Resistance Monitoring And Mutagenesis Of Phytophthora Apsici To Metalaxyl

Phytophthora capsici is the main pathogen causing pepper blight,and metalaxyl is one of the main fungicides for the prevention and treatment of the disease.However,with the extensive use of metalaxyl,Phytophthora has developed resistance to metalaxyl.This dissertation monitored the resistance of 26 strains of P.capsici in different areas,selected some sensitive strains to induce mutant strains,and compared the biological characteristics and pathogenicity of mutant strains and their sensitive strains.To provide a theoretical basis for the risk assessment and comprehensive prevention of metalaxyl resistance in P.capsici in these areas.It also provides the necessary experimental basis and theoretical support for the identification and cloning of pesticide resistance genes by molecular biology techniques in the later stage,and reveals the genetic nature of the resistance of metalaxyl.The main results are as follows:1.Sensitivity of the strains of P.capsici from different regions to metalaxylUsing the method of measuring the growth rate of mycelium,we learned the sensitivity of 26 strains of P.capsici to metalaxyl,and the results indicated that there were 12 sensitive strains and 14 intermediate strains.Among the 8 provinces,5 strains of P.capsici in Liaoning Province belonged to the intermediate strain,indicating that P.capsici in Liaoning Province has developed resistance to metalaxyl.In addition to a sensitive strain in Gansu and Inner Mongolia,respectively,the sensitivity of P.capsici in other provinces is within the sensitive and intermediate range.2.Induction and screening of metalaxyl-resistant mutants of P.capsiciThe above 12 sensitive strains were used as test strains,we use three methods including domestication of chemicals,irradiation of hyphae and zoospores with ultraviolet light to induce them to be resistant to metalaxyl mutagenesis.As a result,6 strains of P.capsici strains with low sensitivity to metalaxyl were obtained by acclimation of the pesticide,and the most resistant strain SD1-9 had an EC50 value of 26.0629 ?g/mL.Two mutant strains were induced by spore ultraviolet irradiation,and no hybrid strains were induced by ultraviolet irradiation of hyphae.3.Biological characters of metalaxyl-resistant mutant strains of P.capsiciThe colonies of 4 mutant strains of P.capsici and their corresponding sensitive parental strains were white and nearly circular.We observed the mycelial morphology of the mutant strain and its corresponding parental sensitive strain under the microscope,and observed the sporangia morphology of each strain under the fluorescence microscope.The results showed that there was no significant difference in mycelial growth rate and sporangia morphology between the susceptible strains and the resistant strains induced by them.Moreover,the average values of sporangia length,width,aspect ratio,stalk length and mastoid height were not significantly different among the susceptible strains and their corresponding mutant strains.4.Pathogenicity of metalaxyl-resistant mutant strain of P.capsici on pepper plants and different fruitsThe pathogenicity of sensitive strains and mutant strains on Xinsujiao No.5 and Qingfeng Yangjiaowang plants was tested with hypocotyl wound inoculation.The result showed that the inoculated plants were significantly wilting at the inoculation site.By comparing the size of disease spots of each plant,it was found that the pathogenicity of tested strains was different for different pepper varieties,and the difference of pathogenicity between the sensitive strains and the mutant strains was not significant for the same plant.The tested strains could also infect green pepper,Dutch cucumber,tomato,eggplant and red pepper.According to the analysis of lesion size data,there are some differences in the pathogenicity of different strains on the same fruit;the pathogenicity of the same strain to different fruits is also significantly different;however,the sensitive strains and their corresponding mutant strains had no significant difference in pathogenicity on the same fruit.