Measures of durability of resistance

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.     

百合地下害虫主要种类调查及生物（源）农药筛选

调查了甘肃省临洮县为害百合的地下害虫种类, 并以主要发生为害种类为供试对象, 采用拌土法测定了几种生物（源）农药对主要害虫的室内毒力和致死中时。调查发现小云斑鳃金龟Polyphylla gracilicornis、棕色鳃金龟Holotrichia titanis为主要发生及为害种类, 不同时间发生种类存在差异, 9月份以小云斑鳃金龟幼虫发生为害为主, 发生量占地下害虫总数的66.16%, 平均种群密度为10.48头/m2, 10月份, 则以棕色鳃金龟幼虫发生为主, 发生量占地下害虫总数的96.86%, 平均种群密度为7.79头/m2, 主要取食百合根系和鳞茎, 造成根系数量减少, 鳞茎出现不规则褐色缺口或凹陷斑。药剂筛选结果表明, 1.8%阿维菌素乳油、200亿孢子/g球孢白僵菌粉剂对两种蛴螬均具有较高的杀虫活性和速效性, 药后7 d时, 校正死亡率在82.22%以上, 对小云斑鳃金龟幼虫和棕色鳃金龟幼虫的LC50分别为0.161、0.060 mg/g和5.558×107、0.362×107孢子/g, LT50分别为2.237 d（2.2 mg/g）、1.393 d（2.2 mg/g）和6.645 d（40.0×107孢子/g）、4.940 d（2.0×107孢子/g）, 这两种生物（源）农药对两种蛴螬的LC50和LT50值均略大于两种化学农药25%二嗪磷乳油、40%辛硫磷乳油处理的, 且对小云斑鳃金龟幼虫的杀虫活性均低于对棕色鳃金龟幼虫的杀虫活性, 致死中时则长于对棕色鳃金龟幼虫的致死中时。     

Localization of metabolic sites of action of herbicides

Time- and concentration-course studies were conducted to determine the effect of thirteen herbicides on photosynthesis, respiration, RNA synthesis, protein synthesis, and lipid synthesis using isolated single leaf cells. Each herbicide was from a different chemical class. Appropriate ¹⁴C-substrates and product purification procedures were used for each process prior to liquid scintillation counting. The most sensitive metabolic site of inhibition was photosynthesis for atrazine, bromacil, dichlobenil, monuron, and paraquat; RNA synthesis for dalapon and dinoseb; protein synthesis for chlorpropham; and lipid synthesis for CDAA, chloramben, 2,4-D, EPTC, and trifluralin. However, with several herbicides, one or more process was almost as sensitive as the one mentioned above. All herbicides inhibited more than one process, and the most sensitive site of inhibition may not be the same process that was inhibited the greatest at the maximum concentration and maximum exposure time used. Therefore, a concept of metabolic sites of action, rather than a primary site of action, appears to be more meaningful for herbicides.     

宁夏枸杞炭疽病发生流行的气象条件分析

根据宁夏枸杞主产区中宁县和银川市芦花台园林试验场2000～2004年不同批次的成熟枸杞果实炭疽病病情指数和气象资料,运用主成分分析结合逐步回归方法,分析了宁夏枸杞炭疽病爆发流行的主要气象因子及其影响.结果表明:影响炭疽病发生的气象因子主要是温度和空气相对湿度,其次是风力和降水.在一定温度范围内,温度越高,对炭疽病的发生越不利;空气湿度越大,越有利于枸杞炭疽病的发生.     

杀虫剂混合使用的增效作用评判分析

用共毒因子重新评价共毒系数大于100的281个混配组合,发现有29.18%的混配组合没有增效作用。根据单剂的LC-P线和共毒因子公式,求出混剂的期望死亡率和"相加作用区间"(期望死亡率±20%期望死亡率),根据混剂的实测死亡率求出95%置信区间,画出期望LC-P线及"相加作用区间"和实测LC-P线及"95%置信区间",发现当共毒系数大于100、共毒因子小于20时,实测LC-P线和期望LC-P线彼此交缠,期望LC-P线的"相加作用区间"和实测LC-P线的"95%置信区间"能高度重叠,表明两条LC-P线之间没有毒力差异;当共毒系数大于100、共毒因子大于20,或者共毒系数小于100、共毒因子小于-20时,实测LC-P线的"95%置信区间"和期望LC-P线的"相加作用区间"只有少量重叠或完全不重叠,体现出了实测LC-P线和期望LC-P线对供试害虫的毒力差异。因此,为了获得有稳定增效作用的混配组合,共毒系数须大于100,同时共毒因子也要大于20。     

Mode of action of famoxadone

Famoxadone is a preventative and curative fungicide recently developed for plant disease control. The molecule and its oxazolidinone analogs (OADs) are potent inhibitors of mitochondrial electron transport, specifically inhibiting the function of the enzyme ubiquinol:cytochrome c oxidoreductase (cytochrome bc₁). Visible absorbance spectral studies on the purified enzyme suggested that famoxadone bound close to the low potential heme of cytochrome b. This binding mode was confirmed in competitive binding experiments by studying the displacement of a radiolabelled OAD from submitochondria. EPR studies on the binding of famoxadone to submitochondria and purified bc₁ suggested its binding mode was more like that of myxothiazol than that of stigmatellin (ligands known to bind near the low potential heme). Zoospores of Phytophthora infestans, when given low concentrations of famoxadone and other OADs, were observed to cease oxygen consumption and motility within seconds and later the cells disintegrated, releasing the cellular contents. Famoxadone was a potent inhibitor of the growth of Saccharomyces cerevisiae when grown on non-fermentable carbon sources and it was an approximately 50-fold less potent inhibitor of growth when the yeast was grown on a fermentable carbon source, glucose. Such physiological observations are consistent with the loss of mitochondrial function imposed by famoxadone and OADs. Single amino acid changes in the apocytochrome b of baker's yeast cytochrome b located near the low potential heme altered the inhibition constants for the inhibitors famoxadone, myxothiazol, azoxystrobin and kresoxim-methyl differentially, thus strongly suggesting different binding interactions of the protein with the inhibitors. © 1999 Society of Chemical Industry     

农药纳米乳剂研究进展

近年来，纳米技术的迅猛发展为现代植物保护开辟了新的应用前景。纳米乳剂作为一种新型纳米载药系统，具有较好的分散性和润湿性、粒径小以及缓释增效等优点，从而提高农药在靶标表面的附着、沉积和渗透，并有效提高农药利用率，减少农药使用量，降低环境风险。本文介绍了纳米乳剂的组成成分以及制备方法，综述了纳米乳剂在农药领域的研究及其应用进展，同时对目前有较大争议的关于纳米乳剂和微乳剂的界限进行了讨论，并对该领域发展前景进行了展望，可为制备性能优异的纳米乳剂提供参考。     

Systems of designation of pathotypes of plant pathogens12

A variety of systems of designation has evolved to name pathotypes of plant pathogens. The systems were evaluated to determine those best suited for particular purposes. Virulence and avirulence/virulence formulae of pathotypes have advantage over the use of consecutive numbers or letters given in chronological order of pathotype discovery. As soon as pathotype information exceeds a certain level of complexity, mathematical codes are most advantageous, in particular two codes, octal notation and coded triplets. A more universal adoption of the most appropriate codes is recommended to ease communication and comparisons of results.     

Investigation of the Mode of Action of Nematode Neuropeptides

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.     

定西地区农业生态经济系统的结构和功能分析

分析了定西地区农业生态经济系统的结构和功能 ,发现水资源时空分布不均 ,种群结构比较单一 ,产业结构不合理 ,使得系统生产能力很低 ,N、P、K不平衡 ,经济效益低下。据此从农业可持续发展的角度出发 ,提出了优化农业生态经济系统结构和提高其功能的对策和建议。     

陕北地区水资源可持续利用评价

以水资源复合系统为基础,建立了陕北地区水资源可持续利用评价指标体系,应用模糊综合评判方法和人工神经网络方法对该地区1996~2005年的水资源可持续利用水平进行了定量评价。结果表明:陕北地区除本身干旱缺水以外,水污染、生态环境恶化、用水效率低和经济水平不高是影响该区水资源可持续利用的主要因素;1996~2005延安市和榆林市的水资源可持续利用水平均处于较弱和中等之间,且呈上升趋势,提高陕北地区水资源可持续利用水平有很大潜力。     

艾比湖地区土地沙漠化遥感动态监测

基于RS和GIS技术,以1990年,2001年和2007年TM、ETM＋影像为信息源,建立目视解译标志,利用ENVI4.5和ARCGIS9.3的图像和数据处理功能,对艾比湖地区1990-2007年沙漠化动态变化进行了监测。结果表明：监测期内严重沙漠化和中度,重度沙漠化土地面积呈明显增加的趋势,轻度沙漠化土地减少。沙漠化...     

厚朴病虫害种类的初步调查

采用标准地法和线路调查法,对湖北恩施市新塘乡双河厚朴基地的厚朴病虫害进行了系统调查,记录主要虫害13种,其中叶部害虫9种,枝干害虫2种,根部害虫2种。厚朴主要病害5种。藤壶蚧、厚朴枝角叶蜂和厚朴新丽斑蚜为湖北省首次报道,小绿叶蝉为厚朴新寄主记录种。同时记录了藤壶蚧的天敌6种,其中寄生小蜂2种,瓢虫4种;厚朴新丽斑蚜的天敌昆虫8种。对藤壶蚧、厚朴枝角叶蜂和厚朴苗木根腐病等重要病虫害的发生规律进行了初步调查,同时提出了防治建议。     

Allelopathy of buckwheat: Assessment of allelopathic potential of extract of aerial parts of buckwheat and identification of fagomine and other related alkaloids as allelochemicals

The allelopathic potential of buckwheat ( Fagopyrum esculentum ) was investigated. Field study showed that living buckwheat reduced weed biomass compared with plots without buckwheat. Laboratory study revealed that root exudates suppressed root and shoot growth of weeds and reduced weed dry weight. Sequential partitioning of the aqueous ethanolic extract of the aerial parts of buckwheat showed that the chloroform extract caused an 80% reduction in radicle elongation of lettuce seedlings at a concentration of less than 100 p.p.m. Fagomine, 4-piperidone and 2-piperidinemethanol were isolated and identified by ¹H and ¹³C nuclear magnetic resonance from the chloroform extract. These compounds caused a 50% inhibition of radicle elongation in lettuce seedlings at concentrations of less than 100 p.p.m. These results suggest that compounds 1, 2, and 3 might act as allelochemicals and affect the growth or germination of different plant species.     

Effects of timing and method of application of Penicillium oxalicum on efficacy and duration of control of Fusarium wilt of tomato

The effects of timing and method of application of Penicillium oxalicum on the control of fusarium wilt of tomato were investigated. Application of P. oxalicum to tomato seedlings in seedbeds reduced disease caused by Fusarium oxysporum f.sp. lycopersici in a growth chamber by 45–49% and in glasshouse experiments by 22–69%. Disease suppression was maintained for 60–100 days after inoculation with the pathogen in the glasshouse. No disease reduction was observed in tomato plants where P. oxalicum was applied to seeds. Treatment with P. oxalicum did not affect the population of F. oxysporum f.sp. lycopersici in the rhizosphere.     

图们江干流区间流域径流变化特征

以图们江干流区间为研究对象，应用Mann-Kendall非参数检验法分析干流区间4个水文站点径流年际与年内变化趋势。在此基础上，采用R/S分析方法分析年径流、季节径流和月径流变化趋势在未来的可持续性，利用Mann-Kendall突变检验方法分析各水文站点年径流、季节径流和月径流发生突变的年份。结果表明：图们江干流区间各水文站径流年际和年内变化趋势均与干流径流变化趋势一致，呈下降趋势，非汛期径流下降的贡献主要来自春季和冬季径流的下降；Hurst指数表明，上游径流变化趋势的持续性最强，下游的持续性相对较弱；1985年是图们江干流区间年径流发生突变的年份，且降水量也发生了变化，可以推测降水量可能是径流不断减少的重要因素。     

效率系数和一致性指数及其在干旱预测精度评价中的应用

基于关中平原2003—2014年Aqua-MODIS数据的条件植被温度指数的干旱监测结果,引入效率系数和一致性指数对自回归求和移动平均(ARIMA)模型和季节性ARIMA模型的预测精度进行了评价,并分析了其在干旱预测精度评价中的适用性。两种干旱预测模型的精度评价结果为ARIMA模型与季节性ARIMA模型的效率系数分别为-0.04与-4.27,一致性指数分别为0.40与0.37,表明ARIMA模型对干旱的预测精度高于季节性ARIMA模型,这与均方根误差、皮尔森相关系数及Kappa系数等的评价结果一致,且效率系数对不同干旱预测模型的预测性能的区分效果尤为显著,对干旱预测模型的精度评价比一致性指数更为合理。因此,效率系数更适合用于遥感干旱预测模型的精度评价。     

天津市需水量预测研究

需水预测关系到对未来水资源供需紧张程度的认识,不仅是不同水平年水资源供需的重要环节,也是城市规划、供水规划和实现水资源可持续发展的一项基础工作。天津市是严重资源型缺水城市,科学、有效的需水量预测研究就尤为重要。本文以1991-2005年统计数据为基础,通过比较多种预测模型,选用指数模型和移动平均数法建立城市需水量综合动态模型,预测到2020年,天津城市总需水量将达到26.91亿m3。在此基础上,分析了提高城镇人均工业产值和农村人均农业产值增长率,对工业和农业需水量的影响。结果显示,在保持高工业增长条件下,保持适当的农业产值增长,可缓解对水资源造成压力。     

Comparison of methods of assessing field populations of Heterodera schachtii

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.     

土壤环境因素对棉花黄萎病菌微菌核存活的影响

 试验研究了土壤温度、湿度、pH值和有机质对棉花黄萎病菌微菌核存活的影响。结果表明:40、30和0℃对微菌核土壤存活影响较大,10和20℃影响较小,尤其以10℃影响最小;土壤含水量越高,对微菌核存活影响越大,在含水量低于15%时,对存活影响较小,尤其以5%的含水量影响最小,表明微菌核对土壤干旱逆境具有较强的抵抗能力;pH值低于5.5或高于8.5的土壤条件对微菌核存活影响较大,pH值为6.5~7.5影响较小;土壤有机质含量越高,微菌核存活率越低,含量低,存活率高。本研究结果表明,只要改善和控制棉花黄萎病菌土壤存活的生态条件,就可以有效地减少土壤存活菌量,达到控制病害发生与发展的目的。