Identification and fungicide sensitivity of Cercospora spp on soybeans in Brazil, etiology of atypical leaf spots on cotton and fungicide sensitivity of Corynespora cassiicola isolates obtained from soybean and cotton

• Ano de defesa: 2024
• Autor(a) principal: Sacon, Deivid
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Fitopatologia
• Palavras-chave em Português: Plantas - Efeito dos fungicidas; Soja - Doenças e pragas - Controle; Algodão - Doenças e pragas - Controle; Folhas - Doenças e pragas; Fungos fitopatogênicos; Cercospora; Corynespora; Fitopatologia
• Link de acesso: https://locus.ufv.br/handle/123456789/34113; https://doi.org/10.47328/ufvbbt.2025.211

Foliar and seeds diseases are limiting factors on soybean and cotton production, particularly Cercospora leaf blight (CLB) and purple seed stain (PSS) on soybean, which have shown an increase in incidence in recent years. This rise may be attributed to recent changes in the disease etiology or to the emergence of fungicide resistance, bringing new challenges for the sustainable management of these diseases. Similarly, target spot, caused by Corynespora cassiicola, has gained prominence due to its early onset, high severity, and challenges in control, particularly in cotton, but also on soybeans. The use of site-specific fungicides, alone or in combination with multisite fungicides, remains a fundamental control measure against 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 is addressed aiming to understand the increasing prevalence of Cercospora leaf blight (CLB) and purple seed stain (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 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 Cercospora leaf blight (CLB) and purple seed stain (PSS), while C. kikuchii and C. physalidis occur less frequently. Molecular analyses revealed widespread resistance mechanisms, including the G143A substitution in Cytb conferring strobilurin resistance and E198A in ß-tubulin linked to benzimidazole resistance. Variability in sensitivity to DMIs and SDHIs suggests additional resistance mechanisms, emphasizing the need for robust fungicide monitoring programs. 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 ß-tubulin. In this scenario, metyltetraprole and pidyflumetofen showed very good fungitoxicity, owing to their high intrinsic toxicity. Additionally, 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. Keywords: Cercospora leaf blight; Resistance; Target spot.