| Sclerotinia sclerotiorum is a dead vegetative pathogenic fungus widely distributed around the world.It can infect a variety of plants,cause crop sclerotinia,and cause huge economic losses.Rapeseed is an important oil crop in China.The yield and quality of rapeseed are seriously reduced by S.sclerotiorum.The serious area of S.sclerotiorum is in the middle and lower reaches of the Yangtze River in China.At present,the prevention and control of S.sclerotiorum mainly depends on chemical agents.Prochloraz is a fungicide with high control effect on S.sclerotiorum,but continuous use of chemical agents is easy to produce resistance.Therefore,it is particularly important to monitor the sensitivity of S.sclerotiorum to prochloraz in the field and to clarify the resistance mechanism of S.sclerotiorum to prochloraz.In this study,106 strains of S.sclerotiorum were isolated and purified from 6 different regions.The physiological characteristics of the strains were observed and the EC50of prochloraz was determined.The resistance strains R-1～R-5 were obtained by UV mutagenesis combined with chemical domestication,and the CYP51 gene sequence and relative expression level were analyzed.The physiological characteristics and pathogenicity of R-1～R-5 were observed.Analyze whether there is cross-resistance between prochloraz and 5 fungicides;the resistance strains were isolated and purified by single spore isolation,and the EC50of prochloraz on the resistant strains was determined.The main results were as follows:（1）The colony morphology and sclerotia production ability of 106 strains of S.sclerotiorum were normal.The average mycelial growth rate was 2.03 cm/d,and the average 100-grain weight was 0.81 g.There was no significant difference in mycelial growth rate and 100-seed weight among different regions.（2）The average EC50value of prochloraz against 106 strains of S.sclerotiorum was0.0204 mg/L,and the range of EC50value was 0.0098-0.0422 mg/L.（3）The resistant strains R-1～R-5 were obtained after 52 generations of UV mutagenesis combined with fungicide domestication,and the resistance ratios were25.97,14.63,11.48,25.45 and 12.37 times,respectively.（4）No point mutation was found in the sequence alignment of prochloraz target gene CYP51.The relative expression of CYP51 gene in the resistance strain grown on PDA containing prochloraz was higher than that in the original strain.（5）The colony morphology of R-1～R-5 became unstable,and the mycelial growth rate decreased significantly compared with the original strain.The ability to produce sclerotia is normal,and there is no significant difference in the number of sclerotia and 100-grain weight compared with the original strain.（6）R-1～R-5 had normal acid production capacity;the ability of R-1～R-5 to form infection cushion decreased;pathogenicity decreased.（7）Cross-resistance analysis showed that there was no cross resistance between prochloraz and tebuconazole,pyraclostrobin,difenoconazole or boscalid,Negative cross resistance was found between prochloraz hand dimethachlone.（8）The ascospores of the resistance strains were isolated and purified to obtain SR-1～SR-5,and the EC50of prochloraz was determined.The results showed that SR-1～SR-5 did not have resistance to prochloraz.In this experiment,the resistance level of prochloraz in 6 regions was monitored,and no resistance of wild strains to prochloraz was found.The cross resistance of prochloraz to 5fungicides was determined,and the mechanism of prochloraz resistance of S.sclerotiorum was briefly analyzed,which provided guidance for the use of fungicides in the field. |
