Physiological and DNA fingerprinting of the bacterial community of Meloidogyne fallax egg masses

Bacterial communities associated with the plant-parasitic nematode Meloidogyne fallax egg masses were compared with those present in the rhizoplane. Two agricultural soils with different nematode population dynamics were used in a glasshouse study, with either potato or tomato as host plant for the nematode. DNA fingerprints and bacterial community level physiological profiles (CLPP) were studied using PCR-DGGE of 16S rRNA genes and Biolog Eco MicroPlates. CLPP and DNA fingerprinting both showed differences between egg mass and rhizoplane bacterial communities. PCR-DGGE showed some bands specific to the egg mass samples. These bands were present in egg masses from both soils. This study shows that egg masses of M. fallax have a distinct bacterial community from that of the adjacent rhizoplane. Soil and host plant factors interactively influence the bacterial egg mass community. Differences in nematode population dynamics between the sample sites cannot be clearly related to the observed differences in the egg mass microbial communities.     

高强高耐水土体固结剂在生态建设中的应用研究

高强高耐水土体固结剂具有应用范围广、早期强度高、水稳定性与耐久性好、湿胀与干缩变形小等特点。长阳县对运用该固结剂修筑梯田土坎、土质晒场和道路的效果进行了实验。结果表明 ,运用该固结剂修筑的梯田土坎、土质晒场和道路均能满足设计强度要求 ,施工工艺简单 ,在无砂石料和运输困难的地方使用固结剂修筑土坎、晒场和道路 ,可节约工程投资 10 %以上     

ICP-MS及其联用技术在植物重金属分析中的应用研究进展

电感耦合等离子体(inductively coupled plasma,ICP)是20世纪80年代发展起来的无机元素分析技术,它具有高分辨率和灵敏度、低检出限、样品耗用少、可同时检测多元素等特点,被广泛地用于无机元素特别是金属元素的分析。ICP与质谱(mass spectrometry,MS)联用极大地促进了无机多元素分析技术的发展。本文综述了ICP-MS及其几种联用技术的原理与性能特点、排除光谱干扰的方法以及在植物重金属分析中的应用实例32篇,以期为植物重金属分析技术的研究提供有益参考。     

An integrative method to quantify contaminant fluxes in the groundwater of urban areas

Background, Aims, and Scope  Groundwater in urban areas is often contaminated and emission sources can be located close to groundwater wells. The delineation of contaminant plumes is difficult because of the various potential emission sources. Thus, detection, quantification and remediation of contaminated sites in a city need more integrative approaches. Methods  A method has been developed which allows quantification of mass fluxes of contaminants in groundwater between control planes. Budget zones along the flow path are defined to calculate a contaminant balance and to quantitatively reveal input areas. Concentrations and water budgets are used to calculate mass balances for each contaminant. The city of Darmstadt (Germany) was chosen to evaluate the method. Results  The groundwater monitoring wells (GMWs) upstream of the city showed anthropogenically superposed background values for all naturally occurring inorganic species. The contaminant concentrations increased in the city (probably influenced by road traffic, gas stations, leaking sewers, etc.). Downstream from the city, concentrations usually decreased. Organic compounds typical for urban environments, such as polycyclic aromatic hydrocarbons (PAH), locally exceeded drinking water regulations. In GMWs with high concentrations of organic contaminants in the city or downstream from industrial areas, a significant increase in Fe²⁺ and Mn²⁺ could be observed, in some cases coinciding with a decrease in NO₃, SO₄ and an increase in NH₄. Discussion  For typical urban contaminants, a positive budget was calculated in several zones, which shows that emissions from urban sources are reaching the groundwater. Negative budgets can be mainly explained with diving plumes and degradation. The input calculated from the individual budget zones is usually higher than the input estimated from urban emissions. Differences between the calculated and the estimated input can be explained with additional sources or (bio)degradation processes. Conclusions  It was confirmed that high concentrations of contaminants do not necessarily correlate with high fluxes. Integrative approaches can reveal areas of high contaminant mass input. The results obtained with the new method are plausible compared to the land use and the estimated urban input. The concentration pattern of Fe²⁺, Mn²⁺, SO₄ and NO₃ is partly due to natural processes, triggered by the degradation of organic matter and organic contaminants. Recommendations  Since this method includes mass balances and flux calculations, avoiding an overestimation of single point contaminant concentration, it is recommended to use this approach to quantify groundwater contamination in cities. Further research is focusing on the role of urban soils as natural reservoirs for the input of contaminants.     

Comparison of predicted and observed response to selection in two breeding populations of perennial ryegrass

To predict any genetic response to selection, two breeding populations of perennial ryegrass, consisting of half-sib families, were evaluated as spaced plants from 1987 to 1989 for several agronomical traits. In each population, the best plants selected through a multitrait Smith and Hazel's index were planted in a polycross to produce the second generation half-sib families. Both generations were evaluated together from 1991 to 1993 as spaced plants. The difference between generations was the observed genetic response, which was compared to that predicted. Rust tolerance, aftermath heading and persistence were significantly improved in both populations. In trial plots used to assess the yield, no effect of mass selection was noticed. Thus, it is concluded that mass selection failed to increase productivity but produced some improvements in disease tolerance and aftermath heading.     

Recurrent Mass Selection for Reduced Seed Dormancy in Cuphea lanceolata and Cuphea laminuligera

Seed dormancy is a domestication barrier in certain Cuphea species. Between and within species variation has been observed for seed dormancy in agronomically promising Cuphea species, e.g., C. laminuligera Koehne and C lanceolata Ait. In tins note, we report on progress made in reducing seed dormancy through recurrent mass selection in the C. lanceolata population LN43 and LN78. The germination percentages of unselected LA12 and LN43 populations increased from 0.0 % to greater than 95.0 % following an after-ripening period of 20 weeks. We observed no germination percentage differences between unselected and selected LN43 populations following two cycles of selection. In contrast, there were highly significant differences between the unselected and selected populations of LA12 following two cycles of selection. The germination percentages of cycle zero (C₀) and cycle two (C₂) populations after-ripened 10 weeks were 10.7 and 92.7 %, respectively. After one cycle of selection in the C. Lanceolata population LN78, the germination percentage of seed after-ripened 10 weeks had increased from 1.3 % for the C_o population to 28.7 % for the C₀ population. In summary, mass selection greatly reduced seed dormancy in LA12 and LN78, but had no effect in LN43.     

Mass selection for crown height in sugar beets (Beta vulgaris L.). 2. Divergent selection in tetraploids

Summary Five cycles of mass selection for high and low crown height in one tetraploid sugar beet population and four cycles of mass selection for high crown height in another tetraploid population gave average gains of 10–15% per cycle. Realised heritabilities were about 0.3. This progress was obtained because special attention was paid to practical aspects for improving the mass selection method.The responses to selection were measured in successive years and evaluated in 1979 (cycles 1–4) and in 1980 (cycle 5). The correlation coefficients between the data obtained in successive years and those from the evaluation trials were very high (r=0.99).In tetraploids. mass selection for crown height can be applied successfully.     

On the optimum grid size in field experiments without replications

Summary In unreplicated field trials a correction for soil heterogeneity is easily achieved by gridding, i.e. by expressing the observations as deviations from a local average. This paper investigates the problem of determining the optimum size of such a neighbourhood to be used in a moving average. The optimum grid size depends on two parameters, i.e. the coarseness of the spatial variation of the trial field and the ratio of genotypic vs. non-genotypic variance. In general these parameters are not known to the breeder. We introduce a method for estimating these parameters from the data. From these estimates the optimum grid size can be obtained using tables presented in this paper.The method has been evaluated by applying it to a series of simulated data. It turned out that the agreement between estimated and true optimum grid size was satisfactory in these simulations.Some theoretical aspects of the results are discussed.     

Participatory plant breeding with maize in Mexico and Honduras

Maize is a staple food crop in many developing countries. However, if seven major maize producing countries are excluded from this group, data indicate that only 34% of the maize area is planted with improved seed despite considerable effort invested in maize breeding. This has led researchers to investigate other options, such as farmer-participatory plant breeding, for delivering the benefits of plant breeding knowledge and technology to farmers in developing countries. This paper describes short-term results from participatory maize breeding studies in Mexico and Honduras. Results from three selection cycles in Mexico suggest that stratified mass selection without pollination control, with selections carried out by researchers in farmers' fields, may be effective at improving yield in farmers' local varieties. In Honduras, mass selection with pollination control, where selections were done by collaborating farmers in their own fields on their own varieties, showed trends (non-significant) towards yield improvement. Farmer selection seemed to offer the greatest yield benefit over experiment station selection on the farm with the lowest yield potential, suggesting that farmer-participatory approaches may be most advantageous in marginal environments where experiment station conditions differ most dramatically from farmers' conditions. These studies highlighted the importance of seed systems knowledge in designing participatory plant breeding programs. For cross-pollinated crops, they also highlighted the need to balance progress from selection and demands on farmers' time and labor in choosing breeding methods. Further work is needed to investigate farmer-participatory breeding approaches that can address post-harvest traits. This revised version was published online in August 2006 with corrections to the Cover Date.