Bremia lactucae: monitoramento, dinâmica populacional e sensibilidade a fungicidas
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Data
2020-05-18
Autores
Franco, Carolina Andrade [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O míldio da alface causado pelo oomiceto Bremia lactucae representa uma das doenças mais importantes na cultura da alface. Sua variabilidade genética tem sido estudada no mundo. O monitoramento constante faz-se necessário pois torna possível avaliar a diversidade do patógeno, auxiliando no melhor uso das ferramentas disponíveis para controle de B. lactucae, como o uso de fungicidas e cultivares resistentes. Assim, objetivou-se com este trabalho monitorar, estudar a dinâmica populacional e determinar metodologias para a avaliação da sensibilidade dos isolados de B. lactucae a fungicidas. Isolados de B. lactucae foram coletados no Rio Grande do Sul em 2015, e no Paraná e São Paulo em 2016. Em relação a sensibilidade de B. lactucae, foram avaliados os fungicidas dimetomorfe, mandipropamida e oxathiapiprolin, submetidos a diferentes doses, aplicados diretamente nas folhas cotiledonares ou na raiz de plântulas de alface. As populações avaliadas de B. lactucae nos estados de Paraná, Rio Grande do Sul e São Paulo possuem semelhança, compartilhando nove dos 15 fatores de virulência avaliados. Foram encontrados 27 fenótipos de virulência, mas apenas os correspondentes aos códigos sextetos 31-00-00, 31-00-02, 31-01-00 e 31-01-02 foram mais frequentes neste estudo. Além disso, a reprodução clonal mostra-se como principal forma de propagação de B. lactucae. Os genes e fatores de resistência das cultivares Argelès (Dm38), Balesta e Bartoli podem ser recomendados como fontes de resistência para o melhoramento genético visando resistência ao míldio da alface para as três populações brasileiras avaliadas neste estudo. Em relação a sensibilidade dos fungicidas avaliados, mesmo na dose de 50 mg L-1, quando aplicado na raiz houve esporulação dos isolados avaliados. Já a dose de 10 mg L-1 dos fungicidas dimetomorfe, mandipropamida e oxathiapiprolin, quando aplicados diretamente nas folhas foi suficiente para inibir a infecção causada pelo míldio da alface. Assim, a pulverização dos fungicidas nas folhas é mais confiável para a avaliação de sensibilidade de B. lactucae em condições similares às avaliadas no presente trabalho.
Lettuce downy mildew caused by the oomycete Bremia lactucae represents one of the most important diseases in lettuce culture. Its genetic variability has been studied worldwide. Constant monitoring is necessary because it makes it possible to assess the diversity of the pathogen, helping to make the best use of the tools available to control B. lactucae, such as the use of fungicides and resistant cultivars. Thus, the aim of this work was to monitor, study population dynamics and determine methodologies for assessing the sensitivity of B. lactucae isolates to fungicides. Isolates of B. lactucae were collected in Rio Grande do Sul in 2015, and in Paraná and São Paulo in 2016. Regarding the sensitivity of B. lactucae, dimethomorph, mandipropamid and oxathiapiprolin fungicides were evaluated, submitted to different doses, applied directly on cotyledons leaves or on the root. The populations evaluated for B. lactucae in the states of Paraná, Rio Grande do Sul and São Paulo are similar, sharing nine of the 15 virulence factors evaluated. 27 virulence phenotypes were found, but only those corresponding to the sextet codes 31-00-00, 31-00-02, 31-01-00 and 31-01-02 were more frequent in this study. In addition, clonal reproduction seems to be the main propagation of B. lactucae. The genes and resistance factors of the cultivars Argelès (Dm38), Balesta and Bartoli can be recommended as sources of resistance for genetic improvement aiming resistance to lettuce downy mildew for the three Brazilian populations evaluated in this study. Regarding the sensitivity of the evaluated fungicides, even at the dose of 50 mg L-1, when applied to the root, there was sporulation of the evaluated isolates. The 10 mg L-1 dose of the fungicides dimethomorph, mandipropamid and oxathiapiprolin, when applied directly to the leaves, was enough to inhibit the infection caused by lettuce downy mildew. Thus, the spraying fungicides on the leaves is more reliable for assessing the sensitivity of B. lactucae under conditions similar to those evaluated in the present study.
Lettuce downy mildew caused by the oomycete Bremia lactucae represents one of the most important diseases in lettuce culture. Its genetic variability has been studied worldwide. Constant monitoring is necessary because it makes it possible to assess the diversity of the pathogen, helping to make the best use of the tools available to control B. lactucae, such as the use of fungicides and resistant cultivars. Thus, the aim of this work was to monitor, study population dynamics and determine methodologies for assessing the sensitivity of B. lactucae isolates to fungicides. Isolates of B. lactucae were collected in Rio Grande do Sul in 2015, and in Paraná and São Paulo in 2016. Regarding the sensitivity of B. lactucae, dimethomorph, mandipropamid and oxathiapiprolin fungicides were evaluated, submitted to different doses, applied directly on cotyledons leaves or on the root. The populations evaluated for B. lactucae in the states of Paraná, Rio Grande do Sul and São Paulo are similar, sharing nine of the 15 virulence factors evaluated. 27 virulence phenotypes were found, but only those corresponding to the sextet codes 31-00-00, 31-00-02, 31-01-00 and 31-01-02 were more frequent in this study. In addition, clonal reproduction seems to be the main propagation of B. lactucae. The genes and resistance factors of the cultivars Argelès (Dm38), Balesta and Bartoli can be recommended as sources of resistance for genetic improvement aiming resistance to lettuce downy mildew for the three Brazilian populations evaluated in this study. Regarding the sensitivity of the evaluated fungicides, even at the dose of 50 mg L-1, when applied to the root, there was sporulation of the evaluated isolates. The 10 mg L-1 dose of the fungicides dimethomorph, mandipropamid and oxathiapiprolin, when applied directly to the leaves, was enough to inhibit the infection caused by lettuce downy mildew. Thus, the spraying fungicides on the leaves is more reliable for assessing the sensitivity of B. lactucae under conditions similar to those evaluated in the present study.
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Palavras-chave
Lactuca sativa L., Dm genes, Míldio da alface, Resistência genética, Resistência a fungicidas