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131.
For the biological control Bemisia tabaci (Genn.) Biotype B (Homoptera: Aleyrodidae) , about 200,700 individuals of the imported parasitoid Eretmocerus hayati Zolnerowich and Rose (Hymenoptera: Aphelinidae) were released during 2000 and 2002 on different host plants in Egypt. The average parasitism rates in different governorates on Lantana camara, Gossypium barbadence (cotton), Helianthus annus (soybean) and Solanum melongena (eggplant) were 10.3 and 14%, 16 and 11.4%, 12.9 and 8.7%, 18 and 13% during 2001 and 2002, respectively. The population of E. hayati correlated significantly with the buildup of the whitefly population in all three governorates, which indicated the establishment of the E. hayati parasitoid on these economically important crops in Egypt.  相似文献   
132.
The relationship between Xenorhabdus nematophilus and Photorhabdus luminescens, the bacterial symbionts of the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora, against the diamondback moth, P. xylostella (L.), pupae showed the pathogenic capability of P. luminescens to be over that of X. nematophilus. They gave 60 and 40?% mortality with LC50 values of 5?×?104 and 5.5?×?105 cells/ml, respectively.The number of bacterial cells influences the rate of killing the pupae of P. xylostella and a direct correlation between mortality of the pupae, percentage of deformed adults and the spraying dose with significant differences were observed. An inverse correlation found between the no. of eggs laid/female, percentage of hatching, adult survival and the spraying dose. These bacterial effects have been attributed to different toxic bacterial enzymes which damage the haemocytes and inhibit activation of the humoral immune system of the insect.  相似文献   
133.
    
Silvicultural approaches at forest plantations with wider initial tree spacing have created potential for increased understory vegetation growth in response to increased light and greater nutrient resources. In consequence understory vegetation can fill a more important role in forest ecosystems, especially in interactions (competition or facilitation) between understorey vegetation and forests trees that might affect tree growth and nutrition. Considerable research has been carried out on plant interference. However, the experimental designs used in these studies vary from one study to another, and from species to species depending on the aims, objectives and practicalities of the studies. Thus there is no optimum design for competition experiments. This review discusses designs available in studying plant interferences in a glasshouse, particularly the effects of below-ground interaction of understorey vegetation and forest trees.  相似文献   
134.
135.
There is an increasing incidence of Zn deficiency in savanna soil under intensive cultivation. The sizes of Zn pools and Zn2+ solubility were studied in a savanna soil under long-term cultivation and varying management practices which included fertilization with NPK, farmyard manure (FYM), NPK + FYM and a control which received neither NPK nor FYM for 50 years. An uncultivated natural site was sampled as a reference for assessing the effect of management history on Zn fractions and solubility. Total Zn ranged from 38 to 63 mg kg-1 in the natural site, and from 28 to 57 mg kg-1 in the cultivated fields. The FYM-fertilized field maintained total and extractable Zn on par with the natural site. Cultivation and management history did not affect the concentration of diethylenetriaminepentaacetic acid- (DTPA) extractable Zn, water-soluble Zn (SOL-Zn), exchangeable Zn (EXCH-Zn) and organically complexed Zn (OM-Zn). For the natural site, residual Zn (RES-Zn) accounted for 48% of total Zn, whereas Mn-oxide-bound Zn (MnOX-Zn) accounted for between 40% and 61% of total Zn in the cultivated fields. Cultivation caused the depletion of RES-Zn especially in FYM- and FYM + NPK-fertilized soils. Solubility studies indicated that some mechanism involving Zn and Fe, but independent of pH, appeared to control Zn2+ concentration in soil solution consistent with the reasonably constant values of pZn2+ + 2pFe3+ in soil solution.  相似文献   
136.
自然(资源)土地覆盖信息对分析和理解当前的陆地形式,尤其是对面临着环境日益恶化的研究区起着重要的作用。本研究综合应用Aster遥感数据和现地实际情况,完善西班牙Guadalteba地区2001年的土地覆盖图,将精度从47%提高到70%。综合土地覆盖图反映了该地区的植物类型分布和目前的自然(资源)土地覆盖状况。基于该图,自然(资源)土地覆盖图显示了自然(资源)和农业用地的当前分布,灌木土地退化图表明了各种灌木区的分布位置及其退化的不同等级,并作了进一步分析和讨论。最终的成果图揭示,Guadalteba地区许多以灌木分布为主导形式的土地已经被改用为农业和其他用途用地。由于人类活动的干扰而导致该地区大部分土地退化,使灌木覆盖仅占约9%的土地面积。图4表3参8。  相似文献   
137.
  总被引:6,自引:0,他引:6  
To clarify the influencing factors of liquefaction of wood in phenol using phosphoric acid as a catalyst and get its liquefaction technology, a study on the liquefaction technology of Chinese fir (Cunninghamia lanceolata) and poplar (triploid Populus tomentosa Carr) under different conditions was conducted. The results indicate that the residue rate decreases with the increase of liquefaction temperature, liquefaction time, catalyst content or liquid ratio. It is also found that the optimum condition of liquefaction for poplar is estimated as: the reaction temperature of 180 ℃, the reaction time of 2.5 h, liquid ratio (phenol/wood ratio)of 4.5 and catalyst content of 8%, and 4.2% residue rate could be obtained. Under the processing parameters of temperature 180 ℃, the reaction time of 2.5 h, liquid ratio (phenol/wood ratio) of 4 and catalyst content of 10%, the residue rate of Chinese fir can reach 5.6%.  相似文献   
138.
A 0.8 kb DNA fragment encoding the major epitope domain of glycoprotein E (gE) of pseudorabies virus (PRV) was inserted downstream of the T7 promoter of an expression vector, pET-28b, to yield the recombinant plasmid pETgE804. After induction by isopropy1-β-D-thiogalactopyranoside (IPTG), a high level expression of fusion protein was obtained. SDS-PAGE and western immunoblotting analysis showed that the fusion protein was 38 kDa and could bind with antisera against PRV. The protein existed mainly in the form of the inclusion body. After being denatured and renatured, the protein was used to prepare the latex antigen. The concentration of antigen, temperature and time for sensitization were optimized. The latex agglutination test (LAT) was able to differentiate sera of PRV-infected pigs from those of gE-deletion vaccine-immunized pigs. The diagnostic specificity and sensitivity of the developed gE latex agglutination test (gE-LAT) were also evaluated by using sets of sera. The diagnostic specificity and diagnostic sensitivity of the gE-LAT were 96.77% and 95.76%, respectively. For comparison between gE-LAT and a commercial blocking enzyme-linked immunosorbent assays (ELISA), 260 serum samples were tested. The coincidence frequency of both assays was 96.94% (252/260). No significant difference was found between the two methods (p>0.05). For comparison between the abilities of gE-LAT and gE-ELISA to detect sera with low titres of gE-specific antibody, 66 sera from 22 pigs were tested. The data indicate that the gE-LAT is of similar sensitivity to gE-ELISA. These results indicate that gE-LAT using recombinant gE might be very useful as a routine screening method for the differential diagnosis of PRV infection.  相似文献   
139.
An efficient regeneration protocol for rapid mass propagation and uptake of heavy metals in Albizia lebbeck (L.), a fast growing, medicinally as well as economically important timber yielding tree was developed. Nodal segments derived from a 20-year-old tree were cultured on MS (Murashige and Skoog) medium supplemented with 10 μM 6-Benzyladenine (BA) and 1 μM α-Naphthalene acetic acid (NAA) showed optimum shoot regeneration frequency (76.6%), number of shoots (23.2 ± 0.28) per explant and shoot length (2.86 ± 0.08 cm) after 10 weeks of culture. After standardizing a reliable protocol for micropropagation, effects of ZnSO4 (0.06–0.48 mM), CuSO4 (0.02–0.2 mM) and CdCl2 (0.0001–0.001 mM) on shoot morphogenesis were also assessed. The regenerated shoots maintained on maintenance medium (MS + 10.0 μM BA + 1.0 μM NAA) containing ZnSO4 (0.06 mM) showed maximum response in terms of shoot number (24.5 ± 0.83) and length (5.9 ± 0.05 cm) after 10 weeks of culture. Proline content showed an increasing trend while chlorophyll (a and b) content exhibited decreasing trend with an increased metal concentrations compared to MM cultures, and maximum increase in proline and decrease in chlorophyll content was recorded in cultures grown on Cd-enriched medium. Best rooting was accomplished on half strength MS medium with 2.0 μM IBA and ZnSO4 (0.06 mM). The plantlets thus obtained were successfully hardened and transferred to greenhouse with 75% survival rate and exhibited normal morphological characteristics compared to donor plant.  相似文献   
140.
    
Combined application of synthetic nitrogen (N) fertilizers and organic materials can enhance soil quality, but little is known about the distribution of fertilizer N among different soil fractions after crop harvest. A pot experiment using 15N tracer was employed to address this question with three treatments, i.e., labeled urea-only (15NU), labeled urea + rice straw (15NU-S) and labeled rice straw + urea (15NS-U) applied to a Ferallic Cambisol (1:1 type soil clay mineral) and a Calcaric Fluvisol (2:1 clay mineral). Soil microbial biomass N, fixed ammonium (fixed NH4+), exchangeable ammonium and soil organic N fractions by hydrolysis (6 N HCl) and their isotope abundance were determined after the rice harvest. Soil newly formed N in urea + straw (U-S) treatments (15NU-S, 15NS-U) was the sum of labeled urea-N in 15NU-S and labeled straw-N in 15NS-U. Compared with 15NU, U-S significantly (P < 0.05) increased the content and percentage of newly formed total soil N, acid insoluble N, amino acid N, and hydrolysable unknown N in both soils. In U-S treatment, straw amendment significantly (P < 0.05) reduced the content and percentage of newly formed fixed-NH4+-N in Fluvisol as compared with 15NU treatments. Soil microbes contributed to the larger percentage of newly formed amino acid N (P < 0.01) in Cambisol as compared with Fluvisol. Fertilizer N in various soil fractions was therefore strongly affected by clay mineral type and microbes after the combined application of organic materials and synthetic N fertilizer.  相似文献   
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