Characteristics of monoclonal antibodies against Piscirickettsia salmonis

A panel of 28 monoclonal antibodies against Piscirickettsia salmonis was produced using a purified fraction of the bacterium. To determine their specificity to the pathogen, the antibodies were assayed by ELISA and indirect immunofluorescence microscopy. Six monoclonal antibodies were selected based on their strong reaction against P. salmonis and absence of cross-reactivity with other common fish pathogens. Western blot analysis showed that the antibodies reacted to several antigens of P. salmonis . Immunofluorescence assays revealed that these antibodies reacted with the same specificity to different isolates of P. salmonis obtained from the south of Chile. This panel of monoclonal antibodies represents an important tool to develop simple, rapid, sensitive and highly specific methods for the detection of the pathogen and diagnosis of the disease.     

Risk factor analysis for sea lice, Caligus rogercresseyi, levels in farmed salmonids in southern Chile

Sea lice, Caligus rogercresseyi, are ectoparasitic copepods, which severely affect the salmon farming industry in southern Chile, reducing the health status of fish and producing both direct and indirect economic losses. Local farmers have reported increasing infestation levels since 2004, reaching a peak in 2007. In response to this situation, the Chilean Fisheries Service (Sernapesca) developed a surveillance programme; the first step of which consisted of a general survey of salmon farms. This survey included documenting counts of parasite burdens on fish and measurements of several husbandry and environmental factors providing an evaluation of risk factors for the observed infestation levels. The information collected was analysed using a linear mixed model technique, which takes into account the clustered structure of data, decomposing the unexplained variation and assigning it to different aggregation levels of the productive system. Geographical zones, fish species, treatment against sea lice performed 1 month before sampling, stocking density, fish weight and water salinity were the variables significantly associated with sea lice burdens. In contrast, treatments performed 2-3 months before sampling, use of photoperiod in sea cages and water temperature, were not significant. There was significant unexplained variation at all aggregation levels, i.e. sub-zone, fish farm and cage level, with the fish farm level showing the greatest variation.     

Epidemiological description of the sea lice (Caligus rogercresseyi) situation in southern Chile in August 2007

Salmon sea lice represent one of the most important threats to salmon farming throughout the world. Results of private monitoring efforts have shown an increase in the number of positive cages and cage-level abundance of sea lice in southern Chile since 2004. As a consequence, the Chilean Fisheries Service implemented an Official Surveillance Program in the main salmon production area of southern Chile to assess the situation of sea lice in fish farms. Results showed that the prevalence of sea lice in the fish farms was 53.4%, ranging from 3.5% in Puerto Aysén to 100% in the Seno de Reloncaví zone. The average sea lice abundance was 11.8 per fish (Geometrical mean (GM)=8.61, 95% CI (2.1-6.9)). The highest levels were found in Seno de Reloncaví (GM=24.99, 95% CI (15.9-39.2)), Hornopirén (GM=14.7, 95% CI (10.4-20.8)) and Chiloé norte (GM=9.75, 95% CI (1-1.9)), and the lowest loads were observed in Puerto Aysén (GM=1.35, 95%CI (1-1.9)) and Puerto Cisnes (GM=1.67, 95%CI (1.1-2.6)). Salmo salar and Oncorhynchus mykiss had the highest abundance levels (GM=6.93, 95% CI (5.7-8.5), and (GM=5.55, 95% CI (3.6-8.5), respectively). O. kisutch showed lower levels (GM=1.34, 95% CI (1-1.7)), apparently being more resistant to infestation. Sea lice in farmed salmon are widely distributed in different zones of southern Chile, and are becoming a serious threat to this industry. Prevalence and abundance levels were found to be generally high, decreasing in southern zones.     

Bayesian mapping of quantitative trait loci (QTL) controlling soybean cyst nematode resistant

The soybean cyst nematode (SCN) is one of the most economically important pathogens of soybean. Molecular mapping of quantitative trait loci (QTL) for resistance to SCN is a proven useful strategy in order to assist in the development of resistant soybean cultivars. In the present study, a Bayesian modeling approach was performed to map QTL controlling genetic resistance to SCN races 3 and 14. For this purpose, a population of recombinant inbred lines derived from the cross between line Y23 (susceptible) and cv. Hartwig (resistant) was used. A total of 144 microsatellites markers (Simple Sequence Repeats) were selected and synthesized for mapping purpose. Posterior marginal parameter distributions were computed using the Reversible Jump Markov Chain Monte Carlo (RJ-MCMC) algorithm. It was determined the existence of four QTLs on three linkage groups (LG); that is LG A2 for race 3, LG C2 for race 14, and LG G for both races. The estimates of posterior modes of the heritability were 0.038 and 0.53 for the LGs A2 and G respectively (race 3). For the race 14 the posterior modes of the heritability were 0.044 and 0.05 for the LGs C2 and G. The identified QTLs explained about 57 and 9 % of the total phenotypic variance, for the races 3 and 14, respectively. These results confirm the effectiveness of the Bayesian method to map QTL controlling resistance to SCN in soybean. Accordingly, integrating QTL mapping with Bayesian methods will enable response to selection for quantitative traits of interest in soybean to be improved.     

Improved zinc tolerance in Eucalyptus globulus inoculated with Glomus deserticola and Trametes versicolor or Coriolopsis rigida

The potential of interactions between saprophytic and arbuscular mycorrhizal (AM) fungi to improve Eucalyptus globulus grown in soil contaminated with Zn were investigated. The presence of 100 mg kg ⁻¹ Zn decreased the shoot and root dry weight of E. globulus colonized with Glomus deserticola less than in plants not colonized with AM. Zn also decreased the extent of root length colonization by AM and the AM fungus metabolic activity, measured as succinate dehydrogenase (SDH) activity of the fungal mycelium inside the E. globulus root. The saprophytic fungi Trametes versicolor and Coriolopsis rigida increased the shoot dry weight and the tolerance of E. globulus to Zn when these plants were AM-colonized. Both saprophytic fungi increased the percentage of AM root length colonization and elevated G. deserticola SDH activity in the presence of all Zn concentrations applied to the soil. In the presence of 500 and 1000 mg kg⁻¹ Zn, there were higher metal concentrations in roots and shoots of AM than in non-AM plants; furthermore, both saprophytic fungi increased Zn uptake by E. globulus colonized by G. deserticola. The higher root to shoot metal ratio observed in mycorrhizal E. globulus plants indicates that G. deserticola enhanced Zn uptake and accumulation in the root system, playing a filtering/sequestering role in the presence of Zn. However, saprophytic fungi did not increase the root to shoot Zn ratio in mycorrhizal E. globulus plants. The effect of the saprophytic fungi on the tolerance and the accumulation of Zn in E. globulus was mediated by its effect on the colonization and metabolic activity of the AM fungi.     

Are plant cell wall hydrolysing enzymes of saprobe fungi implicated in the biological control of the Verticillium dahliae pathogenesis?

We studied the possibility that the antagonistic saprobe fungi Coriolopsis rigida, Trametes versicolor, Fusarium lateritium, Penicillium chrysogenum and Verticillium dahliae-2379 may control V. dahliae disease through the inhibition of the activity of hydrolytic enzymes produced by the pathogen. These saprobe fungi were able to decrease the growth in vitro of V. dahliae. The exudates produced by these fungi seemed to be the main factor responsible for their antagonistic effect. The exudates of all the fungi tested had endopolymethylgalacturonase, endoglucanase and endoxyloglucanase activities. Exudates of P. chrysogenum and V. dahliae-2379 had higher hydrolytic activities than those of V. dahliae. The saprobe V. dahliae-2379 did not decrease the growth of the pathogen V. dahliae but decreased its harmful effect on the growth of tomato. However, no inhibition of the activities of the hydrolytic enzyme of the pathogenic V. dahliae by the no pathogenic V. dahliae-2379 or by the other saprobe fungi was observed. Nevertheless, the protection of tomato by the five antagonistic saprobe fungi against V. dahliae disease could be carried out by the induction of plant defense by the hydrolytic enzymes produced by these fungi.     

Contribution of Arbuscular Mycorrhizal and Saprobe Fungi to the Aluminum Resistance of Eucalyptus globulus

Aluminum in acidic conditions is toxic to plants. Aluminum tolerance in some plant species has been ascribed to arbuscular mycorrhizal fungal symbiosis. In this study, the application of aluminum was found to inhibit mycelia development of saprobe fungi Fusarium concolor and Trichoderma koningii and the hyphal length of the arbuscular mycorrhizal fungi Glomus mosseae and Glomus deserticola in vitro. Several levels of aluminum were applied to Eucalyptus globulus plants and inoculated with arbuscular mycorrhizal fungi alone or together with both saprobe fungi. The application of 1,500 mg kg^?1 decreased the shoot and root dry weight, chlorophyll content and total P, Mg, and Ca concentrations in the shoot of E. globulus. However, both mycorrhizal fungi G. mosseae and G. deserticola inoculated alone increased the shoot dry weight of Eucalyptus, compared with a non- arbuscular mycorrhizal inoculated control treated with 1,500 mg kg^?1 of aluminum. When 1,500 mg kg^?1 of aluminum was applied, T. koningii increased the effect of G. deserticola on the shoot weight of eucalyptus, whereas with 3,000 mg kg^?1, shoot weight and arbuscular mycorrhizal colonization decreased in all treatments. With 1,500 mg kg^?1, the highest accumulation of aluminum in the shoot was obtained when G. deserticola was inoculated together with T. koningii. The possibility of manipulating an arbuscular mycorrhizal inoculation together with a saprobe fungus confers a high aluminum resistance in E. globulus. The effect of such combined inoculation is particularly important in some Chilean volcanic acid soils, mainly those which have been intensively cropped and are without lime addition, which facilitates the increase of phytotoxic aluminum species and limits their agricultural use. Therefore, such dual inoculation in field conditions deserves further investigation. Overall, the arbuscular mycorrhizal and saprobe fungi contribute to the increase in resistance of E. globulus to aluminium.     

Quantifying key parameters related to the life cycle of Caligus rogercresseyi

The salmon louse Caligus rogercresseyi (Boxshall and Bravo 2000) is a common ectoparasite of farmed salmonids in Chile. Sea lice can negatively impact the growth of hosts, adversely affecting aquaculture productivity. Unlike Lepeophtheirus salmonis (Krøyer, 1838), whose life cycle parameters have been well studied due to its importance in the Northern Hemisphere, for C. rogercresseyi no single source exists that quantifies the parameters required to model this ectoparasite's life cycle. Given that different species of sea lice have substantially different biological characteristics, it is important to parameterize the life cycle of C. rogercresseyi using appropriate observational data, rather than simply trying to adapt parameters developed for L. salmonis. Using data from existing literature, we quantified the development and survival rates for each stage in the C. rogercresseyi life cycle. We illustrate how development rates are affected by water temperature and explore the important impacts of salinity on rates of survival. We present equations that can be used to model development periods and survival proportions given certain water temperature and salinity profiles. While key parameters to quantitatively model the life cycle of C. rogercresseyi are presented, further research is required to adequately model the complete population dynamics of this ectoparasite on Chilean salmon farms and consequently to support decision-making to achieve effective control and mitigation.