Control Of Potato Late Blight Research Articles

农药组合防治马铃薯晚疫病试验研究

农药组合防治马铃薯晚疫病试验研究

Combining Different Potato-Associated Pseudomonas Strains for Improved Biocontrol of Phytophthora infestans.

Late blight caused by Phytophthora infestans is considered as the most devastating disease of potato and is a re-emerging problem worldwide. Current late blight control practices rely mostly on synthetic fungicides or copper-based products, but growing awareness of the negative impact of these compounds on the environment has led to the search for alternative control measures. A collection of Pseudomonas strains isolated from both the rhizosphere and the phyllosphere of potato was recently characterized for in vitro protective effects against P. infestans. In the present study, we used a leaf disk assay with three different potato cultivars to compare the disease inhibition capacity of nine selected Pseudomonas strains when applied alone or in all possible dual and triple combinations. Results showed a strong cultivar effect and identified strains previously thought to be inactive based on in vitro assays as the best biocontrol candidates. One strain was much more active alone than in combination with other strains, while two other strains provided significantly better protection in dual combination than when applied alone. A subset of five strains was then further selected to determine their mutual influence on each other’s survival and growth, as well as to characterize their activity against P. infestans in more details. This revealed that the two strains whose dual combination was particularly efficient were only weakly interfering with each other’s growth and had complementary modes of action. Our results highlight the potential to harness the crop’s native rhizosphere and phyllosphere microbiome through re-assembling strains with differing modes of action into small communities, thereby providing more consistent protection than with the application of single strains. We consider this as a first step toward more elaborate microbiome management efforts, which shall be integrated into global strategies for sustainable control of potato late blight.

Translocation of phosphite encourages the protection against Phytophthora infestans in potato: The efficiency and efficacy

Phosphite (Phi)-based fungicides, such as the commercial product Phostrol™, are widely used in potato late blight control. However, the Phi translocation efficiency and the efficacy against pathogen are less discussed. In this study, the Phi concentration were quantified by high performance ion chromatography (HPIC) and the Phi translocation efficiency in potato tissues was evaluated using potato cultivar Russet Burbank with foliar application of the Phostrol solution both under greenhouse and field conditions. In the greenhouse trials, it was found that Phi was translocated from leaves to roots within 3 h and its concentration was significantly increased in the roots 24 h after the Phostrol application. In the field trials, the application rate of Phostrol affected the Phi translocation in potato tubers. To assess the efficacy of Phi against P. infestans, both the inhibition and infection tests were carried out. In the inhibition tests, three most common strains of P. infestans in Canada (US-8, US-23 and US-24) were inoculated on pea agar containing different levels of Phi. In the infection tests, both of detached leaves and whole tubers that received Phi were infected by the three strains of P. infestans. The in vitro tests indicated that the US-8 strain is the most tolerant whereas the US-23 strain is the most sensitive to Phi. Also, the in vivo tests demonstrated the dose-dependent translocation of Phi in potato leaves and tubers decreased the severity of infection by P. infestans. Moreover, potential defense mechanisms related to salicylic acid (SA) and jasmonic acid (JA) pathways that might be activated by Phi were also explored. Overall, the results of the study provided evidences that high Phi translocation efficiency encouraged late blight suppression in potato production.

Low evolutionary risk of iprovalicarb resistance in Phytophthora infestans

Iprovalicarb is a carboxylic acid amide (CAA) fungicide, highly effective in the control of potato late blight, causing by Phytophthora infestans. Due to cross-resistance with other CAA fungicides and moderate resistance risk of P. capsici to iprovalicarb, the evolutionary risk of P. infestans resistance to this fungicide and the contribution of inherited genes and environmental effect was evaluated using a common garden experiment. The results showed that the ratio of heritability and plasticity of iprovalicarb in the seven populations equaled 1.0, indicating both inherited genes and environmental factors were essential to iprovalicarb sensitivity in P. infestans. The pairwise population differentiation determined by SSR loci (FST) between populations ranged from 0.007 to 0.133 and the overall FST was significantly higher than population differentiation in RGR (QST), suggesting constraining selection acting on iprovalicarb sensitivity. We also found a new indicator of growth rate inhibition (GRI) for fungicide sensitivity, which was negatively correlated to growth rate in the absence of iprovalicarb, indicating a trade-off between iprovalicarb resistance and pathogen's growth. The constraining selection plus a trade-off between GRI and growth rate revealed low risk of P. infestans evolving resistance to iprovalicarb.

IPMBlight2.0 - IPM2.0 for sustainable control of potato late blight - exploiting pathogen population data for optimized Decisions Support Systems - FP7

IPMBlight2.0 - IPM2.0 for sustainable control of potato late blight - exploiting pathogen population data for optimized Decisions Support Systems - FP7

Integrated control of potato late blight: predicting the combined efficacy of host resistance and fungicides

Integrating cultivars that are partially resistant with reduced fungicide doses offers growers an opportunity to decrease fungicide input but still maintain disease control. To use integrated control strategies in practice requires a method to determine the combined effectiveness of particular cultivar and fungicide dose combinations. Simple models, such as additive dose models (ADM) and multiplicative survival models (MSM), have been used previously to determine the joint action of two or more pesticides. This study tests whether a model based on multiplicative survival principles can predict the joint action of fungicide doses combined with cultivars of differing partial host resistance. Data from eight field experiments on potato late blight (Phytophthora infestans) were used to test the model; the severity of foliar blight was assessed and scores used to calculate the area under the disease progress curve (AUDPC). A subset of data, derived from the most susceptible cultivar, King Edward, was used to produce dose–response curves from which parameter values were estimated, quantifying fungicide efficacy. These values, along with the untreated values for the more resistant cultivars, Cara and Sarpo Mira, were used to predict the combined efficacy of the remaining cultivar by fungicide dose combinations. Predicted efficacy was compared against observations from an independent subset of treatments from the field experiments. The analysis demonstrated that multiplicative survival principles can be applied to describe the joint efficacy of host resistance and fungicide dose combinations.

Simulating crop-disease interactions in agricultural landscapes to analyse the effectiveness of host resistance in disease control: The case of potato late blight

Disease-resistant potato varieties can play a key role in sustainable control of potato late blight. However, when these varieties are more widely used, resistance breakdown can occur as a result of pathogen adaptation. Here we focussed on potato cultivation in the Netherlands, where new (single gene) resistant varieties have been introduced over the last ten years. This new generation of late blight resistant varieties has moderate yield levels and does not meet all market requirements. As a result, adoption rates for resistant varieties have been low so far. We developed a spatially explicit agent-based model to simulate potato production, disease spread and pathogen evolution at the landscape level. We analysed how late blight severity, resistance durability and potato yield are affected by the spatial deployment of a resistant variety, with a lower potential yield than susceptible varieties. The model was applied to an agricultural region in the Netherlands (596 km2) and was run for a period of 36 years using daily weather data as input for crop growth and disease dynamics. The short- and long-term effects of the deployment of a resistant variety were analysed with the model. With respect to short-term dynamics, years were analysed independently to study between year variation. The model demonstrated that in most years, susceptible fields without fungicide application suffered severe yield losses and resistant fields performed better despite their lower potential yield. Resistance breakdown was observed in a small fraction of fields with the resistant variety, but this did not affect mean potato yield or disease incidence in the short term since it occurred at the end of the growing season. Increasing the fraction of potato fields with the resistant variety strongly reduced late blight infection within a landscape. With respect to the long-term effects, the model showed the emergence and spread of a virulent strain over time. The virulent strain gradually took over the pathogen population, decreasing mean potato yields from fields with the resistant variety. This occurred in all landscape compositions where the resistant variety was deployed to different extents. It was found that low as well as high proportions of fields with the resistant variety could increase durability of resistance. With these findings, the model provided more insight into the opportunities and risks related to the use of plant resistance in disease control, an important and sustainable disease management strategy.

Study on Biological and Economic Considerations in the Control of Potato Late Blight and Potato Tuber Blight

An economic analysis was made of old results from 1993-1996 (22 field trials) and new results from 2010-2013 (12 field trials) obtained in field trials with different doses of fungicides to control potato late blight (PLB) and potato tuber blight (PTB) caused by Phytophthora infestans. The objective was to determine the economically optimal dose for effective control. In 1993-1996, the economic net return was highest for long intervals of about two weeks between treatments and a dose of 60% of the recommended level. The difference between the experimental treatment with the highest net return and the untreated control was 1587 € per hectare (ha-1) in susceptible cultivars, but only 531 € ha-1 in moderately resistant cultivars. In addition, the mean difference in net return between all treated susceptible and all treated moderately resistant cultivars was 874 € ha-1. In the half of the field trials with the lowest maximum attack of PLB, the difference between the experimental treatment with the highest economic income and untreated control was 547 € ha-1, while it was 1571 € ha-1 in the half of the trials with the highest maximum attack. The results for 2010-2013, which were all based on a short treatment interval of about one week between treatments, showed that in table potato the economic net return was highest at 100% and 75% of the recommended dose, whereas in starch potato cultivars it was highest at 50% and 25% of the recommended dose. The net financial result was calculated for 13 different scenarios. As expected, potato price and potato crop yield and quality were of the greatest importance. The price of fungicides affected net profits by between 167 and 656 € ha-1 depending on treatment intervals and dose. These results challenge the way in which late blight is controlled in conventional potato farming today, especially in starch potatoes. We therefore propose investment in future years be based on the dose-range response in cultivars with differing host resistance to both PLB and PTB, and on forecasting and warning with respect to PLB- and PTB-control in different potato cultivars. We believe that such investment could be very valuable in optimizing the use of fungicides in potato cultivation.

Botanicals and Phosphonate Show Potential to Replace Copper for Control of Potato Late Blight.

Potato late blight (PLB) caused by Phytophthora infestans (Pi) is the most harmful disease in potato production worldwide. In organic farming, copper is used despite its persistence in soil and toxicity to soil organisms. To replace copper, suspensions of powders from three promising botanicals, including bark of buckthorn (Frangula alnus, FA), roots of medicinal rhubarb (Rheum palmatum) and galls of the nutgall tree (Galla chinensis), were tested in multi-year field experiments. The current study shows for the first time that botanicals could replace copper under field conditions and best PLB reduction on leaves was achieved with FA, reaching a level close to that of 2 to 3 kg copper per hectare and year. Better results than with copper were achieved with Phosfik® (Ph), a phosphonate-based product. For both FA and Ph, the mode of action is based on induced resistance, for Ph also on direct fungicidal effects. A disadvantage of Ph is the accumulation of residues in potato tubers. Nevertheless, two to three applications with 2 to 3 L/ha of Ph would be feasible to not exceed a minimal risk level (MLR) of 20 mg/kg of phosphorous acid as proposed by the European Food Safety Authority. Due to an excellent environmental profile and a complex mode of action counteracting Pi resistance, phosphonate-based products would be most suitable for sustainable PLB management in integrated pest management (IPM) programmes.

Analysing potato late blight control as a social-ecological system using fuzzy cognitive mapping

Potato late blight, caused by Phytophthora infestans, is one of the main diseases in potato production, causing major losses in yield. Applying environmentally harmful fungicides is the prevailing and classical method for controlling late blight, thus contaminating food and water. There is therefore a need for innovative research approaches to produce food sustainably. Here, we used a systems approach to identify sustainable management strategies for disease control in potato production in the Netherlands. We focussed not only on ecological processes, the classical approach, but also on decision-making concerning disease management. For that, we performed a literature study, stakeholder interviews and modelling using fuzzy cognitive mapping. Interviews were carried out with farmers, representatives of breeding companies and experts. The fuzzy cognitive map allows to identify major concepts and their influence on late blight management. Three management scenarios were analysed using the fuzzy cognitive map. Results show that published research on the control of potato late blight focusses on agronomic practices, plant breeding for resistance to late blight and chemical-based disease suppression. Farmers are strongly influenced by corporate (such as traders, breeders and retail) and public institutes and policies, each pushing their own objectives and interests. The fuzzy cognitive map showed that social and ecological processes are tightly related. The scenario analysis showed that increasing stakeholder cooperation and a change in market demands towards resistant cultivars could improve sustainability of late blight management. In contrast, policies restricting the use of fungicides would result in increased disease severity if no alternative strategies were implemented. Adoption of such strategies would require social-institutional support and facilitation. We conclude that our systems approach improves the understanding of the system dynamics which is necessary for developing and deploying effective strategies for controlling P. infestans.

Efficiency of a computerised decision support system as a tool to reduce fungicide input for the control of potato late blight

VNIIFBlight decision support system is intended to identify weather conditions favourable or unfavourable for the late blight outbreaks on potato. To provide an improved choice of fungicide treatment dates, we investigated the use of a standard five-day weather forecast based disease management decision support system VNIIFBlight as well as the use of information about the late blight resistance level of the cultivars used. The efficiency of this decision support system was compared with a seven-day routine program of fungicide treatments in the course of four-year field trials in Moscow region and six-year virtual trials in four regions of Russia, three regions of Lithuania, and single regions of Canada, Ukraine, Poland, and the Netherlands. According to the results of field experiments, in the case of a high infection pressure (2004 and 2008), yield losses caused by late blight in the untreated control made up 62% and 39%, respectively, whereas the losses for both compared schemes of protection did not exceed 8.2% for both years. In the case of weak disease development (2005 and 2007), for all studied treatments, including the untreated control, yield losses did not exceed 3%. In all years, the use of the VNIIFBlight decision support system significantly reduced the number of fungicidal treatments as compared to the routine scheme of protection; this reduction in 2004, 2005, 2007 and 2008 made up 62, 50, 50 and 17 %, respectively. According to the results of virtual trials, the use of the VNIIFBlight decision support system reduced the number of fungicide treatments of susceptible and resistant potato cultivars by 50% and 60% on average, respectively, as compared with the routine program.

Potato Late Blight Control Using R-Gene Polyculture by GMO

Potato (Solanum tuberosum L.) is the fourth most important crop in the world and one of the top seven important crops in china. Late blight is a devastating disease of potato caused by Phytophthora infestans (Mont.) de Bary, which was the reason of the Great Irish Famine in 1845. Today, late blight remains the No. 1 threat to potato production. In previous research, it proved that it was difficult to control potato late blight just because P. infestans ranked the highest risk in the evolutionary potential and it could easily mutate its Avr genes and thus overcome potato plants carrying corresponding R genes. So, one of the promising solutions for late blight control is to release several R genes simultaneously and to artificially create a resistance polymorphism in the field, such as the strategy so called R gene polyculture. In the past years, scientists gained a great success in cloning R genes conferring late blight resistance, providing a starting point to create R gene polyculture by means of cisgenic technology.

Preliminary Results Regarding Presence of RB Genes Homologues from Solanum Bulbocastanum in some Solanum Species

Phytophtora infestans, the causal organism of late blight, is the most important fungal pathogen of potato. In the strategy of potato late blight control utilization of resistant variety is the most important. For creating new resistant varieties Marker Assisted Selection increase significant the efficiency of this process. Genomes of several Solanum species were reported to contain RB homologues with confirmed broad-spectrum defence function. We tested 8 primers for RB gene homologues from Solanum bulbocastanum on different potato species, including S. bulbocastanum, S. demissum, and S. tuberosum. Some primers amplified only S. bulbocastanum, and others amplified olso S. demissum and S. tuberosum.

Epidemiology and Integrated Control of Potato Late Blight in Europe

Phytophthora infestans, the causal agent of late blight, is a major threat to potato production in northwestern Europe. Before 1980, the worldwide population of P. infestans outside Mexico appeared to be asexual and to consist of a single clonal lineage of A1 mating type characterized by a single genotype. It is widely believed that new strains migrated into Europe in 1976 and that this led to subsequent population changes including the introduction of the A2 mating type. The population characteristics of recently collected isolates in NW Europe show a diverse population including both mating types, sexual reproduction and oospores, although differences are observed between regions. Although it is difficult to find direct evidence that new strains are more aggressive, there are several indications from experiments and field epidemics that the aggressiveness of P. infestans has increased in the past 20 years. The relative importance of the different primary inoculum sources and specific measures for reducing their role, such as covering dumps with plastic and preventing seed tubers from becoming infected, is described for the different regions. In NW Europe, varieties with greater resistance tend not to be grown on a large scale. From the grower’s perspective, the savings in fungicide input that can be achieved with these varieties are not compensated by the higher (perceived) risk of blight. Fungicides play a crucial role in the integrated control of late blight. The spray strategies in NW Europe and a table of the specific attributes of the most important fungicides in Europe are presented. The development and use of decision support systems (DSSs) in NW Europe are described. In The Netherlands, it is estimated that almost 40% of potato growers use recommendations based on commercially available DSS. In the Nordic countries, a new DSS concept with a fixed 7-day spray interval and a variable dose rate is being tested. In the UK, commercially available DSSs are used for c. 8% of the area. The validity of Smith Periods for the new population of P. infestans in the UK is currently being evaluated.

Field efficacy of mandipropamid for the control of potato late blight

The efficacy of mandipropamid (Revus 250 SC) in controlling Phytophthora infestans in potato was evaluated in field trials. The efficacies of Revus 250 SC in comparison with standard fungicides Quadris (azoxystrobin) were tested in several localities in Serbia (Kasarske Livade, Valjevska Kamenica and Opovo) in 2007 and 2008. Both of the tested fungicides exhibited high efficacy in controlling potato late blight. The differencies in the efficacy of Revus 250 SC (96.3- 99.2%) and Quadris (94.1-95.5%) were insignificant. Our experiments showed that the investigated fungicide was highly effective against P. infestans even under high disease pressure.

Rainfall Thresholds as Support for Timing Fungicide Applications in the Control of Potato Late Blight in Ecuador and Peru.

Accumulated rainfall thresholds were studied in seven field experiments conducted in Ecuador and Peru for their value in timing applications of fungicide to control potato late blight, caused by Phytophthora infestans. Fungicide regimes based on accumulated rainfall thresholds ranging from 10 to 70 mm were compared with calendar spray schemes of every 5 or 7 days. Very low thresholds of 10 to 20 mm gave similar levels of control and resulted in similar number of sprays as did calendar spraying. However, neither low thresholds nor calendar sprays were effective in protecting susceptible potato genotypes in over half of the experiments. Thresholds of 25 to 50 mm of rainfall led to reduction in the number of sprays needed to protect resistant cultivars but also resulted in high levels of disease on susceptible cultivars. We conclude that timing fungicide sprays based on accumulated rainfall thresholds could be a successful component of integrated management strategies that include cultivars with moderate or high levels of resistance. The simplicity of measuring accumulated rainfall means that the technology can potentially be used by resource-poor farmers in developing countries.

Microbial toxicity and impacts on soil enzyme activities of pesticides used in potato cultivation

In the conventional cultivation of potatoes, weed control and the control of potato late blight caused by Phytophthora infestans are carried out by the application of herbicides and fungicides. We investigated the impacts of the herbicides metribuzin and linuron and the fungicide fluazinam on soil microbiota in microcosms, in mesocosms and in the field. The toxicity of each pesticide in solution was assessed using the luminescent bacteria test and in soil by a solid phase modification. In microcosm tests, the microbial activity and biomass were estimated by measuring several soil enzyme activities together with soil ATP content. In the mesocosm tests, the separate addition of each pesticide and the simultaneous use of all the pesticides were investigated. We monitored the impacts on ten different soil enzyme activities and measured soil toxicity with the luminescent bacteria test separately in the 5 cm top layer and in the layer from 5 to about 20 cm below the surface. During one season, the impact of the use of pesticides was monitored in the field in plots receiving pesticides for the third consecutive year and in control plots cultivated without the use of pesticides for the 3 preceding years. The pesticide concentrations were monitored in each experiment. The luminescent bacteria toxicity test revealed a strong inhibition by fluazinam. In microcosms the herbicides increased several enzyme activities but metribuzin inhibited luminescence in the bacterial test. Fluazinam was highly toxic in microcosms. In the mesocosm with combined use of pesticides, decreased activities of some enzymes were observed first in the surface soil and at harvesting also deeper in the soil. In the mesocosm experiment with separate use of pesticides, less impacts were observed. In the field experiment the pesticides decreased seven enzyme activities, when calculated per soil fresh weight but activities of four enzyme decreases if calculated per soil organic matter. Controlling weeds by herbicides decreased weed growth and the decreases in enzyme activities were interpreted to be due to the lack of the stimulating impact of weed roots. A strong inhibition in the soil toxicity test and continuing bioavailability of fluazinam were detected throughout the experiments even after winter in the field.

Comparison of two strategies for use of translaminar and contact fungicide in the control of potato late blight in the highland tropics of Ecuador

Strategies based on using the translaminar fungicide cymoxanil for control of potato late blight, caused by Phytophthora infestans, were compared in the highland tropics of Ecuador in three separate field experiments. In one strategy, a commercial formulation of cymoxanil mixed with mancozeb was sprayed sequentially three times early in the season; this was then followed by three sequential sprays of a commercial product containing mancozeb alone. For the other strategy, the same commercial products were alternated. For each strategy, a spray interval of 14 d was used after the contact/translaminar mixture and 10 d after sprays containing mancozeb alone. Both strategies were evaluated with a manually operated knapsack sprayer but with two levels of application quality. High quality was achieved with a constant pressure valve and a new nozzle, while for low quality, fungicide was applied without a valve and using a damaged nozzle. All treatment combinations gave adequate disease control and no consistent effect of application strategy or application quality could be measured on disease severity or yield. However, approximately twice the volume of fungicide was applied using poor quality equipment, regardless of the application strategy. Advantages and disadvantages of the strategies and their potential effects on fungicide resistance are discussed.

Phytophthora infestans Populations in Latvia

Phytophthora infestans Populations in Latvia Potato late blight caused by Phytophthora infestans (Mont.) de Bary is one of the most investigated plant pathogens. However, problems with disease control have increased in recent years, which plant pathologists have explained by its ability of forming oospores in potato leaves. Consequently, the P. infestans population over the world has become more aggressive and virulent and late blight on potato stems is common. Oospores could be found in field conditions in potato leaflets with two or more separate spots. In Latvia the P. infestans mating type A2 was found in the 1980s. A laboratory experiment on the formation of oospores in Latvia was started in 2002. The total number of collected samples was 215. The samples were collected from potato trial fields, conventional fields and from private gardens in different regions of Latvia. Many potato leaflets with two spots were observed at the end of the growing season when the disease severity exceeded 50%. The results showed that the formation of oospores on potato leaflets in the field took place in the P. infestans population in Latvia. Oospores were found in 80-94% of the investigated cases. The occurrence of oospores means that plant rotation and certified seed material are important measures for potato late blight control and the usage of fungicides may not be effective.

Ação de acibenzolar-s-methyl isolado e em mistura com fungicidas no controle da requeima da batata

Visando avaliar o desempenho de acibenzolar-S-methyl (BTH) isolado e em mistura com os fungicidas mancozeb, chlorothalonil e metaxyl-M+chlorothalonil no controle da requeima da batata, foram realizados dois experimentos em cultivos comerciais nos municípios paulistas de Pilar do Sul (cv. Baraka) e Bragança Paulista (cv. Asterix), de maio a agosto e agosto a outubro de 2001, respectivamente. O delineamento experimental foi o de blocos ao acaso com 4 repetições, com cada parcela medindo 25 m². Durante os experimentos foram realizadas um total de 10 pulverizações, a intervalos de 5 a 10 dias com pulverizador costal munido de barra de aplicação contendo 5 bicos TXKV26, pressão constante (4 bar) e volume médio de 800 L/ha. Avaliou-se a severidade nas folhas (0 a 100%), nas hastes ( escala de notas de 1 a 5 ) e a produtividade comercial de tubérculos. O BTH apresentou efeitos significativos de controle quando utilizado isolado e em mistura com fungicidas de contato e sistêmico. Os maiores aumentos relativos de produtividade foram verificados para as misturas de BTH com mancozeb e chlorothalonil.