Azoxystrobinsensitivityin<italic>Magnaporthepoae</italic>populationscollectedfromturfgrassinBeijingandanalysisofitscytochrome<italic>b</italic>(<italic>Cytb</italic>)genesequence

The effect of salicylhydroxamic acid (SHAM) on mycelial growth of Magnaporthe poae from turfgrass and in vitro azoxystrobin sensitivity were determined by mycelial growth rate method. Thereafter, the sensitivities of 114 M. poae isolates to azoxystrobin were determined by the same method. The partial sequence of M. poae cytochrome b (Cytb) gene was cloned and analyzed to investigate the molecular mechanism of the decreased sensitivity to azoxystrobin in M. poae. The results showed that the inhibition of mycelial growth by SHAM solution of different concentrations was significantly different (F = 20.812, P < 0.000 1). Sensitivity of M. poae to azoxystrobin amended with SHAM (40 μg/mL) was not significantly different from that without SHAM (F = 0.041 0, P = 0.842 3). The effective concentration for 50% inhibition of mycelial growth (EC₅₀) values of the tested isolates ranged from 0.001 0-0.146 5 μg/mL, and the average of EC₅₀ values was (0.017 4 ± 0.026 1) μg/mL. The frequency of azoxystrobin sensitivity in M. poae was not normally distributed (W = 0.499 7, P < 0.05), suggesting that sub-populations of decreased sensitivity to azoxystrobin in M. poae emerged. The majority of M. poae isolates (70.18%) have the frequency of EC₅₀ values with unimodal curve distribution (W = 0.970 8, P = 0.064 0 > 0.05), and the mean EC₅₀ value of these isolates was (0.007 8 ± 0.003 7) μg/mL, which can be used as a relative sensitivity baseline. A partial sequence of M. poae Cytb gene (8 639 bp) was obtained by aligning to the reference mitochondrial genome of M. poae. Sequence analysis revealed the presence of a 1 956 bp intron immediately downstream of codon 143. The intron was identified in all 12 isolates of M. poae Cytb with different sensitivity to azoxystrobin, and no point mutations were observed at codons 129, 137 and 143, which were responsible for azoxystrobin resistance reported previously. The results will lay a scientific basis for the effective management of summer patch disease and provide a useful reference for further investigating the molecular mechanism of the decreased sensitivity to QoIs in M. poae.