Monitoring of thiophanate-methyl-resistant strains of the fungi causing Fusarium head blight in Mie Prefecture, Japan

Abstract

Fusarium head blight (FHB) is a significant fungal disease of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) that can cause severe crop losses. The causal pathogens also produce toxins. In this study, 1,280 Fusarium graminearum Schwabe species complex (FGSC) isolates were obtained from sporodochia on symptomatic spikelets of wheat and barley in 437 fields in Mie Prefecture, Japan, from 2008 to 2021. The resistance of the FGSC isolates to methyl benzimidazole carbamate fungicides (MBC) was determined using the minimum inhibitory concentration method and testing for the presence of single nucleotide polymorphisms of the β2-tubulin gene coding region related to MBC resistance. The isolates established in this study had multiple amino acid mutations in the β2-tubulin gene-coding region. The F200Y and F167Y mutations were found among the highly resistant isolates, and the E198Q was found among the moderately resistant isolates. This is the first report of the E198Q mutation being detected outside of China. The isolates with the F200Y mutation, which showed high resistance to thiophanate-methyl, were only detected in 2008 and 2018. Additionally, the isolates with the F167Y mutation, which showed high resistance to thiophanate-methyl, were only detected in 2020 and 2021. In Mie Prefecture, which has a pest management system that controls the FHB once a year during the flowering period of wheat and barley, MBC-resistant strains are still low.