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Identification of QoI mutation in soybean pathogens in Brazil

Flávia Elis de Mello: Londrina State University

<div>Excessive sprays of quinone outside inhibitors fungicides (QoI) in Brazilian soybean crops have contributed to the development of resistant populations of <em>Cercospora kikuchii,</em> <em>Colletotrichum truncatum</em> and <em>Corynespora cassiicola</em>. We investigated the molecular mechanisms of resistance to QoIs in these populations for the target gene cytochrome b and the occurrence of cross resistance. Fungi were isolated from several soybean fields sampled in different seasons. Cross resistance was tested for <em>C. kikuchii</em> and <em>C. cassiicola</em> by radial growth assay in amended media using discriminatory dose (10 μg mL<sup>-1</sup>) of Azoxystrobin (AZX), Picoxystrobin (PCX) and Pyraclostrobin (PRC) fungicides. The change from glycine to alanine at position 143 (G143A) was detected for <em>C. kikuchii</em>, <em>C. cassiicola</em> and <em>C. truncatum</em> isolates. The nucleotide sequence at amino acid position 143 was converted from GGT in sensitive to GCT in resistant isolates.. Positive cross-resistance was observed in more than 86% of <em>C. cassiicola</em> and <em>C. kikuchii</em> isolates. Negative cross-resistance between PRC x PCX and PRC x AZX was observed in <em>C. cassiicola</em> and <em>C. kikuchii</em>, respectively and for AZX x PCX for <em>C. kikuchii</em>. This is the first report of the G143A mutation of these pathogens in Brazil.</div>