Prelecionista: Deivid Sacon
Orientador: Sergio H. Brommonschenkel
Data: Terça, 15/04/2025, às 16h
Local: Online, via Google Meet*

Resumo: Diseases are limiting factors on soybean and cotton production. On soybean, Cercospora leaf blight (CLB) and purple seed stain (PSS) have exhibited increasing incidence in recent years, which may be associated with changes in disease etiology and/or the emergence of fungicide-resistant populations. Similarly, target spot, caused by Corynespora cassiicola, has gained relevance due to its early onset, high severity, and difficulty in control, particularly on cotton, but also affecting soybean. The use of site-specific fungicides, alone or in combination with multisite fungicides, remains a fundamental strategy of management of these diseases, highlighting the critical importance of carefully positioning effective fungicides for optimal management. In this thesis the etiology, fungicide sensitivity, and resistance mechanisms of Cercospora spp. on soybean and Corynespora cassiicola on soybean and cotton crops in Brazil in addressed aiming to understand increasing prevalence of CLB and PSS on soybeans and target spot on soybean and cotton as well as the emergence of atypical lesions in cotton observed during the 2021–2024 crop seasons. A species complex comprising Cercospora sp. P, Cercospora sp. Q, Cercospora alchemillicola, and Cercospora malloti has been identified as the primary causal agents of CLB and PSS, while C. kikuchii and C. physalidis occur less frequently. Molecular analyses revealed widespread fungicide resistance mechanisms, including the G143A substitution in Cytb conferring strobilurin resistance and E198A in β-tubulin linked to benzimidazole resistance. Variability in sensitivity to DMIs and SDHIs suggests additional resistance mechanisms that are under investigation. For Corynespora cassiicola, sensitivity evaluations of 402 isolates collected between 2008 and 2024 showed the prevalence of substitutions associated with fungicide resistance such as B-H278Y and C-N75S in SDH, G143A in Cytb, and E198A and F200Y in β-tubulin. In this scenario, metyltetraprole and pidyflumetofen showed very good fungitoxicity, owing to their high intrinsic toxicity. Pathogenicity tests and molecular characterization demonstrated that C. cassiicola is the causal agent of “atypical” lesions in cotton. Overall, our findings underscore the importance of understanding the disease etiology, pathogen population dynamics over time, to support the implementation and improvement of integrated disease management strategies to reduce the impact of fungal leaf diseases on soybean and cotton production in Brazil.

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