Surveys of cereal diseases and pests in the Netherlands. 4. Occurrence of powdery mildew and rusts in winter wheat

Results of annual surveys of winter wheat fields from 1974 to 1986 were compiled to describe epidemics of powdery mildew and rusts in relation to weather and cultivar resistance.An average of 29 and 70% of fields were infected by powdery mildew in May and July, respectively. Mildew prevalence in May was positively correlated with average temperature in October and with average temperature over the months December, January, February and March. In addition, it was correlated negatively with the average grade of mildew resistance of the cultivars sown each year. Prevalence of mildew in July did not show consistent correlations with weather characteristics nor with mildew prevalence in May.Yellow rust was usually not detected in May and on average 18% of the fields was infected in July. The occurrence of yellow rust decreased after 1977, when the farmers adopted cultivars resistant or moderately resistant to yellow rust.Brown rust was usually not detected in May, while in July on average 48% of the fields was infected. Brown rust intensity in July was high in years with a high March temperature and high precipitation during April and May.Black rust was rare in the Netherlands, with 3 and 1% of the fields infected in July 1977 and 1981, respectively.     

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?     

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.     

Predicting severity of asian soybean rust epidemics with empirical rainfall models

ABSTRACT Although Asian soybean rust occurs in a broad range of environmental conditions, the most explosive and severe epidemics have been reported in seasons with warm temperature and abundant moisture. Associations between weather and epidemics have been reported previously, but attempts to identify the major factors and model these relationships with field data have been limited to specific locations. Using data from 2002-03 to 2004-05 from 34 field experiments at 21 locations in Brazil that represented all major soybean production areas, we attempted to identify weather variables using a 1-month time window following disease detection to develop simple models to predict final disease severity. Four linear models were identified, and these models explained 85 to 93% of variation in disease severity. Temperature variables had lower correlation with disease severity compared with rainfall, and had minimal predictive value for final disease severity. A curvilinear relationship was observed between 1 month of accumulated rainfall and final disease severity, and a quadratic response model using this variable had the lowest prediction error. Linear response models using only rainfall or number of rainy days in the 1-month period tended to overestimate disease for severity <30%. The study highlights the importance of rainfall in influencing soybean rust epidemics in Brazil, as well as its potential use to provide quantitative risk assessments and seasonal forecasts for soybean rust, especially for regions where temperature is not a limiting factor for disease development.     

小麦叶锈病、白粉病和条锈病普遍率与严重度间的关系

 在田间接种条件下,详细地观察了小麦叶锈病、白粉病和条锈病普遍率与严重度之间的关系(I-S关系)。结果表明供试三种病害的I-S关系均可用指数函数描述;在普遍率小于70%左右时,用直线方程拟合效果更好;普遍率大于90%时,对严重度的预测效果较差。分别建立了各病的I-S关系式。小麦生育阶段(拔节期、抽穗开花期、灌浆期)对叶锈病和白粉病I-S关系没有明显的影响,而条锈病的I-S关系在不同生育阶段有一定的差异。文章最后对I-S关系的使用进行了讨论。     

The development of the leaf rust,Puccinia hordei,population during winter,spring and early summer in 11 winter barley cultivars

The overwintering and the epidemic development in spring of leaf rust was studied in 11 winter barley cultivars at two different sites near Wageningen in 1976/1977. The amount of leaf rust decreased through the winter at both sites. Cultivars differed considerably in the amount of leaf rust in late winter. Both the moment and the rate of increase of leaf rust after the winter varied with cultivars. The ultimate amount of leaf rust in a cultivar was therefore determined by three factors: The amount of overwintering leaf rust, the onset of leaf rust increase and the rate of increase. The latter was determined by the partial resistance of the cultivar. Why the epidemics did not start at the same moment is yet unknown. The differential overwintering could be explained from the amounts of leaf rust and powdery mildew at the start of the winter, the effect of powdery mildew being a negative one. The correlation coefficient between the values observed in March and those predicted from the December leaf rust and powdery mildew readings was 0.93. In a second experiment carried out in 1979/1980 with six winter barley cultivars chosen from the first experiment the powdery mildew was succesfully excluded by treatment with fungicides. There was no decrease in the leaf rust over the winter nor a differential cultivar effect on overwintering.     

室内模拟塑料大棚黄瓜白粉病流行预测模型的建立

在室内人工气候箱内,通过人工接种和模拟高温高湿环境的方法研究了黄瓜白粉病的发生和流行趋势,采用SAS统计软件对试验数据进行相关和回归分析,建立了黄瓜白粉病始病期与流行程度的预测模型。始病期预测模型的RMSE值在2以下,流行程度预测模型的RMSE值在6以下,表明模型可对塑料大棚黄瓜白粉病始病期和流行程度进行定量预测。     

Models for predicting potential yield loss of wheat caused by stripe rust in the U.S. Pacific Northwest

Climatic variation in the U.S. Pacific Northwest (PNW) affects epidemics of wheat stripe rust caused by Puccinia striiformis f. sp. tritici. Previous models only estimated disease severity at the flowering stage, which may not predict the actual yield loss. To identify weather factors correlated to stripe rust epidemics and develop models for predicting potential yield loss, correlation and regression analyses were conducted using weather parameters and historical yield loss data from 1993 to 2007 for winter wheat and 1995 to 2007 for spring wheat. Among 1,376 weather variables, 54 were correlated to yield loss of winter wheat and 18 to yield loss of spring wheat. Among the seasons, winter temperature variables were more highly correlated to wheat yield loss than the other seasons. The sum of daily temperatures and accumulated negative degree days of February were more highly correlated to winter wheat yield loss than the other monthly winter variables. In addition, the number of winter rainfall days was found correlated with yield loss. Six yield loss models were selected for each of winter and spring wheats based on their better correlation coefficients, time of weather data availability during the crop season, and better performance in validation tests. Compared with previous models, the new system of using a series of the selected models has advantages that should make it more suitable for forecasting and managing stripe rust in the major wheat growing areas in the U.S. PNW, where the weather conditions have become more favorable to stripe rust.     

The effect of powdery mildew (Erysiphe graminis f. sp. hordei) and leaf rust (Puccinia hordei) on spring barley in New Zealand. I. Epidemic development, green leaf area and yield

Powdery mildew and leaf rust caused large yield losses in spring barley grown near Christchurch, New-Zealand, in two seasons. Disease present during early growth stages was as damaging to yield as disease late in the season. Moderate leaf rust severities after anthesis were most damaging when combined with earlier mildew epidemics. Later growth did not compensate for reduced yield potential induced by early infection. This was attributed, at least in part, to an effect on leaf size, and therefore on green leaf area, at later growth stages. There was a closer relationship, by regression analysis, of yield to green leaf area than to disease severity in three cultivars.
The three cultivars. which differed in yield potential and disease resistance, were not equally sensitive to disease. It is proposed that high yielding cultivars may be the most sensitive to yield constraint by disease.     

The effect of powdery mildew (Erysiphe graminis f. sp. hordei) and leaf rust (Puccinia hordei) on spring barley in New Zealand. II. Apical development and yield potential

Reduced yields caused by powdery mildew and leaf rust in two seasons were associated with reduced plant growth. Combinations of early, late and full epidemics in one season, and 12 epidemic combinations in the second, were designed to identify crop sensitivity to disease by comparing growth and development with healthy plants. Early epidemics reduced ear number by increasing tiller death, and reduced grain number by effects on spikelet, floret or grain abortion, depending on the type of epidemic. Epidemics later in crop growth increased floret and grain abortion and also reduced grain weight.
There was no compensation by later-determined components for reduced growth and delayed development at earlier growth stages. Plants infected at early growth stages were more sensitive to late infections, seen as effects on the later-determined components, than plants which were healthy initially. Interactions occurred between epidemics at different times and are likely to occur between diseases and other constraints.     

Disease severity and pathotype dynamics of Puccinia striiformis f.sp. tritici in Denmark

Disease severity of wheat yellow rust, Puccinia striiformis f.sp. tritici , was analysed in Denmark from 1985 to 1999 in relation to the effects of weather on winter survival, distribution of host cultivars and pathotype dynamics. Below-average temperatures in January and February (midwinter) reduced yellow rust on the susceptible cv. Anja, and in three of four growth seasons following cold winters no yellow rust was observed on any cultivar under natural conditions. The agronomic consequences of dispersal of yellow rust urediniospores from external sources to Denmark, in a period during which large areas were planted with relatively few wheat cultivars, were demonstrated in several cases, most evidently when the Yr9 and Yr17 resistance genes became ineffective. Yr9 was overcome by the pathogen in a period with severe yellow rust epidemics on commercial cultivars, while virulence for Yr17 was first observed in a year with almost no yellow rust. In contrast, the resistance in cv. Kraka ( Yr1, CV ) was increasingly effective in controlling yellow rust, because pathotypes with the matching combination of virulence declined in the pathogen population. Pathotype frequency dynamics were thus influenced by selection forces within the country, and by selection forces in areas where spores were spread to Denmark from outside. The importance of a sufficient level of partial resistance in the wheat germplasm to prevent too much damage by yellow rust epidemics, in the event that the resistance genes are overcome by the pathogen population, is emphasized.     

广东省新推广大豆品种病害的初步调查

本文采用普查和定点调查以及传统的植物病害鉴定方法,在2006年6月至2010年10月对广东省新推广高产优质大豆品种的病害种类、发生危害及分布进行了调查.发现病害共有12种,其中真菌病害9种,分别是锈病、霜霉病、红冠腐病、丝核菌叶枯病、炭疽病、白绢病、白粉病、镰刀菌根腐病和煤烟病;细菌性病害、线虫病害和病毒病害各1种,分别为细菌性叶斑病、根结线虫病和花叶病.主要病害为锈病、霜霉病、红冠腐病、花叶病、丝核菌叶枯病和炭疽病等.不同季节大豆的主要病害发生情况不同.春大豆以霜霉病发生较为严重;而夏大豆则以红冠腐病、锈病、花叶病毒病和丝菌核叶枯病发生较严重.     

小麦新资源对条锈病白粉病的抗性鉴定

１９９１～１９９７年在甘谷田间对远缘小麦新资源进行抗条锈病、白粉病鉴定。结果表明，在供试１６０份材料中，对条锈病免疫或高抗、白粉病免疫的有２５份，其抗性比较稳定，是良好的抗源材料，可供抗病育种利用。     

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.     

Simulation of apparent infection rate to predict severity of soybean rust using a fuzzy logic system

ABSTRACT Few biologically based models to assess the risk of soybean rust have been developed because of difficulty in estimating variables related to infection rate of the disease. A fuzzy logic system, however, can estimate apparent infection rate by combining meteorological variables and biological criteria pertinent to soybean rust severity. In this study, a fuzzy logic apparent infection rate (FLAIR) model was developed to simulate severity of soybean rust and validated using data from field experiments on two soybean cultivars, TK 5 and G 8587. The FLAIR model estimated daily apparent infection rate of soybean rust and simulated disease severity based on population dynamics. In weekly simulation, the FLAIR model explained >85% of variation in disease severity. In simulation of an entire epidemic period, the FLAIR model was able to predict disease severity accurately once initial values of disease severity were predicted accurately. Our results suggest that a model could be developed to determine apparent infection rate and an initial value of disease severity in advance using forecasted weather data, which would provide accurate prediction of severity of soybean rust before the start of a season.     

Genetics of resistance to wheat leaf rust, stem rust, and powdery mildew in Aegilops sharonensis

Aegilops sharonensis (Sharon goatgrass) is a wild relative of wheat and a rich source of genetic diversity for disease resistance. The objectives of this study were to determine the genetic basis of leaf rust, stem rust, and powdery mildew resistance in A. sharonensis and also the allelic relationships between genes controlling resistance to each disease. Progeny from crosses between resistant and susceptible accessions were evaluated for their disease reaction at the seedling and/or adult plant stage to determine the number and action of genes conferring resistance. Two different genes conferring resistance to leaf rust races THBJ and BBBB were identified in accessions 1644 and 603. For stem rust, the same single gene was found to confer resistance to race TTTT in accessions 1644 and 2229. Resistance to stem rust race TPMK was conferred by two genes in accessions 1644 and 603. A contingency test revealed no association between genes conferring resistance to leaf rust race THBJ and stem rust race TTTT or between genes conferring resistance to stem rust race TTTT and powdery mildew isolate UM06-01, indicating that the respective resistance genes are not linked. Three accessions (1644, 2229, and 1193) were found to carry a single gene for resistance to powdery mildew. Allelism tests revealed that the resistance gene in accession 1644 is different from the respective single genes present in either 2229 or 1193. The simple inheritance of leaf rust, stem rust, and powdery mildew resistance in A. sharonensis should simplify the transfer of resistance to wheat in wide crosses.     

Changes in agronomic practices and incidence and severity of diseases in winter wheat in England and Wales between 1999 and 2019

In continuation of the annual national surveys of winter wheat, which began in 1970, samples from between 250 and 350 randomly selected wheat crops in England and Wales between 1999 to 2019 were visually assessed for disease symptoms during the milky ripe development stages (GS 73–75). Septoria tritici blotch was the most prevalent and severe foliar disease each year, although annual levels fluctuated considerably and there was no overall significant change over the two decades. Incidence of brown rust, yellow rust, take-all, and barley yellow dwarf virus also showed no significant overall change during the survey period, whereas glume blotch, powdery mildew, eyespot, and sharp eyespot all showed significant decline. Fusarium ear blight has significantly increased in both incidence and severity, causing a serious epidemic in 2012, when 96% of crops were affected. Tan spot has been the third most prevalent foliar disease since 2009 although severity is still very low. Regional disease levels were consistent over the two decades, providing reliable baselines to measure changes in seasonal disease severity. There were significant changes in agronomic practice with a rise to predominance of minimum tillage over the use of ploughing, decreases in overall disease susceptibility of cultivars grown, a major increase in the use of oilseed rape in the rotation and a long-term trend towards earlier sowing. Fungicide use increased considerably, with over 98% crops sprayed and an average of 3.5 applications made per crop each year since 2014. Implications of changes over the last 21 years are discussed.     

三唑酮(粉锈宁)拌种控制小麦条锈病流行的初步研究

四年试验结果表明,用三唑酮拌种对防治小麦秋苗条锈病,压低田间菌量都有显著作用。这对控制越夏区(包括传播桥梁地带)的菌量保护广大麦区具有实际意义;对翌春条锈病有控制流行的作用,可推迟暴发期8～15天,保产效果为6～15.6％。试验结果还说明,拌种对翌春条锈病的控制作用,是在于压低初始菌量。因此拌种方法,适用于春季菌源以当地为主的地区,适用于春季流行的关键因素是越冬菌量的地区,并且处理的范围越大,越彻底,效果越好。还讨论了用拌种防治秋苗叶锈病和白粉病的作用。     

利用移动式孢子捕捉器捕获的孢子量估计小麦白粉病田间病情

 Experiments were conducted by using RAM Air Sampler for Use with Moving Vehicle to estimate field disease severity of wheat powdery mildew during 2002-2005. Results showed that there was significant correlation between field disease index and trapped spore number. Therefore, two models relating field disease index to spore number trapped were constructed using data from 2002 and 2005, or 2003 and 2004, respectively. These two models can be used to estimate field disease indexes of wheat powdery mildew in different years when disease severity is different.     

Mutants in wheat showing multipathogen resistance to biotrophic fungal pathogens

Five fast-neutron-derived mutants were isolated from the wheat line Hobbit 'sib' that show enhanced field resistance towards Puccinia striiformis f.sp. tritici , the causal agent of yellow rust. Subsequent testing showed the yellow rust resistance phenotypes to differ between mutants, to be expressed at different growth stages and, in some cases, to show an isolate interaction. Three mutants, I3-48, I3-49 and I3-54, exhibited an enhanced yellow rust resistance phenotype from the third seedling leaf onwards, while mutants I3-27 and I3-30 did not show an altered yellow rust phenotype until later growth stages. Additional resistance for brown rust (causal agent Puccinia triticina ) was identified in mutants I3-27, I3-30, I3-48 and I3-49, and for powdery mildew caused by Blumeria graminis f.sp. tritici in mutants I3-27, I3-30, I3-48 and I3-54, although in some cases the resistance was isolate-specific.