Biological control of take-all by fluorescent Pseudomonas spp. from Chinese wheat fields     

Yang MM  Mavrodi DV  Mavrodi OV  Bonsall RF  Parejko JA  Paulitz TC  Thomashow LS  Yang HT  Weller DM  Guo JH 《Phytopathology》2011,101(12):1481-1491

Take-all disease of wheat caused by the soilborne fungus Gaeumannomyces graminis var. tritici is one of the most important root diseases of wheat worldwide. Bacteria were isolated from winter wheat from irrigated and rainfed fields in Hebei and Jiangsu provinces in China, respectively. Samples from rhizosphere soil, roots, stems, and leaves were plated onto King's medium B agar and 553 isolates were selected. On the basis of in vitro tests, 105 isolates (19% of the total) inhibited G. graminis var. tritici and all were identified as Pseudomonas spp. by amplified ribosomal DNA restriction analysis. Based on biocontrol assays, 13 strains were selected for further analysis. All of them aggressively colonized the rhizosphere of wheat and suppressed take-all. Of the 13 strains, 3 (HC9-07, HC13-07, and JC14-07, all stem endophytes) had genes for the biosynthesis of phenazine-1-carboxylic acid (PCA) but none had genes for the production of 2,4-diacetylphloroglucinol, pyoluteorin, or pyrrolnitrin. High-pressure liquid chromatography (HPLC) analysis of 2-day-old cultures confirmed that HC9-07, HC13-07, and JC14-07 produced PCA but no other phenazines were detected. HPLC quantitative time-of-flight 2 mass-spectrometry analysis of extracts from roots of spring wheat colonized by HC9-07, HC13-07, or Pseudomonas fluorescens 2-79 demonstrated that all three strains produced PCA in the rhizosphere. Loss of PCA production by strain HC9-07 resulted in a loss of biocontrol activity. Analysis of DNA sequences within the key phenazine biosynthesis gene phzF and of 16S rDNA indicated that strains HC9-07, HC13-07, and JC14-07 were similar to the well-described PCA producer P. fluorescens 2-79. This is the first report of 2-79-like bacteria being isolated from Asia.  相似文献   

EMS and UV irradiation induce unstable resistance against CAA fungicides in <Emphasis Type="Italic">Bremia lactucae</Emphasis>     

Avia E. Rubin  Ayelet-Chen Werdiger  Mathias Blum  Ulrich Gisi  Helge Sierotzki  Dietrich Hermann  Yigal Cohen 《European journal of plant pathology / European Foundation for Plant Pathology》2011,129(2):339-351

Wild type (WT) field isolates of Bremia lactucae failed to germinate in vitro or infect lettuce leaves in the presence of CAA (carboxylic acid amide) fungicides. Minimal inhibitory concentrations (MIC) for mandipropamid, dimethomorph, benthiavalicarb and iprovalicarb were 0.005, 0.5, 0.5 and 5 μg ml⁻¹, respectively. Mutagenesis experiments showed that spores exposed to EMS (ethyl methane sulphonate) or UV irradiation (254 nm) could infect lettuce leaves in the presence of up to 100 μg ml⁻¹ CAA. The proportion of infected leaves relative to the number of spores inoculated (infection frequency) was inversely related to the concentration of CAA used, ranging between 0 and 160 per 1 × 10⁶ spores. Resistant mutants (RM) lost their resistance within 1–14 reproduction cycles on CAA-treated plants. Crosses were made between RMxWT isolates and RMxRM isolates with an attempt to obtain stable homozygous resistant off-springs. Such crosses yielded few resistant but unstable progeny isolates. Mutagenic treatments given to hybrid isolates also failed to produce stable resistance. Previous gene sequencing data showed that stable resistance to CAAs is based on a single SNP in the cellulose synthase 3 (CesA3) gene of Plasmopara viticola. Therefore, we sequenced a 582 bp DNA fragment of Ces3A of WT, RM and hybrid isolates of B.lactucae. No mutation in this gene fragment was found. We conclude that mutagenic agents like EMS or UV may induce resistance to CAA in Bremia lactucae but this resistance is not stable and not linked to mutations in CesA3 gene.  相似文献   

Resistance mechanism to carboxylic acid amide fungicides in the cucurbit downy mildew pathogen Pseudoperonospora cubensis     

Blum M  Waldner M  Olaya G  Cohen Y  Gisi U  Sierotzki H 《Pest management science》2011,67(10):1211-1214

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   

Benchmark study on glyphosate-resistant crop systems in the United States. Part 2: Perspectives     

Owen MD  Young BG  Shaw DR  Wilson RG  Jordan DL  Dixon PM  Weller SC 《Pest management science》2011,67(7):747-757

A six-state, 5 year field project was initiated in 2006 to study weed management methods that foster the sustainability of genetically engineered (GE) glyphosate-resistant (GR) crop systems. The benchmark study field-scale experiments were initiated following a survey, conducted in the winter of 2005-2006, of farmer opinions on weed management practices and their views on GR weeds and management tactics. The main survey findings supported the premise that growers were generally less aware of the significance of evolved herbicide resistance and did not have a high recognition of the strong selection pressure from herbicides on the evolution of herbicide-resistant (HR) weeds. The results of the benchmark study survey indicated that there are educational challenges to implement sustainable GR-based crop systems and helped guide the development of the field-scale benchmark study. Paramount is the need to develop consistent and clearly articulated science-based management recommendations that enable farmers to reduce the potential for HR weeds. This paper provides background perspectives about the use of GR crops, the impact of these crops and an overview of different opinions about the use of GR crops on agriculture and society, as well as defining how the benchmark study will address these issues.  相似文献   

EDV-gestütztes Meß- und Auswerteverfahren zur Bestimmung der ungesättigten Wasserleitfähigkeit nach der Verdunstungsmethode     

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   

Löslichkeit und Löslichkeitsprodukt von Hydroxylapatit und Rohphosphaten     

H. W. Fassbender  H. C. Lin  B. Ulrich 《植物养料与土壤学杂志》1966,112(2):101-113

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Lösungsgeschwindigkeit von Rohphosphaten     

H. W. Fassbender  B. Ulrich 《植物养料与土壤学杂志》1966,112(3):212-220

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Analysis of fiber content in flax stems by near-infrared spectroscopy     

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   

Soil-living parasitic Hymenoptera: comparison between a forest and an open landscape habitat     

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   

Die Beeinflussung der Bodenlösung durch Saugkerzen aus Ni-Sintermetall und Keramik     

W. Hetsch  F. Beese  B. Ulrich 《植物养料与土壤学杂志》1979,142(1):29-38

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