Vertical dispersal of plant pathogens by splashing. Part I: the theoretical relationship between rainfall and upward rain splash

The theoretical relationship between rainfall intensity, raindrop size distribution and the upward transport of splash droplets is examined to establish a better understanding of the natural rainfall characteristics that can cause upward movement of plant pathogens in a crop. The theory suggests that splash transport is determined by the rain splash intensity index, which is defined as the intensity of the rainfall with raindrops greater than a threshold size. Ulbrich's (1983) empirical model of the size distribution of raindrops is used to calculate the relationship between rainfall intensity and rain splash intensity index. The calculations show that rainfall intensity is not a reliable indicator of the rain splash intensity index, particularly in convective showers. Therefore, a correlation between rainfall volume and upward disease progress is unlikely to provide a reliable basis for forecasting sudden disease outbreaks associated with short-duration convective showers during the summer. Finally, we consider the instruments that have the capability to measure the rain splash intensity index.     

应用实时荧光定量技术评价粉红粘帚霉对水稻纹枯病的田间防治效果

 本研究利用实时荧光定量PCR技术监测施用生防菌前后土壤中粉红粘帚霉67-1和水稻纹枯病菌AG-1IA的数量,并调查发病情况,收割后测产,评估生防菌粉红粘帚霉67-1的田间防治效果。实时荧光定量检测结果表明,粉红粘帚霉67-1防治水稻纹枯病的效果随着用药浓度的增加而增强,各处理间差异极显著。用药后土壤中粉红粘帚霉67-1的含量在一定时间内随培养时间的延长逐渐升高,停止用药后逐渐减少。水稻纹枯病菌在清水对照组中没有显著变化,在处理组中水稻纹枯病菌的数量随时间降低。60 g/667 m²菌量的防效及产量与井冈霉素对照组差异不显著。防病保产结果与实时荧光定量结果基本一致,说明粉红粘帚霉67-1的孢子制剂对水稻纹枯病具有优良的田间防治效果,实时荧光定量PCR技术可以用于生物防治效果的田间评价。     

A new extraction method for benomyl residues in soil and its application in movement and persistence studies

A simple and rapid method for extracting benomyl residues from soils was compared with previous methods. Soil was extracted by shaking for 2 h at room temperature with (1:1) acetone/M aqueous ammonium chloride followed by clean-up by solvent partition and ultraviolet absorption estimation of carbendazim. Recoveries were comparable to those obtained by refluxing with methanolic hydrochloric acid for 4 h, hitherto the most efficient method reported, and were much greater than those obtained by extraction with ethyl acetate or chloroform. The new method gave more tractable extracts than those obtained by refluxing with methanolic hydrochloric acid, which form troublesome metal hydroxide precipitates during clean-up. In field experiments with 2-[¹⁴C]-benomyl and 2-[¹⁴C]-carbendazim, no radioactivity was found more than 25 mm from the soil surface during 10 months after surface application of 1 kg/ha. Carbendazim residues in soils from three field experiments indicated that its persistence is very sensitive to soil pH. The time for 50% loss of initial dose ranged from 26 months at pH 5.5 to less than 3 months at pH 7.2. Biological effectiveness in a crop may therefore depend markedly on differences in soil pH.     

A new method for assessing foliar uptake of fungicides using Congo Red as a tracer

In order to develop a new method for measuring foliar uptake of fungicides, Congo Red was selected as a tracer, and optimum procedures were established for washing, extracting and analyzing it and fungicides from leaf surfaces. Congo Red, a water‐soluble dye, was not absorbed into cucumber or rice leaf, even in the presence of various surfactants, and was completely washable from leaf surfaces by aqueous acetonitrile solutions. Congo Red and fungicides in washings were quantified to calculate the amount of foliar uptake of the latter, by comparing the ratio to Congo Red. The optimum concentration of Congo Red in a formulation should be established in order to minimize its influence on fungicide uptake. Although Congo Red has proved to be useful with a conventional droplet application method, it will give more realistic and practical results with the spraying method used in the present study. © 2001 Society of Chemical Industry     

陇东小麦条锈菌越夏菌量测定及在秋季病情测报中的应用

依据陇东越夏菌量的流行结构,采用菌量指示田及生物捕捉测定侵染源菌量,用人工接菌和自然发病的方法测定越夏海拔下限,以确定菌原有效传播范围。此结果用于陇东条锈病秋季病情测报,其病情预报与实际流行程度相符。     

Vertical dispersal of plant pathogens by splashing. Part II: experimental study of the relationship between raindrop size and the maximum splash height

This paper describes a simple experimental test of the theoretical relationship between raindrop diameter and maximum splash height proposed by Walklate (1989). This relationship contains two empirical parameters to model the characteristics of a splash target that limits upward movement of splash droplets. These parameters are estimated by fitting the proposed relationship to measurements of the maximum height of splashing from a variety of targets including leaves, straw and water films on horizontal plane surfaces. The experimental technique provides a simple and meaningful way to characterize the behaviour of splashing from plant material. This information can be applied to describe the upward movement of inoculum in crop canopies during rainfall.     

Differentiation and quantification of the cereal eyespot fungi Tapesia yallundae and Tapesia acuformis using a PCR assay

Isolates of Tapesia yallundae and Tapesia acuformis were subjected to Random Amplified Polymorphic DNA (RAPD) assay. Amplification products common to isolates of either species were cloned and primers were generated from each sequence for use in conventional PCR. The primer pair derived from a T. yallundae specific RAPD marker amplified a product only from DNA of T. yallundae isolates and not from DNA of a range of other fungal species associated with the stem base disease complex of cereals. Similarly, the primer pair generated from a T. acuformis -specific RAPD marker amplifed a product only from DNA of T. acuformis isolates. Quantitative assays were developed for both species of Tapesia from these primer pairs, using competitive PCR . Competitive PCR was used to determine the level of colonization of seedlings by each species in glasshouse- and field-inoculated cereal hosts and results compared to those for conventional seedling disease assessment.     

结合药液表面张力与苹果树冠层参数预测喷雾药液用量的方法及应用

为了保证果树精准施药,减少药剂流失,通过4种常用表面活性剂调节药液的表面张力,借助界面张力仪、微重力天平和植物冠层扫描仪等测定手段建立了药液表面张力与苹果叶片最大稳定持液量 (R_m) 之间的关系,并结合果树常用冠层参数,提出了一种预估果树施药液量的方法。结果表明:生长前期苹果叶片近轴面的R_m值明显高于生长后期;在同一生长期,苹果叶片远轴面的R_m值均高于近轴面,且R_m值随叶倾角的增大而减小;生长前期苹果叶片远轴面的R_m值受药液表面张力的影响大于近轴面,但随着叶倾角的增大,叶片近、远轴面的R_m受药液表面张力的影响减小。当药液中表面活性剂的浓度未达到其临界胶束浓度 (cmc) 时,药液的表面张力与苹果叶片的R_m值成正相关关系,由此可建立一元线性回归方程,结合果树平均叶片倾角、叶面积指数和冠层地面投影面积等植物冠层参数,可以估算果树的最大施药液用量。采用4种常用的农药制剂验证了所建方法的实用性。该研究结果可以为苹果园喷雾施药时预估药液用量、减少药剂流失提供理论依据。     

Identification of oat-adapted isolates of cereal Septoria in the UK using a detached leaf technique

Isolates of Septoria spp. from cereals were tested for their relative pathogenicity to detached seedling leaves of three cereal species. Each of 23 isolates showed unequivocal adaptation to either oats, or wheat, or barley. Five oat-adapted isolates were from Prince Edward Island, Canada, where S. avenue is prevalent on oats; three were from the UK, where there are few oat crops and where adaptation to oats has not been reported.
Oat-adapted isolates tended to have pycnidiospores of above-average length and could be referred to S. avenae. Wheat-adapted and most barley-adapted isolates had shorter spores and could be referred to S. nodorum. UV-fluorescent pigment was produced on oxgall agar by all wheat-adapted isolates, but only by a minority of oat-adapted and barley-adapted isolates.
It is suggested that adaptation to cereal species is a more useful character than spore length for classifying isolates.     

Serological detection of grapevine virus a using antiserum to a nonstructural protein, the putative movement protein

ABSTRACT Grapevine virus A (GVA) is implicated in the etiology of the rugose wood disease. The coat protein (CP) and the putative movement protein (MP) genes of GVA were cloned and expressed in Escherichia coli and used to produce antisera. Both the CP and the MP were detected with their corresponding antisera in GVA-infected Nicotiana benthamiana. The MP was first detected at an early stage of the infection, 6 to 12 h after inoculation, and the CP was detected 2 to 3 days after inoculation. The CP and MP were detected by immunoblot analysis in rugose wood-affected grapevines. The MP could be detected in GVA-infected grapevines that tested negative for CP, both with CP antiserum and with a commercially available enzyme-linked immunosorbent assay kit. The study shows that detection of the nonstructural MP may be an effective means for serological detection of GVA infection in grapevines.     

Histology of the infection of tritordeum and its parents by cereal brown rusts

The reactions of tritordeum lines and their Hordeum chilense and Triticum spp. parents to infection by Puccinia recondita f.sp. tritici, P. recondita f.sp. agropyri and P. hordei were studied at the seedling stage. The histological observations indicated that tritordeum behaves as the wheat parent, whatever the H. chilense parental line reaction. Tritordeum is to be considered a host of wheat brown rust where genes for hypersensitive resistance may occur; these are apparently contributed by the wheat parent. Both H. chilense and wheat are highly resistant to barley brown rust, and the reaction of tritordeum is that of the wheat parent with respect to the levels of necrosis associated with the early aborted infection units. The tritordeum reaction is also that of the wheat parent to a rust collected on H. jubatum (putatively P. recondita f.sp. agropyri ), with the susceptibility or resistance of H. chilense being overruled by the wheat parent reaction.     

Aggressiveness and its role in the adaptation of plant pathogens

Aggressiveness, the quantitative component of pathogenicity, and its role in the adaptation of plant pathogens are still insufficiently investigated. Using mainly examples of biotrophic and necrotrophic fungal pathogens of cereals and Phytophthora infestans on potato, the empirical knowledge on the nature of aggressiveness components and their evolution in response to host and environment is reviewed. Means of measuring aggressiveness components are considered, as well as the sources of environmental variance in these traits. The adaptive potential of aggressiveness components is evaluated by reviewing evidence for their heritability, as well as for constraints on their evolution, including differential interactions between host and pathogen genotypes and trade-offs between components of pathogenicity. Adaptations of pathogen aggressiveness components to host and environment are analysed, showing that: (i) selection for aggressiveness in pathogen populations can be mediated by climatic parameters; (ii) global population changes or remarkable population structures may be explained by variation in aggressiveness; and (iii) selection for quantitative traits can influence pathogen evolution in agricultural pathosystems and can result in differential adaptation to host cultivars, sometimes leading to erosion of quantitative resistance. Possible links with concepts in evolutionary ecology are suggested.     

RunMACRO: a program to facilitate sensitivity analyses using the water flow and solute movement model MACRO

Sensitivity analyses of pesticide leaching often involve a large range of simulations based on nearly identical set-ups. Using RunMACRO it is possible to make large numbers of simulations with a minimum of exertion. Running many nearly identical model set-ups is tedious and might introduce errors in selecting the correct values from a long range of parameter files that are appropriate to the model set-up. RunMACRO makes the task easier and minimises the risk of errors in the generation of parameter files and model executions. Using RunMACRO, it is possible to create a suite of MACRO simulations based on a single parameter file where the range or a list of values for one to three parameters is specified. RunMACRO then creates a parameter file for each of the simulations and runs the simulations one by one. RunMACRO can easily be modified to be used with other simulation programs that use ASCII-based parameter files and can be started from a command prompt. RunMACRO is available free to use and modify from the Geological Survey of Denmark and Greenland's home page.     

Chemical control of isolated invasive conifers using a novel aerial spot application method

Conifer species, which have formed the foundation of commercial forestry industry in many countries, are known to be invasive in natural ecosystems, especially in the Southern Hemisphere. Controlling isolated invasive conifers before they reach reproductive maturity is an essential element of any strategy that aims to reduce spread rate of these species. Using a novel helicopter‐mounted spot‐application gun, which delivers a precise dosage to the crown of each tree, the objective of this research was to test the efficacy of three triclopyr‐based treatments against the four most vigorous wilding conifer species (Pinus contorta, Pinus nigra, Pinus sylvestris and Pseudotsuga menziesii) under New Zealand field conditions. Herbicides tested were triclopyr at two different rates and a combination of triclopyr and picloram. Treated trees covered a wide range of heights (c. 0.5–16 m), and measurements of mortality taken two years post‐herbicide application were used to examine variation in efficacy of the herbicides. Successful treatment was defined by a mortality rate of 85% or higher. A logistic regression model was fitted to the mortality data and used to derive threshold tree heights at which 85% mortality occurred, H₈₅. For all four species, the most effective treatment was application of 1000 ml of herbicide mixture per tree that contained 120 and 20 g, respectively, of the active ingredients triclopyr and picloram. There was a significant decline in efficacy of this treatment with increases in tree size for all four species. Values of H₈₅ for this treatment were 7.4 m for P. nigra, 8.3 m for P. menziesii, 9.7 m for P. contorta and >10 m for P. sylvestris. The methods developed here could be used to effectively manage emerging conifer infestations before they become problematic.     

Correlation of endothal and fluorescent dye concentrations following concurrent application to tidal canals

Herbicide residue samples are expensive and time-consuming to collect and analyze. The potential for using ‘Rhodamine WT’ to simulate endothal dissipation in moving water was tested in the weed-infested Three Sisters tidal canals (Citrus Co., FL). Concurrent applications were made using a variety of application techniques. Significant correlations between dye and endothal concentrations were found in each treatment, indicating that ‘Rhodamine WT’ concentrations can be used to predict endothal movement and concentrations. The ratios of endothal:dye half-lives were similar (0.2, 0.25, 0.17) for three of the application methods tested, indicating that estimations of dye half-lives could be used to predict those for endothal.     

Assessment of leaching potential of aldicarb and its metabolites using laboratory studies

The metabolites of pesticides can contaminate groundwater and pose a risk to human health when this water is used for drinking. This paper reports the results of a laboratory study on aldicarb and its main metabolites, aldicarb sulfone and aldicarb sulfoxide. Aldicarb and its metabolites showed K_oc values (6–31) which were lower than that of atrazine (55), indicating that they are very mobile in soil. They are less persistent than atrazine (DT₅₀ = 25 days), with DT₅₀ values from less than 1 day and up to 12 days. Aldicarb behaved as a non‐leacher, whereas its metabolites clearly showed the characteristics of leachers. Aged residue leaching experiments showed that aldicarb can occur at high concentrations in the leachate, together with its two metabolites. The leachate composition depends on the incubation time of the parent compound. Aldicarb and its metabolites can form various mixtures in groundwater on the basis of the time elapsing between the application of the insecticide and the first significant rainfall. This study confirms the characteristics of contaminants of aldicarb and especially its metabolites, as reported in the literature. © 2001 Society of Chemical Industry     

菠萝凋萎相关病毒-1实时荧光定量RT-PCR检测体系的建立与应用

菠萝凋萎相关病毒-1( Pineapple mealybug wilt associated virus-1, PMWaV-1)是田间检出率最高的菠萝凋萎病毒。本研究根据PMWaV-1 CP基因保守序列设计特异性TaqMan探针和引物, 建立并优化了PMWaV-1实时荧光定量RT-PCR检测方法。优化后的反应体系制备的标准曲线为 y=-3.307×logx+38.18, 相关系数 r2为0.998。试验结果表明, 该方法能特异性地检测PMWaV-1, 对PMWaV-2、3和阴性对照均无反应; 最低检测限达到40拷贝。重复性试验表明批内和批间变异系数均小于1.98%, 是一种操作简便、特异性强、灵敏度高、重复性较好的PMWaV-1定量检测方法。样品检测结果表明PMWaV-1在菠萝植株老叶、嫩叶和吸芽中的病毒含量呈递减趋势。     

城市绿地有害生物风险分析体系构建及应用

为探索建立统一的城市绿地有害生物风险评价尺度,引入有害生物风险分析(PRA)理论.基于国际PRA规定程序,结合城市绿地生态系统特点及模糊数学理论,利用德尔菲法及层次分析法,探讨城市绿地有害生物风险分析体系工作程序、评价指标和评价值的计算方法.利用此方法评价了上海城市绿地中新发现的16种害虫和7种病害的风险性.结果表明:咖啡豹蠹蛾等3种害虫、柳杉赤枯等4种病害风险指数在0.6～0.8,风险级别为高;棉褐带卷叶蛾等9种害虫、杨树锈病等3种病害风险指数在0.4～0.6,风险级别为中;木樨瘿螨等4种害虫风险指数在0.2～0.4,风险级别为低.根据不同风险等级,提出相关风险管理策略.     

Microscopy and image analysis in the study of plant pathogens and the application of pesticides

Problems associated with the preparation of diseased plant material for transmission electron microscopy (TEM) and the uses of TEM to meet the specific needs of plant virologists are discussed. Methods of collecting spray droplets for analysis by an image-analysing computer method are described.     

分子插件法及其在农药分子设计中的应用

新农药创制是一项艰难复杂的系统性工程,而新农药分子的设计是该工程的源头,也是最重要的一环。文章对传统的农药分子设计方法进行了简单的归纳总结,并在课题组多年新农药创制实践的基础上提出了一种新的设计方法——分子插件法,并以吡啶二芳酮和芳氧吡啶乙酮为例,介绍了分子插件的设计及其在新农药创制中的应用。该方法的优点在于可将功能基团模块化,便于快速衍生和筛选,从而大大缩短农药的创制周期,满足对速度竞争的要求。