Resistance of Corynespora cassiicola from soybean to QoI and MBC fungicides in Brazil

• Published in: Plant pathology Vol. 71; no. 2; pp. 373 - 385
• Main Authors: Mello, Flávia E. de, Lopes‐Caitar, Valéria S., Xavier‐Valencio, Sheila A., Silva, Helen P., Franzenburg, Sören, Mehl, Andreas, Verreet, Joseph‐Alexander, Balbi‐Peña, Maria I., Marcelino‐Guimaraes, Francismar C., Godoy, Cláudia V.
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01-02-2022
• Subjects: Association analysis; Benzimidazoles; Corynespora cassiicola; cross‐resistance; CytB gene; fungicide resistance; Fungicides; Heteroplasmy; Mutation; mutations E198A, F200Y and G143A; Pesticides; Quinones; Resistance factors; Soybeans; Sprays; Target spot; Tubulin; Brazil; Paraguay
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/ppa.13474

Fungicide sprays on soybean in Brazil have contributed to the selection of less sensitive isolates of Corynespora cassiicola. We collected 59 isolates of C. cassiicola from three Brazilian states and two isolates from Paraguay. We investigated their EC50 to quinone outside inhibitors (QoI) and methyl benzimidazole carbamate (MBC), any cross‐resistance to compounds within QoI and MBC groups, and characterized the polymorphisms in their cytb and β‐tubulin genes. Local associations of polymorphisms identified in each gene were statistically correlated with assays results. In total, 79% and 74% of the isolates were classified as resistant to QoI and MBC fungicides, respectively. There was positive cross‐resistance to active ingredients within QoI and MBC groups. For QoI, all isolates presented heteroplasmy in G143A of cytb gene; the mutations F129L and G137R were not found. For MBC, 63% of isolates possessed E198A and 21% possessed F200Y mutations, associated with reduced control by MBC fungicides. Heteroplasmy was identified in two and one isolates from Brazil with E198A and F200Y mutations, respectively. The resistance factor for isolates with E198A (10.9) was statistically similar to the isolate with F200Y (8.8) mutation. Genic association analysis of the in vitro assays using discriminatory doses proved them to be accurate. Reduced sensitivity of C. cassiicola to QoI and MBC was also identified in isolates from Paraguay and resistance to QoI and MBC was widely present in C. cassiicola isolates from the main soybean‐producing states in Brazil. Thus, integrated management measures should be adopted to manage soybean target spot in these countries.
The G143A, F200Y, and E198A mutations are associated with less efficacy of quinone outside inhibitors (QoI) and methyl benzimidazole carbamate (MBC) fungicides, respectively, to control Corynespora cassiicola on soybean in Brazil.