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21.
The standard ELISA method for detection of PVY in dormant potato tubers was compared with recently developed methods: (1) a hybridization technique, using a complementary DNA-probe to PVYN; (2) three modifications of ELISA (standard monoclonal, Flegg & Clark polyclonal or monoclonal). Sap of six Dutch cultivars secondarily infected with PVY was subjected to these methods directly after lifting and after six subsequent one-week intervals during storage at 20°C. During storage the detectability of PVY decreased, irrespective of the diagnostic method applied. However, decrease was less in susceptible than in resistant cultivars. Although the hybridization technique yielded slightly better results than the standard ELISA procedure, it was time-consuming and involved hazardous reagents. The modifications of ELISA investigated were not, in general, more sensitive than standard ELISA. 相似文献
22.
While the use of external skeletal fixation was once associated with substantial postoperative morbidity, clinical and experimental studies have led to technological advances and modifications in application techniques that have greatly improved the results obtained with this treatment modality. The past decade saw numerous advances in external skeletal fixator implants, components and instrumentation, including improvements in fixation pin design, and the development of new linear external skeletal fixation systems and economical circular external skeletal fixation systems specifically engineered for use in dogs and cats. In addition, a greater understanding of fixator biomechanics and the pathobiology of the bone-fixation pin interface have improved fixator application practices. This article reviews many of the more significant recent advances in external skeletal fixation. 相似文献
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The epidemic simulator EPIMUL was modified and used to study how induced resistance affected the development of epidemics in host mixtures. In the model, induced resistance resulted from the interaction of host tissue with avirulent spores and caused a reduction in the efficacy of virulent spores deposited afterwards. We denned three parameters to describe induced resistance: the level of protection, defined as the magnitude of reduction in the virulent spore efficacy for infecting host tissue; the host surface area protected by an interaction with one avirulent spore; and the duration of protection of the host tissue, in days. In our simulations, induced resistance slowed the epidemics and gave better disease control in the mixtures, even if protection lasted for only 2 days. The disease reduction in the mixture attributable to induced resistance was approximately proportional to the level of protection. The effect of induced resistance increased as the protected area increased. Epidemics were virtually unaffected by induced resistance restricted to the infection site, but the effect of induced resistance initially increased rapidly as larger areas were protected. There was little further gain as the protected area increased from 2·6% to 26%. The influence of induced resistance was reduced when the interactions between virulent and avirulent pathogens were reduced. 相似文献
25.
Fungi known to produce lytic enzymes were used in an attempt to control wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (FOL). Some of the fungal species (Penicillium oxalicum, Penicillium purpurogenum and Aspergillus nidulans) damaged hyphae of FOL in vitro and reduced the numbers of microconidia in the soil. Treatments with fungi did not result in a reduction in either chlamydospores of FOL in soil or populations of FOL in the rhizosphere of tomato. P. oxalicum was the most effective agent of biocontrol, and it reduced disease severity in both non-autoclaved (20% decrease) and sterile soil. In sterile soil, P. oxalicum reduced disease with different levels of severity (27% decrease at high levels and 50% decrease at low levels). Disease control by A. nidulans and P purpurogenum was only achieved when disease severity was low in sterile soil (55% and 45%, respectively). 相似文献
26.
Ergot disease spread rapidly in Zimbabwe amongst replicated plots of male-sterile sorghum A-lines, from a group of centrally situated and precociously inoculated plants. Prominent secondary conidiation by the pathogen, Claviceps africana , on the surface of exuded honeydew provided airborne spores which were trapped in a Burkard continuous spore trap and showed diurnal peaks of concentration in air close to the primary source of inoculum. The rate of disease spread ( r =0·2; range 0·14–0·58) closely matched that recorded for other plant pathogens such as Phytophthora infestans and Puccinia graminis tritici , and it is concluded that the characteristic secondary conidia of C. africana were the principal epidemiological agents within the experimental area. Ergot spread by windborne secondary conidia has significant epidemiological and economic implications for sorghum hybrid breeding in southern Africa. 相似文献
27.
Racial diversity and complexity in regional populations of Erysiphe graminis f.sp. hordei in France over a 5-year period 总被引:2,自引:3,他引:2
The evolution of race patterns in three French regional populations of the barley powdery mildew pathogen Erysiphe graminis f.sp. hordei over a 5-year period showed rapid adaptation to newly introduced host resistance genes. In all three regions, the main change consisted of the replacement of initially abundant races by pathotypes differing markedly from them by their virulence gene combinations. This explained the increase in diversity during the first 3 years of the survey, when the second group of pathotypes became more common in the populations, and its subsequent decrease due to the decline of the first group of races. The mean number of virulence genes per isolate did not vary noticeably over time in the three populations, remaining at about four out of 12 genes tested. However, the distribution of the isolates into virulence complexity classes was greatly modified, fitting a binomial distribution by the end of the study, although significant deviations were apparent in the first 2 years (1986 and 1987). The data indicate that selection, migration and recombination are the most important factors shaping race structure and evolution in powdery mildew populations, and that mutation is of limited significance. No convincing evidence was obtained for the existence of stabilizing selection sensu Vanderplank as the mechanism limiting virulence complexity. Implications regarding spatial and temporal deployment of race-specific resistance genes to control powdery mildew are discussed. 相似文献
28.
Although the basic function of T and B lymphocytes in ferrets has been known for some time, the function of mononuclear phagocytes has not been described in this species. The present study has characterised basic oxidative responses in ferret macrophages, and has investigated the effects of endogenous and exogenous modulators of macrophage function on oxidative capacity in vitro. Macrophages derived from the blood or lungs of ferrets were shown capable of generating the reactive oxygen intermediate (ROI) molecules superoxide and hydrogen peroxide, and secreting a lysosomal enzyme (acid phosphatase), in response to appropriate stimuli. A T cell supernatant (derived from mitogen-stimulated peripheral blood lymphocytes) was able to activate both blood- and lung-derived macrophages for enhanced ROI production, while specific ROI inhibitors (superoxide dismutase and catalase) were able to partially ablate ROI activity. The accumulation of nitrite in culture supernatants, as an indicator for the production of reactive nitrogen intermediates, could not be demonstrated by ferret macrophages derived from either tissue source. In contrast to the enhancing effects of TCS on the oxidative function of blood-derived macrophages, exposure to bacterial LPS caused marked suppression of ROI and lysosomal enzyme production by these cells. Finally, the generation of superoxide anion, following phagocytosis of live or heat-killed Mycobacterium bovis or zymosan, indicated that ROI production in response to phagocytic stimulation was relatively weak in ferret blood-derived macrophages. These results are discussed in relation to the study of immune function in a novel species, and with particular reference to research into tuberculosis (Tb), since ferrets are important wildlife vectors of bovine Tb in New Zealand. 相似文献
29.
Candida albicans infection of the forestomachs of a calf 总被引:1,自引:0,他引:1
R F Cross P D Moorhead J E Jones 《Journal of the American Veterinary Medical Association》1970,157(10):1325-1330
30.