A dynamic simulation model for powdery mildew epidemics on winter wheat*

A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991–98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics.     

烯丙异噻唑对水稻叶片中NAA、ABA含量的影响与稻瘟病抗性的关系

经过１０余年小麦白粉病综合治理系统研究,摸清了东北春麦区小麦白粉病初菌源来源及侵染循环规律,建立了准确度达８６％以上的预测小麦白粉病发生与流行的预测式,明确了东北春麦区小麦白粉病菌的小种种群构成及毒力频率。     

应用real-time PCR定量检测小麦条锈菌潜伏侵染量方法的建立

 小麦条锈病是我国小麦主要病害之一。快速、及时地诊断与定量监测处于潜育状态下的病叶,对准确估计越冬、越夏后的病情,制定正确的防治方案具有重要的意义。根据小麦条锈菌Puccinia striiformis的β-tubilin基因序列设计对该病原菌的种具有特异性的引物betaf/betar,并分别在普通PCR和real-time PCR扩增时对该引物的特异性和灵敏性进行了测定。结果表明该引物对小麦条锈菌特异性高,可稳定扩增出243 bp的目标条带。Real-time PCR的灵敏度为普通PCR的100倍。应用此特异性引物,建立了real-time PCR测定系统,定量测定了条锈菌在小麦叶片接种后组织内的DNA随时间的变化。结果表明,在接种后12 h,可在小麦叶片内检测到条锈菌,且条锈菌在小麦叶片内潜育期间随时间呈指数增长。接种第6 d后叶片内的菌量有明显的增加。建立的小麦条锈菌的real-time PCR早期定量测定方法,为及时、快速监测小麦条锈病在潜育期间的发病规律以及为该病的预测、防治提供依据。     

应用real-time PCR 定量检测田间小麦条锈菌潜伏侵染的研究

 为快速、及时地定量检测处于潜育状态下的小麦条锈菌菌量,本研究于2009－2010年实施田间试验,在北京和甘肃各设3个试验小区,将小区分割成1 m×1 m或1.5 m×1.5 m的小格。初春刚返青叶片出现症状前,在每小格内采集30片叶,提取叶片基因组DNA,应用已建立的real-time PCR定量测定方法,计算每个样本的分子病情指数(molecular-detected disease index, MDI）。在本试验的天气条件和试验设计下,采样10 d后,调查田间标记采样点的发病情况,计算病情指数DI,比较MDI和DI的关系,建立回归模型。结果表明：甘肃甘谷3个试验小区的MDI和DI存在极显著的相关性（R₂¹=0.813 6,R₂²=0.884 5,R₂³=0.592 8）;北京上庄3个试验小区的MDI和DI也存在极显著的相关性（R₂¹=0.742 3,R₂²=0.578 4,R₂³=0.858 4）。本研究证明了应用分子生物学方法可估测小麦条锈病潜育侵染程度的可能性,为建立分子定量测定田间潜育侵染量系统提供了可靠依据。     

基于小麦白粉病菌rDNA ITS序列的PCR分子检测

 Wheat powdery mildew(Blumeria graminis f.sp.tritici) is the one of main wheat diseases in China.Based on the internal transcribed spacer(ITS) sequences of ribosome of B.graminis f.sp.tritici,three molecular primer pairs(F1/R,F2/R and F3/R) were designed to detect the fungal pathogen of wheat powdery mildew.The species specificity of these primers was confirmed.F1/R was demonstrated a higher sensitivity than the other two primer pairs,and could detect as low as 1 pg DNA of B.graminis f.sp.tritici.Furthermore,F1/R primer pair was used to detect the pathogen DNA extracted from wheat leaves showing chlorosis and typical symptoms of powdery mildew caused by artificial inoculation with B.graminis f.sp.tritici.The preliminary results demonstrated the usefulness of this primer pair and its potential applications in efficient detection of wheat powdery mildew pathogen from leaves with latent infections at early growth stages of wheat.     

Gene expression profile and physiological and biochemical characterization of hexaploid wheat inoculated with Blumeria graminis f. sp. tritici

Wheat (Triticum aestivum L.) powdery mildew has direct effects on photosynthesis- and energy-related pathways. Because it is prevalent in Sichuan Province, China, knowledge concerning Pm40-mediated wheat powdery mildew resistance is important for understanding host–pathogen interactions. The aim of this study was to understand physiological changes during the host–pathogen interaction, including gene expression, photosynthetic and chlorophyll fluorescence parameters, chlorophyll content, and antioxidant activity, specific to the resistance response to powdery mildew. The Pm40-expressing L693 and Pm40-deficient L1095 wheat lines were employed for comparison analyses. Fifty-eight and 26 expressed sequence tags (ESTs) were obtained from forward and reverse suppression subtractive hybridization cDNA libraries constructed from Bgt-infected L693 and L1095 leaves, respectively, and 69% of the ESTs in the forward library were related to photosynthesis- and energy metabolism-related pathways. Our data indicate that photosynthesis and carbon metabolism as well as nitrogen metabolism related to photosynthesis are the main pathways involved in Pm40-mediated wheat powdery mildew resistance and that an acetyl CoA-like gene might be a key regulatory factor in these pathways. This study provides new insight into the physiological and genetic mechanisms of resistance to wheat powdery mildew.     

Relating disease progress to cumulative numbers of trapped spores: apple powdery mildew and scab epidemics in sprayed and unsprayed orchard plots

A technique for relating the progress of plant diseases caused by airborne fungal pathogens to cumulative numbers of trapped spores is proposed. The relationship involves two epidemiological parameters—a disease asymptote and the infection efficiency (disease units/spore) of inoculum. The technique was evaluated using data on apple powdery mildew and scab epidemics in sprayed and unsprayed apple orchard plots. For powdery mildew, the observed relationships were close to those proposed in the unsprayed plot, but changed after or during the period of fungicide application in sprayed plots. Parameter estimates gave useful comparative information on the epidemics. The technique was not useful for scab because of the discontinuous patterns of infection.     

苦瓜白粉病病原菌和生理小种的鉴定及苦瓜对白粉病的抗性遗传分析

为明确海南省苦瓜白粉病的病原菌、生理小种及苦瓜对白粉病的抗性遗传规律,结合形态学鉴定和分子鉴定解析白粉病菌及生理小种种类,通过显微镜观察白粉病菌侵染过程,并应用主基因+多基因混合遗传模型分析法探讨苦瓜对白粉病的主要抗性遗传规律。结果表明:采集自海南省6个市(县)的苦瓜白粉病病原菌均为单囊壳白粉菌Sphaerotheca fuliginea,属生理小种2F,该菌在侵染苦瓜叶片时有4个关键时期:接种后4 h为分生孢子萌发高峰期,8 h为附着孢形成高峰期,16～24 h为次生菌丝形成高峰期,5 d为分生孢子梗形成高峰期。将其接种于苦瓜抗、感品系,对白粉病的抗性符合2对加性-显性-上位性主基因+加性-显性多基因模型,主基因和多基因共同控制苦瓜对白粉病的抗性,其中以主基因遗传为主,且会受到环境变异的影响。根据苦瓜抗性遗传规律,F2代主基因遗传率最高,受环境影响最小,在苦瓜的白粉病抗性育种中,以早期世代F2代作为有效选择世代。研究表明白粉病菌侵染叶片的前2 d是白粉病防治的最佳时期,所以在白粉病易发的物候期,可将防治时间提前1～2 d。     

Real-time PCR as a promising tool to monitor growth of Venturia spp. in scab-susceptible and -resistant apple leaves

Apple scab, the most important disease of apple worldwide, is caused by Venturia inaequalis. Currently, evaluation of fungal pathogenicity and host resistance is based on a symptomatic disease rating. However, this method does not provide an accurate measurement of the degree of infection and cannot detect early fungal development in symptomless leaves. In this study, a Venturia-specific real-time PCR assay was developed using primers designed around the specific internal transcribed spacer 2 (ITS2) region of the 5.8S rRNA gene. Using SYBR? Green I technology, the assay can accurately quantify Venturia DNA over a concentration range of at least five orders of magnitude. Detection sensitivities were in the order of 100?fg. The method was used to quantify Venturia genomic DNA levels in leaves of three apple cultivars with different levels and types of scab resistance and artificially infected with V. inaequalis. The assay clearly discriminated between Venturia levels in monogenic resistant (‘Topaz’), polygenic resistant (‘Discovery’), and susceptible (‘Golden Delicious’) cultivars, and proved especially useful to quantify pathogen levels during the initial latent stage of infection. The real-time PCR data of ‘Golden Delicious’ were consistent with the observed evolution of the degree of sporulation during a time-course experiment. Although measurements were influenced by the presence of co-extracted PCR-inhibitors, the impact of these compounds was independent of the apple cultivar or the initial amount of fungal DNA present. In conclusion, real-time PCR amplification of the ITS2-5.8S rDNA of Venturia spp. is a faster, more objective and more sensitive method to monitor fungal growth and to evaluate host resistance than phenotypic disease rating scores.     

Changes induced by powdery mildew in the salicylic acid and polyamine contents and the antioxidant enzyme activities of wheat lines

Investigations were made on four wheat (Triticum aestivum L.) lines under greenhouse conditions, in order to reveal the role of stress-protective materials, namely salicylic acid, polyamines and antioxidant enzymes in the level of tolerance to powdery mildew infection caused by Blumeria graminis (DC.) Speer f.sp. tritici ém. Marchal. The four lines showed different levels of tolerance, assessed on the Saari-Prescott scoring scale: TC26 and TC33 proved to be susceptible and TC9 and TC19 resistant. In most of the lines, infection caused changes in the activities of antioxidant enzymes, especially in the case of guaiacol peroxidase. Four peroxidase isoenzymes, which responded differently to powdery mildew infection could be detected by gel electrophoresis. Infection had only a slight effect on the levels of salicylic acid (free and bound forms) in inoculated plants; while the levels of polyamines, especially spermidine and spermine increased after infection. Correlation analysis was also performed to examine how close a relationship exists between the parameters investigated. It was concluded that salicylic acid, polyamines and antioxidant enzymes have an important role in plant responses and defence mechanisms during this biotic stress and that in some cases there were significant relationships between them. However the levels of these compounds either initially or after pathogen inoculation, could not explain the degree of tolerance to powdery mildew in the four wheat lines investigated.     

Prior Inoculation with Non-pathogenic Fungi Induces Systemic Resistance to Powdery Mildew On Cucumber Plants

A spray inoculation of the first leaf of 2-leaf stage cucumber plants with a non-pathogenic isolate of Alternaria cucumarina or Cladosporium fulvum before a challenge inoculation with the pathogen Sphaerotheca fuliginea induced systemic resistance to powdery mildew on leaves 2–5. Systemic resistance was expressed by a significant (p < 0.05) reduction in the number of powdery mildew colonies produced on each leaf of the induced plants, as compared with water-sprayed plants. Systemic resistance was evident when a prior inoculation with each of the inducing fungi was administered 1, 3 or 6 days before the challenge inoculation with S. fuliginea. Increasing the inoculum concentration of A. cucumarina or C. fulvum enhanced the systemic protection and provided up to 71.6% or 80.0% reduction, respectively, in the number of colonies produced on upper leaves, relative to controls. Increasing the inoculum concentration of S. fuliginea used for challenge inoculation, increased the number of powdery mildew colonies produced on both induced and non-induced plants. Pre-treated plants, however, were still better protected than controls, indicating that the level of systemic protection was related to the S. fuliginea inoculum concentration. The induction of systemic resistance against powdery mildew by biotic agents, facilitates the development of a wide range of disease management tools.     

Disease-weather relationships for powdery mildew and yellow rust on winter wheat

Key weather factors determining the occurrence and severity of powdery mildew and yellow rust epidemics on winter wheat were identified. Empirical models were formulated to qualitatively predict a damaging epidemic (>5% severity) and quantitatively predict the disease severity given a damaging epidemic occurred. The disease data used was from field experiments at 12 locations in the UK covering the period from 1994 to 2002 with matching data from weather stations within a 5 km range. Wind in December to February was the most influential factor for a damaging epidemic of powdery mildew. Disease severity was best identified by a model with temperature, humidity, and rain in April to June. For yellow rust, the temperature in February to June was the most influential factor for a damaging epidemic as well as for disease severity. The qualitative models identified favorable circumstances for damaging epidemics, but damaging epidemics did not always occur in such circumstances, probably due to other factors such as the availability of initial inoculum and cultivar resistance.     

小麦条锈病菌和白粉病菌多重TaqMan Real-time PCR方法的建立

<正>小麦条锈病(Puccinia striiformis f.sp.tritici,Pst)和小麦白粉病(Blumeria graminis f.sp.tritici,Bgt)是我国小麦生产上的重要病害。条锈病主要发生在西北、华北、长江中下游和西南各省、自治区;白粉病则在西南各省和河南、山东、湖北、江苏、安徽等省发生较重,且西北、东北麦区也日趋严重[1]。条锈病菌依靠夏孢子造成小麦初侵染和再侵染并随气流远距离传播导致大区流行,白粉病菌则依赖于分生孢子或子囊孢子进行初侵染和再侵染。二者作为典型的气传病害,空中的接种体在     

非自然越夏区小麦白粉病模拟鉴定病圃

作者于1990～1995年根据陕西省关中麦区小麦白粉病侵染循环特点,人工模拟自然发病条件,在非自然越夏区杨陵(省农科院试验地)成功地建立起白粉病菌可周年存活,且秋、春季均能充分诱发感染的混合菌系病圃,宜对小麦种质材料进行全生育期抗白粉病鉴定。利用该病圃已对陕西省1000余份小麦品种(系)及部分国内外抗源亲本材料做了抗病性鉴定和利用评价。     

新疆泽普县小麦白粉病流行的时间动态及预测模型

2012年-2019年对泽普县春季小麦白粉病田间发生情况进行了系统调查, 并对数据进行了分析和模型拟合, 明确了当地白粉病春季发生和流行的特点?其病害春季流行曲线为典型的单峰S形曲线, 符合Logistic或Gompertz模型?在此基础上, 通过Pearson相关系数法分析了多年来该地小麦不同生育期白粉病病情指数与66个主要气象因子之间的相关关系, 筛选出影响小麦白粉病发生流行的关键气象因子为1月下旬平均日照时间?2月下旬平均气温?1月上旬-3月上旬平均气温和10月下旬-4月中旬平均日照时间, 并采用多元回归分析法建立了基于关键气象因子的小麦扬花期?灌浆初期和灌浆中期的病害预测模型?此研究结果可为当地小麦白粉病的防控提供技术支撑?     

Effect of aerated compost tea on grapevine powdery mildew, botrytis bunch rot and microbial abundance on leaves

Aerated compost tea (ACT), prepared from immature compost, was applied to foliage and fruit of grapevines (Vitis vinifera) to assess its potential for suppressing two important diseases: botrytis bunch rot, caused by Botrytis cinerea, and powdery mildew, caused by Erysiphe necator. An ACT applied to leaves of Cabernet Sauvignon vines in pots 7 days before inoculation with E. necator conidia reduced mean powdery mildew severity on the three youngest expanded leaves (at inoculation) to less than 1 %; mean severity on non-treated, inoculated leaves was 15 %. Multiple applications of ACTs at two vineyards in different growing seasons suppressed powdery mildew to <1 % mean severity on Chardonnay leaves (non-treated 79 % severity) and bunches (non-treated 77 % severity), and on Riesling leaves (non-treated 24 % severity). The same treatments reduced the incidence of Chardonnay bunches with latent B. cinerea and Riesling bunches with sporulating B. cinerea, although the level of botrytis bunch rot in both experiments was not economically damaging. The numbers of culturable bacteria, fungi and yeasts on Chardonnay leaves were higher than pre-treatment levels 10 days after ACT application, as were fungal numbers on Riesling leaves 21 days after treatment. Suppression by ACTs of two fruit and foliar pathogens of grapevine with different biology and epidemiology indicated potential for their use as a tactic in integrated disease management. Further testing of ACTs in a range of viticultural environments and application regimes will contribute to a better understanding of the impact of this tactic on disease, grape and wine quality.     

A host-pathogen simulation model: powdery mildew of grapevine

An epidemiological model simulating the growth of a single grapevine stock coupled to the dispersal and disease dynamics of the airborne conidia of the powdery mildew pathogen Erysiphe necator was developed. The model input variables were either climatic (temperature, wind speed and direction) or related to the pathogen (location and onset of primary infection). The environmental input variables dictated plant growth and pathogen spread (latent period, infection, lesion growth, conidial spore production and release). Input parameters characterized the crop production system, the growth conditions and the epidemiological characteristics of the pathogen. Output described, at each time step, number, age and pattern of healthy and infected organs, infected and infectious leaf area and aerial density of spores released. Validation of the model was achieved by comparing model output with experimental data for epidemics initiated at different times of host growth. Epidemic behaviour for two contrasting years of crop development and 7 phenological stages at the time of primary infection (PI) was examined. For PI occurring at day 115 a vine with late budbreak (1998) showed 58% of primary leaves diseased at flowering compared with only 19% for a vine with early budbreak (2003). Depending on the phenological stage at PI (1–4 leaves), the proportion of diseased primary leaves decreased from 42% to 6% at flowering. Simulations suggested that differences resulted from the interplay between the timing of the first sporulation event, the phenological stage at the time of initial infection, and the age structure and spatial distribution of the leaf population.     

Modelling and forecasting epidemics of apple powdery mildew (Podosphaera leucotricha)

A model developed to simulate epidemics of powdery mildew on vegetative shoots of apple generates two types of output. Firstly, it forecasts disease severity (percentage of host tissue infected) by incorporating effects on disease development of the amount of healthy susceptible tissue and current infectious (sporulating) disease, the level of initial inoculum (overwintered 'primary' mildew) and weather conditions. The effects of weather variables are considered on only two aspects of the fungal life cycle: initial spore germination and the subsequent development during the incubation period. Secondly, the model generates indices of the relative favourability of weather conditions on disease development by incorporating effects of weather on conidial production/dispersal and germination. On each day, forecasts of the (relative) severity of new infection and total current infectious disease are given for both types of output. The model was evaluated by comparing its predictions with the mildew epidemics observed in two unsprayed orchards over four years. In all the years, the temporal patterns of the predicted and the observed disease were generally similar. The pattern of the disease severity forecasts was marginally closer to the observed than that derived from two weather indices. Potential roles of the model in practical management of apple powdery mildew are discussed.     

Influence of crop growth and structure on the risk of epidemics by Mycosphaerella graminicola (Septoria tritici) in winter wheat

Generally, it is recognized that inocula of Septoria tritici present on the basal leaves of winter wheat crops are spread towards the top of the canopy by splashy rainfall. This mechanism of inoculum dispersal is commonly accepted to be a key limit on disease progression. Therefore, attempts to forecast epidemics of S. tritici often quantify rainfall by some means, but largely ignore measurement of pathogen and host variables. In the present study, we show that new wheat leaves emerge initially at a height below established leaves that can contain sporulating lesions of S. tritici . This presents the possibility of horizontal inoculum transfer, even without splashy rainfall. The extent and duration of overlap between emergent and established leaves was found to differ considerably with cultivar and sowing date. Nitrogen application had little effect on overlap, because differences in crop phenology, e.g. leaf area and nodal length, were relative. However, estimates of raindrop penetration to the base of crop canopies suggested that vertical movement of inoculum is affected by nitrogen application. Crops receiving more nitrogen are denser, and therefore less rainfall reaches the base of the canopy. The interactions between crop and pathogen development are discussed with reference to the implications for predicting disease risk. In particular, cultivar traits that promote disease escape are quantified.     

南瓜白粉病不同病情等级下叶际细菌群落结构和多样性

南瓜白粉病是一种危害严重的真菌病害,研究不同病情等级下细菌群落组成的异同对进一步研究南瓜白粉病的生物防治具有重要意义。采集来自3个不同发病等级的南瓜白粉病叶片(R1、R2和R3),运用高通量测序方法分析比较了不同发病等级的南瓜叶片的细菌群落结构和多样性,发现三个不同病情等级下细菌群落结构存在显著差异。在门水平上,三个病情等级下优势门均为Actinobacteria(放线菌门)、Bacteroidetes(拟杆菌门)、Proteobacteria(变形菌门)和Firmicutes(厚壁菌门);在属水平上,R1病情等级下优势属是Methylobacterium、Sphingomonas和Acinetobacter,R2病情等级下为Acinetobacter、Kluyvera和Pantoea,R3病情等级下为Methylobacterium、Kluyvera和Pantoea。南瓜白粉病菌可以改变南瓜叶际细菌群落结构,影响细菌群落多样性。Kluyvera、Pantoea和Erwinia的相对丰度与病情等级呈正相关,随着病情严重发生,丰度得到增强,表明它们可能与白粉菌存在协同作用。这些结果对进一步研究南瓜叶际微生态从而防控白粉病提供了科学参考依据。