A new virus disease of watercress in England1     

J. A. WALSH  C. M. CLAY  A. MILLER 《EPPO Bulletin》1989,19(3):463-470

In 1983 plants showing symptoms typical of watercress chlorotic leafspot agent (WCLSA) were found in Kent (GB). Later, plants showing similar symptoms were found in Dorset (1986) and Hampshire (1987), the main watercress-producing regions of England. These plants, unlike those infected with WCLSA, contained virus particles which were isometric with diameters of 37-38 nm. An antiserum to the virus was produced, with a titre in immunodiffusion tests of 1/128 and this gave good results in immunosorbent electron microscopy (ISEM) and ELISA tests on crude plant sap. Purified preparations of the virus reacted positively in ISEM and immunodiffusion tests with an antiserum to watercress yellow spot virus, a partially described virus occurring in France. Tests suggest that the crook root fungus Spongospora subterranea f.sp. nasturtii is probably the vector of this virus but other means of transmission cannot be excluded. Virus incidence within watercress beds varied, with little or no infection in the water inlet region of the bed where there are also low levels of crook root infection, higher levels in the central region and highest levels at the outlet region where crook root infection is also highest.  相似文献   

Screening for Sclerotinia resistance in Helianthus tuberosus L. (Jerusalem artichoke) varieties, lines and somaclones, in the field and in vitro     

A. C. CASSELLS  M. WALSH 《Plant pathology》1995,44(3):428-437

Yields in large-scale 'continuous' cultivation of H. tuberosus (Jerusalem artichoke) can be greatly reduced by Sclerotinia sclerotiorum , which causes a basal stem and tuber rot. In 34 varieties/lines of H. tuberosus from European, Russian and Canadian breeding programmes, responses to the pathogen varied from field resistance to 34% stem rot, cultivars Nahodka and Columbia showing c. 25% stem rot after three seasons of cultivation on the same site. Attempts to develop an in-vitro selection for S. sclerotiorum resistance based on culture of H. tuberosus nodes on media precolonized with Sclerotina were unsuccessful. There was a strong positive correlation between capacity of nodes to grow in vitro on calcium-free medium and field resistance. Somaclones of'Nahodka' selected on the latter basis showed no field infection when grown on land that was heavily contaminated with the pathogen, and they were resistant to artificial inoculation with the pathogen.  相似文献   

大型灯泡贯流式泵站振动研究概述     

王新  李同春  塔娜 《中国农村水利水电》2009,(2):83-85

机组和泵房的振动是泵站运行中最为常见的问题，直接影响泵站的安全可靠运行。对大型灯泡贯流式泵站振动研究现状和抗振安全评价计算分析方法作了详细的介绍，对研究机组振动诱发泵房振动的共振校核法、拟静力法、谐响应求解法和瞬态动力时程法等进行了阐述，并对这几种方法进行了分析比较，就其存在的问题作了总结概述。  相似文献   

Tumbleweeds in the Western Australian cropping system: seed dispersal characteristics of Salsola australis     

C P D BORGER  M WALSH  J K SCOTT†  & S B POWLES 《Weed Research》2007,47(5):406-414

Salsola australis, like other agricultural weed species of the Salsola genus, produces a mobile seedbank. Aspects of this mobile seedbank were investigated in three field trials, including total seed production, rate of seed shedding, rate at which seeds lose germinability and the distance and directionality of plant movement. Total seed production was highly variable (ranging from 138 to 7734 seeds per plant), but was directly related to aboveground plant biomass at maturity. Following senescence, mature plants broke free of their root system and the wind driven plants moved considerable distances (1.6–1247.2 m). Half of the mobile plants moved <100 m, as they became entangled with other S. australis plants within the stand. Seed shedding commenced before the plants became mobile and increased with movement, but was also related to the aging and weathering processes experienced by stationary or mobile plants. All plants retained a proportion of their seed in spite of movement, weathering and ageing of the plants, although germinability of retained seed dropped to <2% after 2 months. Salsola australis engages in broad scale seed dispersal similar to that observed in other species of the Salsola genus, allowing this species to maintain a high rate of invasion and range expansion.  相似文献   

The Influence of Soil Type and Pine Species on the Carabid Community of a Plantation Forest with a History of Pine Beauty Moth Infestation     

WALSH  P. J.; DAY  K. R.; LEATHER  S. R.; SMITH  A. 《Forestry》1993,66(2):135-146

The community composition of Carabid beetles, some species ofwhich are known predators of pine beauty moth, was examinedwithin a Scottish plantation forest. Sites differing in soiltype and the species of trees planted were sampled with pitfalltraps in most weeks of a 3—year period. There were faunaldifferences between sites with lodgepole pine on deep peat andother sites in the study (lodgepole pine on iron-pan soil, speciesmixture of lodgepole and Scots pine, and pure stands of Scotspine). In general deep peat sites supported fewer species andindividuals of carabids. Three Carabus species were implicatedas likely predators of Panolis flammea pupae and each was lessabundant on the sites with lodgepole pine. It is suggested thatthe susceptibility to pine beauty moth of lodgepole pine growingon deep peat substrates is at least partly attributable to impoverishedpredator faunas.  相似文献   

Evaluation of cholesterol additions to a soyabean meal-based diet for juvenile Pacific white shrimp, Penaeus vannamei (Boone), in an outdoor growth trial     

E.O. DUERR  W.A. WALSH 《Aquaculture Nutrition》1996,2(2):111-116

Cholesterol is considered a required nutrient for penaeid shrimps, but an optimal level has not been defined. A 68-day grow-out trial was conducted in 1300-L outdoor tanks in Hawaii, USA, to determine the cholesterol level required in a soyabean meal-based diet for juvenile Pacific white shrimp, Penaeus vannamei (Boone). Test feeds were prepared by adding six cholesterol levels (1.0-10.2 g kg^?1, as-fed basis) to a standard diet high in plant-protein meals, starch and flour. These feeds were provided to the shrimp three times daily. Harvest weights and weekly growth increments varied significantly among diets. The 2.3 g kg^?1 and 4.2 g kg^?1 cholesterol diets yielded better growth than the 1.0 g kg^?1 and 10.2 g kg^?1 diets. Survival and feed conversion ratios did not vary significantly among diets. Significant dietary cholesterol effects on growth of P. vannamei in conditions resembling commercial grow-out indicate that its inclusion in practical diets at more accurately defined levels is necessary. Optimal cholesterol levels for juvenile shrimp may be lower than those now utilized, and may vary relative to the contribution of free sterols from natural foods in shrimp ponds.  相似文献   

几种甘蓝型油菜幼苗抗旱性特征的比较研究     

关周博  田建华  胡银岗  李少钦  董育红  郑磊  韦世豪  塔娜  王学芳  张文学  李殿荣 《上海交通大学学报(农业科学版)》2014,21(5):46-51

以EV1、EV2、EV3、EV4、EV5、EV66个抗旱性不同的油菜品种为试验材料,通过不同浓度PEG-6000渗透溶液模拟干旱胁迫处理,研究油菜幼苗的抗旱指数、根长、苗高和根冠比等性状变化,探索在大田环境条件下的苗期生长特征。结果表明,水分胁迫下EV2的抗旱指数最大,EV6的抗旱指数最小;不同浓度PEG胁迫下,各品种差异显著, EV1、EV2、和EV3的根长、苗高和根冠比较大,而EV5和EV6的表现较差。在大田油菜五叶期时,EV2的冠层覆盖面积最大,与其它品种之间存在极显著性差异;总生物量以EV2、EV3和EV1较大,根系干重以EV2较大,而且三者之间存在显著相关性;与抗旱指数进行通径分析,冠层覆盖面积对抗旱性的直接通径系数最大,达到0.5975。冠层覆盖面积的大小反映了早期活力的强弱,早期活力强,相应的品种抗旱指数高,抗旱性强。  相似文献   

Effect of increasing the banking of a racetrack on the occurrence of injury and lameness in Standardbred horses     

DL EVANS  JS WALSH RJ 《Australian veterinary journal》1997,75(10):751-752

  相似文献   

Dicoumarol toxicity in cattle associated with ingestion of silage containing sweet vernal grass (Anthoxanthum odoratum)     

DJ RUNCIMAN  AM LEE  KFM REED  JR WALSH 《Australian veterinary journal》2002,80(1):28-32

A diagnosis of dicoumarol toxicity in a herd of Friesian cattle was made following investigation of the deaths of three mature cows and eleven yearling heifers. Affected stock had been fed wrapped, bailed silage containing approximately 90% sweet vernal grass ( Anthoxanthum odoratum ). Sweet vernal grass contains coumarin, which can be converted to dicoumarol, a vitamin K antagonist, through the action of moulds. Most deaths were preceded by lethargy, severe anaemia and subcutaneous and internal haemorrhage. Dicoumarol toxicosis was suspected based on clinical signs, necropsy findings and prolonged prothrombin and activated partial thromboplastin times. Dicoumarol analysis of blood from affected animals and silage confirmed the diagnosis.  相似文献   

Agglomeration and Competition among Chinese Cities: An Investigation of Taiwanese High‐Tech Foreign Direct Investment     

KENG‐HSIANG CHENG  YU‐CHING CHIAO  HSIN‐YU SHIH  TAI‐YU LEE  TA‐SHUN CHO 《Growth and change》2011,42(4):517-548

The purpose of this study was to investigate how Taiwanese high‐tech firms' foreign direct investment (FDI) leads to agglomeration and competition among cities in China. By using social network analysis to analyze 1,111 subsidiaries affiliated with 270 multinational corporations (MNCs) during the years between 1988 and 2006 in 30 major Chinese cities, this study finds that: 1) agglomeration in Chinese cities falls into three primary categories: the hub cluster, the communication‐extended cluster, and the computer‐extended cluster. Among the aforementioned clusters, the hub cluster is the most critical in terms of firm location, and therefore is often a high‐priority investment site for Taiwanese high‐tech firms. 2) Chinese cities fall into four primary groups, or “blocks”: the core block, the coast block, the inland block, and the periphery block; these groups were determined by applying a structural equivalence analysis of which members of each type are in competition with one another. By linking the findings of the urban network characteristics to Chinese regional economic policies, this study provides guidance to aid executives in determining the optimal location for future FDI. Implications and suggestions for host country governments in terms of firms' investment strategies are also discussed.  相似文献