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G Soil (g + soil)
Selected AbstractsResistance of potato cultivars to Synchytrium endobioticum in field and laboratory tests, risk of secondary infection, and implications for phytosanitary regulationsEPPO BULLETIN, Issue 1 2005R. P. Baayen Laboratory (Spieckermann) tests, pot tests and field tests provided concordant evidence for the partial nature of resistance of potatoes to pathotypes 1 (D1) and 6 (O1) of Synchytrium endobioticum. Susceptible potato cultivars produced large warts (> 16 mm in diameter) in Spieckermann tests and had low field resistance levels (1,6). Field-resistant cultivars (levels 7,9) produced small warts or no warts at all in Spieckermann and field tests. In pot tests, at low inoculum levels (1 sporangium per 25 g soil) susceptible cultivars still developed warts, whereas field-resistant ones did not develop any warts below 25 sporangia per g soil. Above 35 sporangia per g soil, 100% disease incidence was observed in susceptible cultivars but only minimal wart development in field-resistant ones. Tests with continuous cultivation of potato cultivars in infected soil during three consecutive years showed that field-resistant cultivars will not support build-up of inoculum in soil. It is concluded that field-resistant cultivars do not create a risk of secondary infection, the criterion given for resistance in EU Directive 69/464/EC. [source] Direct examination of soil for sporangia of Synchytrium endobioticum using chloroform, calcium chloride and zinc sulphate as extraction reagentsEPPO BULLETIN, Issue 1 2005G. C. M. Van Leeuwen Fields infested with Synchytrium endobioticum can be descheduled when the soil is found free from sporangia of S. endobioticum. For direct examination, EPPO Standard PM 3/59 describes a soil extraction technique based on the use of a sieve shaker with six sieves. We compared recovery of sporangia between this (modified) method and an extraction method employed by the Dutch Plant Protection Service (PPS method). Recovery was determined using an inoculum dilution series: 125, 25, 5, 1, 0.2 or 0.04 sporangia per g soil. Extraction reagents used were chloroform and calcium chloride in the method described by EPPO, calcium chloride and zinc sulphate in the PPS method. At 125 sporangia per g soil, the mean density determined for the modified EPPO method was 228 sporangia per g soil when chloroform was used. Using calcium chloride, recovery percentage was higher for the modified EPPO method than for the PPS method (286, 136%, n.s. P < 0.05). The advantage of the modified EPPO method was the larger soil volume to be processed; its disadvantages were use of complex equipment and noxious reagents (chloroform). Both extraction methods showed high variation in recovery between samples, making accurate estimation of sporangial densities in soil awkward. [source] Spatial characterization of arbuscular mycorrhizal fungal molecular diversity at the submetre scale in a temperate grasslandFEMS MICROBIOLOGY ECOLOGY, Issue 2 2008Daniel L. Mummey Abstract Although arbuscular mycorrhizal fungi (AMF) form spatially complex communities in terrestrial ecosystems, the scales at which this diversity manifests itself is poorly understood. This information is critical to the understanding of the role of AMF in plant community composition. We examined small-scale (submetre) variability of AMF community composition (terminal restriction fragment length polymorphism fingerprinting) and abundance (extraradical hyphal lengths) in two 1 m2 plots situated in a native grassland ecosystem of western Montana. Extraradical AMF hyphal lengths varied greatly between samples (14,89 m g soil,1) and exhibited spatial structure at scales <30 cm. The composition of AMF communities was also found to exhibit significant spatial autocorrelation, with correlogram analyses suggesting patchiness at scales <50 cm. Supportive of overall AMF community composition analyses, individual AMF ribotypes corresponding to specific phylogenetic groups exhibited distinct spatial autocorrelation. Our results demonstrate that AMF diversity and abundance can be spatially structured at scales of <1 m. Such small-scale heterogeneity in the soil suggests that establishing seedlings may be exposed to very different, location dependent AMF communities. Our results also have direct implications for representative sampling of AMF communities in the field. [source] Methods for evaluating human impact on soil microorganisms based on their activity, biomass, and diversity in agricultural soilsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2006Rainer Georg Joergensen Abstract The present review is focused on microbiological methods used in agricultural soils accustomed to human disturbance. Recent developments in soil biology are analyzed with the aim of highlighting gaps in knowledge, unsolved research questions, and controversial results. Activity rates (basal respiration, N mineralization) and biomass are used as overall indices for assessing microbial functions in soil and can be supplemented by biomass ratios (C : N, C : P, and C : S) and eco-physiological ratios (soil organic C : microbial-biomass C, qCO2, qNmin). The community structure can be characterized by functional groups of the soil microbial biomass such as fungi and bacteria, Gram-negative and Gram-positive bacteria, or by biotic diversity. Methodological aspects of soil microbial indices are assessed, such as sampling, pretreatment of samples, and conversion factors of data into biomass values. Microbial-biomass C (µg (g soil),1) can be estimated by multiplying total PLFA (nmol (g soil),1) by the FPLFA -factor of 5.8 and DNA (µg (g soil),1) by the FDNA -factor of 6.0. In addition, the turnover of the soil microbial biomass is appreciated as a key process for maintaining nutrient cycles in soil. Examples are briefly presented that show the direction of human impact on soil microorganisms by the methods evaluated. These examples are taken from research on organic farming, reduced tillage, de-intensification of land-use management, degradation of peatland, slurry application, salinization, heavy-metal contamination, lignite deposition, pesticide application, antibiotics, TNT, and genetically modified plants. [source] Sensitive detection of Ralstonia solanacearum in soil: a comparison of different detection techniquesPLANT PATHOLOGY, Issue 4 2000P. M. Pradhanang The sensitivity and specificity of various methods were compared for routine detection of Ralstonia solanacearum in a sandy loam soil. Populations fewer than 102 CFU per g soil were detected by dilution plating on a modified semiselective medium (SMSA). In comparison, a tomato bioassay was shown consistently to detect populations at or greater than 7·5 × 105 CFU per g soil. An indirect enzyme-linked immunosorbent assay (ELISA) was as sensitive as the tomato bioassay, but detected as few as 104 CFU per g soil when the suspension was first incubated in SMSA broth prior to testing. Detection using a nested polymerase chain reaction (PCR) was equally as sensitive as that using culture on SMSA agar, but only when the infested soil sample was first enriched overnight in SMSA broth prior to the nested PCR. Longer incubation periods in SMSA broth also increased the sensitivity of pathogen detection using a conventional PCR method, permitting detection of as few as 102 CFU per g soil after 60 h enrichment in SMSA broth. When evaluated using naturally infected field soils in Nepal, isolation of R. solanacearum on SMSA was reliable only when pathogen populations were higher than those of saprophytic soilborne bacteria. As few as 5 × 102 CFU of R. solanacearum per g were recovered from naturally infested soil, whereas the sensitivity of indirect ELISA was 106 CFU g,1. [source] Field studies on the environmental fate of the Cry1Ab Bt-toxin produced by transgenic maize (MON810) and its effect on bacterial communities in the maize rhizosphereMOLECULAR ECOLOGY, Issue 8 2005SUSANNE BAUMGARTE Abstract Field studies were done to assess how much of the transgenic, insecticidal protein, Cry1Ab, encoded by a truncated cry1Ab gene from Bacillus thuringiensis (Bt), was released from Bt-maize MON810 into soil and whether bacterial communities inhabiting the rhizosphere of MON810 maize were different from those of the rhizosphere of nontransgenic maize cultivars. Bacterial community structure was investigated by SSCP (single-strand conformation polymorphism) of PCR-amplified 16S rRNA genes from community DNA. Using an improved extraction and detection protocol based on a commercially available ELISA, it was possible to detect Cry1Ab protein extracted from soils to a threshold concentration of 0.07 ng/g soil. From 100 ng of purified Cry1Ab protein added per gram of soil, only an average of 37% was extractable. At both field sites investigated, the amount of Cry1Ab protein in bulk soil of MON810 field plots was always lower than in the rhizosphere, the latter ranging from 0.1 to 10 ng/g soil. Immunoreactive Cry1Ab protein was also detected at 0.21 ng/g bulk soil 7 months after harvesting, i.e. in April of the following year. At this time, however, higher values were found in residues of leaves (21 ng/g) and of roots (183 ng/g), the latter corresponding to 12% of the Cry1Ab protein present in intact roots. A sampling 2 months later indicated further degradation of the protein. Despite the detection of Cry1Ab protein in the rhizosphere of MON810 maize, the bacterial community structure was less affected by the Cry1Ab protein than by other environmental factors, i.e. the age of the plants or field heterogeneities. The persistence of Cry1Ab protein emphasizes the importance of considering post-harvest effects on nontarget organisms. [source] | ||||||||||