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排序方式: 共有163条查询结果,搜索用时 15 毫秒
81.
Annelies Vercauteren Isabelle De Dobbelaere Erik Van Bockstaele Martine Maes Kurt Heungens 《European journal of plant pathology / European Foundation for Plant Pathology》2011,129(4):621-635
Phytophthora ramorum, a recently described North American and European pathogen, has three clonal lineages. The NA1 and NA2 lineages are found
in North American forests and nurseries, while the EU1 lineage appears mainly in European nurseries. P. ramorum is heterothallic, having two mating types A1 and A2. All NA1 and NA2 isolates are of A2 mating type. When first collected,
all EU1 isolates were of A1 mating type, with the exception of one A2 isolate collected in Belgium in 2002. Screening 410
other Belgian isolates for mating type revealed two additional EU1-A2 isolates collected in 2002 and 2003. PCR-RFLP, AFLP
and SSR markers were used to determine the nature of the mating type change. The three isolates show no indications of sexual
recombination or mitotic crossing over, indicating that mutation or mitotic gene conversion is the most likely explanation
for the mating type change. We compared the pathogenicity and sporulation characteristics of the EU1-A2 isolates to those
of EU1-A1 and NA1-A2 isolates on four host plants. Despite small differences in pathogenicity on some hosts, the EU1-A2 isolates
were similarly aggressive to each other and to the EU1-A1 isolates and more aggressive than the NA1-A2 isolates. Sporulation
characteristics were also comparable among EU1-A2 isolates and between EU1-A1 and EU1-A2 isolates, except for EU1-A2 isolate
BBA 26/02. The limited genotypic and phenotypic differences between EU1-A2 isolates probably evolved after the mating type
change, which may have occurred several years before the isolates were detected. There are strong indications that the EU1-A2
population has been eradicated from Belgium. 相似文献
82.
83.
The Cost of Off-Flavor 总被引:1,自引:0,他引:1
Carole R. Engle Gayle L. Pounds Martine van der Ploeg 《Journal of the World Aquaculture Society》1995,26(3):297-306
Off-flavor problems in farm-raised catfish Ictalurus punctatus increase production costs and pose inventory management problems for catfish farmers. Multiperiod mathematical programming techniques were used to test the effect of 16 different off-flavor scenarios on expected net returns above variable cost with and without cash flow restrictions. The patterns of off-flavor incidence had less effect on farm profits than whether or not fish are off-flavor during certain key months of the year. To be feasible, systems designed to purge off-flavor from catfish would need to cost less than $0.05 to $0.06/kg (if cash flow is not a consideration) or $0.04/kg to $0.25/ke (with cash flow considerations). 相似文献
84.
Eels (Anguilla anguilla L.) were slaughtered using two procedures. The commercial method consisted of desliming the fish in dry salt followed by evisceration. The alternative method consisted of stunning and killing in water with a combination of electricity and oxygen removal. Eels slaughtered as commercially exhibited aversive reactions and consequently a higher level of muscular activity before death. In raw fillets, differences appeared clearly between the two batches. The alternative slaughter by electricity and gas led to redder, firmer flesh with a higher pH. Myofibrillar proteolysis, lipid oxidation and loss of freshness (as evaluated by K‐value) were reduced. After hot‐smoking, which is a process that greatly modifies the fish flesh properties, differences between batches were less pronounced. However, eels slaughtered by the alternative method were characterized by a higher pH and a redder colour of the dark muscle, a desirable property form a commercial point of view. When assessed by sensory difference tests, appearance seemed to be the only attribute that allowed panellists to discriminate the two batches. Overall, it is concluded that slaughter by electricity and gas improved the quality of raw and smoked eels compared with the commercial method. 相似文献
85.
Tran TQ Quessy S Letellier A Desrosiers A Boulianne M 《Canadian journal of veterinary research》2010,74(3):185-192
The humoral and cell-mediated immune (CMI) response to 2 commercial killed Salmonella Enteritidis (SE) vaccines (Layermune and MBL SE4C) was evaluated in laying hens. Layers were distributed in 2 experimental groups. The first received a single immunization at 16 wk of age, while the second experimental group was immunized at 12 wk of age and again at 18 wk of age. Serum immunoglobulin (Ig)G antibodies were measured using a commercial SE ELISA kit and showed persistent levels from 3 to 32 and 34 wk post-vaccination. The vaccination protocol using 2 immunizations showed a higher seroconversion level than the single vaccination. However, our results for bacterial intracellular survival indicated that IgG titers were not linked with bacterial killing. Local IgA production was measured in the intestines and oviducts with an in-house SE whole cell antigen ELISA. Only the MBL SE4C vaccine elicited IgA antibody production when tested on intestine and oviduct mucosal secretions, 3-weeks post-vaccination in both immunization protocol groups. To evaluate the CMI response, the splenic T-cells and B-cells populations were analyzed using flow cytometry. The CD3/B-cell ratio decreased 3 wk after the second immunization in the twice vaccinated Layermune group due to an increase in B-cells. 相似文献
86.
Comparative analysis of three chemometric techniques for the spectroradiometric assessment of canopy chlorophyll content in winter wheat 总被引:3,自引:0,他引:3
Clement Atzberger Martine Guérif Willy Werner 《Computers and Electronics in Agriculture》2010,73(2):165-173
Hyperspectral data sets contain useful information for characterizing vegetation canopies not previously available from multi-spectral data sources. However, to make full use of the information content one has to find ways for coping with the strong multi-collinearity in the data. The redundancy directly results from the fact that only a few variables effectively control the vegetation signature. This low dimensionality strongly contrasts with the often more than 100 spectral channels provided by modern spectroradiometers and through imaging spectroscopy. With this study we evaluated three different chemometric techniques specifically designed to deal with redundant (and small) data sets. In addition, a widely used 2-band vegetation index was chosen (NDVI) as a baseline approach. A multi-site and multi-date field campaign was conducted to acquire the necessary reference observations. On small subplots the total canopy chlorophyll content was measured and the corresponding canopy signature (450-2500 nm) was recorded (nobs = 42). Using this data set we investigated the predictive power and noise sensitivity of stepwise multiple linear regression (SMLR) and two ‘full spectrum’ methods: principal component regression (PCR) and partial least squares regression (PLSR). The NDVI was fitted to the canopy chlorophyll content using an exponential relation. For all techniques, a jackknife approach was used to obtain cross-validated statistics. The PLSR clearly outperformed all other techniques. PLSR gave a cross-validated RMSE of 51 mg m−2 for canopy chlorophyll contents ranging between 38 and 475 mg m−2 (0.99 ≤ LAI ≤ 8.74 m2 m−2). The lowest accuracy was achieved using PCR (RMSEcv = 82 mg m−2 and ). The NDVI, even using chlorophyll optimized band settings, could not reach the accuracy of PLSR. Regarding the sensitivity to artificially created (white) noise, PCR showed some advantages, whereas SMLR was the most sensitive chemometric technique. For relatively small, highly multi-collinear data sets the use of partial least square regression is recommended. PLSR makes full use of the rich spectral information while being relatively insensitive to sensor noise. PLSR provides a regression model where the entire spectral information is taken - in a weighted form - into account. This method seems therefore much better adapted to deal with potentially confounding factors compared to any 2-band vegetation index which can only avoid the most harmful factor of variation. 相似文献
87.
88.
High population densities of Macrolophus pygmaeus on tomato plants can cause economic fruit damage: interaction with Pepino mosaic virus?
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89.
90.
The need to understand how anthropogenic landscape alteration affects fauna populations has never been more pressing. The
importance of developing an understanding of the processes behind local extinction is widely acknowledged, but inference from
spatial patterns of fauna distribution continues to dominate. However, this approach is limited in its ability to generate
strong predictions about future distributions and local extinctions, especially when population-level responses to landscape
alteration are subject to long time lags. We review the potential for indices of physiological stress and condition to contribute
to understanding of how landscape pattern affects species persistence. Such measures can indicate habitat quality from the
perspective of the individual animal, and can reveal environmental stressors before their negative consequences begin to manifest
at a population level. Spatial patterns of chronic stress may therefore yield valuable insight into how landscape alteration
influences species. We propose that the emerging disciplines of conservation physiology and macrophysiology have much to offer
spatial ecology, and have great potential to reveal the physiological pathways through which habitat alteration affects fauna
populations and their persistence in fragmented landscapes. 相似文献