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排序方式: 共有101条查询结果,搜索用时 9 毫秒
1.
Brian N. Hogg Keith Stokes Min B. Rayamajhi John Geiger Paul D. Pratt 《Weed Research》2020,60(3):212-220
Schinus terebinthifolia is a dioecious tree native to South America that has become an invasive weed in Florida, southern California, southern Arizona, Texas and Hawaii and has been naturalised in over 20 countries. Biological control is considered a viable long-term control option for S. terebinthifolia because release from natural enemies appears to be at least partly responsible for its success in Florida. We examined leaf phenology of S. terebinthifolia over a period of 15 months at five sites in central and southern Florida to provide information that may help in predicting the impacts of potential biocontrol agents for this weed. We documented leaf lifespan, the seasonality of leaf development and abscission and the survivorship of leaves that emerged during either spring, summer or autumn. Average leaf lifespan was >4.5 months at all sites, and leaf phenology followed the seasons closely. Although S. terebinthifolia possesses leaves throughout the year, leaf production was greatest from April to September, and most leaves were abscised in February and March. Spring- and summer-emerging leaves were also longer-lived than leaves produced during autumn. These results suggest that leaves of S. terebinthifolia would be most vulnerable to herbivory during the spring and summer months when newly growing leaf tissue is most plentiful. Biocontrol agents capable of damaging these tissues during spring/summer might be an effective means of controlling this invasive weed. 相似文献
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Three groups (n = 147) of New Zealand mixed breed lambs averaging 170 d of age and 31.7 kg in weight were killed after a diet of pasture to determine whether the total depth of soft tissues over the 12th rib 11 cm from the dorsal midline (GR) could be measured in live lambs with sufficient accuracy to warrant its use as a selection tool for breeding flock replacements. Relationships among live and carcass measurements and carcass chemical composition also were determined. An ultrasonic measurement of GR in the live lambs was a more accurate predictor of carcass GR (r = .87) and percentage carcass fat (r = .80) than was a measurement of GR made with a needle (r = .80 and .67, respectively). Both measurements were sufficiently accurate to permit culling of over-fat lambs from breeding flock replacement prospects. The best single indicator of percentage carcass fat (r = .87) was a shoulder fat measurement, followed closely by carcass GR (r = .85). Both were superior to USDA yield grade for estimating carcass chemical composition in these young, lightweight lambs. These two measurements also were most highly related to percentage carcass protein (r = -.78 and r = -.77, respectively). These results indicate possibilities for improving the method of evaluating the composition of U. S. lamb carcasses. 相似文献
4.
Oliveira CM Silva Ferreira AC Guedes De Pinho P Hogg TA 《Journal of agricultural and food chemistry》2002,50(7):2121-2124
This work describes a new potentiometric method to evaluate the resistance to oxidation of white wines. Reduction and oxidation titrations were made, and coefficient of variation obtained were 10.87 and 2.65%, respectively. The antioxidant powers of ascorbic acid (Aas) and sulfur dioxide (SO(2)) were evaluated by this method, SO(2) proving to be much less active in this respect than ascorbic acid. The two agents did not demonstrate any antioxidant synergy. A relationship between oxygen present and ascorbic acid was found by the proposed method (1 mmol of O(2) <--> 0.84 mmol of Aas). This method enables the distinction of different wines on the basis of their resistance to oxidation. 相似文献
5.
Short-term power spectra of the fluctuations in the precipitable water vapor measured with a dual-channel microwave radiometer are presented. The spectra, taken over 34-hour sampling periods, encompass periodicities from I day to about 10 minutes. The fluctuation power is associated with the average precipitable water vapor for the sampling period. The background noise spectrum of the radiometric instrument is also discussed. 相似文献
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"Tubules-Within-a-Tubule" Hierarchical Order of Mesoporous Molecular Sieves in MCM-41 总被引:1,自引:0,他引:1
The recently discovered mesoporous aluminosilicate MCM-41 consists of hexagonal arrays of nanometer-sized cylindrical pores. It is shown that this material can be synthesized by cooperative condensation of silicate and cylindrical cationic micelles. Careful control of the surfactant-water content and the rate of condensation of silica at high alkalinity resulted in hollow tubules 0.3 to 3 micrometers in diameter. The wall of the tubules consisted of coaxial cylindrical pores, nanometers in size, that are characteristic of those of MCM-41. The formation of this higher order structure may take place through a liquid crystal phase transformation mechanism involving an anisotropic membrane-to-tubule phase change. The hierarchical organization of this "tubules-within-a-tubule" particle texture is similar to that of the frustules of marine diatoms. 相似文献
8.
Chemical and microbial properties of the forest floor were measured in 4-year-old shelterwood treatment plots in the montane coastal western hemlock biogeoclimatic zone of British Columbia, Canada, and compared to those in adjacent old-growth and 4-year-old clearcut plots. Forest floor pH, exchangeable Mg, total C and total N concentrations were similar in all three treatments. Bray-extractable P was significantly lower in humus from shelterwood plots, exchangeable Ca was significantly lower in humus from clearcut plots, and exchangeable K was significantly higher in humus from old-growth plots. Indices of available C (basal respiration rate, microbial biomass and metabolic quotient) were significantly higher in old-growth plots than in the two harvested treatment plots. The relative increase in maximum microbial metabolic rate due to the addition of organic nutrients was significantly greater in clearcut plots. Principal component analysis (PCA) ordination of humus samples based on C source utilization patterns of microbial communities (i.e., Biolog assay) showed distinctive clustering by treatment, although indices of substrate richness, evenness and diversity were the same in all three treatments. The relative utilization rates of substrates with the highest factor loadings on PCA axes 1 and 2 were dissimilar in each treatment. We conclude that forest floors can develop under shelterwood harvested stands to exhibit chemical and microbial properties atypical of either clearcut or old-growth plots. 相似文献
9.
John M. Martin Andrew C. Hogg Petrea Hofer Frank A. Manthey Michael J. Giroux 《Cereal Chemistry》2014,91(2):176-182
A small increase in amylose content may impact end‐product quality of wheat. The effect of elevated amylose content in durum wheat is not known. We surveyed 255 durum wheat accessions and found two genotypes that lacked the SGP‐A1 protein. These genotypes were crossed to Mountrail, an adapted durum genotype, to create populations segregating for the SSIIa‐Ab null allele. Our goal was to determine the influence of allelic variation at the SSIIa‐A locus on semolina properties and end‐product quality with noodles as a test product. Amylose content increased 3% and cooked noodle firmness increased 2.8 g·cm for the SSIIa‐Ab class compared with the SSIIa‐Aa class for the PI 330546 source, but no change in either trait was detected between classes for the IG 86304 source. The SSIIa‐Ab class had a 10% reduction in flour swelling compared with the SSIIa‐Aa class for both crosses. Grain protein and semolina yield did not differ between SSIIa‐A classes. The relationship between flour swelling power and noodle firmness did not differ between SSIIa‐A allelic classes within a cross. The different results for amylose content and noodle firmness between these sources may be because the two sources of the SSIIa‐Ab null mutation contributed different linkages to the segregating populations. Results show that the SSIIa‐Ab allele could be used to produce durum‐based products that are slightly more firm in texture. However, the effect of the SSIIa‐Ab allele may depend on the source. 相似文献
10.
Bordetella bronchiseptica and toxigenic type D Pasteurella multocida as agents of severe atrophic rhinitis of swine 总被引:1,自引:0,他引:1
Bordetella bronchiseptica and toxigenic type-D Pasteurella multocida were cultured from pigs in each of five herds diagnosed as having severe atrophic rhinitis (AR). B. bronchiseptica alone, P. multocida alone, or both organisms isolated from four herds were inoculated intranasally into 1-week-old gnotobiotic pigs which were necropsied 4 weeks post-inoculation (PI). Nasal turbinate atrophy in B. bronchiseptica-inoculated pigs was moderate to severe, while P. multocida-inoculated pigs had slight to severe atrophy. Pigs inoculated with both organisms had moderate to complete turbinate atrophy. P. multocida was reisolated at necropsy from all pigs receiving the organism except those having no turbinate damage. B. bronchiseptica and P. multocida from a fifth herd were simultaneously inoculated into six naturally farrowed 6-day-old SPF pigs. Necropsy performed 4 weeks PI revealed severe to complete turbinate atrophy. Nasal turbinates were normal for control pigs in both experiments. 相似文献