Study On Resistance-induced And Resistance Mechanisms Of Podosphaera Xanthii To Triazole Fungicides

In this dissertation, five kinds of triazole-resistant strains to Podosphaera xanthiiwere obtained by chemical taming and UV irradiation in the laboratory. And studiedon the biological characteristics and resistance mechanisms of sensitive strains andresistant strains of Podosphaera xanthii. The main contents were followed:1The infection process of the hull-less pumpkin powdery mildew and studyabout its sensitivity to the triazole fungicideThe Infection process of P.xanthii on hull-less pumpkins was observed byscanning electron microscope, the results showed that the conidia germ tube formedin12hours after inoculation, hyphae formed in24hours after inoculation, extendedhypha and mycelia formed in36-72hours after inoculation, chains of conidia formedin96hours after inoculation. Through the laboratory control-efficiency test, studiedabout the five kinds of triazole fungicides on pumpkin powdery mildew. The resultsshowed that the myclobutanil12.5%EC had the best control effect powdery mildew,the test was90.15%, the tebuconazole25%EC had the lowest control effect was72.15%y. The sensitivity of pumpkin powdery mildew were affected in differentapplication time, The EC50values of propiconazole, flusilazole, hexaconazole,myclobutanil and tebuconazole to P. xanthii treated in different times after inoculationwere determined, the results showed that the sensitive time of the propiconazole andthe myclobutanil to P. xanthii on hull-less pumpkin were24hours after inoculation,the flusilazole and the tebuconazole to P. xanthii on hull-less pumpkin were96hoursafter inoculation, the hexaconazole to P. xanthii on hull-less pumpkin was48hoursafter inoculation. Established sensitivity base-lines of the five kinds fungicides topumpkin powdery mildew, the EC50values of the myclobutanil was lowest and it was61.93μg·mL-1, the tebuconazole was highest and it was1504.87μg·mL-1, the EC50values of the propiconazole, the flusilazole and the hexaconazole were between thoseabove two and they were441.98,929.39and67.44μg·mL-1respectively.2The resistance induction of the five kinds of triazole fungicides on hull-lesspumpkin powdery mildew. Combining chemical taming with UV irradiation in the laboratory,myclobutanil-resistant strains, hexaconazole-resistant strains, propiconazole-resistantstrains, flusilazole-resistant strains and tebuconzole-resistant strains of P.xanthii wereobtained after continuous culturing7generations. The resistant level of the other fourresistant strains were high resistance, besides the propicona zole-resistant strains wasresistant. Continuous culture the highest level of resistance the resistant strains5generations in no-application and found the resistance was stable. By the test, theresults showed that there was cross-resistance between the flusilazole10%EW andthe tebuconazole25%EC while the myclobutanil12.5%EC and the tebuconazole25%EC performs negative cross-resistance, no cross-resistance among otherfungicides.3The study about biological properties of those above five resistant strainsAccording to the study on the biological properties of those above five resistantstrains, the results showed that conidium germination time of the sensitive strains wasearlier than the five resistant strains, sensitive strains began to germinate12h afterinoculation, but the resistant conidium needed24hours. The pathogenicity and thesporulation quantity of resistant strains was slightly higher than the sensitive strains.There were significant differences between the resistant strains and the sensitivestrains in pathogenicity and the sporulation quantity. The results showed that the sporegermination rate, the number of germ tubes and the sporulation quantity of the fiveresistant strains were all slightly higher than the sensitive strains, but the hyphaebranch number was slightly lower than the sensitive strains and there were nosignificant differences between the resistant strains. The frequency of the resistantstrains changes were not obvious after mixed culturing the conidium of the resistantstrains and the sensitive strains7generations by80to20, but the frequency ofresistant strains got lower or even disappeared after culturing in the opposite way.4DNA extraction and identification from the hull-less pumpkin powdery mildew,and preliminary study on its resistance mechanisms to the triazole fungicideBy comparing the CTAB and SDS method for genomic DNA extraction form the hull-less pumpkin powdery mildew, results showed that the SDS method was betterthan the CTAB, and the extracted DNA by the SDS method had a higherconcentrations and fewer impurities than the CTAB method. Using universal primersto amplify DNA gene sequences of pumpkin powdery mildew, establishedphylogenetic trees, identified the pathogenic bacteria of pumpkin powdery mildewwas Podosphaera xanthii. by extracting genomic DNA of the resistant strains, usingF.R primer to amplify the DNA gene sequences of the resistant strains, though thesequences comparison, we found that the base mutation rates of tebuconazole resistantstrains was4.8%, the flusilazole resistant strains was1.6%and the other threenucleotides pairs of resistant strains had no mutatation.