of the weed seeds sown were still viable after 2 years’burial in the soil. Most of the seed decline occurred between July and October and was slightly greater on burnt than on baled areas. Only part of this seed loss was accounted for by germination and emergence of seedlings during summer and autumn. Plants emerging in the crop represented less than 26% of viable seeds present in the soil at time of drilling the crop. Few seedlings emerged in spring. The viability of shed seeds varied with year and with weed density. High infestations were associated with lower seed viability and also fewer heads per plant.     

Recombinant glutathione transferases from flufenacet-resistant black-grass (Alopecurus myosuroides Huds.) form different flufenacet metabolites and differ in their interaction with pre- and post-emergence herbicides

BACKGROUND

Black-grass (Alopecurus myosuroides Huds.) has become a problematic weed in cereals in Europe. Besides resistance to post-emergent herbicides becoming increasingly widespread, enhanced metabolism of inhibitors of the synthesis of very-long-chain fatty acids (VLCFAs), such as flufenacet, is evolving. Yet, cross-resistance patterns and evolution of this resistance remains poorly understood.

RESULTS

The cDNA sequences of five glutathione transferases (GSTs) upregulated in flufenacet resistant black-grass were identified and used for recombinant protein expression. Moderate to slow detoxification of flufenacet was verified for all candidate GSTs expressed in E. coli, and the most active protein produced flufenacet-alcohol instead of a glutathione conjugate, in the presence of reduced glutathione (GSH). Moreover, cross-resistance to other VLCFA-inhibitors e.g., acetochlor and pyroxasulfone and the ACCase inhibitor fenoxaprop was verified in vitro. Various other herbicides of different modes of action including VLCFA-inhibitors were not detoxified by the candidate GSTs.

CONCLUSIONS

As several in planta upregulated GSTs detoxified flufenacet in vitro, the shift in sensitivity observed in black-grass populations, is likely a result of an additive effect. The polygenic character and the relatively low turnover rate of the individual GSTs may explain the slow evolution of flufenacet resistance. In addition, flufenacet resistance was accompanied by cross-resistance with some, but not all, herbicides of the same mode of action, and furthermore to the ACCase inhibitor fenoxaprop-ethyl. Hence, not only the rotation of herbicide modes of action, but also of individual active ingredients is important for resistance management. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

The effect of controlling Alopecurus myosuroides Huds. and Avena fatua L. individually and together, in mixed infestations on the yield of wheat

Mixed infestations of Alopecurus myosuroides and Arena fatua growing in wheat were controlled individually or together in three experiments. Difenzoquat and ciofop-isohutyl were applied at the early tillering or early stem extension stages of the crops. Early control of both species resulted in significantly higher yields than later control, even though weed emergence was incomplete at the early applications. Herbicides, re-applied at the second date, improved the control of wild-oats hut not of black-grass; yields were not enhanced by this second application Halving the dose of herbicide gave little reduction in weed control or crop yield at the early date, but there was a greater response to dose with the later application. Yields were lower where only one weed was controlled. This work shows the need for broad spectrum control early in the life of the crop to safeguard yield where black-grass, and wild oats occur together in large numbers.     

Influence of temperature on the activity of AC 222,293 against Avena fatua L. and Alopecurus myosuroides Huds.

Foliage applications of AC 222,293 were more active against Alopecurus myosuroides Huds. plants growing at high (26/16°C day/night) compared to either medium (16/10°C) or low (11/7°C) temperatures. Soil activity was unaffected by temperature. Enhanced activity against A. myosuroides required exposure to the high temperatures for only 24 h immediately post spraying and correlated with the accumulation of greater levels of the biologically active acid in the apical meristem region during this period. Both foliage and soil activity of AC 222,293 were greatest against Avena fatua L. plants growing at medium (16/10°C) compared to either high (26/16°C) or low (11/7°C) temperatures. Foliar activity decreased slowly with increasing periods of high temperatures post spraying and then only at doses lower than those recommended for field use. Reduced performance at the high temperatures correlated with lower levels of the biologically active acid in the meristem region, despite greater uptake and translocation. This was due to increased metabolism of the parent herbicide and formation of metabolites other than the free acid.     

The effect on yield of mixtures and sequences of herbicides for the control of Alopecurus myosuroides Huds. and broad-leaved weeds in winter cereals

Mixed infestations of Alopecurus m yosuroides Huds. and broad-leaved weeds in winter cereals were controlled with a commercial formulation of ioxynil + bromoxynil + mecoprop. used in mixtures or as sequences with isoproturon or clofop-isobutyl. As well as controlling A. myosuroides the mixtures, applied in the autumn, gave good control of Veronica persica Poir., Galium aparine L. Lilhospermum arvense L. and Viola arvensis Murr. weeds which were resistant to isoproturon used alone. A. myosuroides had the major influence on crop yield in three experiments. High infestations of A. myosuroides reduced the broad-leaved weeds so that crop yields were only slightly improved when all the weeds were controlled compared with the control of A. myosuroides alone. In the remaining experiment. V. persica was very competitive with wheat; additional control of A. myosuroides improved yields considerably. Ioxynil + bromoxynil + mecoprop gave better final control of broad-leaved weeds when applied in the spring rather than the autumn but the sequence of a spring application following isoproturon or clofop-isobutyl in the autumn did not improve yields compared with the mixtures applied in the autumn. In all experiments, the highest yields were obtained from controlling both A. myosuroides and broad-leaved weeds in the autumn, provided that good control of A. myosuroides was obtained.     

The biochemical and physiological effects and mode of action of AC 222,293 against Alopecurus myosuroides Huds. and Avena fatua L

AC 222,293 was found to exert its mode of action through inhibition of acetolactate synthase, the first enzyme in the biosynthetic pathway of the branched chain amino acids. In vitro AC 222,293 was found to be only a very weak inhibitor of the enzyme, in contrast to the potent inhibition by the free acid, suggesting that action of the herbicide in vivo is dependent on deesterification. Enzyme preparations from susceptible Avena fatua and Alopecurus myosuroides and tolerant wheat (cultivar Fenman) were all equally sensitive with an I₅₀ of approximately 5 · 10⁻⁷ M. Inhibition of treated plants is prevented when valine, leucine, and isoleucine are supplied via the nutrient solution. Prominent secondary effects are inhibition of DNA synthesis and cell division and the action of the herbicide is characterised by cessation of leaf growth.     

Competition between Avena sterilis ssp. macrocarpa Mo. and cultivars of wheat

A pot experiment was done in the glasshouse to study the competition between Avena sterilis ssp. macrocarpa Mo. and six wheat cultivars of different lengths of growth cycle. The competitiveness of wild oat was similar for all six wheat cultivars with respect to grain weight, straw weight, number of ears and total accumulation of nitrogen. The cultivar with the longest cycle was the most affected by wild oat competition as regards height, because a large part of its stem extension and some of the heading took place after the panicles of wild oat had expanded. Wild oat competition with wheat plants was greater than the competition among wheat plants themselves. The wild oat had a similar tolerance to all the wheat cultivars.     

Some effects of burning cereal straw on seed viability, seedling establishment and control of Alopecurus myosuroides Huds.

Straw burning destroyed many Alopecurus myosuroides(blackgrass)seeds lying on the soil surface and, compared with straw baling, resulted in a smaller weed infestation in a subsequent direct-drilled winter wheat crop. The larger the amount of straw burnt, the higher the temperature reached on the soil surface and consequently the greater the control of the weed. Seeds that were fully imbibed were less susceptible to destruction by heat than were dry seeds. A shallow soil covering protected most seeds although some were stimulated to germinate. After straw burning the soil surface was a better environment for seed germination or seedling development than that under stubble. Differences in seedling numbers between treatments were not always proportional to differences in the numbers of viable seeds in the soil. Quelques effets du brûlage des pailles des céréales sur la viabilité des semences et l'implantation des plantules d'Alopecurus myosuroïdes Huds. et influence sur sa destruction Le brûlage des pailles a détruit de nombreuses semences d'Alopecurus myosuroïdes (vulpin) se trouvant à la surface du sol, ce qui a eu pour effet, par comparaison avec la récolte de la paille, de réduire l'infestation de la mauvaise herbe dans la culture suivante, un blé d'hiver en semis direct. Plus grande est la quantité de paille brûlée plus la température au niveau du sol est élevée et, par suite, meilleure est la destruction de la mauvaise herbe. Les semences qui avaient été complètement imbibées se sont montrées moins susceptibles d'être détruites par la chaleur que les semences sèches. L'existence d'une couche meuble superficielle sur le sol s'est révélée comme un meilleur environnement pour la germination des semences ou le développement des plantules que sous le chaume. Les différences entre le nombre des plantules selon les traitements n'ont pas toujours été proportionnelles aux quantités de semences viables présentes dans lesol. Einige Auswirtcungen des Verbrennens von Getreidestroh auf die Lebensfähigkeit der Samen, das Auflaufen und die Bekämpfung von Alopecurus myosuroides Huds. Das Verbrennen von Stroh zerstörte viele Samen von Alopecurus myosuroides(Ackerfuchsschwanz) die auf der Bodenoberfläche lagen und hatte, im Vergleich zum Ballenpressen, eine geringere Verseuchung in im Direktsaatverfahren nachgebauten Weizen zur Folge. Je grösser die Strohmenge war, desto höher war die Temperatur auf der Bodenotrerfläche und umso besser war die Bekämpfung des Ackerfuchsschwanzes. Samen, die mit Wasser vollgesogen waren, wurden durch die Hitze weniger geschädigt als trockene. Durch eine flache Bodenabdeckung wurden die meisten Samen geschützt, bei einigen wurde aber die Keimung stimuliert. Nach dem Strohverbrennen waren die Bodenverhältnisse für die Keimung und die Entwicklung der Keimlinge günstiger als in der Stoppel. Die Unterschiede in der Keimpflanzenzahl zwischen den Behandlungen waren nicht immer proportional zu den Unterschieden in der Anzahl lebensfähiger Samen im Boden.     

Effects of depth of seed burial and soil aggregate size on seedling emergence of Alopecurus myosuroides, Galium aparine, Stellaria media and wheat

Seedling emergence of Alopecurus myosuroides Huds., Stellaria media L. (Vill.), Galium aparine L. and wheat (Triticum aestivum L.) was compared at a range of depths of soil cover from 2 to 11 cm. The covering soil was a fertile agricultural soil with 60% clay content which had been sieved into four aggregate sizes. The aggregate sizes used were 26-50 mm. 14-25 mm. 6-13 mm and below 6 mm. Total emergence of all species was reduced with increased depth of sou cover. With A. myosuroides and S. media, total emergence was lowest in fine soil conditions. Alopecurus myosuroides showed a marked interaction whereby response to depth of sowing was least with fine tilth. The time to 50% emergence showed a similar response. With all four species, seedling emergence was slowest at greater depths of sowing and with the finest tilth, the differences tending to increase with increasing depth of sowing. A vert high proportion of the time to 50% emergence was accounted for by the lag time between sowing and the first recorded emergence.     

甲基二磺隆等防除麦田野燕麦和看麦娘的效果

防除以看麦娘和野燕麦为主的禾本科杂草,春季使用15%炔草酸WP 450 g/hm2、3%甲基二磺隆OF300~450 mL/hm2、3.6%二磺.甲碘隆WG 300~375 g/hm2、6.9%精唑禾草灵EW 1 500~2 250 mL/hm2和5%唑啉·炔草酸EC 1 350~1 500 mL/hm2均有较理想的防效,鲜重防效均在90%以上,高于株防效。     

Prevalence of cross‐ or multiple resistance to the acetyl‐coenzyme A carboxylase inhibitors fenoxaprop,clodinafop and pinoxaden in black‐grass (Alopecurus myosuroides Huds.) in France

BACKGROUND: Repeated use of acetyl‐CoA carboxylase (ACCase) inhibitors, especially fenoxaprop and clodinafop, since the late 1980s has selected for resistance in Alopecurus myosuroides Huds. (black‐grass) in France. We investigated whether resistance to pinoxaden, a phenylpyrazoline ACCase inhibitor to be marketed in France, was present in French black‐grass populations. We investigated pinoxaden resistance conferred by five mutant ACCase isoforms. Using 84 French black‐grass field samples, we also compared the frequencies of other mechanisms endowing resistance to fenoxaprop, clodinafop or pinoxaden. RESULTS: ACCase mutant isoforms Leu‐1781, Gly‐2078 and, likely, Cys‐2027 conferred cross‐resistance to pinoxaden, while isoform Asn‐2041 possibly conferred moderate resistance. Other mechanisms of resistance to fenoxaprop, clodinafop and pinoxaden were detected in 99, 68 and 64% of the samples investigated, respectively. Cross‐ or multiple resistance to fenoxaprop or clodinafop and pinoxaden was not systematically observed, suggesting a diversity of mechanisms exist. CONCLUSION: Pinoxaden resistance was observed before pinoxaden release in France. Only a fraction of the mechanisms endowing fenoxaprop or clodinafop resistance also confer pinoxaden resistance. Pinoxaden resistance was likely mostly selected for by ACCase inhibitors, and, in some cases, possibly by herbicides with other modes of action. This illustrates the necessity to use metabolisable herbicides cautiously where black‐grass has evolved non‐target‐site‐based resistance. Copyright © 2009 Society of Chemical Industry     

Dormancy of Bromus rubens L. seeds in relation to temperature, light and oxygen effects

Freshly harvested mature Bromus rubens L. seeds are dormant. This dormancy corresponds to the inability of seeds to germinate in the dark at temperatures above 15°C, but is practically not apparent at temperatures between 5 and 15°C. Continuous white light markedly inhibits germination of dormant seeds, even at low irradiances, and reinforces their sensitivity to oxygen deprivation. However, prolonged illumination with white light does not alter subsequent germination in the dark. Breaking of dormancy during dry storage at 20°C results in a widening of the temperature range within which a high rate of germination occurs, and in almost complete disappearance of sensitivity of seeds to light. The structures surrounding the embryo (glumellae, caryopsis envelopes and possibly endosperm) are mainly responsible for dormancy and photosensitivity of whole seeds, probably because they limit the oxygen supply to the embryo. However, the embryo itself appears to play a role in dormancy. The results obtained are discussed in relation to dormancy of cereal seeds, and in relation to field establishment of B. rubens as a weed. La dormance des semences de Bromus rubens L. en relation avec les effets de la température, de la lumière et de l'oxygène Les semences mûres de Bromus rubens L. fraîchement récoltées sont dormantes. Leur dormance correspond à une inaptitude à germer à l'obscuritéà des températures supérieures à 15°C, mais elle ne se manifeste pratiquement pas entre 5 et 15°C. La lumière blanche continue inhibe nettement la germination des semences dormantes, même à de faibles énergies, et renforce leur sensibilitéà la privation d'oxygène. Cependant, un éclairement prolongé n'a aucune conséquence sur la germination ultérieure à l'obscurité. L'élimination de la dormance pendant la conservation au sec, à 20°C, se traduit par un élargissement de la gamme thermique qui assure une bonne germination et par la disparition presque complète de la sensibilité des semences à la lumière. Les structures qui entourent l'embryon (glumelles, enveloppes du caryopse et peut-être albumen) sont, en grande partie, responsables de la dormance et de la photosensibilité des semences entières, sans doute parce qu'elles limitent l'apport d'oxygène à l'embryon. Toutefois, l'embryon lui-même semble participer à la dormance. Les résultats obtenus sont discutés par comparaison avec la dormance des semences des céréales et en relation avec l'implantation, dans les cultures, de B. rubens en tant que mauvaise herbe. Dormanz der Samen von Bromus rubens L. in Bezug auf Temperatur, Licht und Sauerstoffversorgung Frisch geerntete Samen von Bromus rubens L. sind im Dunkeln bei Temperaturen über 15°C dormant, während diese Dormanz bei Temperaturen zwischen 5 und 15°C praktisch nicht vorliegt. Ständiges weißes Licht hemmt die Keimung dormanter Samen deutlich, sogar bei niedriger Intensität, und verstärkt ihre Empfindlichkeit gegenüber Sauerstoffmangel. Ständige Beleuchtung mit weißem Licht verändert jedoch nicht die folgende Dunkelkeimung. Das Brechen der Dormanz während der trockenen Lagerung bei 20 °C führt zu einem vergrößerten Temperaturbereich, in dem die Samen gut keimen, und läßt ihre Lichtempfindlichkeit fast vollständig verschwinden. Die Strukturen um den Embryo (Spelzen, Schale der Caryopse und möglicherweise Endosperm) sind hauptsächlich für die Dormanz und die Lichtempfindlichkeit des ganzen Samens verantwortlich, vermutlich deshalb, weil sie die Sauerstoffversorgung des Embryos einschränken. Aber auch der Embryo selbst scheint bei der Dormanz eine Rolle zu spielen. Die Untersuchungsergebnisse werden im Vergleich zur Dormanz von Getreidesamen und hinsichtlich des Vorkommens von Bromus rubens als Unkraut diskutiert.     

Evidence that wheat cultivars differ in their ability to build up inoculum of the take‐all fungus,Gaeumannomyces graminis var. tritici,under a first wheat crop

The effect of wheat cultivar on the build‐up of take‐all inoculum during a first wheat crop was measured after harvest using a soil core bioassay in field experiments over five growing seasons (2003–2008). Cultivar differences in individual years were explored by analysis of variance and a cross‐season Residual Maximum Likelihood (REML) variance components analysis was used to compare differences in those cultivars present in all years. Differences between cultivars in the build‐up of inoculum were close to or at significance in two of the five trial years (2004 P < 0·05; 2006 P < 0·07), and current commercially listed cultivars were represented at both extremes of the range. In 2007 and 2008, when environmental conditions were most favourable for inoculum build‐up, differences were not significant (P < 0·3). In 2005 the presence of Phialophora spp. at the trial site restricted the build‐up of take‐all inoculum under all cultivars. The cross season REML variance components analysis detected significant differences (range: 3·4–47·8% roots infected in the soil core bioassay; P < 0·01) between the nine cultivars present in all years (excluding 2005). This is the first evidence of relatively consistent differences between hexaploid wheat cultivars in their interactions with the take‐all fungus, and this could give an indication of those cultivars that could be grown as a first wheat crop, in order to reduce the risk of damaging take‐all in a second wheat crop. This phenomenon has been named the take‐all inoculum build‐up (TAB) trait.     

不同猕猴桃品种RAPD分析及其与抗溃疡病的关系

对不同猕猴桃品种的分子生物学试验表明：猕猴桃的DNA浓度在920 μg/mL符合RAPD分析的要求。通过60个随机引物的PCR扩增,报道了6个不同品种和类型猕猴桃种质资源的RAPD多态性,计算了它们之间的遗传距离,构建了聚类图,并讨论了其亲缘关系。聚类分析图反映出来源于安徽省主要猕猴桃产区的6个样品可以分为3组,其中抗病与感病的相对较为集中,由此可推断出现这种聚类的原因可能是由于它们基因组中有相同的DNA片段。抗病品系都有一条1 458 bp DNA片段,而感病品系均没有该带。故该片段可能与猕猴桃植株抗溃疡病相关。RAPD多态性从分子水平上反映出了猕猴桃种质资源不同品种及不同类型间复杂的遗传背景,为抗病育种的亲本选配提供了依据,也为合成猕猴桃抗溃疡病探针并用于检测猕猴桃抗溃疡病种质和分子标记辅助育种奠定了基础。     

Investigations in the regulation of common bunt (Tilletia tritici) of winter wheat with regard to threshold values,cultivar susceptibility and non-chemical protection measures

Journal of Plant Diseases and Protection - The objectives of the present study were the determination of treatment threshold values for control of common bunt of wheat (Tilletia tritici) and...     

Preference and infestation level of Anastrepha fraterculus (Wiedemann, 1830) on fruits of some Psidium guajava L. cultivars and relation to their physicochemical parameters

This study aimed to verify the preference and infestation level of Anastrepha fraterculus (Diptera: Tephritidae) [South American fruit fly] in fruits of guava cultivars and to correlate them to variables such as peel coloration, soluble solids and pH of fruit cultivars. The following cultivars were used: Pedro Sato, Paluma, Cascão and Século XXI. The infestation was evaluated in cages, considering two scenarios: no-choice and multiple choice. In both tests, evaluations of the fruit attraction to insects were conducted for a period of 1′, 3′, 5′, 10′, 20′, 30′, 1 h, 2 h, 6 h, 12 h and 24 h. The visit of A. fraterculus on the assayed cultivars in relation to the time was studied by logistic regression. After 10 days, the number of larvae in each fruit was recorded. In the multiple choice test, the visit proportions were significantly higher in the fruits of cvs. Século XXI and Pedro Sato than in those of cvs. Paluma and Cascão. In the no-choice test, the visit proportions were significantly lower in the Paluma fruits. In both tests, the rate of fruit infestation by A. fraterculus did not differ among cvs. Pedro Sato, Paluma and Cascão, whereas the fruits of cv. Século XXI were more infested. The indexes of pH did not interfere with the infestation of A. fraterculus, whereas a high rate of soluble solids and low color angle appear to be crucial for discriminating the fruits of the most susceptible cultivars. Infestation rate of Século XXI fruits displayed significant correlations with: °Brix (r= 0.7078) and color angle (h) (r= –0.9499) of guava fruits under the multiple choice conditions.     

The effect of different frequencies of harrowing in the autumn or spring on winter wheat, and on the control of Stellaria media (L.) vill., Galium aparine L. and Brassica napus L.

Cultivating with a flexible tine harrow in the autumn reduced densities of Stellaria media (L) Vill., Galium aparine L. and Brassica napus L. plants and thinned the wheat crop. Effects were more severe with two passes at right angles (plant stands were approximately halved) than with a single cultivation. Despite crop thinning, wheat yields were not reduced by autumn harrowing owing to compensatory increases in 1000-grain weights. Summer biomass of S. media and G. aparine was reduced more by spring than by autumn harrowing, while biomass of B. napus was only reduced by autumn harrowing. It was concluded that weakly rooted climbing or scrambling species are more easily controlled by cultivating in the spring, while species that develop a tap-root are more readily controlled by cultivating at an early growth stage in the autumn. L'effet de différentes fréquences d'hersage en automne on au printempssur le blé d'hiver, etsur les controles suivants Stellaria media (L.) Vill., Galium aparine L. et Brassica napus L. Les façons culturales effectuées à 1'automne avec une herse à trilles flexibles réduisaient le nombre de Stellaria media (L.) Vill., Galium aparine L. et Brassica napus L. et éclaircissaient la culture de blé. Les effets étaient plus importantes après deux passages perpendiculaires (densité des plantes divisée par environ 2) que par un seul passage. En dépit de l'éclaircissement, les rende-ments du blé n'ont pas été réduits par le hersage d'automne grâce à une compensation par le poids de 1000 grains. La biomasse d'été de S. media et G. aparineétait plus réduite par un hersage de printemps que d'automne, alors que la biomasse de B. napus n'était réduite que par un hersage d'automne. Les espéces grimpantes et faible-ment enracinées sont done plus facilement com-battues par des travaux de printemps, alors que celles qui présentent un racine pivotante sont plus facilement combattues par un hersage d'automne, à un stade précoce. Die Wirkung verschieden häufigen Eggens im Herbst oder im Frühjahr auf Wintenveizen und auf die Bekämpfung von Stellaria media (L.) Vill., Galium aparine L. und Brassica napus L. Eggen im Herbst mit einer beweglichen Zinkenegge verringerte die Dichte von Stellaria media (L.) Vill., Galium aparine L. und Brassica napus L. und reduzierte den Weizenbestand. Die Wirkungen waren durch 2 Arbeitsgänge im rechten Winkel zu einander, wobei der Pflanzenbestand ungefähr halbiert wurde, gegenüber einer einzelnen Bearbeitung ver-stärkt. Aufgrund eines ausgleichenden Anstiegs des Tausendkorngewichts wurden die Weizenerträge trotz Ausdünnung der Bestände nicht durch Eggen im Herbst reduziert. Die Sommerbiomasse von S. media und G. aparine wurde mehr durch Eggen im Frühjahr als durch Eggen im Herbst verringert, während die Biomasse von B. napus nur durch Eggen im Herbst reduziert wurde. Daraus folgt, daß schwach wurzelnde und kletternde Arten einfacher durch Eggen im Frühjahr bekämpfbar sind, Arten mit einer Pfahlwurzel besser im Herbst zu einem früheren Entwicklungsstadium.