Possible Root Infection of Cercospora beticola in Sugar Beet

A potential primary infection site of the foliar pathogen Cercospora beticola in sugar beet is described. Sugar beet seedlings of the susceptible cv. Auris were grown in a standard soil for 14 days. A monoconidial culture of a C. beticola isolate was grown to produce conidia. In experiment 1, roots were immersed in a conidial suspension of isolate code IRS 00-4, or in tap water (control), for 2 days. After incubation seedlings were potted in a peat – fine river sand mixture and placed at low relative humidity (RH) (<80%) or high RH (100%). Twelve days after infection, seedlings at high RH showed more disease incidence (90%) than seedlings grown at low RH (disease incidence = 25%), whereas no disease symptoms developed in the control seedlings. Cercospora leaf spots (CLSs) developed on the cotyledons, leaves, petioles and stems of the seedlings. In experiment 2, roots were immersed in a conidial suspension of isolate code IRS 00-2 for 5 h. Thirty-four days after infection at high RH, 100% disease incidence was observed in the treated seedlings and one CLS in the control treatment. First indications of leaf spot development were observed as reddish purple discolouration of individual parenchymatic cells. Because splash dispersal and symptoms due to infested soil were excluded, we showed that it is possible to obtain CLS symptoms in sugar beet seedlings when their roots were immersed in conidial suspensions of C. beticola, thus demonstrating that roots can be a primary infection site.     

Reduced sensitivity of Cercospora beticola isolates to sterol-demethylation-inhibiting fungicides

In a survey conducted during October 1995, single-lesion isolates of the sugar beet leaf-spot fungus, Cercospora beticola , were tested for sensitivity to the sterol demethylation inhibiting fungicides (DMIs) flutriafol and bitertanol. The isolates were collected from fields in three different areas of northern Greece. Fields at Serres and Imathia had been sprayed with DMIs for about 15 years to control sugar beet leaf-spot. At the third site, Amyndeon, DMI fungicides had not been used. From each area 150 isolates were tested. ED₅₀ values were calculated for individual isolates by regressing the relative inhibition of colony growth against the natural logarithm of the fungicide concentration. The mean ED₅₀ values for flutriafol for the Serres, Imathia and Amyndeon populations were 1·07, 0·73 and 0·5 µg mL⁻¹, respectively (significantly different at P  = 0·05). For bitertanol the mean ED₅₀ values for the Serres and Imathia populations were 0·72 and 0·81 µg mL⁻¹, respectively, which were not significantly different at P  = 0·05. The mean ED₅₀ value of the Amyndeon population was 0·48 µg mL⁻¹, which was significantly lower than those of the other two populations ( P  < 0·05). A cross-resistance relationship was found to exist between the two triazole fungicides tested when log transformed ED₅₀ values of 60 isolates were subjected to a linear regression analysis ( r  = 0·81).     

Characterization of CbCyp51 from field isolates of Cercospora beticola

The hemibiotrophic fungus Cercospora beticola causes leaf spot of sugar beet. Leaf spot control measures include the application of sterol demethylation inhibitor (DMI) fungicides. However, reduced sensitivity to DMIs has been reported recently in the Red River Valley sugar beet-growing region of North Dakota and Minnesota. Here, we report the cloning and molecular characterization of CbCyp51, which encodes the DMI target enzyme sterol P450 14α-demethylase in C. beticola. CbCyp51 is a 1,632-bp intron-free gene with obvious homology to other fungal Cyp51 genes and is present as a single copy in the C. beticola genome. Five nucleotide haplotypes were identified which encoded three amino acid sequences. Protein variant 1 composed 79% of the sequenced isolates, followed by protein variant 2 that composed 18% of the sequences and a single isolate representative of protein variant 3. Because resistance to DMIs can be related to polymorphism in promoter or coding sequences, sequence diversity was assessed by sequencing >2,440 nucleotides encompassing CbCyp51 coding and flanking regions from isolates with varying EC(50) values (effective concentration to reduce growth by 50%) to DMI fungicides. However, no mutations or haplotypes were associated with DMI resistance or sensitivity. No evidence for alternative splicing or differential methylation of CbCyp51 was found that might explain reduced sensitivity to DMIs. However, CbCyp51 was overexpressed in isolates with high EC(50) values compared with isolates with low EC(50) values. After exposure to tetraconazole, isolates with high EC(50) values responded with further induction of CbCyp51, with a positive correlation of CbCyp51 expression and tetraconazole concentration up to 2.5 μg ml(-1).     

Herbicides – a two‐edged sword*

Summary Weeds cause yield losses and reductions in crop quality. Prior to the introduction of selective herbicides, the drudgery of manual weeding forced farmers to adhere to a suit of weed management tactics by carefully combining crop rotation, appropriate tillage and fallow systems. The introduction of selective herbicides in the late 1940s and the constant flow of new herbicides in the succeeding decades provided farmers with a new tool, ‘the chemical hoe’, putting them in a position to consider weed control more independently of the crop production system than hitherto. The reliance on herbicides for weed control, however, resulted in shifts in the weed flora and the selection of herbicide‐resistant biotypes. In the 1980s, the public concern about side‐effects of herbicides on the environment and human health resulted in increasingly strict registration requirements and, in some countries, political initiatives to reduce the use of pesticides were launched. Today, the number of new herbicides being introduced has decreased significantly and integrated weed management has become the guiding concept. Farmers also have the option of growing herbicide‐resistant crops where the biology of the crop has been adapted to tolerate herbicides considered safe to humans and environmentally benign. This paper discusses some of the recent developments in herbicide discovery, technology and fate, and sketches important future developments.     

SIMPEROTA 1/3 – a decision support system for blue mould disease of tobacco*

Blue mould (Peronospora tabacina) is the most serious threat to German tobacco crops. In order to efficiently control the disease whilst minimizing the risk of nontolerable fungicide residue levels on tobacco leaves, a decision support system has been developed which optimizes the timing of fungicide treatments. The DSS consists of two models, SIMPEROTA 1, which forecasts the dates of blue mould first appearance and SIMPEROTA 3 which forecasts the dates of fungicide applications. Crucial biological processes are included in the models (infection, mycelium growth, sporulation and spore release). Input parameters are temperature, relative humidity and leaf wetness recorded on an hourly basis. Validation with data from 2003 and 2006 showed that SIMPEROTA 1 gave satisfying results. The model is suitable for practical use and can be employed for steering monitoring efforts of extension services and for the timing of the first fungicide treatment. SIMPEROTA 3 gives advice on follow‐up treatments and the length of spraying intervals, but this model needs to be validated before being introduced into practice.     

AgmedaWin – a tool for easy and flexible management of meteorological data*

Decision support systems in plant protection need plausible and complete meteorological data as the main input. While meteorological data are provided by the German meteorological service, several states in Germany have built up their own meteorological networks. These states use the software AgmedaWin to import, manage, present, evaluate and export the measured data. At the core of the program is a flexible import module which facilitates the import of files in different formats from all types of meteorological stations by using import profiles to describe the structure of the files. Several algorithms are integrated in AgmedaWin to ensure plausibility and completeness of the data. The program also includes a module to compare the data of neighbouring stations. AgmedaWin is being used so far in seven states of Germany since 2005. With an XML–based export interface the data are transferred from AgmedaWin to the Internet system ISIP ( http://www.isip.de ) in which all data are stored and used as input for decision support systems. Furthermore the unprocessed meteorological data can be evaluated in ISIP or downloaded as files in different formats by external users.     

甜菜褐斑病内生拮抗菌的筛选、鉴定及其防效测定

 Three hundred and one endophytic bacteria strains were isolated from healthy sugar beet plants in severely diseased plots in Changji County,Xinjiang Province.Three endophytic bacteria strains,1-5,4-1 and 4-3,showed relatively strong antagonistic against Cercospora beticola.Strain 1-5 was identified as Paenibacillus polymyxa,while strains 4-1 and 4-3 were as Bacillus flexus and Stenotrophomonas sp. by their morphological,physiological and biochemical characteristics.The results from several experiment trials showed that the endophytic bacteria could reduce the disease incidence of sugar beet.The control efficiency reached from 67.6% to 80.2%, indicating that biocontrol with endophytic bacteria was an alternative and potential method to control sugar beet fungi disease.     

Characterization of cytochrome b from European field isolates of Cercospora beticola with quinone outside inhibitor resistance

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on quinone outside inhibitor (Q_OI) fungicides. Despite the dependence on Q_OIs for disease control for more than a decade, a comprehensive survey of Q_OI sensitivity has not occurred in the sugar beet growing regions of France or Italy. In 2010, we collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the Q_OI fungicide pyraclostrobin using a spore germination assay. In total, 213 isolates were identified with EC₅₀ values greater than 1.0???g?ml^?1 to pyraclostrobin, all of which originated from Italy. To gain an understanding of the molecular basis of Q_OI resistance, we cloned the full-length coding region of Cbcytb, which encodes the mitochondrial Q_OI-target enzyme cytochrome b in C. beticola. Cbcytb is a 1,162-bp intron-free gene with obvious homology to other fungal cytb genes. Sequence analysis of Cbcytb was carried out in 32 Q_OI-sensitive (<0.080???g?ml^?1) and 27 Q_OI-resistant (>1.0???g?ml^?1) isolates. All tested Q_OI-resistant isolates harboured a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay developed to discriminate Q_OI-sensitive and Q_OI-resistant isolates based on the G143A mutation could detect and differentiate isolates down to approximately 25?pg of template DNA. Microsatellite analyses suggested that Q_OI resistance emerged independently in multiple genotypic backgrounds at multiple locations. Our results indicate that Q_OI resistance has developed in some C. beticola populations in Italy and monitoring the G143A mutation is essential for fungicide resistance management in this pathosystem.     

Antifungal activity of sugar beet chitinase against Cercospora beticola: an autoradiographic study on cell wall degradation

Two independent bioassays demonstrated an antifungal effect of a basic sugar beet chitinase on Cercospora beticola , the causal agent of leaf spot disease in sugar beet ( Beta vulgaris ). In one assay, the growth of submerged spore cultures of C. beticola in microtitre wells was followed by measuring the increase in absorbance at 620 nm. Addition of chitinase to the culture resulted in a delay in germination and a slower initial growth rate. A more detailed picture of the action of the chitinase on the fungal cell wall was provided by an autoradiographic study. An intense labelling was observed at the apex of fungal hyphae grown in medium containing [³H] N -acetylglucosamine, through incorporation of the radioactive chitin monomer into newly synthesized chitin in the cell wall. After fixation of the fungal specimen, the radioactive labelling could be removed by treatment with purified chitinase, i.e. nascent chitin chains were hydrolysed by the enzyme. When the fungal culture was subjected to a chase phase prior to fixation, the radioactive depositions were less accessible to hydrolysis by the chitinase. HPLC analysis of the radioactive hydrolysis products released from the apex of the fungal hyphae showed that the main products were small chito-oligosaccharides, mainly dimers, trimers and tetramers of chitin.     

Computer‐aided design of improved warning systems – a case study for Botrytis control in flower bulbs*

Development and improvement of warning systems are often done empirically, relying on extensive field testing. As this approach is both costly and time‐consuming, there is a need for a more rational and efficient alternative. In a study to explore the options for improvement of a Botrytis warning system in flower bulbs, we applied a computer‐based approach to systems design. The approach consisted of the construction and evaluation of modified versions of the warning system using epidemiological knowledge, data sets of recorded and forecast weather and a simulation model of epidemic development and fungicide spray impact. Performance of modified versions was evaluated with regard to fungicide input, efficacy of disease control and sensitivity to the prediction error in weather forecasts. This approach can be more efficient than a purely empirical one, as it enables the designer to limit the number of alternative versions to be field‐tested on the basis of explicit performance criteria. It also has the advantage that it provides insight into the potentials for improvement of the warning system.     

Eucablight – collating and analysing pathogenicity and resistance data on a European scale*

The Concerted Action on potato late blight ‘Eucablight’ ( http://www.eucablight.org ) was launched in 2003 to promote collaboration between researchers across Europe and to collate the previously fragmented data on host resistance to late blight and characterization of populations of its causal agent, Phytophthora infestans. Fundamental to the project was the development of standardized protocols, databases and data collection tools with which data from across Europe could be centralized. The ultimate aim was to capitalize on the vast resource of data available in order to allow a pan‐European analysis to be conducted. The P. infestans database is currently populated with information relating to over 15 000 isolates from 20 European countries. The host resistance database holds primary disease data, and derived statistics, from more than 50 field trials assessing mainly foliage blight resistance. The use of five standard cultivars in these trials facilitated the comparison of resistance information across years and regions. The host database is structured, and made accessible, in such a way that DSS builders can access the model parameters they need to construct locally adapted forecasting systems. In this presentation we describe the database and the data analysis tools that have been developed in this project and how they are directly applicable to other host‐pathogen systems.     

SIMBLIGHT1 – a new model to predict first occurrence of potato late blight*

Prediction of the first occurrence of potato late blight (Phytophthora infestans) given by the SIMPHYT1 model, which has been used for about 20 years, has not been found satisfactory in years with high soil moisture. Consequently, a new model, SIMBLIGHT1, has been developed. As input parameters SIMBLIGHT1 requires temperature, relative humidity and information on soil moisture, crop prevalence and cultivar susceptibility. SIMBLIGHT1 calculates a cumulative risk index for several groups of emergence dates and signals the start of the epidemic once a given threshold is overridden. Model validation and comparison of SIMBLIGHT1 with SIMPHYT1 were performed with field data from 11 years. Results were promising and SIMBLIGHT1 gave better results than SIMPHYT1 when soils of potato fields were waterlogged. Efforts are currently being made to improve SIMBLIGHT1 and in the long term this model will replace SIMPHYT1.     

VIPS – a web‐based decision support system for farmers,agricultural extension services and agricultural scientists*

In Norway, the new web‐based warning system called VIPS aims to give open access to all the information needed for farmers to reduce their reliance on plant protection products. VIPS calculates warnings for 70 weather stations for several pests in selected fruits, vegetables and cereals. Registered users may adjust the climatic data used in the models and record field observations to get private warnings. They may also use the system to record farm practices. VIPS is unique in several aspects: (1) it has a general user interface for all crops and pests, and the user gets a quick overview of which pests to look out for; (2) all warnings are site‐specific and linked to an authorized weather station which supplies validated meteorological data. The extension service supplies the validated biological data necessary to run the models; (3) the presentation is layered under the weather stations of each county. The first level gives information of danger (red), possible danger (yellow) and no danger (green) for each model (past 5 days/coming 5 days). The next three levels give information of the specific model, historical data and exact values of the input parameters used in the models for the calculations.     

Warning system in Portugal – organization and technical basis of forecasting*

The forecasting and warning system in Portugal started in 1964 with a control programme applied against Plasmopara viticola, the most important pathogen of grapevine. Since then, studies and new techniques have been developed and applied to other important pests of vineyards and orchards, on the basis of epidemiological and climatic data that supports technical evaluation of the risk. In the last few years, mathematical models have been evaluated as an important part of the control strategy, integrated with biological data from field monitoring. At the moment, forecasting models are available for Plasmopara viticola, Venturia pirina, Venturia inaequalis and Cydia pomonella. The integration of forecasting models with field observations is used to formulate warnings that are sent out to farmers about the need to spray or not.     

The effect of benzothiadiazole and fungal extracts of Cercospora beticola and Fusarium graminearum on phosphoenolpyruvate carboxylase activity in cucumber leaves

Journal of Plant Diseases and Protection - The cytosolic phosphoenolpyruvate carboxylase (PEPC) catalyses the anaplerotic synthesis of oxalacetic acid resulting in the replenishment of citric acid...     

PUCREC/PUCTRI – a decision support system for the control of leaf rust of winter wheat and winter rye*

During a three‐year project from 2003 to 2006, two models have been developed to predict leaf rust (Puccinia recondita and P. triticina) occurrence and to simulate disease incidence progress curves on the upper leaf layers of winter rye (PUCREC) and winter wheat (PUCTRI). As input parameters the models use air temperature, relative humidity and precipitation. PUCREC and PUCTRI firstly calculate daily infection favourability and a cumulative infection pressure index and, in a second step, disease incidence is estimated. An ontogenetic model (SIMONTO) is used to link disease predictions to crop development. PUCREC and PUCTRI have been validated with data from 2001 to 2005. Both models give satisfactory results in simulating leaf rust epidemics and forecasting dates when action thresholds for leaf rust control are exceeded.