Molecular Diagnosis of Thiophanate-Methyl-Resistant Strains of Fusarium fujikuroi in Japan

Abstract

Fusarium fujikuroi is the pathogen of rice bakanae disease and is subclassified into gibberellin and fumonisin groups (G and F groups). Thiophanate-methyl (TM), a benzimidazole fungicide, has been used extensively to control F. fujikuroi. Previous investigation showed that F-group strains are TM sensitive (TMS), whereas most G-group strains are TM resistant (TMR) in Japan. The minimum inhibitory concentration in TMS strains was 1 to 10 μg ml−1, whereas that in TMR strains was >100 μg ml−1. E198K and F200Y mutations in β2-tubulin were detected in TMR strains. A loop-mediated isothermal amplification-fluorescent loop primer method was developed for diagnosis of these mutations and applied to 37 TMR strains and 56 TMS strains. The results indicated that 100% of TMR strains were identified as having either the E198K mutation (41%) or the F200Y mutation (59%), whereas none of the TMS strains tested showed either mutation. We found one remarkable TMR strain in the F group that had an F200Y mutation. These results suggest that E198K and F200Y mutations in β2-tubulin contribute to TM resistance in F. fujikuroi.