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In Northern Europe, inter-row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed-free inter-row zone. However, hoeing has a lesser effect on weeds growing in the intra-row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall-growing, competitive, cruciferous weeds in the intra-row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra-row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH4-N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra-row plants/m2 of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra-row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra-row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra-row weeds and limit crop losses. 相似文献
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Manual weeding of intrarow weeds in direct-sown leek and bulb onion crops grown organically can be very labour-intensive. Four field experiments, two in direct-sown leek and two in direct-sown bulb onion were made in this investigation to study the effects of physical and cultural methods on intrarow weed numbers, time consumption for hand-weeding and marketable yield parameters. The physical methods considered were: pre-emergence flaming and harrowing, and post-emergence hoeing close to the row (only leek) and vertical brush weeding. The cultural methods were: seed priming, slurry placement and cultivar choice (only leek). Generally, flaming plus brush weeding gave the highest intrarow weed control at 92% and 87%, respectively, in the two leek experiments and 39% (only brush weeding was effective) and 74%, respectively, in the two onion experiments. Time consumption for hand-weeding after the different treatments was linearly related to the remaining numbers of intrarow weeds, with no significant influences of the experimental factors on the general relationship. Generally, the cultural methods had no significant influence on the effects of physical weeding in terms of their effect against intrarow weeds. They did not affect the tolerance or robustness of the crop plants against negative impact from the physical control methods. However, generally, seed priming and cultivar choice did improve yield in the leek experiments and seed priming also did so in the one experiment with onion. 相似文献
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Reducing tillage intensity affects the cumulative emergence dynamics of annual grass weeds in winter cereals 
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下载免费PDF全文 Annual grass weeds such as Apera spica‐venti and Vulpia myuros are promoted in non‐inversion tillage systems and winter cereal‐based crop rotations. Unsatisfactory weed control in these conditions is often associated with a poor understanding of the emergence pattern of these weed species. The aim of this study was to investigate, understand and model the cumulative emergence patterns of A. spica‐venti, V. myuros and Poa annua in winter cereals grown in three primary tillage regimes: (i) mouldboard ploughing, (ii) pre‐sowing tine cultivation to 8–10 cm soil depth and (iii) direct drilling. Direct drilling delayed the cumulative emergence of A. spica‐venti and V. myuros (counted together) in contrast with ploughing, while the emergence pattern of P. annua was unaffected by the type of tillage system. The total density of emerged weed seedlings varied between the tillage systems and years with a higher total emergence seen under direct drilling, followed by pre‐sowing tine cultivation and ploughing. The emergence patterns of all species were differently influenced by the tillage systems, suggesting that under direct drilling, in which these species occur simultaneously, management interventions should first and foremost consider that A. spica‐venti and V. myuros emerge over a longer period to avoid control failures. 相似文献
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Bacterial biofilms are surface-attached communities of microorganisms that are protected by an extracellular matrix of biomolecules. In the biofilm state, bacteria are significantly more resistant to external assault, including attack by antibiotics. In their native environment, bacterial biofilms underpin costly biofouling that wreaks havoc on shipping, utilities, and offshore industry. Within a host environment, they are insensitive to antiseptics and basic host immune responses. It is estimated that up to 80% of all microbial infections are biofilm-based. Biofilm infections of indwelling medical devices are of particular concern, since once the device is colonized, infection is almost impossible to eliminate. Given the prominence of biofilms in infectious diseases, there is a notable effort towards developing small, synthetically available molecules that will modulate bacterial biofilm development and maintenance. Here, we highlight the development of small molecules that inhibit and/or disperse bacterial biofilms specifically through non-microbicidal mechanisms. Importantly, we discuss several sets of compounds derived from marine sponges that we are developing in our labs to address the persistent biofilm problem. We will discuss: discovery/synthesis of natural products and their analogues-including our marine sponge-derived compounds and initial adjuvant activity and toxicological screening of our novel anti-biofilm compounds. 相似文献
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For more than 50 years the identity of "calorigen," the agent that triggers pronounced heat production in the flowers and inflorescences of some thermogenic plants, remained obscure. Mass spectroscopic analysis of highly purified calorigen extracted from the male flowers of Sauromatum guttatum Schott (voodoo lily) revealed the presence of 2-hydroxybenzoic (salicylic) acid. Application of salicylic acid at 0.13 microgram per gram (fresh weight) to sections of the upper part of the plant's immature spadix, known as the appendix, led to temperature increases of as much as 12 Celsius degrees. These increases duplicated, in both magnitude and timing, the temperature increases produced by the crude calorigen extract. The sensitivity of appendix tissue to salicylic acid increases daily with the approach of anthesis and is controlled by the photoperiod. Thus, at least in some Arum lilies, salicylic acid functions as an endogenous regulator of heat production. 相似文献
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Liubava Znova Bo Melander Aleksander Lisowski Jacek Klonowski Jaroslaw Chlebowski Gareth T. C. Edwards 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2018,68(2):139-148
This research introduces a new share design (L-share) that reduces the undesired random soil movement, providing a more controlled disturbance of the upper soil layer. Purpose: The aim of this study was to evaluate draught forces and soil movements when operating the new share. Materials and Methods: Experiments were conducted in a laboratory set-up using a soil bin with a fine loamy soil texture. The soil was compacted to a bulk density of 1500?kg?m?3, with a penetration index of 486?kPa and a mean water content of 10%. The cultivation depths were 30, 50 and 70?mm and the operation speeds were 0.84, 1.67 and 2.31?m?s?1. Cubes were used to measure soil movement by recording the displacement from their initial positions. The soil surface and furrow profile were measured by using a 2D laser range scanner. Results: The results showed that increasing operation speed and cultivation depths generally increased draught forces and soil movement. Changing the cultivation depth from 30 to 50?mm resulted in a 63% greater longitudinal force (Fx), and 71% greater Fx when increasing the cultivation depth from 50 to 70?mm. Conclusion: The study showed that the new L-share mounted on a modified spring tine only causes minor soil movement and thereby minimising the undesirable soil movement. 相似文献
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Margareta Melander 《Euphytica》2006,150(1-2):123-130
Summary A 57-kDa readthrough portion of the Tobacco rattle virus (TRV) replicase gene was isolated in two replicates and sequenced. Sequence comparisons showed the isolated sequences to have a homology of 93–94% compared to other TRV isolates at the DNA level and code for proteins with 98–99% similarity to other corresponding TRV sequences at the amino acid level. The isolated sequences were cloned into binary vector constructs, which were transformed to the potato cultivar Matilda. Ten obtained transgenic potato lines were challenged with TRV mediated by the natural nematode vector in greenhouse trials. In a first trial all transgenic lines demonstrated fewer symptoms compared to an untransformed Matilda control. However, the infection pressure in this first trial was in general very low and to get more reliable results a second greenhouse trial with the two most promising lines was performed the following season. In this trial both transgenic lines had significantly fewer symptoms compared to the untransformed control. The symptom reduction for the best line was 78% compared to the control. Thus, introduction into potato of a gene encoding the 57-kDa TRV replicase portion is a possible way to improve resistance to TRV in potatoes. 相似文献
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Paul G. Wahome Kevin R. Beauchesne Anna C. Pedone John Cavanagh Christian Melander Paul Zimba Peter D. R. Moeller 《Marine drugs》2015,13(1):65-75
Aquatic microbes produce diverse secondary metabolites with interesting biological activities. Cytotoxic metabolites have the potential to become lead compounds or drugs for cancer treatment. Many cytotoxic compounds, however, show undesirable toxicity at higher concentrations. Such undesirable activity may be reduced or eliminated by using lower doses of the cytotoxic compound in combination with another compound that modulates its activity. Here, we have examined the cytotoxicity of four microbial metabolites [ethyl N-(2-phenethyl) carbamate (NP-1), Euglenophycin, Anabaenopeptin, and Glycolipid 652] using three in vitro cell lines [human breast cancer cells (MCF-7), mouse neuroblastoma cells (N2a), and rat pituitary epithelial cells (GH4C1)]. The compounds showed variable cytotoxicity, with Euglenophycin displaying specificity for N2a cells. We have also examined the modulatory power of NP-1 on the cytotoxicity of the other three compounds and found that at a permissible concentration (125 µg/mL), NP-1 sensitized N2a and MCF-7 cells to Euglenophycin and Glycolipid 652 induced cytotoxicity. 相似文献
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Lars Olav Brandsæter Kjell Mangerud Lars Andersson Trond Børresen Guro Brodal Bo Melander 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2020,70(4):318-332
ABSTRACTThere is a need both in organic farming and on farms using integrated pest management for non-chemical measures that control the perennial weed flora. The effect of mechanical weeding and fertilisation on perennial weeds, fungal diseases and soil structure were evaluated in two different experiments in spring cereals. Experiment I included six strategies. The first strategy was (1) without specific measures against perennial weeds. The other strategies encompassed one or two seasonal control measures; (2) rhizome/root cutting with minimal soil disturbance in autumn, (3) hoeing with 24?cm row spacing, (4) combined hoeing and disc harrowing in autumn, (5) ‘KvikUp’ harrowing in spring, and (6) ‘KvikUp’ harrowing in spring and autumn. Experiment II included factor (i) inter-row hoeing and (ii) fertilisation level. This experiment included the comparison between normal row spacing (12?cm) with weed harrowing versus double row spacing (=24?cm) in combination with inter-row hoeing and 4 fertilisation levels (50–200?kg N ha?1). In experiment I the strategies consisting of no or one direct weed control measure (1, 2, 3 and 5) clearly did not control the perennial weeds. The two seasonal control measures (4 and 6) gave a satisfactory weed control and highest crop yield. The combination of best weed control and no measured harmful effects on soil structure or increase of fungal diseases may explain the highest yields for these strategies. In Experiment II, hoeing and 24?cm spacing gave less perennial biomass compared to 12?cm spacing. Grain yields increased linearly with increasing nitrogen input. The study shows that both inter-row hoeing and weed harrows, are important elements in integrated pest management practice and organic farming. In addition, our results indicate that efficient mechanical weeding is possible without harmful effects in crop rotation consisting of various spring cereals as regards soil structure and plant health. 相似文献