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1.
ABSTRACT Conventional models for the durability of resistant cultivars focus on the dynamics of the frequency of resistance genes. This leads to a definition of the durability of resistance as the time from introduction of the cultivar to the time when the frequency of the virulence gene reaches a preset threshold. It is questionable whether this is the most appropriate way to measure durability. Here we use a simple epidemiological model to link population dynamics and population genetics to compare three measures of durability: (i) the expected time until invasion of the virulent genotype, by mutation or immigration, and subsequent establishment of a population (T(invasion)); (ii) the virulence frequency related measure of the time for the virulent genotype to take-over the pathogen population ( T(take-over)); and (iii) the additional yield, measured by the additional number of uninfected host growth days (T(additional)). Specifically, we show how the measures of durability are affected by deployment and epidemiological parameters. We use a combination of numerical solution and analytical approximation of a model for the population dynamics of avirulent and virulent genotypes of a pathogen growing in dynamically changing populations of resistant and susceptible cultivars. The three measures of durability are compared. Some consequences of the results for durable resistance in multilines and mixtures and the regional deployment of resistant cultivars are discussed. 相似文献
2.
Seasonal patterns of dispersal of ascospores of Cryphonectria parasitica (chestnut blight) 总被引：1，自引：0，他引：1
Infected barks of chestnut blight cankers, caused by Cryphonectria parasitica , were collected from a naturally infected orchard and incubated at different temperatures. Cankers started to discharge ascospores about a week after incubation at 15–25°C; most ascospores were collected at 20 and 25°C. When incubated at 5, 10 or 30°C, only a few cankers released a small number of ascospores and only during the later stages of incubation. However, the rate of formation of perithecia was not affected by the incubation temperature. The number of airborne ascospores was monitored using a volumetric spore trap in a chestnut orchard during 1996 and 1997. In both years, the number of ascospores trapped daily varied greatly, but in general it increased sharply from March onwards, reached a peak in May, and then declined steeply. There was a significant correlation between daily counts of ascospores and air temperature. Time-series transfer function (TF) analysis showed a positive association of the daily number of ascospores with increasing temperature, rain events and wet/humid conditions. In general, values predicted by the TF model agreed well with the observed pattern. However, a multiple regression equation based on TF analysis failed to provide a satisfactory prediction of the daily number of ascospores. 相似文献
3.
塔克拉玛干沙漠腹地人工绿地三种灌木的离子吸收特性 总被引：6，自引：1，他引：5
塔克拉玛干沙漠腹地人工绿地长期使用矿化度 4.0g/L以上的地下水灌溉 ,柽柳、梭梭和沙拐枣三种灌木仍然能够正常生长 ,表现出较强的抗盐特性。通过对三种不同年龄的灌木及其根、茎和凋落物的盐分分析 ,表明 :不同种类和年龄灌木对可溶性离子的吸收特性存在较大的差异 ;同一种灌木不同器官的离子吸收特性差异显著 ,表现出三种灌木在抗盐机理方面不同的生理和生态学特性 ,即 :柽柳从土壤中吸收的大量盐分离子 ,通过叶片的泌盐腺排出体外 ,使植物体内的盐分离子含量保持在相对较低的水平 ,这类植物属于泌盐类植物 ;梭梭能够从外界环境吸收大量的盐分 ,在植物体内储藏 ,并且依靠植物肉质同化枝吸收大量的水分 ,使得植物体内的盐分浓度维持在一定的限度内 ,这类植物属于盐多汁类植物 ;而沙拐枣通过根部运输系统的超滤 ,使得过量的盐被阻止在体外 ,保持植物体内较低的盐分浓度 ,此类植物主动避开盐分 ,属于拒盐类植物 相似文献
4.
Christopher D. Keating Lindy M. Holden-Dye Robert J. Walker 《Pest management science》1996,46(3):263-266
The neuropeptide AF2 has a complex set of actions on the dorsal muscle strip of Ascaris suum, including a potentiation of the acetylcholine-stimulated muscle contraction. Caffeine at 100 μm and 5 mm inhibited this potentiation, as did 100 μm theophylline in two out of six studies. The cyclic-AMP-potentiating compounds IBMX, dibutyryl cAMP and forskolin had no effect on the AF2-induced potentiation of the acetylcholine-stimulated muscle contraction. These preliminary data suggest that the potentiating action of AF2 is not mediated by a cAMP pathway. 相似文献
5.
Massimo Pilotti Valentina Lumia Giovanni Di Lernia Angela Brunetti 《European journal of plant pathology / European Foundation for Plant Pathology》2012,134(1):61-79
Ceratocystis platani is a quarantine fungal pathogen agent of canker stain, a destructive disease affecting Platanus. Despite its diagnosis being critical for disease control, there is still no effective diagnostic tool as all known mycological and biological detection assays are problematical. In this study we developed highly effective Real-Time PCR methods based on the use of an intercalating dye, EvaGreen, and on a Taqman probe. We designed primers and probe on the internal transcribed spacer (ITS) region of rDNA, and used them for the amplification and detection of a 95?bp C. platani amplicon. Inference of standard curves revealed that both Real-Time procedures have similar and high values of amplification efficiency when applied to a range of templates, e.g. genomic fungal DNA and DNA extracted from diseased wood. The methods were sensitive with a detection limit of 10?fg???l?1? C. platani genomic DNA. They were specific as they did not yield any detection signal when applied to non-target fungal taxa colonizers of Platanus wood. Reliability was demonstrated through the positive detection of a collection of C. platani isolates and of wood samples collected from naturally infected trees. Robustness was positively verified through detection on artificially infected trees, which were tested at different times after death, up to 27?months. Generating a standard curve with a target-amplicon-containing plasmid enabled an absolute quantification and a comparison between the discoloured wood of resistant and susceptible genotypes. The importance of the methods for studies on pathogen epidemiology and host resistance is also discussed. 相似文献
6.
利用河西走廊东部5个气象站1961—2007年近47 a的逐月积雪深度和积雪日数的常规观测资料,分析河西走廊东部最大积雪深度和积雪日数月、季节和年的空间分布以及时间变化特征。结果表明:受海拔高度、地理位置以及天气系统等影响,河西走廊东部积雪日数、最大平均积雪深度和极端最大积雪深度的分布从东南向西北递减,高海拔地区多于低海拔区,山区多于平原区。时间变化上,积雪日数47 a来呈平稳变化趋势,震荡减少,变率很小,积雪深度呈增加趋势;河西走廊东部积雪日数最多出现在1月,最少出现在9月,积雪深度最大出现在3月,最小出现在12月;积雪日数冬季最大,春季次之,秋季最小;积雪深度春季最大,秋季次之,冬季最小;相关系数法分析表明,积雪日数和积雪深度都是冬季的变化主导了年尺度的变化;河西走廊东部积雪日数1990s中期以前以6~7 a、9~10 a和2~3 a的周期为主,1990s中期以后周期主要表现为6~7 a和2~3 a;积雪深度1970s中期以前以6~7 a和2~3 a周期为主,1970s中期~1990s中期9~10 a、12~13 a和2~3 a反应明显,1990s中期以后周期又表现为6~7 a和2~3 a。 相似文献
7.
采用三维坐标体系追根挖掘法对晋西黄土高原半阴坡虎榛子、黄刺玫和三裂绣线菊3种灌木根构型进行了研究。研究结果表明，3种灌木根系水平分布范围较广，垂直分布范围较窄，虎榛子主要集中分布在0～60cm土层中，黄刺玫集中分布在0～40cm土层中，根系空间构型表明虎榛子和黄剌玫以水平根和斜生根为主，无明显主根，7a生三裂绣线菊根系错综复杂，根系中有一定数量的2～3级分枝根，表现出了较其他两种灌木较强的适应性。 相似文献
8.
Intact spinach chloroplasts were used to determine if clomazone, 5-OH clomazone, and/or 5-keto clomazone inhibited the chloroplastic isoprenoid pathway. When isopentenyl pyrophosphate was used as a precursor, neither clomazone nor the clomazone metabolites (5-OH clomazone and 5-keto clomazone) inhibited the formation of products separated by HPLC in the organic phase. However, when pyruvate, a substrate for the first committed step of the pathway, was used as a precursor, both 5-keto clomazone and fosmidomycin reduced the formation of a non-polar product and increased the formation of a polar product in the organic phase. Only 5-keto clomazone, not 5-OH clomazone or clomazone, inhibited the formation of an additional product other than fosmidomycin in the aqueous phase from pyruvate incorporation. In an in vitro assay, 5-keto clomazone inhibited DXP synthase, the enzyme catalyzing the first committed step of the chloroplastic isoprenoid pathway. Therefore, our studies show that neither clomazone nor 5-OH clomazone inhibits the chloroplastic isoprenoid pathway, only 5-keto clomazone does. 相似文献
9.
R. R. STANGEjr D. JEFFARES C. YOUNG D. B. SCOTT J. R. EASON & P. E. JAMESON 《Plant pathology》1995,45(3):407-417
Thirty-six isolates of the fasciation-inducing bacterium Rhodococcus fascians were evaluated for the presence and location of the fas-1 gene, which codes for an isopentenyl transferase, the committed step in cytokinin biosynthesis. The presence of fas-1 was determined by PCR using a set of primers to the most conserved regions of the gene and by Southern hybridization to genomic digests using the PCR fragment as a probe. Both methods revealed the presence of the gene in 18 virulent isolates and the absence of the gene in 18 avirulent isolates. Thus, there is a strong relationship between the presence of the gene and virulence of the organism. The location of fas-1 was determined by probing blots of linear and circular DNA. For most of the virulent isolates, the gene was localized to a 200 ± 10 kb linear plasmid. Three virulent isolates lacked a plasmid of this size, but contained fas-1 either on a linear plasmid of 130 kb or on a large circular plasmid. 相似文献
10.
H. van Os 《European journal of plant pathology / European Foundation for Plant Pathology》1964,70(1):18-26
The carnations which are normally grown are practically all infected with various viruses, and therefore attempts were made to obtain virus-free plants of a number of varieties by means of heat treatment and meristem culture. Incubators were designed in which the plants could be subjected to a heat treatment at a temperature of 37°C and at a high degree of humidity of the air. The ultimate percentage of virus-free plants in 1960 amounted to an average of 1.3%. This is sufficient to obtain a virus-free clone, but not enough to build up a virus-free assortment within a short time. The factors which may affect the percentage of successful isolations are discussed, viz. the effect of the season, of varietal differences and of differences between the material supplied by different growers. When the virus-free plants are propagated in practice it is essential that the material should be closely inspected and tested at regular intervals. The new material was found to possess most favourable qualities. It is sold with a special certificate. 相似文献
11.
In a gnotobiotic piglet infected with 50.10(6) oocysts of Cryptosporidium parvum, developmental stages of the parasite were found in the duodenum, anterior jejunum and middle jejunum on the first day post infection (1 DPI). During the studies of the ultrastructure, trophozoites and meronts of C. parvum were encountered in the microvillous zone of enterocytes, and the outer membrane of parasites was a continuation of the membrane of microvilli. Unusual was the attachment of C. parvum trophozoite on the opening of a goblet cell, as well as a meront localized in the cytoplasm in the enterocyte of anterior jejunum. These findings show that C. parvum is very adaptive and capable of developing in a still undescribed location. 相似文献
12.
Leaf mesophyll protoplasts and cell suspension cultures obtained from resistant and susceptible cultivars of hop ( Humulus lupulus ) exhibited differential cell death responses when treated with sterile culture filtrates (CF) obtained from four isolates of Verticillium albo-atrum showing a range of virulence towards hop. The extent of cytotoxicity was correlated with both the virulence of the isolates and the resistance of the cultivars. Cytotoxicity was attributed to a low-molecular-weight, heat-labile, component of CF. Cell cultures from a susceptible and a resistant cultivar exhibited similar, growth-related, patterns of sensitivity to CF. The extent of inhibition of callus growth caused by CF treatment was related to the level of the resistance of the cultivar. 相似文献
13.
An instrument for measuring the vapour pressures of pesticides has been constructed using a suitably adapted gas chromatographic oven. Using this apparatus and a method involving gas saturation, followed by chromatographic analysis of the trapped pesticide vapour, the vapour pressures of a number of pesticides and non-pesticides have been determined. It has been demonstrated that this procedure gives repeatable and accurate values by statistical comparison of the results obtained with data abstracted from the literature. 相似文献
14.
A.F.H. Besemer 《EPPO Bulletin》1972,2(7):31-38
The effect of a soil fumigant on soil-borne pests and pathogens depends largely on a sufficient distribution through the top soil and the availability of the fumigant or the biologically active degradation products in the water phase. Nearly all the fumigants are dispersed in the soil mainly in the vapour phase and therefore the amount of air between the soil particles is very important. Consequently on light soils it is relatively easy to obtain an efficient control, but on heavy or wet soils and on soil types with a high humus content it is rather difficult to get reliable results. The concentration of the fumigant in the upper few cm. of the soil is often insufficient to get good control after injection of the material at 15–20 cm. depth. The effect may be improved by using a plastic cover or a «split plot>> application.
The elimination of most of the fumigant, to avoid a phytotoxic effect is a cause for concern on wet soils and on soil types with a high organic content. Factors influencing the decrease of the fumigant residue in the soil are discussed. The soil fumigant application gives rise to important changes in the whole ecosystem in the soil. Information on the influence on non-target organisms is scarce. The application of dichloropropene and of chloropicrin may lead to a noticeable effect on the nitrificating bacteria.
The soil application of fumigants may give rise to residues in plants of the parent chemical or, to a larger extent, to residues of metabolites e.g. Br- after soil disinfection with Br- containing fumigants such as methylbromide, EDB1 ), etc. The enrichment of the soil with Br- may cause phytotoxic effects on susceptible crops such as carnations. The fate of the metabolites arising from dichloropropene and related compounds has not been fully clarified. 相似文献
The elimination of most of the fumigant, to avoid a phytotoxic effect is a cause for concern on wet soils and on soil types with a high organic content. Factors influencing the decrease of the fumigant residue in the soil are discussed. The soil fumigant application gives rise to important changes in the whole ecosystem in the soil. Information on the influence on non-target organisms is scarce. The application of dichloropropene and of chloropicrin may lead to a noticeable effect on the nitrificating bacteria.
The soil application of fumigants may give rise to residues in plants of the parent chemical or, to a larger extent, to residues of metabolites e.g. Br
15.
Disease severity, based on six parameters (time from inoculation to flecking, and eruption of uredinia, uredinial density and the amounts of urediniospoies produced), was assessed on leaf discs cut from four cultivars of Populus spp. raised with either a long (15 h) or a short (10 h) photoperiod. The discs were inoculated with race 4 of Melampsora medusae and subsequently incubated with either a long (15 h) or a short (10 h) photoperiod. While disease severity, based on most parameters, was lower in discs from the continuing long photoperiod (15 h pre- and 15 h post-inoculation) than from the continuing short photoperiod (10 h pre- and 10 h post-inoculation), maximum severity was developed by discs given a combination of a short pre- and a long post-inoculation photoperiod. The relative contribution of the cultivar, the pre- and the post-inoculation photoperiod and their second- and third-order interactions to variation in disease severity depended on the parameter employed to assess severity. The parameters used are elements of disease monocycles and their possible significance in modelling epidemics is discussed. 相似文献
16.
The nature of a reductive system which actively degrades mexacarbate in the rat intestine and liver was investigated. The system is characterized by its stability against heat and protease treatments and its requirements for a flavin cofactor and an acidic pH for a maximum activity. As a result of purification and spectroscopic identification attempts the system responsible for the above reductive activity was identified to be flavoprotein. Under anerobic conditions such flavoproteinflavin cofactor systems degrade mexacarbate first to 4-N-desmethylmexacarbate and then to polar water-soluble metabolites. 相似文献
17.
Brown JK 《Phytopathology》2000,90(4):320-323
ABSTRACT A method of estimating the frequency of recombination in field populations of ascomycete fungi is presented. This is a development of a technique described by J. Zhan, C. C. Mundt, and B. A. McDonald, in which field plots were inoculated with isolates of Mycosphaerella graminicola of known genotypes and then, later, the proportions of the fungal populations in the plots that originated as recombinant progeny of matings between the inoculated isolates or as immigrants from the local population were estimated. It is argued that J. Zhan, C. C. Mundt, and B. A. McDonald's method is inappropriate in terms of its approach to statistical inference and that the lack of confidence intervals for rates of recombination (r) or immigration (m) is a further weakness. An improvement to their method would involve the use of inoculated isolates that can be clearly distinguished from the local population, for instance, by the use of DNA markers. There should also be sufficient markers for there to be a negligible probability that progeny of matings between inoculated isolates will have the same genotype as either of their parents. With this experimental design, estimates of r and m can be found by a standard maximum likelihood method, while confidence intervals for the parameters can be estimated by a simple bootstrap procedure. The method appears to be about an order of magnitude more efficient than are the existing ways of estimating the frequency of recombination in ascomycete fungi. 相似文献
18.
D. A. COOKE P. L. MATHIAS DAPHENE M. CHAWARSZCZYNSKA L. J. COPPOCK 《Plant pathology》1983,32(3):339-343
Population assessment methods for Heterodera schachtü were compared in two tests. In the first there were no consistent differences between numbers of H. schachrü extracted by Fenwick cans (at two laboratories), a flotation column and an automatic cyst extraction apparatus, from dried soils from three sites containing no other cyst nematodes. The second, made on 54 commercial sugar beet fields, compared numbers of H. schachtü extracted from dried soil samples by Fenwick cans (at two laboratories) with results of a bioassay of soil samples and a subsequent examination of roots in the field. Most samples were placed into the same broad groups by the cyst extraction and bioassay methods and the two techniques were equally good at predicting field infestations. 相似文献
19.
N. A. M. van Steekelenburg 《European journal of plant pathology / European Foundation for Plant Pathology》1983,89(3):75-86
The survival ofDidymella bryoniae and the incidence of ascospores in glasshouses, outdoors and under controlled conditions were studied. The fungus was able to overwinter in the open as dormant mycelium. Dry and undecomposed crop residues remained a source of infection for more than one year. Moisture and a minimum temperature between 5 and 10°C were needed for fructification. For ascospore release a high relative humidity was not sufficient, the substrate had to be moist during a short period. Ascospores could be trapped throughout day and night both outdoors and in glasshouses, but there was a marked peak during a period of 3 h in the evening. Both on days with and without rain about the same numbers of ascospores were trapped from crop residues in the open. Ascospore release was favoured by watering the plants in the glasshouse. Under controlled conditions the release of ascospores was determined by humidity and not by light or darkness. In a cucumber crop in the glasshouse the first ascospores were trapped at about the same time the first symptoms on the plants appeared. In the glasshouse with introduced diseased plant debris, particularly when the debris became wet when the plants were watered, the disease was more severe and yield was less than in a glasshouse without introduced plant debris. Airborne ascospores may cause the primary infection of a cucumber crop. Therefore, hygienic measures must be taken to eliminate plant debris as source of infection, both in glasshouses and outdoors. 相似文献
20.
P. H. J. F. Van Den Boogert G. Jager 《European journal of plant pathology / European Foundation for Plant Pathology》1983,89(5):223-228
Addition of live mycelium ofRhizoctonia solani to three slightly, acid sands collected in winter from a field after a previous potato crop resulted in accumulation of hyperparasites and less infestation of sprouts of infected seed potatoes. A similar effect was observed in alkaline marine sandy loam soils, but only after a second addition of live mycelium. The predominant hyperparasite in these experiments wasVerticillium biguttatum. 相似文献