Immunoreactivity of fractionated antigens obtained from autoclaved extracts of an arthritogenic isolate of Erysipelothrix rhusiopathiae

The immunoreactive antigens in heat-extracted (autoclaved) preparations of an arthritogenic strain of Erysipelothrix rhusiopathiae (isolate VRS 229, serotype 1a) have been identified by gel diffusion precipitin (GDP) tests and a novel application of the enzyme linked immunosorbent assay (ELISA) procedure. Antigens precipitated by ethanol treatment of autoclaved extracts of this strain were resolved into 4 major peaks (A,B,C and D) after gel permeation chromatography on Sephacryl S200. Peak A was confirmed as a protein peak (Lowry positive) which was excluded from the gel. This peak was identified to be ELISA-reactive when assayed with serum from pigs infected with other isolates corresponding to serotypes 1a, 1b and 2. However, it did not form precipitin lines in GDP tests. Peak B was Lowry-positive and also contained carbohydrates. It was not as reactive in ELISA tests but rapidly formed precipitin lines with serum from pigs infected with the homologous isolate, but only erratically with serums from pigs infected with other serotype 1a and 1b isolates, and not with serotype 2 isolates. Peaks C and D were high in carbohydrate and phosphate content respectively but were both non-reactive in GDP tests and only slightly so by ELISA. Since serotypes 1 and 2 are the most predominant among isolates from infected pigs it is likely that the commonly recognised A antigen is a useful ELISA reagent for the diagnosis of E. rhusiopathiae infection; B antigen on the other hand, would probably be of limited diagnostic value.     

Comparison of inoculation regimes for the experimental production of swine erysipelas arthritis: II Serological findings in a gel diffusion precipitin test and enzyme-linked immunosorbent assay

The serological response of pigs to Erysipelothrix rhusiopathiae inoculation was monitored by a gel diffusion precipitin test (GDPT) using a crude, serotype-specific, autoclaved antigen and an enzyme-linked immunosorbent assay (ELISA) using a heat-extracted, alcohol precipitated and molecular seived antigen previously shown to react with serum from pigs infected with serotypes 1 or 2. All pigs receiving 3 or 5 weekly intravenous inoculations of either a highly virulent (VRS 229) or a lowly virulent isolate (VRS 252) produced GDPT-reactive antibody within 3 weeks, but only 44% were still reactive at 8 to 9.5 weeks. The ELISA response was significantly higher in pigs inoculated with the highly virulent strain, and was similar in pigs receiving 3 or 5 doses of either strain. In a dose-response trial, after 3 doses of VRS 229, GDPT reactivity occurred earlier and was stronger in pigs given higher doses of E. rhusiopathiae, but the response peaked 3 to 5 weeks after the start of challenge and was short lived. GDPT reactivity correlated with dose, but not with the severity of arthritis. The ELISA demonstrated specific IgG antibody was present by 2 weeks, and persisted to at least 11 weeks. The ELISA reactivity was significantly higher in pigs with arthritis than in pigs that received low doses and were not arthritic. Within groups of pigs with arthritis a significant, dose dependent, linear ELISA response developed but did not correlate with the presence or degree of arthritis at slaughter. Non-arthritic pigs had similar low ELISA responses to uninoculated controls.     

Host-mediated interactions between pathogen genotypes

Barley c ltivars with different resistance genes were inoculated with various sequences of virulent and non-virulent isolates of Erysiphe graminis f.sp. hordei. The resistance induced in incompatible reactions decreased infection by virulent isolates while, conversely, the degree of susceptibility induced in compatible reactions was sufficient to increase the ability of normally non-virulent isolates to infect a resistant host. The net effect of interactions was always overall reduction of conidial production when compared with inoculation of a virulent isolate alone.
Each interaction between isolates was dependent on the host cultivar, the pathogen isolates used and on the inoculation sequence. Often, induced resistance was most obvious when a nonvirulent isolate was inoculated prior to a virulent isolate. Induced susceptibility was usually more apparent when the virulent isolate was inoculated first. However, on the cultivar Wing, induced susceptibility was more apparent following prior inoculation of a non-virulent isolate. On the cultivar Hassan, prior inoculation with a virulent isolate sometimes induced susceptibility, but in some cases more susceptibility was induced by prior inoculation with a non-virulent isolate. In the latter instances, although relatively little infection developed, the majority of the spores produced were those of the normally non-virulent isolate.
There was some evidence of non-virulent isolates acquiring the ability to infect normally incompatible hosts. This effect disappeared after several generations in the absence of the virulent isolate.     

Current status of biological control of paddy weeds in Vietnam

Rice is a staple food in Vietnam and accounts for > 7.7 × 10⁶ cultivated ha, which provide 35.5 × 10⁶ t of rice, of which 4.2 × 10⁶ t were exported in 2004. The enlargement of the cropping area and the enhancement of rice yield have rapidly increased the amount of agrochemicals, including herbicides, in crop production in Vietnam. From 1990–2003, the percentage of herbicides in total pesticides has increased ≈ 10-fold to 30.2%. In addition, the improper use of herbicides caused environmental hazards, unsafe agricultural products, and human health problems. Biological management integrated with traditional weed control techniques might help to reduce the dependence on synthetic herbicides and build eco-friendly, sustainable agricultural production in Vietnam. This paper reviews the efforts in establishing a strategy for biological management of weeds that was conducted in recent years by Vietnamese weed scientists. This has included cropping system management, water and soil management, integrated pest management, and utilization of plant allelopathy as major components of the strategy. Many plants with strong allelopathic potential can be a source for biological weed suppression and soil fertility improvement. The utilization of allelopathic properties in rice might also help to provide new rice cultivars with weed-suppressing characteristics.     

Dermal and serological response against Pseudomonas aeruginosa in sheep bred for resistance and susceptibility to fleece-rot

Genetically select lines of Merino sheep have been bred at Trangie (NSW Agriculture and Fisheries) for resistance (R) or susceptibility (S) to fleece-rot and flystrike. It is believed that fleece characters are primarily responsible for the R or S phenotype. When transferred to the wetter coastal environment of Sydney, R and S sheep with no more than 6 weeks wool cover, continued to show significant differences in the incidence and severity of fleece-rot dermatitis. To test the hypothesis that these sheep might also exhibit differences in their local skin reactions and immune responsiveness, 3 intradermal injections of killed Pseudomonas aeruginosa were administered at monthly intervals. After primary intradermal challenge, R sheep had a higher incidence of skin induration and a stronger inflammatory response (increased induration diameter) than S sheep. Compared to S sheep, R sheep also developed higher levels of circulating antibodies against whole cell antigen and both inner and outer membrane proteins of P. aeruginosa. These responses were maintained in R sheep with each consecutive challenge while S sheep showed a decline in their immune responsiveness. Differences in antibody response against outer membrane proteins were also detected when antigenically naive sheep from each genetic line were sensitised by epicutaneous challenge with P. aeruginosa under experimental wetting conditions. Intradermal challenge of these animals 6 months later with outer membrane proteins, revealed a late maximum (72 h) in the development of induration diameters for R sheep while S animals showed maximal induration diameters by 24 h. However, there was no significant difference in induration response between 24 h and 72 h within each group of sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Root exclusion methods for partitioning of soil respiration: Review and methodological considerations

Soil respiration is a vital process in all terrestrial ecosystems, through which the soil releases carbon dioxide (CO₂) into the atmosphere at an estimated annual rate of 68-101 Pg carbon, making it the second highest terrestrial contributor to carbon fluxes. Since soil respiration consists of autotrophic and heterotrophic constituents, methods for accurately determining the contribution of each constituent to the total soil respiration are critical for understanding their differential responses to environmental factors and aiding the reduction of CO₂ emissions. Owing to its low cost and simplicity, the root exclusion (RE) technique, combined with manual chamber measurements, is frequently used in field studies of soil respiration partitioning. Nevertheless, RE treatments alter the soil environment, leading to potential bias in respiration measurements. This review aims to elucidate the current understanding of RE, i.e., trenching (Tr) and deep collar (DC) insertion techniques, by examining soil respiration partitioning studies performed in several ecosystems. Additionally, we discuss methodological considerations when using RE and the combinations of RE with stable isotopic and modeling approaches. Finally, future research directions for improving the Tr and DC insertion methods in RE are suggested.     

Peripheral blood lymphocyte subsets in fleece rot-resistant and -susceptible sheep

Objective To compare haematological values and lymphocyte phenotypes in the peripheral blood of fleece rot-resistant and -susceptible sheep.
Procedure Experiments were conducted on 2- and 3-year-old Merino rams, flock 1 (17 rams) and flock 2 (32 rams), respectively. Within each flock, individual rams were classified as fleece rot-resistant or -susceptible, based on established criteria. Total and differential white cell counts, and indirect fluorescent antibody tests specific for B cells and T cells were performed on all sheep. The concentration of various subsets of circulating lymphocytes was then determined in each sheep.
Results There were no significant differences between fleece rot-resistant and -susceptible sheep from either flock in the mean total or differential white cell counts. However, fleece rot-resistant rams in flock 1 did have a significantly higher concentration of circulating SBU-T1⁺ cells than fleece rot-susceptible rams from the same flock. No such difference was noted in the rams from flock 2. While all rams in flock 1 were free of clinical fleece rot, 24 rams in flock 2 (comprising all 17 fleece rot-susceptible and 7 of 15 fleece rot-resistant animals) had clinical signs of the disease. Fleece rot-free rams in this flock (irrespective of their classification as fleece rot-resistant or -susceptible) had significantly higher concentrations of circulating SBU-T1⁺ cells compared with fleece rot-affected animals. They also had significantly higher concentrations of circulating B cells, and total lymphocytes.
Conclusions An examination of peripheral blood lymphocyte subsets in fleece rot-resistant and -susceptible sheep revealed a possible association between resistance to fleece rot and the concentration of circulating SBU-T1⁺ cells.     

黄瓜枯萎病病株镰孢菌的分离与鉴定

采集来自哈尔滨、长春、沈阳、北京、保定、银川、西宁及杭州等8个地区黄瓜大棚内的43株枯萎病病株,采用常规组织分离法,共分离获得478株镰孢菌。根据形态学鉴定,确定它们属于7种镰孢菌,其中尖孢镰孢菌(Fusarium oxysporum)占77.62%,锐顶镰孢菌(Fusarium acuminatum)占0.21%,木贼镰孢菌(Fusariumequiseti)占3.97%,腐皮镰孢菌(Fusarium solani)占15.48%,半裸镰孢菌(Fusarium semitectum)占1.46%,轮枝镰孢菌(Fusarium verticillioides)占0.84%,以及层出镰孢菌(Fusarium proliferatum)占0.42%。对所有菌株进行致病性测定。结果表明,只有尖孢镰孢菌(Fusarium oxysporum)具有致病性,发病率为71.43%;而其他菌株均未发病,表明其他菌株为非致病菌株。