Sensitivity of Cercospora spp. to SDHI, QoI, DMI and SBI fungicides and resistance to QoI fungicides in Brazil

Abstract

The most widely used control strategy for PSS (Purple Seed Stain) and CLB (Cercospora Leaf Blight), caused by the fungus Cercospora, is fungicides, which are essential for managing these diseases. However, cases of reduced sensitivity of these fungi to fungicides have been reported, as well as an increase in mutations for different chemical groups. Therefore, it is crucial to monitor the sensitivity of fungal species to the main fungicides used in soybean crops and identify the presence of mutations. This study aimed to evaluate the sensitivity alteration of Cercospora spp. species in response to different fungicides, as well as to identify the G143A mutation in the cytb gene, related to resistance to the QoI chemical group. Isolates of Cercospora spp. were collected from different soybean-producing regions in Brazil. To determine the sensitivity of the isolates, the effective concentration (EC₅₀) was determined in vitro using fungicides from different chemical groups, including SDHI, QoI, DMI, and SBI. The fungicide concentrations added to the PDA culture medium were: 1 mg.L^-1, 10 mg.L^-1, 50 mg.L^-1, and 100 mg.L^-1, with a control treatment of 0 mg.L^-1. For the identification of the G143A mutation in the cytb gene, genetic sequencing was performed on 29 isolates. The SDHI fungicides showed EC₅₀ values ranging from 53.91 to 100 mg.L^-1 for Cercospora spp., indicating reduced sensitivity. The AZB fungicide (QoI) presented an EC₅₀ value of 100 mg.L^-1 for the tested species, which were insensitive. The DMI fungicides showed variations in EC₅₀ values (0.12 to 100 mg.L^-1), with species exhibiting variable sensitivity. The FPM fungicide (SBI) showed the lowest EC₅₀ values <1 mg.L^-1, with species being extremely sensitive. Resistance mutations in the G143A gene were detected in 86% of the isolates. Therefore, the results show that Cercospora species exhibited variations in sensitivity to fungicides, with DFZ, MFTZ, and FPM fungicides being the most fungitoxic and BFZ, BIX, FXD, PFF, and AZB being the least fungitoxic. The identification of the G143A mutation in the isolates underscores the importance of continuous monitoring and the use of practices that contribute to resistance management.