Resistance assessment of pyraoxystrobin in Magnaporthe oryzae and the detection of a point mutation in cyt b that confers resistance.

Pyraoxystrobin is a new QoI fungicide developed in China. The present study was aimed at determining the baseline sensitivity of M. oryzae to pyraoxystrobin and investigating the potential resistance risk and resistance mechanism of pyraoxystrobin in M. oryzae. The results showed that the mean EC50 of 109 M. oryzae isolates to pyraoxystrobin was 0.0094 μg/mL and the sensitivity exhibited a unimodal distribution. The established baseline sensitivity could provide critical data for monitoring sensitivity changes of M. oryzae to pyraoxystrobin in rice fields. The potential resistance risk was assessed by investigating the biological characteristics of the resistant mutants obtained by fungicide adaptation. The results indicated that the resistance risk of pyraoxystrobin in M. oryzae was medium to high with positive cross-resistance between pyraoxystrobin and azoxystrobin, but without cross resistance between pyraoxystrobin and carbendazim, isoprothiolane, and prochloraz. Further investigation revealed that the pyraoxystrobin-resistant mutants had a G143S mutation in the cyt b protein. Molecular docking confirmed that the G143S substitution conferred high resistance to pyraoxystrobin in M. oryzae. Collectively, the results of this study provided essential data for monitoring the emergence of resistance and developing resistance management strategies for pyraoxystrobin.