The Resistance Of Litchi Anthracnose Pathogen Colletotrichum Gloeosporioides To Three Types Of Fungicides

Litchi anthracnose,caused by Colletotrichum gloeosporioides（Penz.）Sacc.,is one of the most important fungal diseases.At present,chemical agents,sterol biosynthesis inhibitors,benzimidazoles and strobilurins,are widely used in the prevention and treatment of C.gloeosporioides.However,these chemical agents are highly specialized and have a single site of action.If they are used alone or overdose for a long time,they will cause resistance of pathogens and reduce efficacy.Detecting and understanding the resistance of C.gloeosporioides to commonly used fungicides can provide a basis for scientific use of field fungicides.In this study,a total of 821 isolates collected from litchi orchards in Guangdong,Guangxi,Fujian,Hainan,Sichuan and Yunnan Province were used for testing their resistance and mechanism to prochloraz,azoxystrobin and thiophanate-methyl.The main results were as follows:1.The sensitivities of 300 C.gloeosporioides strains to prochloraz were tested by mycelial growth rate method,and the sensitivity baseline was 0.0447±0.0013μg/m L.It had better sensitivity to prochloraz and lower resistance level in China,and there only were two low-resistant strain,18FJCT02-02 and 18GXBL03-05.Nine resistant mutants were obtained with fungicide training and UV irradiation induction,their EC₅₀values ranged from 0.28 to 23.59μg/m L.The results of biological characteristics studies showed that the mutants’sporulation was lower than the parent strains,but there were no significant differences in mycelial growth,dry weight of mycelial,conidia germination and pathogenicity.The resistance mechanism of C.gloeosporioides to prochloraz was clarified.The 188th amino acid in the CYP51 gene sequence of sensitive strains was asparagine（N）,and mutants was histidine（H）.The mutation of CYP51 gene in C.gloeosporioides was related to the resistance to azoxystrobin.2.The sensitivitives of 185 C.gloeosporioides strains to azoxystrobin were tested by spore germination method,and the sensitivity baseline was 0.0102±0.0023μg/m L.The resistance frequency in Fujian,Guangdong,Guangxi,Hainan,Sichuan,and Yunnan provinces was 45.83%,61.76%,70.59%,64.44%,25.00%,33.33%,among which,Guangdong,Guangxi,and Hainan had higher levels of resistance.Analysis of the biological characteristics found that sensitive strains had stronger sporulation than resistant strains,but there were no significant differences in mycelial growth,dry weight of mycelial,conidia germination and pathogenicity.Laboratory cross-resistance test results indicated that there was positive cross-resistance between azoxystrobin and pyraclostrobin.The results of resistant mechasim showed that the 143th amino acid in the Cytb gene of sensitive strains were glycine（G）,and resistant strains were alanine（A）;the 387th of sensitive strains were isoleucine（I）,and resistant strains were valine（V）.Therefore,it was suggested that the main reason for the resistance of C.gloeosporioides to azoxystrobin was the mutation of the amino acid of the Cytb gene.3.The minimum inhibitory concentration（MIC）to thiophanate-methyl was 1.25μg/m L.The sensitivities of 791 strains to thiophanate-methyl were tested by the MIC method.564 strains were resistant strains,accounting for 71.30%;227 strains were sensitive strains,accounting for 28.70%,with high resistance level.MIC method greatly saved the workload of resistance monitoring.