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101.
Abstract. The infectivity of the bacterial fish pathogen Aeromonas salmonicida subsp. salmonicida to Atlantic salmon, Salmo salar L., in sea water was investigated and found to be similar to that reported for fresh water. The minimal infective dose in short duration bath exposures (1–3 days) was 104 colony-forming units (cfu) per ml, while prolonged exposure for three weeks, but not for 1 week, produced infection with 102 cfu/ml. Intragastric intubation of A. salmonicida established infection with doses of >105 cfu. Release of bacteria from dead or morbid infected fish was monitored and found to be in the order of 105 –108 cfu/fish/h. These results emphasize the importance of removing dead fish from farm sites. 相似文献
102.
Abstract. A comparison was made between the effects of Aeromonas salmonidda extracellular protease and total extracellular products (ECP) following intramuscular injection into juvenile Atlantic salmon, Salmo salar L. Thus, 20, 10, 5, 2.5 and 1.5 units of salt-free protease in 0.2 ml water were compared with ECP preparations with the same levels of proteolytic activity. The highest concentration of ECP produced a gross pathology with a large furuncular lesion 36 h after injection. The corresponding protease preparation had a lesser effect, although a furuncle was formed and tissue liquefaction was produced. These effects were less marked with reduced concentrations. At the lowest level studied, no significant effect was observed with protease alone but ECP (0.8 μg of protein) produced a small, characteristic lesion similar to that achieved with 5 units of isolated protease. 相似文献
103.
The role of Aeromonas salmonicida extracellular products in the pathology of furunculosis 总被引:5,自引:0,他引:5
Abstract. The extracellular products (ECP) of Aeromonas salmonicida , prepared by the cellophane overlay method, are lethal to rainbow trout when administered parenterally. Sublethal doses when injected i.p. or i.m. are shown to reproduce all the lesions that have been described in the literature as being associated with furunculosis. In addition, meningitis may be an important feature of furunculosi s and is reproduced by injection of ECP. A serum factor, probably an α-globulin, present in normal serum of rainbow trout, is capable of neutralizing the toxic effects of ECP. The pathology is discussed with reference to the proteolytic and leucocidal properties of the ECP and its effects upon the eosinophilic granular cells which are caused to disperse and degranulate with the possible release of histamine. 相似文献
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Gerson Laerson DRESCHER Leandro Souza DA SILVA Qamar SARFARAZ Gustavo DAL MOLIN Laura Brondani MARZARI Augusto Ferreira LOPES Cesar CELLA Daniela Basso FACCO Rodrigo Knevitz HAMMERSCHMITT 《土壤圈》2020,30(3):326-335
Nitrogen (N) is a key nutrient for rice production, and its bioavailability in paddy soils is strongly coupled to soil organic matter (SOM) cycling. A better understanding of potentially available N forms in soil, such as alkaline hydrolyzable N (AH-N), and their depth distribution will support the development of best management practices to improve the N use efficiency of rice while minimizing adverse environmental effects. Fifteen rice (Oryza sativa L.) fields from Southern Brazil were selected, and stratified soil samples were taken to a depth of 60 cm before crop establishment. Selected soil physical and chemical properties were analyzed to evaluate their relationships with AH-N contents in the soil profile. The AH-N contents below 20 cm varied extensively (increased, reduced, or constant) compared with that above 20 cm. Although clay and clay + silt contents were highly correlated to AH-N for some soils, the major property dictating AH-N distribution by depth was total N (TN), as the correlation between TN and AH-N was mainly by direct effect. The proportion of TN recovered as AH-N across sites and depths presented high amplitude, and thus AH-N was not a constant N pool across depths, indicating that AH-N can be affected by soil management practices even when TN showed no major changes. The distinct distribution of AH-N across soil sampling sites and depths indicates that depths greater than 20 cm should be considered when calibrating the AH-N index for N fertilizer recommendations for flooded rice in Southern Brazil. 相似文献
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乡镇企业概念动态化探究 总被引:2,自引:0,他引:2
在过去的近三十年中,乡镇企业在转移富余劳动力,发展县域经济等方面作出了卓越的贡献.但是,随其内外环境的变化,乡镇企业的发展遭到质疑,有学者认为乡镇企业的名称应改为中小企业或者是民营企业.本文通过对乡镇企业历史变迁、概念内涵变化的探究,提出乡镇企业概念内涵的界定应:扬弃约束,体现其在"三农"中的作用. 相似文献
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【目的】 针对水稻生产中的减肥、减药措施,前期自主开发了水稻优标体系。本研究通过分析应用优标体系的稻米产量和污染物含量以及土壤质量,评估优标体系在实际农业生产中的应用效果,以期为该优标体系的合理设计和及时调整提供科学依据。【方法】 基于在江苏省、上海市水稻种植区连续实施1—5年的定点优标体系试验区,以常规施肥用药水稻栽培体系(简称常规体系)为对照。采集水稻籽粒和稻田土壤样品,测定稻米产量、委托SGS检测稻米农药残留和重金属含量;采用内梅罗指数法评价土壤肥力;分别采用TTC还原法、靛酚蓝比色法、3,5-二硝基水杨酸比色法测定土壤脱氢酶、脲酶、蔗糖酶活性;利用16S rDNA高通量测序分析土壤微生物多样性。【结果】 采用优标体系较常规体系在氮肥施用量减少46.8%,代以添加有机肥、EM菌剂、叶面肥、锌肥;以生物制剂为核心,协同使用低毒、低残留化学农药,保证了稻米的高安全标准。在保证水稻产量、质量安全的前提下实施优标体系显著提高了土壤全氮与有机质含量;且连续实施1—4年的优标体系土壤肥力综合评分均高于常规体系,但连续实施5年后的优标体系土壤肥力综合评分值低于常规体系。连续实施2年优标体系脲酶、脱氢酶、蔗糖酶的活性均高于常规体系。实施优标体系的稻田土壤细菌群落多样性与丰度提高,优标体系实施1年和连续实施5年的土壤细菌丰富度上升比例重复变化的菌为拟杆菌门(Bacteroidetes)和绿弯菌门(Chloroflexi);优势菌属为Terrimonas(尚无确切名称)和黄杆菌属(Flavobacterium)。相关性分析结果显示,优标体系实施1年,土壤中拟杆菌门、绿弯菌门丰度变化分别与pH肥力指数、全磷肥力指数变化呈正相关;优标体系连续实施5年,土壤中拟杆菌门、绿弯菌门丰度变化均与pH肥力指数变化呈正相关。另外,拟杆菌门、绿弯菌门丰度变化与土壤脱氢酶活性变化呈正相关。【结论】 实施优标体系在保证水稻产量、质量安全的前提下,可有效改善土壤质量,提升土壤细菌群落多样性,进而有助于恢复土壤肥力。 相似文献