Species diversity, resistance to MBC fungicides, and low sensitivity to azoxystrobin in field isolates of Colletotrichum spp. associated with soybean anthracnose in Mato Grosso and Goiás States, Brazil

The diversity of Colletotrichum species that cause soybean anthracnose results in different levels of sensitivity to the fungicides used in disease management. The inefficacy of fungicides in Brazil has already been reported, leading to losses in soybean production. This study aimed to determine the species diversity and inhibitory effects of fungicides on Colletotrichum spp. isolates associated with soybean anthracnose, and to characterize possible resistance mutations to quinone outside inhibitors (QoIs) and methyl benzimidazole carbamates (MBCs). C. plurivorum and C. musicola isolates showed low sensitivity to azoxystrobin in in vitro bioassays (EC50 > 100 μg.mL−1), while C. truncatum and C. sojae isolates were sensitive (EC50 < 50 μg.mL−1). However, only one C. musicola isolate carried the resistance mutation G143A. C. plurivorum and C. musicola isolates were resistant to thiophanate-methyl and showed the E198A mutation in the β-tub gene, whereas C. truncatum and C. sojae isolates were sensitive and lack the resistance mutation. Thus, the precise identification of the Colletotrichum species involved in the pathosystem and the monitoring of fungicide resistant isolates are urgently needed. Due to the detection of low sensitivity to azoxystrobin and resistance to thiophanate-methyl, together with the practical difficulty of identifying Colletotrichum species promptly in the field, these fungicides may not be effective in controlling anthracnose in soybean in Mato Grosso and Goiás States, Brazil. Fungicides with different modes of action should be investigated as well as anti-resistance strategies to extend the useful life of the chemicals used to control this disease.