栉孔扇贝大规模死亡致病病原的研究

对2000-2002年山东沿海6个疫区患病栉孔扇贝进行电镜观察，在消化腺、外套膜、肾和肠的结缔组织细胞和间质细胞中发现一种球形病毒．并引起相直的病理学变化。该病毒具囊膜，直径为130～170nm，核衣壳直径为90～140nm。病毒分离纯化后．观察到的病毒囊膜表面覆有长20nm的纤突。病毒在细胞质中的囊泡样结构内完成装配，其内未发现包涵体存在。从发病疫区栉孔扇贝组织中分离出病毒毒种对键康扇贝进行人工感染。结果显示，各感染实验组发病扇贝表现出与自然海区发病扇贝相同的临床症状。病毒注射组死r二率为?5％，病毒浸浴组死亡率为68．7％．灭活病毒注射组和空白对照组死亡率皆为12．5％。病毒注射、浸浴组与灭活病毒注射组、空白对照组死亡率差异显著。电镜复检结果显示，各感染实验组发病扇贝组织中分布有大量病毒粒子，与自然海区发病扇贝组织所观察到的病毒粒子在形态特征和病理学特征上完全一致。以上结果证明，病毒是导致栉孔扇贝大规模死亡的直接病原。     

Can placement of seed away from relic stubble limit Rhizoctonia root rot in direct-seeded wheat?

Rhizoctonia root rot of wheat can be a problem in no-till systems, especially during the transition from conventional tillage. There are no effective chemical controls or resistant varieties, leaving only cultural methods to manage this disease. In a no-till system, residue and inoculum of soilborne pathogens are not moved by cultivation, therefore the inoculum may be concentrated in the seeding row of the previous year. Using GPS tracking systems with sub-meter accuracy, the seeding row could be placed away from the row of the previous year. We tested the hypothesis that seeding away from the relic row may reduce Rhizoctonia root rot. In two field experiments, plants were sampled at three distances from the seed row, as well as from fumigated plots. Intact soil cores were also removed from the field, planted with seeds at various distances from the previous row, and grown in the greenhouse under controlled conditions. Pasteurized cores served as controls. Disease levels were higher in the field in the second year, but there was no consistent effect of seed row placement on disease or plant parameters. However, soil fumigation and pasteurization had significant effects, indicating that soilborne pathogens were active. Inoculum of Rhizoctonia is not produced in the crowns and lower stems of the plant, but the pathogen survives in living and dead roots of the previous year crop, volunteers, and grassy weeds. Thus, high inoculum densities may be present in between the relic rows, as well as within the rows. If this is the situation with Rhizoctonia, precision placement of seed rows would not be efficacious.     

Impact of weather variables and season on sporulation of Phytophthora pluvialis and Phytophthora kernoviae

Phytophthora pluvialis and Phytophthora kernoviae are the causal agents of important needle diseases on Pinus radiata in New Zealand. Little is known about the epidemiology of the diseases, making the development of control strategies challenging. To investigate the seasonality and climatic drivers of sporulation, inoculum traps, consisting of pine fascicles floating on water in plastic containers, were exchanged fortnightly at five sites in P. radiata plantations between February 2012 and December 2014. Sections of needle baits were plated onto selective media and growth of Phytophthora pluvialis and P. kernoviae recorded. To explore the generalizability of these data, they were compared to detection data for both pathogens from the New Zealand Forest Health Database (NZFHDB). Further, equivalent analyses on infection of Rhododendron ponticum by P. kernoviae in Cornwall, UK allowed the comparison of the epidemiology of P. kernoviae across different host systems and environments. In New Zealand, inoculum of P. pluvialis and P. kernoviae was detected between January–December and March–November, respectively. Inoculum of both species peaked in abundance in late winter. The probability of detecting P. pluvialis and P. kernoviae was greater at lower temperatures, while the probability of detecting P. pluvialis also increased during periods of wet weather. Similar patterns were observed in NZFHDB data. However, the seasonal pattern of infection by P. kernoviae in the UK was the opposite of that seen for sporulation in New Zealand. Phytophthora kernoviae was likely limited by warmer and drier summers in New Zealand, but by colder winter weather in the UK. These results emphasize the importance of considering both environmental drivers and thresholds in improving our understanding of pathogen epidemiology.     

RT-PCR法克隆广谱抗病基因TGA2及其蛋白表达载体构建

本试验采用Trizol Reagent提取拟南芥总RNA,设计相关引物,采用反转录PCR方法克隆TGA2转录因子;利用酶切连接方法,将该基因正向导入蛋白表达载体.经过相关检验,TGA2转录因子连接到pMXB10载体内含肽(Intein)的N端,成功构建包含TGA2转录因子的pMXB10-TGA2蛋白表达载体.     

Control of Phytophthora cryptogea in the hydroponic forcing of witloof chicory with the rhamnolipid-based biosurfactant formulation PRO1

Rhamnolipids, extracellular metabolites of Pseudomonas aeruginosa with surfactant properties, proved to be very effective in controlling the spread of brown root rot disease caused by Phytophthora cryptogea in the hydroponic forcing system of witloof chicory ( Cichorium intybus var. foliosum ). The biosurfactant was applied as the product PRO1, a formulation of 25% rhamnolipids in oil. Both an in vitro screening and in vivo experiments in a mini-hydroponic system demonstrated the ability of PRO1 to control brown root rot. A 25  µ g mL⁻¹ rhamnolipids nutrient solution was enough to obtain good control of an artificial infection with a zoospore suspension of P. cryptogea . The biosurfactant PRO1 performed well in a semicommercial system under growers' conditions. A treatment of 25  µ g mL⁻¹ rhamnolipids (100  µ g mL⁻¹ PRO1) reduced the disease incidence significantly in two independent experiments. However, PRO1 was not effective when a mycelial suspension was used as inoculum. Rhamnolipids have good potential to limit the spread of P. cryptogea in the hydroponic forcing system of witloof chicory, and can be used as a preventive measure against brown root rot.     

Relation between cropping frequency of peas and other legumes and foot and root rot in peas

The relation between the frequency of legume crops in a rotation and the root rot severity in pea was examined in a field survey. Additionally, greenhouse experiments were performed with soil samples from legume rotation trials or from farmers' fields. The frequency of pea crops in current rotations proved to be much less than the recommended value of one in six years. The correlation between pea root rot and the number of years that pea or other legumes were not grown on the field under consideration (called crop interval) was weak. Root rot severity correlated better with the frequency of peas or legumes in general over a period of 18 years, but the frequency still explained only a minor fraction of the variation in disease index. Some experimental data pointed to the occurrence of a highly specific pathogen microflora with continuous cropping of only one legume species, but this phenomenon probably does not occur in farmers' fields. In field samples, root disease index for pea correlated well with that for field bean. The survival of resting structures of pathogens such asAphanomyces euteiches probably explains why the frequency of legume cropping has a higher impact than crop interval on root disease incidence. Pea-free periods and legume frequencies have a poor predictive value for crop management purposes.     

Evaluation of the API 50CH and API ZYM systems for rapid characterization of Clavibacter michiganensis subsp. sepedonicus, causal agent of potato ring rot

API 50CH and API ZYM systems were used to characterize fifty-three strains of Clavibacter michiganensis subsp. sepedonicus from different geographic locations and several reference strains of the same and different species, including other potato pathogens. Clavibacter michiganensis subsp. sepedonicus strains displayed a high level of homogeneity, both in carbohydrate utilization and in enzymatic activity. Using API 50CH and API ZYM it was possible to differentiate C. michiganensis subsp. sepedonicus strains from the remaining taxa analysed in this study, which included representative strains of the other subspecies of C. michiganensis as well as other bacterial pathogens affecting potatoes. Therefore, these systems could be used as an effective method to characterize C. michiganensis subsp. sepedonicus. Such a procedure would constitute an alternative system to the conventional nutritional and physiological identification tests currently included in the official methods employed in the European Union to detect and identify this bacterium. The results obtained with the API systems agreed with the current taxonomic classification of C. michiganensis, clearly separating sepedonicus from the other subspecies belonging to this species.     

Top 20 environmental weeds for classical biological control in Europe: a review of opportunities, regulations and other barriers to adoption

Classical biological control remains the only tool available for permanent ecological and economic management of invasive alien species that flourish through absence of their co‐evolved natural enemies. As such, this approach is recognized as a key tool for alien species management by the Convention on Biological Diversity (CBD), the European and Mediterranean Plant Protection Organization (EPPO) and the European Strategy on Invasive Alien Species (ESIAS). Successful classical biological control programmes abound around the world, despite disproportionate attention being given to occasional and predictable non‐target impacts. Despite more than 130 case histories in Europe against insect pests, no exotic classical biological control agent has been released in the EU against an alien invasive weed. This dearth has occurred in the face of increasing numbers of exotic invasive plants being imported and taking over National Parks, forests and amenity areas in this region, as well as a global increase in the use of classical biological control around the world. This paper reviews potential European weed targets for classical biological control from ecological and socioeconomic perspectives using the criteria of historical biological control success, taxonomic isolation from European native flora, likely availability of biological control agents, invasiveness outside Europe and value to primary industry and horticulture (potential for conflicts of interest). We also review why classical biological control of European exotic plants remains untested, considering problems of funding and public perception. Finally, we consider the regulatory framework that surrounds such biological control activities within constituent countries of the EU to suggest how this approach may be adopted in the future for managing invasive exotic weeds in Europe.     

Introductions of non-native plant pathogens into Great Britain, 1970–2004

An analysis of records of plant pathogens first identified in Great Britain from 1970 to 2004 (inclusive) was undertaken to determine the numbers of new species that have become established over time. Results show that the numbers of newly recorded pathogens have not varied significantly. Of the 234 pathogens recorded for the first time between 1970 and 2004, 157 were fungi, 27 were oomycetes, 26 were viruses, 23 were bacteria, and one was a phytoplasma. Approximately 53% of pathogens were found on ornamental crops, 16% on horticultural crops, 15% on wild native species, 12% on agricultural crops, 2% on pasture plants and 2% on exotic forestry tree species. Where the origin of introductions was known or strongly suspected, 47% came from the Netherlands. About 38% of newly recorded pathogens with information on the location of first record were discovered in the South East region of England. Plant Pathologists regarded 19% of all new pathogens as important because of actual or potential economic/environmental losses. The results indicate that the numbers of new or important pathogens establishing in recent years are not increasing and that most new findings are associated with ornamental plants.     

Effects of three esca-associated fungi on Vitis vinifera L.: V. Changes in the chemical and biological profile of xylem sap from diseased cv. Sangiovese vines

A vineyard of Vitis vinifera cv. Sangiovese was surveyed for incidence of esca and xylem sap collection. Sap samples were collected from healthy vines and from those with dual infection by Phaeomoniella chlamydospora (Pch) and Togninia minima (Tmi) or triple infection by Pch, Tmi and Fomitiporia mediterranea (Fme), during each early spring in a 3-year period (2001–2003). In order to analyse the possible trends in the climatic data, temperature and rainfall were assessed. At sap harvesting, aliquots of sap were assayed for phytotoxicity and extracted with ethyl acetate for phytotoxin recovery. Moreover, the exopolysaccharide (EPS) content was evaluated on several sap samples during the bleeding period. Conidia of Pch and Tmi, mycelium of Fme and their secondary metabolites were found in the sap of the esca-affected vines, indicating that the pathogens and their by-products together with some defence substances were accumulated and then translocated. Bioactivity tests showed toxicity of the sap from esca-affected vines to healthy detached leaves of cv. Sangiovese. The daily amount of sap, the pH, and the volume (J_v) and solute (J_s) fluxes were analysed as a function of the infecting fungi. Pullulan, glucogalactomannan(s) and arabinogalactan(s) are the main EPS in the esca-infected vines, whereas in the sap of healthy vines no traces of pullulan were found. Scytalone and isosclerone usually produced in vitro by Pch and Tmi were also detected in the sap of vines infected by Pch and Tmi or by Pch, Tmi and Fme. The endogenous phytohormone content of healthy vines evaluated by the cutting bioassay was different from that of infected vines. Four phenolics belonging to three classes e.g., benzoic acid derivatives, stilbenes and flavonol-glycosides were separated and identified by HPLC.