Studies On Resistance-induced And Mechanism Of Sphaerotheca Fuliginea To Hexaconazole

In this dissertation, Hexaconazole-resistant strains to Sphaerotheca fuliginea were obtained by chemical taming and UV irradiation in the laboratory, And studied on biological characteristic and resistant mechanism of sensitive strain and resistant strain of S. fuliginea.1. The sensitivity of Sphaerotheca fuliginea to hexaconazole was tested in vitro culture of cotyledon to 50 strains collected from shandong in lab. The results showed that the sensitivity of strains ranged from 0.0030μg/ml to 0.16μg/ml, the mean EC50 value was 0.028μg/ml,it could be as baseline sensitivity of Sphaerotheca fuliginea to hexaconazole because frequencies of fifty strains accords with Gaussian distribution.2. The hexaconazole-resistant strains were obtained by UV irradiation or chemical taming or UV irradiation and chemical taming in the laboratory. Resistance factor of a highly resistant strain,10~5 fold, was obtained by UV irradiation and chemical taming.3. Time of pycnidiospore germination of the HR strains were later than their parent strains without significant difference, But contrary to time of mycelia sporulation. Germinating time of all spores was 40 hours after inoculation, ratio of pycnidiospore germination of sensitive and resistant strains was very low, 10%~20%. But Sporulation capacity of spore was very high. Spores appeared six days after inoculation,A mass of bunched spore was observed eight days, And symptom appeared nine days after inoculation.4. Sporulation quantity of resistant strain was 1.51×10~5 spores/ml ten days after inoculation. and sensitive strain was 1.18×10~5 spores/ml at the same condition.There was no significant difference between that. Disease index of cucumber that inoculated resistant strain was 30,and disease index of cucumber that inoculated sensitive strain was 25, that showed pathogenicity of resistant strain was higher than sensitive strain but no significant difference.5. Hexaconazole-resistant strains exhibit no cross-resistance to tebuconazole, myclobutanil, polyoxin and azoxystrobin because resistant factor was nearly 1, and positive resistance to kresoxim-methyl for resistant factor was 5.85.6. The germination percentage of aonidia, the number of germmination tubes per conidium, and the number of penetration sites per conidium of highly resistant strain were higher than sensitive strain. And the number of branches per hypha was contrary to that. Fitness parameters of resistant and sensitive strains had no significant difference without fungicides.7. Competition ability of resistant and sensitive strains were measured. The results showed that frequency of resistant strains was no significant difference when spores of resistant and sensitive strains mixed with 80:20 were incubated after 7 generation with no fungicide treatment; when mixed with 50:50, and frequency of high resistant strain was slowly descent; When mixed with 20:80, frequency of resistant strain was lower than sensitive strain, it imply that the resistance of Sphaerotheca fuliginea may be disappear without fungicide pressure.8. The contents of esterases isoenzymes, peroxidase isoenzymes and soluble proteins were compared between resistant strain and sensitive strain. The results showed that the electrophoretic patterns of resistant strain and sensitive strain was the same, but the quantity of that was not.