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51.
BACKGROUND: Pseudoperonospora cubensis, the causal oomycete agent of cucurbit downy mildew, is responsible for enormous crop losses in many species of Cucurbitaceae, particularly in cucumber and melon. Disease control is mainly achieved by combinations of host resistance and fungicide applications. However, since 2004, resistance to downy mildew in cucumber has been overcome by the pathogen, thus driving farmers to rely only on fungicide spray applications, including carboxylic acid amide (CAA) fungicides. Recently, CAA‐resistant isolates of P. cubensis were recovered, but the underlying mechanism of resistance was not revealed. The purpose of the present study was to identify the molecular mechanism controlling resistance to CAAs in P. cubensis. RESULTS: The four CesA (cellulose synthase) genes responsible for cellulose biosynthesis in P. cubensis were characterised. Resistant strains showed a mutation in the CesA3 gene, at position 1105, leading to an amino acid exchange from glycine to valine or tryptophan. Cross‐resistance tests with different CAAs indicated that these mutations lead to resistance against all tested CAAs. CONCLUSION: Point mutations in the CesA3 gene of P. cubensis lead to CAA resistance. Accurate monitoring of these mutations among P. cubensis populations may improve/facilitate adequate recommendation/deployment of fungicides in the field. Copyright © 2011 Society of Chemical Industry 相似文献
52.
Ulrich Krahmer 《植物养料与土壤学杂志》1987,150(6):392-394
A Computer-aided Measuring and Evaluation Method for the Determination of the Hydraulic Conductivity in the Unsaturated State according to the Evaporation Method Multiple methods for the determination of the unsaturated flow depend on the water content or the soil-moisture tension have been published by so far. Their major drawback is the large consumption of time for the measuring and/or for the evaluation. The here presented combination of devices for the application of the evaporation method including its software permit a faster determination of parameters and a presentation in an analytic mode. 相似文献
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Barton FE Akin DE Morrison WH Ulrich A Archibald DD 《Journal of agricultural and food chemistry》2002,50(26):7576-7580
The conventional means of measuring the fiber content of flax is time-consuming and laborious, and the results obtained vary with the analysis technique used. The plant tissues must first be "retted", a process by which the fibers are separated from the rest of the stem, either by indigenous organisms in the soil when the stems are left in the field or by water (anerobic bacteria) or enzymatic retting. The fiber content is then determined by mechanical or manual separation. In this study, fiber content of flax stems was measured rapidly and objectively by near-infrared spectroscopy (NIRS) using whole pieces of stem in a large cell, in reflectance mode. Compared to the conventional method, the standard error of performance of the NIRS method was between 0.96 and 1.45% (dry matter basis), depending on the model and data processing used. NIRS calibrations were generated by hand separation of fiber from water-retted specimens. The water retting procedure takes several days to complete and requires considerable trained labor to complete the hand separation step. The NIRS procedure was conducted on pieces of stem to simulate measurement in the field. 相似文献
56.
Werner Ulrich 《Pedobiologia》2004,48(1):59-69
Community structures and local diversity patterns of parasitic Hymenoptera with soil and leaf litter hosts were studied in a German beech forest and a meadow. Hymenoptera appeared to be one of the most species-rich taxa associated with the soil. Eighty-eight species were found in the meadow (total density of 128 ind. m−2 yr−1) and 188 species (149 ind. m−2 yr−1) in the forest. The mean parasitism rates were above 60% for parasitoids of mycetophagous Diptera and between 7% and 26% for parasitoids of saprophagous Diptera. Species overlap between both habitats was higher than expected from a random sample model. Species common to both habitats were primarily parasitoids of predatory Coleoptera. High mean densities of these species support the hypothesis of a positive correlation between local abundance and range size. 相似文献
57.
Influencing soil solution by suction cup material (Ni, ceramics) The influence of suction cup material (ceramics, Ni) on the chemical composition of the soil solution was tested in the laboratory by percolating soil solutions of different concentration (pH ~ 4.0). Ceramic cups of P 80 material can be used for the collection of soil solution and its determination for the concentrations of H, Na, K, NH4, Ca, Mg, Mn, Al, S, Cl and NO3. They can't be used to determine P-concentrations. The cups must be prepared and preconditioned by leaching large amounts of equilibrium soil solution which should not be oversaturated with respect to the solubility product of AlOHSO4. The changes in the concentration of extracted soil solution when it passes through the cups depend upon the extracted volume. The lower the volume, the greater are the changes. Sintered Ni-cups show many severe disadvantages (decreasing permeability, insufficient resistence against acid solutions, large variability among single cups), and can only be used for cases where Na, Ca, K, and S are to be determined. Ceramic cups of the type ‘Czeratzki’ are comparable with those of P 80. However, they can only be used, when the concentrations don't vary too much and large amounts of water can be extracted. 相似文献
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Aspects of phytoremediation of organic pollutants 总被引:1,自引:0,他引:1
Phytoremediation is a quite novel technique to clean polluted soils using plants. In theory, phytoremediation methods are
cheap, are accepted by the public and, compared to physical or chemical approaches, are ecologically advantageous. Until today,
however, there are only a few examples of successful applications. One reason is that the processes involved are complex,
and a full clean up may require many years. Plants affect the water balance of a site, they change redox potential and pH,
and stimulate microbial activity of the soil. These indirect influences may accelerate degradation in the root zone or reduce
leaching of compounds to groundwater. Compounds taken up into plants may be metabolised, accumulated, or volatilised into
air. Based on these processes, several phytoremediation methods have been developed: Phytoextraction, rhizofiltra-tion, phytostabilisation,
rhizo and phytodegradation, pump and tree, land farming, phytovolatilisation, hydraulic control and more. Already in use are
plants (and here willow, poplar and grass) for the degradation of petroleum products, aromatic hydrocarbons (BTEX), chlorinated
solvents, explosives and cyanides. However, phytotoxicity and pollutant mass balances were rarely documented. Often, the success
of the projects was not controlled, and only estimates can be made about the applicability and the potential of phytoremediation.
This lack of experience about possibilities and limitations seems to be a hindrance for a broader use of these techniques. 相似文献
60.
Kappelmeyer Uwe Kuschk Peter Stottmeister Ulrich 《Water, air, and soil pollution》2003,147(1-4):317-330
Chemodenitrification is of importance in both soils and the treatment of some types of wastewater. During model experiments,the impact of various conditions, such as pH and especially artificial humic matter and oxygen on this process was studied to build upkinetic models. The chemodenitrification rate decreased due to the ongoingautoxidation/polymerization of hydroquinone to artificial humic matterfrom 11.02 μg (L h)-1 after 7 days autoxidation to 5.38 μg (L h)-1 after 14 days at pH 4 under aerobic conditionsand an initial nitrite concentration of 250 μg L-1. At the same pH,with the same nitrite concentration, and in the presence of Roth humic matter(2 mg L-1) under aerobic conditions, the chemodenitrification rate was0.73 μg (L h)-1, whereas under anaerobic conditions itwas considerably higher (2.88 μg (L h)-1). In anothermodel experiment, it was shown that the amount of nitrite incorporated into the artificial humic matter was less then 1%. Further, it was found that the main reaction product of chemodenitrification is NO. 相似文献