Resistance to quinone-outside inhibitor (Qoi) fungicides in colletotrichum species isolated from anthracnose disease occurring in Thailand

Abstract

Colletotrichum species are plant pathogens causing anthracnose diseases in many crops that result in significant reduction of quality and quantity of the crop products. Management of these diseases has become increasingly difficult recently due to the development of fungicide resistance in pathogens. Thus, monitoring for fungicide sensitivity in the pathogen is important to manage these diseases. The isolates of Colletotrichum species were isolated from anthracnose disease on various crops collected during 2016-2017 in central and southern Thailand. They were tested for their mycelium growth sensitivity to azoxystrobin, a quinone-outside inhibitor (QoI) fungicide and their internal transcribed spacer (ITS) and 5.8S regions of rDNA were analyzed. The results showed that eleven out of twenty four isolates of Colletotrichum species were resistant to azoxystrobin. They were able to grow on PDA amended with 100 mg/l azoxystrobin in the presence of salicylhydroxamic acid (SHAM) at 100 mg/l. Moreover, two isolates of azoxystrobin-resistant Colletotrichum spp. produced much larger lesions than azoxystrobin-sensitive isolates on mango fruits after treatment with 100 mg/l azoxystrobin. This is the first report on the occurrence of azoxystrobin resistance in Colletotrichum species present in Thailand and will contribute to the management of these important diseases in the future.