Validação do método de microplaca e estudos sobre a resistência ao fungicida fluxapiroxade em populações de Pyricularia graminis-tritici no Brasil
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Data
2017-08-31
Autores
Casado, Priscila Santos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Na primeira etapa da nossa pesquisa propusemos e testamos a utilização de um método baseado em leitor automatizado de microplacas para detectar resistência a fungicidas em populações do fungo hemibiotrófico fitopatogênico Pyricularia graminis-tritici (Pygt) associado à brusone do trigo no Brasil. A disponibilidade de um método mais rápido, acurado e eficiente para detecção de resistência a fungicidas facilitaria a tomada de decisão sobre o manejo químico da brusone do trigo no país. Como há indícios da ineficácia de fungicidas triazóis (DMI) no controle da brusone do trigo e evidências da ocorrência generalizada de resistência a estrobilurinas (QoI) em populações de Pygt no Brasil, inicialmente, testou-se a aplicação do método de microplacas para detecção de resistência a estes dois grupos de fungicidas. O método de microplaca foi acurado em discriminar a variação fenotípica na sensibilidade entre isolados do patógeno aos fungicidas DMI tebuconazol e epoxiconazol e ao fungicida QoI azoxistrobina. Economicamente, ambos os métodos representam um alto investimento inicial. Portanto, é necessário analisar, de forma integral, as necessidades de cada laboratório ou grupo de pesquisa quanto à aquisição dos equipamentos necessários para a fenotipagem visando detecção de resistência a fungicidas em atividades de rotina. Na segunda etapa do nosso estudo buscou-se evidências de resistência ao fungicida SDHI fluxapiroxade em populações de Pygt. Para se estabelecer o baseline de populações do patógeno da brusone do trigo ao fungicida fluxapiroxade, determinou-se a distribuição de frequência de padrões de sensibilidade, com base na EC50 (concentração suficiente para inibir 50% do crescimento micelial fúngico) de cada isolado. Fenótipos extremos de sensibilidade e resistência a fluxapiroxade foram detectados nas diferentes populações do patógeno. Considerando que os fungicidas da segunda geração de SDHI são de alto risco para desenvolvimento de resistência em populações de fipatógenos, é necessária a avaliação do registro e recomendação de uso contínuo do fluxapiroxade, como único princípio ativo numa formulação para o manejo da brusone e de outras doenças do trigo no Brasil. Como estratégia anti-emergência para evitar resistência a SDHI, esse fungicida só poderia ser registrado em co-formulações com outro princípio ativo de baixo risco para resistência.
In the first part of our study, we proposed and tested the use of an automated microplate reader to detect resistance to fungicides in populations of the plant pathogenic hemibiotrophic fungus Pyricularia graminis-tritici (Pygt) associated with the wheat blast disease in Brazil. The availability of a faster, more accurate and efficient method for detecting resistance to fungicies would facilitate the decision making on the chemical management of wheat blast in the country. Because there is indication of inefficacy of triazole fungicides (DMI) for wheat blast control and evidence of the widespread occurrence of strobilurin (QoI) resistance in pathogen populations in Brazil, initially, we tested the application of the microplate method for detecting resistance to these two fungicide groups. The microplate method was accurate in discriminating the phenotypic variation in sensitivity between isolates of the pathogen to the fungicides DMI tebuconazole and epoxiconazole and the fungicide QoI azoxystrobin. Economically, both methods require a high initial investment. Therefore, it is necessary to fully analyze the needs of each laboratory or research group regarding the acquisition of the equipments necessary for phenotyping to detect resistance to fungicides in routine activities. In the second part of our study, using the microplate method, we searched for evidence of resistance to the SDHI fungicide fluxapiroxade in populations of Pygt. To establish the baseline of populations of the wheat blast pathogen to fluxapiroxade, the frequency distribution of sensitivity patterns was determined based on the EC50 (concentration sufficient to inhibit 50% mycelial fungal growth) of each isolate. Extreme phenotypes of sensitivity and resistance to fluxapiroxade were detected in the different pathogen populations. Whereas the second generation of SDHI fungicides are at high risk for development of resistance in populations of plant pathogens, it is necessary to review the labeling and recommendation of continuous application of fluxapyroxad, as the sole active ingredient in any formulation for chemical management of wheat blast and other wheat diseases in Brazil. As an antiemergence strategy to avoid the resistance to SDHI, this fungicide could only be labeled in co-formulations with another active ingredient of low risk for resistance.
In the first part of our study, we proposed and tested the use of an automated microplate reader to detect resistance to fungicides in populations of the plant pathogenic hemibiotrophic fungus Pyricularia graminis-tritici (Pygt) associated with the wheat blast disease in Brazil. The availability of a faster, more accurate and efficient method for detecting resistance to fungicies would facilitate the decision making on the chemical management of wheat blast in the country. Because there is indication of inefficacy of triazole fungicides (DMI) for wheat blast control and evidence of the widespread occurrence of strobilurin (QoI) resistance in pathogen populations in Brazil, initially, we tested the application of the microplate method for detecting resistance to these two fungicide groups. The microplate method was accurate in discriminating the phenotypic variation in sensitivity between isolates of the pathogen to the fungicides DMI tebuconazole and epoxiconazole and the fungicide QoI azoxystrobin. Economically, both methods require a high initial investment. Therefore, it is necessary to fully analyze the needs of each laboratory or research group regarding the acquisition of the equipments necessary for phenotyping to detect resistance to fungicides in routine activities. In the second part of our study, using the microplate method, we searched for evidence of resistance to the SDHI fungicide fluxapiroxade in populations of Pygt. To establish the baseline of populations of the wheat blast pathogen to fluxapiroxade, the frequency distribution of sensitivity patterns was determined based on the EC50 (concentration sufficient to inhibit 50% mycelial fungal growth) of each isolate. Extreme phenotypes of sensitivity and resistance to fluxapiroxade were detected in the different pathogen populations. Whereas the second generation of SDHI fungicides are at high risk for development of resistance in populations of plant pathogens, it is necessary to review the labeling and recommendation of continuous application of fluxapyroxad, as the sole active ingredient in any formulation for chemical management of wheat blast and other wheat diseases in Brazil. As an antiemergence strategy to avoid the resistance to SDHI, this fungicide could only be labeled in co-formulations with another active ingredient of low risk for resistance.
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Palavras-chave
Método rápido, Acurado, Resistência a fungicidas, Mutação, Seleção Natural, Fast, Accurate method, Resistance to fungicides, Mutation, Natural selection