Elm (Ulmus sp.) shoots from in vitro micropropagated plants were tested with Ophiostoma ulmi culture filtrates, at different dilutions to determine the susceptibility of different host clones to Dutch elm disease (DED). ‘Commelin’, a susceptible Dutch hybrid, showed a high wilting index but that of American elm was higher. Although U. pumila × japonica (Sapporo gold 2) was the most tolerant to spore inoculation, its wilting index was as high as that of ‘Commelin’. The absorption capacity and wilting index of the elm shoots showed consistent correlation to isolate effectiveness (as determined by inoculation experiments), to production of toxin (cerato-ulmin) and to filtrate dilution. This method could be used to assess the effectiveness of the different O. ulmi isolates and for the detection of elm genotypes that are highly susceptible to Dutch elm disease. 相似文献
Data of the 1997–1998 epidemic of classical swine fever (CSF) in The Netherlands were analysed in survival analysis to identify risk factors that were associated with the rate of neighbourhood infections. The study population consisted of herds within 1000 m of exclusively one previously infected herd. Dates of virus introduction into herds were drawn randomly from estimated probability distributions per herd of possible weeks of virus introduction. (To confirm the insensitivity of the results for this random data-selection procedure, the procedure was repeated 9 times (resulting in 10 different datasets).) The dataset had 906 non-infected and 59 infected neighbour herds, which were distributed over 215 different neighbourhoods. Neighbour herds that never became infected were right-censored at the last date of the infectious period of the infected source herd. Neighbour herds that became empty within the infectious period or within the following 21 days due to preventive depopulation or due to the implemented buying-out programme were right-censored 21 days before the moment of becoming empty. This was done as a correction for the time a herd could be infected without being noticed as such.
The median time to identified infection of neighbour herds was 2 weeks, whereas the median time to right censoring of non-infected neighbour herds was 3 weeks. The risk factors, radial distance ≤500 m, cattle present on source herd and increasing herd size of the neighbour herd were associated multivariably with the hazard for neighbour herds to become infected. We did not find an association between time down wind and infection risk for neighbour herds. Radial dispersion of CSFV seemed more important in neighbourhood infections than dispersion along the road on which the infected source herd is situated. The results of this study support the strategy of preventive depopulation in the neighbourhood of an infected herd. Recommendations are presented to adapt the applied control strategy for neighbourhood infections. 相似文献
Summary A study of Ctenocephalides fells strongylus and of its effect on the performance of sheep and goats was made. Fleas showed more affinity for sheep than goats. There was a high concentration between lamb and kid mortality and the degree of flea infestation. The clinical effects of flea infestation are highlighted. The factors responsible for flea infestation and its control are discussed. 相似文献
Abstract Variation in budburst, height increment and growth cessation within and among five Norwegian Ulmus glabra (Huds.) populations was recorded in an experimental trial during the fourth and fifth growing seasons. Budburst occurred first in inland populations and last in coastal populations, and latitude of origin was less important for timing of budburst than distance from the coast. Height increment and date of growth cessation were correlated to latitude, height increment decreased with increasing latitude of origin, whereas growth cessation occurred first in northern populations and later with increasing southern origin. Thus, the phenological traits vary in accordance with the climate from where the populations have been derived. There was a general large within-population variation in phenological traits. The results are discussed in relation to conservation of adaptive trait variation of the species. 相似文献
Ophiostoma novo‐ulmi, the cause of the current pandemic of Dutch elm disease, is considered one of the 20 worst pests to have been introduced to New Zealand. An attempt to eradicate the pathogen came close to success, but was eventually stopped and replaced by management programmes. These programmes are slowing the spread of the pathogen. If left uncontrolled it is likely that New Zealand will lose 90% of its elm trees. Although elms are exotic trees in New Zealand, the loss of such a large number of popular amenity trees is likely to have numerous social, cultural, environmental and economic effects. It is estimated that this disease could cost public and councils over NZD $350 million in tree removal and replacement costs. Control of O. novo‐ulmi is limited, but biological control using d‐factor viruses has been proposed. Although O. novo‐ulmi was not eradicated from New Zealand, the eradication programme had many successes; in particular, the effective interaction of good management and science in the early years of the campaign. Also highlighted in this review are several tactics and steps that could be applied to eradication attempts for other species. 相似文献
Background, Aim and Scope
Faced with higher peak discharges in the foreseeable future, the Dutch government has decided to increase the discharge capacities
of the Dutch Rhine and Meuse rivers. Instead of raising the dikes, river widening measures are to be undertaken, in and along
the riverbed. Such measures include surface level lowering along the rivers, channel deepening, the addition of high-discharge
channels and the removal of hydraulic obstacles. To cover or reduce the costs of river widening, a coupling with aggregates
(sand and/or gravel) extraction has been considered. Although the rationale of this concept is basically sound, it has met
with considerable resistance, especially along the southernmost stretch of the Dutch Meuse River, in the Maaswerken project
area.
Main Features:
The Dutch river widening projects are quite unique in size and occurrence, and the number of publicly documented case histories
available for the planning of such works is inevitably few. We review the planning and decision-making process for the Maaswerken
project, which is in a more advanced stage than that of the corresponding project for the Rhine. Sediment handling and aggregates
extraction are focused on, which are key issues to this case.
Results:
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Discussion:
In the study area, there is a conflict of interests between the extractive industry and the local communities. The industry
faces a policy of phasing out mineral extraction; river widening presents the last significant prospects in the area. The
general public, however, has come to resent mineral extraction because of its historical impacts. Aiming at a manageable process,
the Maaswerken project management kept most stakeholders in a basically reactive position: the general public was kept informed
and enabled to submit formal reactions to draft planning decisions. Aggregate extraction plans and extraction volumes were
only discussed with the industry. Despite not being represented, the public influenced this negotiation process by expressing
dissatisfaction with interim outcomes through the media and political channels. Plans had to be reconsidered, and this closed
process turned out to be only seemingly efficient.
Conclusions:
The level of public concern regarding the Maaswerken project suggests that the overall level of stakeholder involvement may
have been insufficient, even though it complied with pertinent environmental and planning legislation. A participation deficit
seems to have mainly occurred when defining the project's preconditions: a predefined, controversial role for the extractive
industry was implicit in self-financed river widening. As planning and decision making in large projects such as the Maaswerken
are prone to be affected by a negative public opinion, it is recommended that social feasibility is assessed and addressed
at the very outset.
Perspectives:
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During the 1970s Europe was invaded by two subspecies of the Dutch elm disease pathogen Ophiostoma novo-ulmi : subsp . americana from the west and subsp. novo-ulmi from the east. As a result their geographic ranges began to overlap in several areas. Only a weak prezygotic barrier to hybridization exists between the subspecies and in 1980 two hybrids were detected in the Netherlands. A subset of 107 O. novo-ulmi isolates collected in a subspecies overlap zone in Limburg, Netherlands in 1983 was characterized for three phenotypic markers and seven RAPD PCR markers. By phenotype, 33% were shown to be hybrid whereas by RAPD markers 69% were shown to be hybrid. Some isolates shown to be hybrid by phenotype were not revealed to be hybrid by PCR and vice versa. Combining the phenotype and RAPD data the estimated hybrid frequency was ∼78%. The mean growth rate of Limburg hybrid isolates was significantly faster than that of the Limburg subsp. novo-ulmi isolates but not significantly different from Limburg subsp. americana isolates. The Limburg hybrid isolates were just as pathogenic as the parent subspecies on both clonal Ulmus procera and on U. × Commelin. A subset of 100 isolates collected in another subspecies overlap zone at Orvieto, Italy in 1986 was also assessed with RAPD markers and ∼ 72% were shown to be hybrids. When 20 isolates of a 'pure' subsp. novo-ulmi population in the Baltic Ports area of Poland collected in 1980 were assessed by RAPD markers three isolates exhibited early introgression of subsp. americana DNA. This study therefore demonstrates very rapid emergence of O. novo-ulmi subspecies hybrids and introgressants in Europe in the early 1980s. In terms of two major fitness characters, growth rate and pathogenicity, these early hybrids were as fit as their parent subspecies. It is likely that complex hybrid swarms are now expanding across the continent. 相似文献
The ability of isolate Vd-48 of Verticillium dahliae to induce resistance against subsequent challenge with Ophiostoma novo-ulmi was examined in Ulmus minor . In the first experiment, conditioning inoculation of 5-year-old elm trees (2–3 m in height) with Vd-48 15 days prior to challenge inoculation with O. novo-ulmi significantly reduced wilting ( P ≤ 0·05) compared with trees not conditioned with Vd-48. However, in another experiment on 6-year-old trees (2–3·5 m in height), no protection was achieved when the length of time between conditioning and challenge inoculations was 45 or 60 days. In a further experiment, inoculations with Vd-48 alone resulted in severe wilting in 22 out of 118 trees (6–10 years old and 4–7 m in height). Across the 2 years of this last trial, nine trees showed massive feeding wounds made by Scolytus sp., while O. novo-ulmi strains were isolated from six trees. Vd-48 provided a variable prophylactic effect against O. novo-ulmi in U. minor . Major difficulties with this approach to control Dutch elm disease are discussed. 相似文献