Study On The Resistance Of Nomura Reinhardtii To Dichlorvos Induced By Ultraviolet Light

To screen out the mutant strain of Nomuraea rileyi with strong resistance to dichlorvos,a common organophosphate insecticide,in this paper,ultraviolet mutagenesis of Nomuraea rileyi was used to make 4 mutations of ultraviolet mutagenesis and the domestication of the mutants with dichlorvos.The mutant strains were tested for resistance levels,genetic stability,mycelial growth inhibition rate,the amount of spore produced after secondary culture,and chitinase activity to verify the virulence of the mutant strains on the larva of Orthosia songi Chen et Zhang sp.Nov and dichlorvos synergistic use of insecticidal effects.The results of the study are as follows:1 The comparison of the growth of Nomuraea rileyi original strain on plates containing different concentrations of dichlorvos shows that the lethal concentration of dichlorvos against Nomuraea rileyi spores is 1291 mg/L,and this is a marker of the lethal mutagenesis.2 In this experiment,after the UV-induced mutagenesis was between 70%and 80%,the optimal irradiation time for UV mutagenesis of Nomuraea rileyi is 2 min and 2.5min.After two times UV mutagenesis,6 strains with rapid spore production,abundant spores,and average fall diameter of 18.75 mm are screened out.The numbers are Nr-UVY1?Nr-UVY2?Nr-UVY3?Nr-UVY4?Nr-UVY5?Nr-UVY6.3 After four times of ultraviolet mutagenesis and acclimation of the drug,mutation strains Nr-UVY1 and Nr-UVY6 were obtained that are screened on plates containing dichlorvos at a concentration of 3875 mg/L.Dichlorvos resistance level measurement result display,the starting strain has the lowest EC₅₀value of 851 mg/L and its lethal concentration is 1291 mg/L.However,the two mutation strains could grow colonies and produce spores on plates containing 3875mg/L dichlorvos.The EC₅₀value of mutant Nr-UVY1 is 1888mg/L,and the EC₅₀value of mutant Nr-UVY6 is 2184mg/L.The original strain of Nomuraea rileyi is sensitive control strain with a resistance level of 1,and the resistance levels of mutant strains Nr-UVY1 and Nr-UVY6 are 2.22 and 2.57 times that of the original strain,respectively.The genetic stability of the mutant strains Nr-UVY1 and Nr-UVY6 showed that after 7 consecutive generations of transformation,the diphtheria-resistant strains showed little difference in the growth inhibitory rate,and the inheritance of resistance was basically stable.4 Different concentrations of dichlorvos have different degrees of inhibition on the mycelia growth of the two mutant strains and the original strains.The higher the concentration,the more significant the inhibition is.Compared with the original strains,the hyphae of the two mutant strains have significant and stable resistance to dichlorvos,the inhibition rate of the mycelial growth of the mutant strain Nr-UVY6 on the medium containing 1291mg/L dichlorvos is 37.01%.The strain Nr-UVY1 is 42.38%and the starting strain is 77.59%.With the increase in the number of transfer,the sporulation capacity of the two mutant strains and the starting strains have decreased.The sporulation volumes of the two mutant strains are significantly higher than that of the original strain,and the spore production of the mutant Nr-UVY6 is always higher than that of the mutant strain Nr-UVY1 and the starting strain more than twice.As for the stability of sporulation of the three strains at each generation,the stabilitys of the two mutation strains were higher,and the mutant Nr-UVY6 shows higher stability than Nr-UVY1.Determination of chitinase activity by means of transparent circle method,the mutant strain Nr-UVY6 has the highest chitinase activity with an R₂/R₁ratio of 1.5,and the R₂/R₁ratio of the mutant Nr-UVY1 was 1.1,which was the same as that of the original strain.5 Observation of the larva of Orthosia songi Chen et Zhang sp.Nov infected with Nomuraea rileyi found that the dead larvae produced local black spots at the initial stage of infection,and white mycelium and green conidium powder are produced at the middle stage of infection,and the body of insects is infected at the later stage of infection,gradually they lose water and stiffness eventually shrinks.The results of virulence test show that the two strains have obvious lethal effects on the larvae of Orthosia songi Chen et Zhang sp.Nov.The cumulative lethal rate of mutant Nr-UVY1 to larvae is 85%within 8days,and the LT₅₀value is 6.2678 days.The cumulative lethal rate of Nr-UVY6 to larvae reaches 91.67%within 8 days,and its LT₅₀value is 5.7617 days.The synergistic effect of the mutant strains and dichlorvos is significant.The cumulative corrected mortality rates of the mutant strains Nr-UVY1 and Nr-UVY6 when used in conjunction with dichlorvos,respectively,are 93.35%and 96.70%on the 3rd day,and they are all as high as 100%on the 4th day.The LT₅₀values are significantly reduced,their LT₅₀values are 1.5830 days and 1.5436 days,respectively.