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ABSTRACT The role of fimbrial and afimbrial adhesins of Xylella fastidiosa in biofilm formation was assessed by visualization of cell aggregates of mutant strains after incubation on glass surfaces. FimA- or FimF- fimbrial mutants adhered as solitary cells at a slightly lesser frequency to glass surfaces than the parental strain; however, cell aggregates were not formed, unlike the wild-type strain. Conversely, whereas the XadA- and HxfB- nonfimbrial mutants also exhibited a much lower frequency of adherence to glass surfaces than the wild-type strain, most of the cells retained on the surfaces were in cell aggregates of different sizes, much like that of the parental strain. Neither fimbrial or afimbrial mutants formed a mature biofilm on the sides of flasks of broth cultures, unlike the dense biofilm formed by the wild-type strain. Although FimA- and FimF- mutants did not form cell aggregates on glass surfaces when incubated as individual strains, aggregates of a FimA- or FimF- mutant were observed when co-incubated with either a XadA- mutant or HxfB- mutant, respectively. These results are consistent with a model in which the fimbrial adhesins FimA and FimF are involved preferentially in cell-to-cell aggregate formation whereas the afimbrial adhesions XadA and HxfB preferentially contribute to initial cell binding to surfaces, whereupon further cell aggregation can occur. In each of five separate experiments, FimA, FimF, XadA, and HxfB mutants of X. fastidiosa all were less virulent to grape than the corresponding wild-type strain. Fimbrial and afimbrial mutants might produce a reduced biofilm within vessels of grape and, hence, be deficient in various cell-density-dependent traits required for movement through the plant and, thus, virulence. 相似文献
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<正>蚜虫隶属半翅目蚜虫总科,是世界上分布最广的微小昆虫之一。世界已知4 700余种,中国分布约1 100种[1-2]。蚜虫种类多、繁殖快、世代重叠,还存在孤雌生殖与两性生殖世代交替等独特生物学现象。许多蚜虫种类是非常重要的农作物害虫,其刺吸式口器可吸食植物汁液,造成植物生长不良,其唾液也对植物有毒害作用[3-4]。受蚜虫为害的植物具有多种不同症状,如生长率降低、产生叶斑、泛黄、发 相似文献
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高原人体生理适应学理论在进藏旅游中的应用 总被引：2，自引：0，他引：2
青藏铁路的贯通运行,带来了国内外进藏旅游热.然而,青藏高原毕竟是世界屋脊,高海拔带来的低氧及其引发的高原疾病依然威胁着游客的身体健康.健康高原旅行是当前游客进藏旅游的基本前提,通过综合国内外高原医学工作者对高原医学生理学的研究成果,提出阶梯进藏旅游的方法.旨在对越来越多的短期赴西藏高原旅行的人群以正确的健康指导,从而减... 相似文献
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David G. Heckel Linda J. Gahan Fred Gould Joanne C. Daly Stephen Trowell 《Pest management science》1997,51(3):251-258
Genetic linkage maps of Heliothis virescens and Helicoverpa armigera are being used to identify and characterize resistance-conferring genes. The insensitive acetylcholinesterase conferring resistance to organophosphorus insecticides and the insensitive sodium channel conferring resistance to pyrethroids have both been mapped in H. virescens. The linkage mapping approach permits a genetic dissection of resistance, even when the mode of action and lethal target are not precisely known, such as for the insecticidal toxins from the bacterium Bacillus thuringiensis (Bt). We have identified and mapped a major Bt-resistance locus in a strain of H. virescens exhibiting up to 10000-fold resistance to Cry1Ac toxin and are currently developing a linkage map for H. armigera with a set of ‘anchor’ loci to facilitate comparison with H. virescens. Both species are currently experiencing their first significant selective pressure in the field by transgenic cotton expressing Cry1Ac, and timely identification of resistance mechanisms and their underlying genetic basis will be essential in successfully managing the Bt resistance that will eventually appear. ©1997 SCI 相似文献
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Dutch elm disease (DED) is a vascular wilt disease that causes the occlusion and cavitation of xylem vessels. Therefore, it is hypothesized that those elms that are less vulnerable to cavitation by drought might be more resistant to DED. To test this hypothesis, the relationship between xylem vulnerability to cavitation and susceptibility to DED was examined in progenies of crosses between susceptible and resistant individuals of Ulmus minor. Hydraulic conductivity and xylem vulnerability curves were evaluated and anatomical features such as vessel size, length and grouping were measured. Next, elms were inoculated with Ophiostoma novo‐ulmi, the cause of DED, and pre‐dawn and midday water potentials, stomatal conductance and wilting percentages were assessed. Progenies of R × R crosses showed significantly lower mean wilting percentages (30–50%) than the progeny of S × S crosses (75%). Fifty percent conductivity loss was reached at c. ?1 MPa, pointing out a high vulnerability of this species to drought‐induced cavitation. Crown wilting percentage as a result of inoculation and xylem vulnerability to cavitation by water stress did not show any significant correlation. Nevertheless, significant differences in theoretical hydraulic conductivity and vessel size parameters (diameter, length and size distributions) were found among the tested progenies. Susceptible trees had significantly wider and longer vessels. Xylem structure of resistant elms seems to restrict pathogen spread rather than prevent cavitation. 相似文献
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硝磺草酮的除草活性及对玉米的安全性 总被引：2，自引：0，他引：2
通过温室盆栽试验,研究茎叶喷施硝磺草酮对反枝苋、稗草和千金子的活性及对玉米的安全性。结果表明硝磺草酮对玉米和反枝苋、千金子、稗草的选择性指数分别为6．73、5．95、5．34。说明硝磺草酮对玉米和杂草的选择性很强,可安全地使用茎叶处理法防除玉米田杂草。 相似文献
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Ramwell CT 《Pest management science》2005,61(2):144-150
In order to accurately predict the fate and behaviour of herbicides following application to hard surfaces, an understanding of the processes involved is required. Previous studies have demonstrated that herbicides with a low soil organic carbon partition coefficient (K(oc)) are preferentially removed from concrete and asphalt surfaces. It is possible, therefore, that sorption may play a role in retaining herbicides to hard surfaces. This study provides an indication of the extent to which herbicides may sorb to concrete and asphalt, and examines the results in the light of other research to identify the significance of sorption in describing herbicide losses after application. There was measurable sorption of herbicides to concrete and asphalt although this was limited compared with that to soils, especially for concrete. An exponential relationship between experimentally derived values of K(p) and literature values of K(oc) for asphalt was established (r(2) = 0.931); there was a weaker relationship for concrete (r(2) = 0.606). The experimentally derived K(p) values could be used to enhance the prediction of herbicide loss to receiving waters following application. It is probable that the fate of herbicides applied to concrete and asphalt surfaces depends more heavily on physical processes than is the case in soils. 相似文献
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Donkersley Philip Silva Farley W. S. Carvalho Claudine M. Al-Sadi Abdullah M. Elliot Simon L. 《植物病害和植物保护杂志》2019,126(5):489-489
Journal of Plant Diseases and Protection - In the original publication, Narouei-Khandan et al.’s reference detail was incorrectly crosslinked with another article and missed to include in the... 相似文献
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苯并噻二唑对漂浮育苗烟草白粉病的诱导抗性及其对烟苗安全性研究 总被引：1，自引：0，他引：1
测定了苯并噻二唑对烟草白粉病菌的毒力、防治烟草白粉病的持效期以及对烟苗的安全性。结果表明,苯并噻二唑对烟草白粉病具有很高的诱导活性,随着药剂浓度的增加,烟草白粉病的发病率和病情指数均显著降低,它对烟草白粉病菌的EC50和EC90分别为3.30μg/mL和10.49μg/mL;苯并噻二唑对烟草白粉病具有较长的持效期,50%苯并噻二唑水分散粒剂23g/hm2 2次喷雾处理4叶期烟苗,30d后的防效仍然达到100%,它对烟草新生烟叶具有良好的保护作用;此外,50%苯并噻二唑水分散粒剂>95g/hm2喷雾烟苗会给烟苗造成严重药害,主要表现为烟苗生长滞缓,叶片坏死和黄化。 相似文献
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Widespread anticoagulant resistance was discovered in populations of the brown rat (Rattus norvegicus Berk.) in an area of roughly 8000 km2 in north-west Germany. Resistance testing was performed by feeding tests and/or by measuring blood clotting response after intraperitoneal injection of a sublethal testing solution. A hierarchical resistance system was found with warfarin resistance at the base followed by bromadiolone/coumatetralyl resistance to difenacoum resistance at the top. Warfarin resistance was spread over the whole area with reduced incidence towards the edges. Difenacoum resistance represented the highest level found so far and was restricted to the inner zone of the resistance area where it occurred with a frequency of 6% of all individuals tested. Breeding experiments with bromadiolone-resistant rats showed that expression of the bromadiolone resistance gene differed in the two sexes, suggesting additional sex-linked modifying effects to the resistance gene. Control strategy within the resistance area with respect to prevention of further selection for resistance is discussed. 相似文献
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田头菇危害黄姜及防治研究 总被引：2，自引：1，他引：1
报导了田头菇[Agrocybe praecox(Pers.exFr)Fayod]危害黄姜（Dioscorea zingiberensisC.H.wright)根状茎的症状、病原形态和发生环境。选用无病种姜;用50％多菌灵可湿性粉剂1000倍液浸种姜以及清除白草等措施可以防治。 相似文献
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L. Benjamini 《Phytoparasitica》1980,8(3):151-161
The efficacy of two treatments in protecting sugar beet sprouts from damage by birds was tested. Dense sowing of inexpensive sugar beet seeds as an alternative food between the rows of the commercial planting reduced the damage to the commercial crop by about 9%. The same treatment followed by foliar spray (2.25 kg a.i./ha) of Mesurol — a chemical repellent — gave a ～20% reduction in damage, but losses were still heavy. The effects of plot size and of local conditions are discussed. 相似文献
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Davies TE O'Reilly AO Field LM Wallace B Williamson MS 《Pest management science》2008,64(11):1126-1130
Naturally derived insecticides such as pyrethrum and man-made insecticides such as DDT and the synthetic pyrethroids act on the voltage-gated sodium channel proteins found in insect nerve-cell membranes. The correct functioning of these channels is essential for the normal transmission of nerve impulses, and this process is disrupted by binding of the insecticides, leading to paralysis and eventual death. Some insect pest populations have evolved modifications of the sodium channel protein that inhibit the binding of the insecticide and result in the insect developing resistance. This perspective outlines the current understanding of the molecular processes underlying target-site resistance to these insecticides (termed kdr and super-kdr), and how this knowledge may in future contribute to the design of novel insecticidal compounds. 相似文献
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B. Ney M. O. Bancal P. Bancal I. J. Bingham J. Foulkes D. Gouache N. Paveley J. Smith 《European journal of plant pathology / European Foundation for Plant Pathology》2013,135(3):561-580
Plant tolerance to biotic stresses (mostly limited here to fungal pathogens and insects) is the ability of a plant to maintain performance in the presence of expressed disease or insect herbivory. It differs from resistance (the capacity to eliminate or limit pests and pathogens by genetic and molecular mechanisms) and avoidance (the ability to escape infection by epidemics). The ways to tolerance of pests and diseases are multiple and expressed at different scales. The contribution of organs to the capture and use of resources depends on canopy and root architecture, so the respective locations of disease and plant organs will have a strong effect on the crop’s response. Similarly, tolerance is increased when the period of crop sensitivity lies outside the period within which the pest or pathogen is present. The ability of the plant to compensate for the reduced acquisition of resources by the production of new organs or by remobilization of reserves may also mitigate biotic stress effects. Numerous examples exist in the literature and are described in this article. Quantification of tolerance remains difficult because of: (i) the large number of potential mechanisms involved; (ii) different rates of development of plants, pests and pathogens; and (iii) various compensatory mechanisms. Modelling is, therefore, a valuable tool to quantify losses, but also to prioritize the processes involved. 相似文献
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为评价杀螨剂对朱砂叶螨的毒力和对加州新小绥螨的安全性，本文采用玻片浸渍法、叶片残毒法和浸叶法测定了乙唑螨腈、丁氟螨酯、乙螨唑、哒螨灵、螺螨酯和联苯肼酯对朱砂叶螨的毒力，并对这6种杀螨剂对加州新小绥螨卵孵化率和雌成螨存活率进行了测定。结果表明，6种杀螨剂用叶片残毒法测定的毒力大于玻片浸渍法测定的毒力。朱砂叶螨雌成螨对螺螨酯和乙螨唑不敏感，其余4种杀螨剂都表现出较高的毒性。哒螨灵田间使用剂量显著降低加州新小绥螨雌成螨存活率，10倍田间使用剂量处理24 h后死亡率达100%。乙螨唑和哒螨灵田间使用剂量处理后加州新小绥螨卵仅有1%和0.33%的孵化率。因此，建议应用加州新小绥螨防治害螨时，应尽量避免哒螨灵和乙螨唑的施用。 相似文献
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《Physiological and Molecular Plant Pathology》2002,60(3):121-129
Detached leaves of 25 barleys, ranging from highly susceptible to highly resistant to Pyrenophora teres f. teres and Pyrenophora teres f. maculata, were tested for their reaction to three phytotoxins isolated from cultures of the fungus: toxin A [ L, L - N -(2-amino-2-carboxyethyl)aspartic acid], toxin C (aspergillomarasmine A) and toxin B (anhydroaspergillomarasmine A). 0.75 m M toxin A caused mainly dark yellow chlorotic symptoms but little necrosis, whereas leaves treated with 0.25 m M toxin C developed distinct necrotic symptoms and zones of light yellow chlorosis. Toxin B is only weakly toxic, and toxin B and control solutions containing aspartic acid in the concentration of 0.75 m M did not cause any symptoms. The best differentiation between the barleys was obtained by scoring chlorosis after 120 h, and the optimal toxin concentrations for this differentiation were 0.75 m M toxin A and 0.25 m M toxin C, respectively. Results with different toxin concentrations inducing distinct variation in symptom expression indicate that the two toxins have different potencies as phytotoxins. The reaction of the barleys to toxins A and C correlated well with their reaction to infection by P. teres f. teres and P. teres f. maculata, suggesting that toxins A and C may be used to select resistant barley lines in the early stages of a breeding programme. 相似文献
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