Absence of three known benzimidazole resistance mutations in Trichostrongylus tenuis, a nematode parasite of avian hosts

Benzimidazole (BZ) resistance is widespread in nematode parasites of livestock, but very little is known about the levels of BZ resistance in parasites with avian hosts. We investigated BZ resistance in Trichostrongylus tenuis, a nematode parasite of red grouse, Lagopus lagopus scotica. BZ anthelmintics had been in use in this system for up to 15 years, yet existing phenotypic evidence for resistance was inconclusive. We screened 1530 individuals from 14 populations at the principal β-tubulin locus for BZ resistance (isotype 1, residue 200) and 940 of these at two further resistance sites (isotype 1, residue 167; isotype 2, residue 200). No BZ resistant genotypes were found. Alternative mechanisms may be responsible for BZ resistance in this system, or the method and timing of treatments may reduce selection pressure for BZ resistance by creating substantial refugia for susceptible genotypes.     

Tolerance of Senecio vulgaris to Infection and Disease Caused by Native and Alien Rust Fungi

ABSTRACT Plant defense strategies against pathogen attack can be divided into either resistance or tolerance. Variation in tolerance is expressed as differences in the relationship between host fitness (or yield) and the degree of infection. Plant tolerance of pathogen attack remains poorly understood both in terms of its specific mechanisms and in terms of the evolutionary processes by which it has arisen. Theoretical models predict that it is the result of coevolution between host and pathogen, suggesting greater tolerance in interactions with native as opposed to introduced pathogens. Therefore, we quantified and compared the degree of tolerance expressed in the interaction of Senecio vulgaris with the rust fungus Coleosporium tussilginis, which is native to the UK, and the introduced rust fungus Puccinia lagenophorae. We used the reaction norm approach to quantify tolerance and its components. The S. vulgaris-C. tussilaginis interaction expressed a significantly greater degree of tolerance, as reductions in host growth and fitness per unit infection were significantly less than with P. lagenophorae. The key mechanism for this greater tolerance to C. tussilaginis was a significantly smaller reduction in photosynthesis per unit infection than with P. lagenophorae, at both leaf and whole plant scales. There was no significant difference in the relationship between whole plant photosynthesis and host reproduction. We discuss these responses in the context of coevolution for tolerance in host-pathogen interactions.     

Mediation of partial resistance to rice blast through anaerobic induction of ethylene

ABSTRACT The correlation between anaerobic soil conditions and increased resistance to rice blast disease has long been observed without benefit of an adequate explanation. We researched flood depth, dissolved oxygen (DO), and ethylene relative to expression of partial blast resistance in cvs. M-201, Newbonnet, LaGrue, Mars, and Cypress. Cultivar blast index (BI) and flood DO decreased with increasing flood depth. BIs were positively correlated with DO. Total leaf blast lesions were 3.4 and 3.2 times greater in cvs. M-201 and LaGrue growing in a 5.0-mul liter(-1) DO nutrient solution than when growing in a 0.1-mul liter(-1) DO solution. Treatment with 0.25 mM ethephon, which releases ethylene, lowered BIs of Newbonnet, LaGrue, and Cypress growing upland when applied drench, foliar, or foliar-drench. If flooded, BIs of ethephon-treated cultivars were decreased by drench and foliar-drench applications only. BIs of upland plants were unchanged, whereas BIs of analogous flooded plants increased following treatment with 0.31 mM aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor. We hypothesize that varying anaerobic conditions mediate production of phytohormones, particularly ethylene, which modify expression of inherent partial blast resistance in these rice cultivars.     

Evanescent-wave biosensor for field serodiagnosis of tortoise mycoplasmosis

Disease has become an increasingly important issue for wildlife management over the past two decades. Adequate surveillance is fundamental for disease prevention and control, thus there is an increasing need for diagnostic assays for wildlife management. The objective of this study was to evaluate the performance of a field-portable biosensor adapted for rapid detection of specific antibodies in tortoise plasma that reflect a history of exposure to Mycoplasma agassizii, which is an agent of tortoise upper respiratory tract disease. Banked plasma samples were tested in two blinded trials, and the parameters that define the reliability of a diagnostic test were estimated based on externally validated tortoise plasma controls. The mean sensitivity of the biosensor (ability to identify exposed tortoises in the group of all exposed individuals) was 78%; the mean specificity (unexposed individuals with negative test result, out of all unexposed individuals tested) was 73%; the mean positive predictive value (exposed individuals with positive test, out of all individuals with positive test) was 82%; the mean negative predictive value (unexposed individuals with negative test, out of all individuals with negative test) was 68%. In a 15-min field-portable format, the biosensor was able to discriminate between true seropositive (n=34) and true seronegative (n=23) tortoise plasma with overall accuracy of 84%. The goals established for the tortoise population can help managers decide whether potential diagnostic errors should impact management decision-making, and whether the benefits of the field-portable format of the biosensor assay outweigh any potential disadvantages.     

Spatiotemporal Description of Epidemics Caused by Phoma ligulicola in Tasmanian Pyrethrum Fields

ABSTRACT Spatial and temporal patterns of foliar disease caused by Phoma ligulicola were quantified in naturally occurring epidemics in Tasmanian pyrethrum fields. Disease assessments (defoliation incidence, defoliation severity, incidence of stems with ray blight, and incidence of flowers with ray blight) were performed four times each year in 2002 and 2003. Spatial analyses based on distribution fitting, runs analysis, and spatial analysis by distance indices (SADIE) demonstrated aggregation in fields approaching their first harvest for all assessment times between September and December. In second-year harvest fields, however, the incidence of stems with ray blight was random for the first and last samplings, but aggregated between these times. Spatiotemporal analyses were conducted between the same disease intensity measures at subsequent assessment times with the association function of SADIE. In first-year harvest fields, the presence of steep spatial gradients was suggested, most likely from dispersal of conidia from foci within the field. The importance of exogenous inoculum sources, such as wind-dispersed ascospores, was suggested by the absence of significant association between defoliation intensity (incidence and severity) and incidence of stems with ray blight in second-year harvest fields. The logistic model provided the best temporal fit to the increase in defoliation severity in each of six first-year harvest fields in 2003. The logistic model also provided the best fit for the incidence of stems with ray blight and the incidence of flowers with ray blight in four of six and three of six fields, respectively, whereas the Gompertz model provided the best fit in the remaining fields. Fungicides applied prior to mid-October (early spring) significantly reduced the area under disease progress curve (P < 0.001) for defoliation severity, the incidence of stems with ray blight, and the incidence of flowers with ray blight for epidemics at all field locations. This study provides information concerning the epidemiology of foliar disease and ray blight epidemics in pyrethrum and offers insight on how to best manage these diseases.