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The susceptibility of French bean plants to infection by the Rothamsted strain of tobacco necrosis virus as measured by the local-lesion method is increased by a rise in temperature and usually by darkening the plant before inoculation. If part only of a leaf is darkened, that part becomes more susceptible. Plants in full light also become more susceptible if carbon dioxide is removed from the air, whereas the susceptibility of plants in the dark is not altered.
Darkening leaves decreases their content of malic, fumaric, succinic and glycolic acids and increases the content of citric acid; the content of oxalic and malonic acids remains constant. These changes occurred in winter and summer and whether or not darkening increased susceptibility.
The effect on susceptibility of individual acids infiltrated into the leaf was measured in leaves kept in the light or in the dark before inoculation. None of the acids used produced any large change in susceptibility.  相似文献   

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When plants were kept at 36°C. for some time before inoculation, their susceptibility to infection by five mechanically transmissible viruses was greatly increased. When kept at 36° after inoculation, fewer local lesions were produced than at lower temperatures, but the effects of the post-inoculation treatment differed with different viruses. Tomato spotted wilt and tobacco mosaic viruses multiply in plants at 36°, and the post-inoculation treatment reduced the local lesions they caused to numbers that varied between 10 and 90% of the control; these two viruses also have large thermal coefficients of heat inactivation. By contrast, tobacco necrosis, tomato bushy stunt and cucumber mosaic viruses, were much affected by post-inoculation treatment, lesion formation being completely prevented by exposure to 36° for a day or more. These three viruses appear not to multiply in plants at 36°, and although they have high thermal inactivation points, they have small temperature coefficients of thermal inactivation.
The extent to which lesion formation was affected by pre- or post-inoculation exposure of plants to 36° depended not only on the length of the treatment, but also on the physiological condition of the plants.
The symptoms of infected plants changed considerably if kept at 36°. At 36° Nicotiana glutinosa , inoculated with tobacco mosaic virus, gave chlorotic local lesions instead of necrotic ones, and became systemically infected. When systemically infected plants were brought to ordinary glasshouse temperature, the infected tissues all collapsed and died in a day.  相似文献   

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Infection of the adult worker honeybee with Nosema apis reduces or obviates brood feeding and causes her to commence foraging earlier than a healthy bee. The length of foraging activity and the total length of life of infected bees is reduced.
In colonies infected with N. apis the rate of brood rearing is severely depressed during April, May and June, the degree of depression being proportional to the percentage infection.
Infection decreases during July, August and September, and consequently the rate of brood rearing increases, but the resulting addition in foraging population is usually too late to increase the honey crop.  相似文献   

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The reported low toxicity of schradan to honey-bees has been confirmed. This has led to the consideration of the possibility that this systemic insecticide might be present in nectar and subsequently appear in honey in an unchanged form.
Using radioactive schradan labelled with 32P, it has been shown that spray applications of this insecticide to mustard and borage plants result in the contamination of nectar. A series of nectar samples taken over a 4-week period following spraying showed on radio assay a progressive decrease in total 32P content and also in the amount of schradan present in proportion to the decomposition products. The highest figure recorded for the schradan content of nectar was 21 p.p.m.
Tests on the stability of schradan in contact with the honey stomach of the bee and also in contact with the enzyme invertase, in vitro , showed that no appreciable breakdown occurred. Furthermore it was shown that schradan was stable in contact with honey over a period of 2 1/2 months.
It is concluded that this systemic insecticide may appear in an unchanged form in the honey obtained from the nectar of plants which have been sprayed less than 4 weeks previously.  相似文献   

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An attempt was made to find the causes of increased susceptibility to virus infection when tobacco plants are kept in the dark before inoculation. The changes in certain nitrogen fractions, viz. insoluble-N, amino-N, amide-N, ammonia-N and nitrate-N, and in dry matter and water content were followed in tobacco plants subjected to a period of darkness before inoculation with tobacco aucuba mosaic virus. Only nitrate-N was strongly correlated with the susceptibility to infection, but the evidence suggests that the correlation is indirect and not causal.
Dry matter and water content, determined either as dry matter percentage of fresh weight or measured separately on a leaf-disk basis Ivere found to vary directly with variation in susceptibility.  相似文献   

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The administration of carbon dioxide in sublethal concentrations or for sublethal periods of time gave rise to an increased resistance to its effect in a strain of Drosophila melanogaster susceptible to the toxic effects of this gas. The effect did not appear to be permanent.
The successive administration by spraying of sublethal concentrations of DDT and BHC did not increase the resistance of a strain of D. melunoguster to their effects, either in the insects sprayed or their progeny. Only when the dosages were such as to give a high death-rate did a significant increase of resistance of the progeny of the treated insects take place; the tendency was if anything to increase susceptibility, although the indications were not in favour of DDT acting as acumulative poison.
In a preliminan series of tests the topical application of D D T in sublethal doses to the adult insects resulted in a reduction in the amount or in the rate of egg laying.  相似文献   

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目的:了解嗜血杆菌引起前列腺感染的状况及其耐药性。方法:取3790例患者的前列腺液进行培养,鉴定和药敏试验。结果:3790例前列腺感染患者中,110例嗜血杆菌培养阳性,阳性率为2.90%;对氨苄西林,阿莫西林和哌拉西林的耐药率为11.8%-35.5%,对头胞曲松,头胞哌酮,头胞他啶,头胞噻肟,头胞西丁,头胞克洛,头胞呋辛钠的耐药率为5.3%-18.4%:对氨曲南,亚胺培南的耐药率为0-5.3%;对环丙沙星,氧氟沙星,诺氟沙星的耐药率为0-21.0%;对阿米卡星,庆大霉素,克拉霉素,复方新诺明的耐药率2.90%-53.9%,产β-内酰胺酶株对氨苄西林的耐药率为50.0%-56.5%。结论:嗜血杆菌引起的前列腺感染不容忽视,对非产酶株的前列腺感染的治疗,氨苄西林可作为首选药物。  相似文献   

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