Detection and molecular characterization of carbendazim-resistant Colletotrichum truncatum Isolates causing anthracnose of soybean in Thailand

Abstract

© 2020 Blackwell Verlag GmbH A loss of fungicide efficacy, particularly for carbendazim, was noted in soybean fields in Thailand and was considered to be due to the development of Colletotrichum truncatum resistance. The carbendazim sensitivity of C. truncatum populations isolated from various soybean fields in Thailand was thus evaluated with in vitro sensitivity assays and molecular characterization of mutations in the sequences of the ß2-tubulin (TUB2) gene that confer carbendazim resistance in the pathogen. Among 52 isolates, 46 isolates were classified as highly resistant (HR) to carbendazim (EC50 > 1,000 µg/ml). All HR isolates grew on PDA amended with carbendazim at 1,000 µg/ml. Six isolates were classified as carbendazim sensitive (S) (EC50 < 1 µg/ml). Mycelial growth on PDA amended with 1 µg/ml carbendazim was inhibited by over 50% compared with growth on PDA alone. When a partial TUB2 gene from the isolates was amplified and analysed using predicted amino acid sequences, an alteration from glutamic acid to alanine at codon 198 (E198A) was found in 45 HR isolates for which the EC50 was higher than 2000 µg/ml. This mutation resulted from a nucleotide substitution from adenine to cytosine (GAG → GCG). The other HR isolate, CtPhS_1, with EC50 of 1,127 µg/ml, had an alteration at codon 200 (F200Y) (TTC → TAC).