| Strawberry grey mould is one of the most serious diseases caused by Botrytis cinerea in strawberry production,mainly occurring on strawberry fruit and causing severe fruit rot.At present,the control of strawberry grey mould at home and abroad is mainly based on chemical control,the main control agents are succinate dehydrogenase agents,such as flutriafol hydroxamate,acetamiprid,pyraclostrobin,flumioxazin and other fungicides.However,due to the diverse host species,rapid mutation and high reproductive capacity of Staphylococcus griseae,and with the widespread use of modern fungicides,Staphylococcus griseae has developed multiple resistance to a variety of agents,leading to unsatisfactory results in the actual control of strawberry grey mould.In our laboratory,we found that two SDHI fungicides,flutriafol hydroxamate and biphenylpyrazinam,have a strong inhibitory effect on the growth of mycelium of Staphylococcus griseoides.Therefore,in this paper,we further investigated the biological effects of flutriafol hydroxamate and biphenylpyrazinam,on Strawberry gray mold and their resistance risk assessment.The results of the study were as follows.The EC50 values ranged from 0.02μg/m L to 3.10μg/m L,with a mean EC50 value of0.57±0.55μg/m L.The susceptibility baseline was a single-peaked curve and no resistant strains were found.The spore germination method was used to determine the susceptibility of 110 strains of grey mould of strawberry to pydiflumetofen to establish a susceptibility baseline.The EC50 values ranged from 0.02μg/m L to 0.14μg/m L,with a mean EC50 value of 0.07±0.02μg/m L.After treatment with 0.5μg/m L and 5μg/m L(EC50)of flumioxazin,there were no significant changes in the mycelial morphology,nucleus distribution and cell wall formation of the strawberry grey mould;however,the permeability of the mycelial cell membrane of the strawberry grey mould increased and a large amount of electrolytes were exuded;the respiration rate and succinate dehydrogenase activity of the mycelium were significantly inhibited;the subcellular structure of the mycelium was destroyed and the intracellular damage was relatively severe.The mycelial subcellular structure was disrupted and the intracellular matrix was relatively severely damaged.40μg/m L of flumioxazin hydroxylamide showed good efficacy against strawberry fruit,with 68.68%protection.400μg/m L of flumioxazin hydroxylamide was 60.59%effective in treating strawberry fruit.Seven strains of strawberry grey mould resistant mutants were obtained by UV mutagenesis using three susceptible strains as parents,with a resistance frequency of 1.86 x 10-4.Compared with the parental strains,the mycelial growth rate of the mutants was enhanced or reduced to different degrees,and there was no uniform trend in the growth rate at different temperatures.The growth rate of strains 68R-1,88R-F3 and 88R-F9 was slower than that of the parental strains,and the growth rate of strain 66R-F9 was not significantly different from that of the parental strains.Fluazoxystrobin-resistant mutants 68R-1 and66R-F9 were cross-resistant to fluindazox and biphenylpyrazinam,while mutant 68R-2 was not cross-resistant to fluindazox,biphenylpyrazinam and prothioconazole.The pathogenicity results showed that the pathogenicity of the resistant strain was weaker than that of the parental strain.The other mutants were not mutated.Based on the above results,the risk of resistance to fluazifop-hydroxamate in strawberry was tentatively determined to be moderate to high.The susceptibility of 102 strains of strawberry gray mold to bifenthrin was determined using the mycelial growth rate method and a baseline susceptibility was established.102strains of strawberry gray mold showed EC50 values ranging from 0.05μg/m L to 3.07μg/m L,with an average EC50 value of 0.96±0.67μg/m L and a single-peak susceptibility curve.No resistant strains were found.The spore germination method was used to determine the susceptibility of 68 strains of strawberry grey mould to bifenthrin and to establish a susceptibility baseline.The EC50 values ranged from 0.02μg/m L to 0.13μg/m L,with a mean EC50 value of 0.06±0.02μg/m L and a single-peaked curve.After treatment with 1μg/m L or 10μg/m L of bifenthrin,there were no significant changes in mycelial morphology,nucleus distribution and cell wall formation;however,mycelial cell membrane permeability increased and electrolytes leaked out;mycelial respiration rate and succinate dehydrogenase activity were significantly inhibited.40μg/m L of bifenthrin showed good efficacy on strawberry fruit.Biphenylpyrazine at 400μg/m L was 37.61%effective in treating strawberry fruit.The frequency of resistance to bifenthrin was 3 x 10-4,including two highly resistant strains,three moderately resistant strains and four low resistant strains.The mutants were all stably inherited,but showed a decrease in resistance index and no uniform trend in growth rate at different temperatures,with strains 3R-P11,3R-P13 and3R-P14 growing faster than the parental strains at 25°C and strains 66R-P6,66R-P1,66R-P3 and 66R-P5 growing slower than the parental strains.The spore production of the resistant mutants was significantly reduced;except for the biphenylpyrazinam resistant mutant 66-P6,which was interactively resistant to fluazoxystrobin,the biphenylpyrazinam resistant mutant was not interactively resistant to fluoxystrobin,fluazoxystrobin and prothioconazole.The pathogenicity results showed that the resistant strains were less pathogenic than the parental strains.After all mutants were sequenced,there were no point mutations in the SDHA,SDHB and SDHC subunits of the mutants,but only in the SDHD subunit of strain 3R-P10,the mutation type was TTC to TTG,amino acid position 30 F to L and phenylalanine to leucine Based on these results,it can be tentatively concluded that the risk of resistance to biphenylpyrazinam in strawberry is medium to high.In summary,the biological activities of flutriafol hydroxamate and bifenthrin against strawberry grey mould were clarified in this study to provide suitable alternative agents for the control of strawberry grey mould.The risk levels of resistance（both moderate to high）to fluazifop-Pyrimethanil and bifenthrin were evaluated,providing theoretical data for the monitoring and scientific use of resistance to strawberry grey mould. |
