Potato diseases caused by soft rot erwinias: an overview of pathogenesis

Three soft rot erwinias, Erwinia carotovora ssp. carotovora , E. carotovora ssp. atroseptica and E. chrysanthemi are associated with potatoes causing tuber soft rot and blackleg (stem rot). Latent infection of tubers and stems is widespread. As opportunistic pathogens, the bacteria tend to cause disease when potato resistance is impaired. Pathogenesis or disease development in potato tubers and stems is discussed in terms of the interaction between pathogen, host and environment, microbial competition and recent findings on the molecular basis of pathogenicity. Emphasis is placed on the role of free water and anaerobiosis in weakening tuber resistance and in providing nutrient for erwinias to multiply. Blackleg symptoms are expressed when erwinias predominate in rotting mother tubers, invade the stems and multiply in xylem vessels under favourable weather conditions. Soft rot erwinias tend to out-compete other bacteria in tuber rots because of their ability to produce larger quantities of a wider range of cell wall-degrading enzymes. However, despite extensive studies on their induction, regulation and secretion, little is known about the precise role of the different enzymes in pathogenesis. The putative role of quorum-sensing regulation of these enzymes in disease development is evaluated. The role certain pathogenicity-related characters, including motility, adhesion, siderophores, detoxifying systems and the hrp gene complex, common to most bacteria including symbionts and saprophytes, could play in latent and active infections is also discussed.     

腐败组织中毒鼠磷的GC／NPD、GC／ECD检验

本文初步建立了一套混合溶剂提取、中性层析氧化铝小柱净化及GC／ECD和GC／NPD分析的腐败生物样材中毒鼠磷的检验方法。GC／ECD的检出限为1ng;GC/NPD的检出限为20ng。     

十种常用农药与球孢白僵菌的生物学相容性

球孢白僵菌孢子粉与10种常用农药相容性的测定结果显示,随着孢子浓度上升,所试农药对孢子的抑制作用均有不同程度的增强。在1/10田间常规使用浓度下,百菌清和代森锰锌均能抑制或杀死孢子(萌发率<1％)。除阿维菌素外,所有杀虫剂均与白僵菌孢子相容,在常规使用浓度的10倍稀释液中孢子萌发率达90％以上。吡虫啉、蚜虱灵、灭多威和氟虫腈与孢子的相容性最好,其中吡虫啉和蚜虱灵对孢子萌发率的影响不明显随药剂浓度的变化而变化,即使在田间常规使用浓度下孢子萌发率也在95％以上,而阿维菌素与白僵菌的相容性极差。因此,应用白僵菌制剂防治害虫,选择生物学相容性好的农药以低剂量与白僵菌制剂混用,既可使菌剂增效,又可大幅度降低化学药剂用量。     

特种脱水蔬菜研究进展

综述了国内外特种脱水蔬菜的生产状况和趋势，特种脱水蔬菜的加工技术，特种脱水蔬菜生产成果及展望。     

Key issues and research priorities in landscape ecology: An idiosyncratic synthesis

Landscape ecology has made tremendous progress in recent decades, but as a rapidly developing discipline it is faced with new problems and challenges. To identify the key issues and research priorities in landscape ecology, a special session entitled “Top 10 List for Landscape Ecology in the 21st Century” was organized at the 16th Annual Symposium of the US Regional Association of International Association of Landscape Ecology, held at Arizona State University (Tempe, Arizona, USA) during April 25–29, 2001. A group of leading landscape ecologists were invited to present their views. This paper is intended to be a synthesis, but not necessarily a consensus, of the special session. We have organized the diverse and wide-ranging perspectives into six general key issues and 10 priority research topics. The key issues are: (1) interdisciplinarity or transdisciplinarity, (2) integration between basic research and applications,(3) Conceptual and theoretical development, (4) education and training, (5)international scholarly communication and collaborations, and (6) outreach and communication with the public and decision makers. The top 10 research topics are: (1) ecological flows in landscape mosaics, (2) causes, processes, and consequences of land use and land cover change, (3) nonlinear dynamics and landscape complexity, (4) scaling, (5) methodological development, (6) relating landscape metrics to ecological processes, (7) integrating humans and their activities into landscape ecology, (8) optimization of landscape pattern, (9)landscape sustainability, and (10) data acquisition and accuracy assessment. We emphasize that, although this synthesis was based on the presentations at the“Top 10 List” session, it is not a document that has been agreed upon by each and every participant. Rather, we believe that it is reflective of the broad-scale vision of the collective as to where landscape ecology is now and where it may be going in future. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal distribution of phytoplasmas in Australian grapevines

The distribution and persistence of phytoplasmas were determined in Australian grapevines. Phytoplasmas could be detected using the polymerase chain reaction (PCR) from shoots, cordons, trunks and roots throughout the year, and phytoplasmas appear to persistently infect Australian grapevines from year to year. Phytoplasmas were not always detected in samples from the same sampling area from one sampling period to the next. Phytoplasma detection by PCR was improved by sampling from shoots, cordons and trunks, especially during October (early spring). The diseases expressed by the 20 grapevines used in the distribution and persistence studies were monitored. Australian grapevine yellows disease (AGY) was expressed by 17/20 grapevines at some time during the study, whilst only 4/20 and 15/20 grapevines expressed restricted growth disease (RG) and late season leaf curl disease (LSLC), respectively. All grapevines with RG and LSLC also had AGY. The three diseases were persistently expressed in some grapevines and remission of disease was observed in others. The results of PCR detection in the same grapevines indicated that phytoplasmas were more frequently detected in AGY-affected grapevines that also expressed RG and LSLC compared with grapevines expressing AGY alone. Phytoplasmas were detected in symptomless plant material but less frequently compared with AGY-affected material.     

旱地(土娄)土长期定位施肥土壤剖面硝态氮分布与累积研究

通过12a大田长期定位试验研究了在自然降水条件、冬小麦—大豆轮作(或休闲)种植制度下,0～400cm土娄土剖面硝态氮分布与积累的特点。结果表明,长期单施氮肥,氮的表观利用率特别低,仅0.51%,氮肥配施钾、磷肥,氮的表观利用率为25%～35%,氮磷钾平衡施肥及配施有机肥,氮的表观利用率达到50%;施N肥方式显著影响土壤硝态氮积累和淋移,旱地土娄土长期单施化学氮肥或氮钾、氮磷、氮磷钾肥使土壤NO-3-N大量积累和淋移;氮磷钾与有机肥的配合施用能有效地缓解土壤对硝态氮的积累,提高氮肥利用率。     

江河源区草地资源现状及其可持续发展

在分析青海省江河源区草地资源现状的基础上，进一步剖析了造成该区域草地生态环境恶化的综合因素，提出了合理利用和保护天然草地，优化草地生产结构，加强基础设施建设，建立饲草料生产基地，遏制草地退化，使草地生态进入良性演替，实现江河源区草地资源可持续利用和草地畜牧业可持续发展的对策。     

日粮中添加柑桔皮粉对产蛋后期蛋鸡钙磷代谢的影响

将 48周龄黄金褐蛋鸡 10只随机分成两组 ,对照组喂基础日粮 ,试验组用 2 5 %的柑桔皮粉等量替代基础日粮中的玉米 ,结果表明 :试验组钙磷表观代谢率为 65 79%、46 3 9% ,钙比对照组 (62 3 0 % )提高了 3 49个百分点 (P <0 0 5 ) ,磷比对照组 (4 7 5 2 % )降低了 1 13个百分点 (P >0 0 5 )。     

国内外养羊业发展特点与趋势

当前肉羊业在大洋洲、美洲、欧洲和一些非洲国家得到迅猛发展，世界羊肉，特别是羔羊肉的生产和消费显著增长。肉羊产业具有周转快、投资少、效益高等特点，已成为我国在资源短缺、畜禽产品需求日益增加的背景下，保持畜牧业可持续发展的重要途径之一。本文还仔细分析我国肉羊生产存在的不足和发展的优势，并结合国内外养羊业发展的趋势提出了及时调整养羊业的生产方向和产品结构，研究和推广先进实用的养羊综合配套技术等发展我国养羊业的建议。