Ecologie des champignons parasites dans le sol—IX. Mesures du potentiel infectieux des sols naturellement infestes de Pythium SP

The technique of estimating inoculum potential of soils infested by Pythium (Bouhot 1975a,b,c) has been applied to more than 600 soil samples. 24 examples of soils, representing the several kinds of results, are presented. In order to improve the linearity of the inoculum density-disease regression, the four mathematical transformations of disease percentages, proposed by Baker (1971), are compared: logarithm of disease percentages, successful infection transformation (LN I/I — ×), log-log and Probit-log. For 80–90% of observed soils the log-log and Probit-log transformations give a straight regression line and allow the differentiation of soils by the use of UPI₅₀ (LD 50 point). The Probit-log appears to be the best to reduce the variance of replications. On the contrary for some soils the inoculum-disease relation is a concave curve different from the ideal curve proposed by Baker. The hypothesis of competition between saprophytic colonization of Pythium and of soil microflora is proposed as an explanation and suggests the opportunity to find a new model for the techniques using plants as bait and organic amendment.     

番茄晚疫病及其抗病育种研究

本文综述了国内外对番茄晚疫病菌特征特性、生理小种以及番茄抗晚疫病机制、抗性遗传规律、抗病育种等方面的研究进展,并对当前生产和研究中存在的问题和今后研究方向进行讨论。     

Mise au point sur l'incidence du virus Yo et méthodes de lutte mises en oeuvre en France pour la production de semences de pommes de terre

Summary Potato seed health status is currently at a high level in the three main seed growing regions in France (Table 1). PVY is the most common virus and a recent survey showed that 80% of infected samples were with the Y⁰ type whereas only 12% were with the Yⁿ type. However, the health status had not always been as good: from 1973 to 1976, an epidemic by PVY affected all crops with the maximum infection incidence occurring in 1976 (Table 2, Fig. 1) while at the same time leafroll infection became less common. Since 1977 the situation has been improving (Table 3) and the lowest level of infection was recorded in 1981. However, since 1971 PVY has remained the predominant virus (Table 4). The 1974–1976 epidemic could have been caused by the transmission of PVY by aphid species other than those of potatoes, for exampleRhopalosiphum padi which developed large populations in May and June in 1974, 1975 and 1976 following particularly mild winters (Fig. 1) favourable to their survival. This high level of infection by PVY occurred in Europe in general and it has been shown that previous control strategies based on the monitoring of only the potato aphids should be modified to take into account these new findings. The basic rules for producing healthy seed have been for a long time clonal production of healthy nuclear material, early roguing of infected plants and early haulm kill within a traditional lineal selection system. The more recent micropropagation technique has been used since 1977 in Brittany and ELISA testing is now routine. Since about 10 years, systematic use of mineral oils has helped to reduce greatly the spread of PVY and a forecast method against virus spread and advice to growers have been developed. At the same time, breeding for resistance has been carried out and highly resistant cultivars should soon be on the approved list of French cultivars. Selection for resistance to infection which can manifest itself at more or less high levels after one or more growing seasons in regions favourable to infection (Table 5) has also been the object of important time-consuming research. In conclusion, rapid progress in the under-standing of PVY epidemiology has been made during the last 10 years and has allowed the development of forecasting models which will be evaluated in the future.

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Zusammenfassung Der Gesundheitszustand der Saatkartoffeln in den drei Hauptanbaugebieten Frankreichs ist gegenw?rtig sehr gut (Tab. 1). Das PVY ist das meist verbreitete Virus. Eine jüngere Untersuchung hat ergeben, dass PVY^o in ungef?hr 80% der Proben vorkommt gegen nur 12% für PVYⁿ. Dieser Gesundheitszustand war jedoch nicht immer so gut: von 1973 bis 1976, hat sich eine PVY-Epidemie über alle Kulturen ausgebreitet, mit einem Maximum an Befall in 1976 (Tab. 2, Abb. 1), in der gleichen Zeit wurde das Blattrollvirus eher seltener. Seit 1977 hat sich die Lage bedeutend verbessert mit einem Minimum an Befall in 1981 (Tab. 3). Seit 1976 hat PVY immer dominiert (Tab. 4). Die Epidemie der Jahren 1974–76 konnte erkl?rt werden mit der PVY-übertragung durch nicht Kartoffelblattl?use, wie zum BeispielRhopalosiphum padi welcher in den Jahren 1974, 1975 und 1976 nach den milden Winter auftrat (Abb. 1), was die überlebensrate der Populationen erh?hte und massive Flüge in Mai und Juni erreichte. Dieser hohe PVY-Befallsgrad war generell in Europa und erbrachte somit den Beweis, dass die überwachungsstrategie welche nur die Kartoffelblattl?use in Betracht nahm verbessert werden musste, mit der Berücksichtigung dieser neuen Erkenntnissen. Seit langer Zeit bezieht sich das Grundprinzip der Saatgutproduktion auf den Freilandtest, Anbau von gesundem Material, frühe S?uberung der kranken Pflanzen, sowie das frühe Krautabt?ten im Rahmen einer klassischen Erhaltungszucht. Die jüngere Technik der Mikrovermehrung wird seit 1977 in der Bretagne angewendet und das ELISA-Verfahren gilt jetzt als Routine Test. Die seit zehn Jahren betriebene systematische Mineral?lbehandlung hat wirksam dazu beigetragen die Verbreitung des PVY zu bek?mpfen und es wurde ein Prognosesystem der Virusinfektionrisiken und eine Entscheidungsberatung der Produzenten ausgearbeitet. Parallel dazu wird geforscht um PVY-resistente Sorten zu züchten. Sorten mit sehr hoher Resistenz sollten n?chstens in die franz?sische Sortenliste eingetragen werden. Die Resistenz-Züchtung, welche sich durch einen mehr oder weniger hohen Prozentsatz Virusbefall nach einem oder mehrj?hrigen Anbau in einer günstigen Lage für die Virusübertragung ergibt, ist auch ein wichtiges langzeitiges Forschungsobjekt (Tab. 5). So haben unsere Erkenntnisse über die PVY^o-Epidemiologie sehr rasche Fortschritte w?hrend den 10 letzten Jahren gemacht. Es wurde uns auch m?glich Prognose-Modelle aufzustellen, deren Wirksamkeit in der n?chsten Jahren geprüft werden muss.

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Cette contribution a été présentée lors de la réunion de la Section Virologie tenue à Cambridge du 15 au 19 Septembre 1986.     

Grazing management for more resilient mixed livestock farming systems on native grasslands of southern South America

Droughts in southern South America affect grazing systems in many ways. They reduce biomass productivity; decrease livestock feed intake, weight and reproductive performance; increase farmers’ costs; and reduce farm income. It was hypothesized that simple grazing management variables affect the resilience of grazing systems to droughts at the paddock and farm scales. The effects of grazing management on herbage and animal production were assessed at paddock level, and how technological and structural variables relate to the production and economic performances at farm level. Results of a grazing experiment controlling herbage allowance at paddock level showed that resistance of herbage accumulation and animal live weight to drought was significantly higher for paddocks with higher pre‐drought herbage allowance than for those managed to low herbage allowance treatments. A strong positive linear relationship was found between pre‐drought herbage height and resistance of herbage accumulation rate (p < .01). In a longitudinal study of nine farms in Uruguay, resistance of cow pregnancy rate to drought was positively correlated with cow pregnancy rate (r = .72, p = .02) and farm net income (r = .78, p = .02), and negatively correlated with sheep‐to‐cattle ratio (r = ?.80, p = .01). These correlations suggest that farms with higher incomes and low proportions of sheep in the herd withstand drought better (in terms of pregnancy rate). Four common regional production strategies were identified that react differently when farmers face drought, and these results can aid farmers in those regions to design more resilient mixed livestock farming systems and can inform policymakers about effective strategies for mitigating drought impacts in the region.     

Biochemical and functional characterization of lymphocytes from a horse with lymphosarcoma and IgM deficiency

Neoplastic lymphocytes from a horse with lymphosarcoma and IgM deficiency were analyzed for ability to grow in culture; surface and cytoplasmic IgM; functional activity in blastogenesis, cytoxicity, and suppressor assays; and activities of six enzymes involved in purine and pyrimidine metabolism. The cells lacked surface and cytoplasmic IgM. They had elevated activity of adenosine deaminase and reduced activity of purine nucleoside phosphorylase. Neoplastic cells were nonresponsive in blastogenesis assay and did not kill allogeneic lymphocyte target cells or YAC-1 targets in a lectin-dependent cytotoxicity assay, however, the cells were active in a suppressor assay. They were grown for 16 weeks in cultures supplemented with interleukin 2, during which time the cells retained suppressive activity. These results are consistent with a T cell lymphoma of suppressor cell origin, and may explain the deficiency of IgM observed in some horses with lymphoreticular neoplasms.     

Some properties of beta toxin produced by Clostridium haemolyticum strain IRP-135

Six culture media were evaluated for the optimization of β-toxin production by Clostridium haemolyticum (strain IRP-135) using both batch and dialysis culture techniques. The lethal component of β-toxin remained active for 13 days when maintained at 37°C but was inactivated by heating at 60° for 20 min. A 1 : 10,000 dilution of trypsin inactivated the toxin in 15 min. Preliminary data from electrophoresis in SDS acrylamide gel indicate the molecular weight of the β-toxin to be approximately 32,000.     

Cell-mediated immunity in the dog in relation to disease: A review

Canine cell-mediated immunity and its in vitro testing is reviewed. Lymphocyte stimulation tests and the leukocyte migration inhibition test are discussed as corollaries of in vivo cell-mediated immunity. Cloning of progenitor populations, characterization of cell surface markers and DL-A typing for studies of canine immunity are also reviewed.     

德摩根拓扑代数的R0,R1分离公理

引进德摩根拓扑代数的Ｒ０，Ｒ１分离公理，证明了Ｒ０，Ｒ１的遗传性和可乘性并建立了Ｒ０，Ｒ１与Ｔ０，Ｔ１，Ｔ２之间的关系。     

Use of remote sensing tools to predict focal areas for sea turtle conservation in the south-western Atlantic

1. Fisheries bycatch of non-target species in the commercial fleet is a major source of anthropogenic injury and mortality for sea turtles and marine megafauna.
2. The Río de la Plata maritime front (RLPMF) and its adjacent international waters – comprising part of the Argentine and Uruguayan exclusive economic zones, is a highly important fishing ground in the south-western Atlantic Ocean as well as feeding and development grounds for sea turtles.
3. This paper analyses the distribution of the bottom and pelagic trawling fishery within the RLPMF using information from Vessel Satellite Monitoring System. With this information, areas of highest trawling intensity were defined and further evaluated their overlap with sea turtle habitat-use areas from available sea turtle satellite tracking information.
4. Results besides identifying high-susceptibility areas for sea turtle bycatch by the commercial trawler fleet along the RLPMF, provide predictive tools to identify vulnerable areas to interaction of sea turtles and the commercial fishing fleet.
5. Implementation of bycatch mitigation measures, such as reduced fishing effort areas by the Argentine and Uruguayan fisheries management agencies has the potential to benefit the fisheries as well as marine megafauna. Furthermore, there is a need for additional research on the impact that this fleet can have on sea turtles present in the area.

     

Effects of pseudorabies virus infection upon cytotoxicity and antiviral activities of porcine alveolar macrophages

Alveolar macrophages (AM) infected with Pseudorabies virus (PRV) were compared to noninfected AM for cytotoxicity against foreign or transformed cells and production of interferon (IFN). Five PRV strains were used to infect AM including strains that are known to be highly virulent for pigs, i.e. strain 4892 and strain S-62 as well as strains that are regarded as mild or nonvirulent, i.e. BUK and Bartha. The multiplicity of infection ranged from 0.005 to 0.05 TCID₅₀/cell. The target cells in the cytotoxicity assays were either chicken red blood cells, PRV-infected vero cells, or human myeloblastoma cells (K562 cell line). For the producton of IFN, AM cultures were treated with polyinosinic: polycytidylic acid (Poly I:C) diluted in tissue culture media at a concentration of 5 μg/10⁶ cells. Culture supernatants were collected at various times poststimulation and tested for antiviral activity using the Vesicular Stomatitis Virus replication inhibition test. Swine AM were able to lyse chicken red blood cells in an antibody-independent way but not in an antibody-dependent way, whereas lysis of PRV-infected vero cells was accomplished both ways. The cytotoxicity against chicken red blood cells was reduced in the PRV-infected AM as compared to noninfected cells, particularly in AM infected with virulent PRV strains. Specific ⁵¹Cr release values for AM infected with S-62 and 4892 strains were 14 and 19, while the noninfected AM had values of 36. Similarly, in the antibody-dependent cytotoxicity assay against PRV-infected vero cells there was no activity of AM against K562 cells. The production of IFN was readily stimulated with Poly I:C. The optimal time for supernatant collection was between 12 and 16h poststimulation. The antiviral activity was abrogated by treatment of the supernatant with antiserum against human leukocyte IFN; it was therefore considered to be due to interferon-alpha (IFN) released from the macrophages. The antiviral activity present in supernatants of PRV-infected AM was reduced compared to noninfected AM. The difference between AM cultures infected with virulent strains of PRV and noninfected AM cultures was statistically significant at P 0.025. The results provide support to the premise that the role of AM in lung defense can be compromised by PRV infection.