Studies On Ultraviolet Mutation Breeding And Biological Characteristics Of Metarhizium Anisopliae

Metarhizium anisopliae is an important entomogenous fungus,which has a wide host range,strong pathogenicity,no toxicity and residue to human,livestock and agriculture,and has broad application prospects.Ultraviolet light is one of the important factors restricting the field application of M.anisopliae.In this study,5 generations of high virulence strains were screened by continuous UV mutagenesis,and their growth characteristics,extracellular enzyme activity were analyzed.The mutant strains were used to control peanut pest in field.(1)Screening and identification of initial strains.The virulence of 23 M.anisopliae strains to Tenebrio molitor was determined by insect dipping method,and the highly virulent strain M18-8-4 was obtained as the initial strain,with the LT50 of 3.68d,cavader rate is 100%.M18-8-4 strain was identified as M.anisopliae by morphology and molecular analysis.(2)UV breeding of M.anisopliae M18-8-4 and screening of highly virulent strains.According to the relationship between ultraviolet irradiation time and spore survival rate of M.anisopliae,when the survival rate of spore is 20%,which is favorable for forward mutation,and the ultraviolet mutagenesis time was determined to be 5 min.UV mutagenesis was carried out with M18-8-4 as the initial strain,and the virulence to T.molitor was determined.The mutation strain F1-M18-8-4 was isolated from the first infected insect used as the first generations mutation strain until F5 generations was obtained.The virulence of the mutant strain was tested with T.molitor,Aphis medicaginis,Frankliniella occidentalis,Spodoptera exigua and Holotrichia parallela,result showed that F2-M18-8-4 has the highest virulence,and the lethal time is 2.76 d,3.16 d,2.13 d,2.31 d and 2.86 d,respectively.(3)Biological characteristics of F2-M18-8-4 strain.The results of morphological identification showed that the initial strain M18-8-4 has olive green powder on the front surface,a small amount of white mycelium on the edge and light yellow on the back.The mutant strain F2-M18-8-4 is also powdery olive green on the front surface,with a large number of fluffy hyphae growing on the edge and colonies growing in concentric circles.There is no obvious difference on the back between F2-M18-8-4 and the starting strain.The colony growth rate has no significant difference between the original strain and F2-M18-8-4 on the 2nd day,while on the 4th and 6th days the growth diameter of F2-M18-8-4 reached 3.85cm and 5.38cm.In terms of sporulation,the sporulation of F2-118-8-4 was significantly higher than the original strain after 7 days of culture,reaching 0.74×107 spores/cm2.After UV irradiation,the number of viable colonies of mutant strain F2-M18-8-4 was 37.50,which was significantly different from that of the original strain 31.40.(4)Studies on extracellular enzyme activity of mutant strain F2-M18-8-4.The results showed that the protease activity and chitinase activity of F2-M18-8-4 was 30.66IU/mL and 53.64 IU/mL respectively,which was significantly higher than that of the original strain.There was no significant difference in lipase activity between mutant strain F2-M18-8-4 and the original strain.(5)Control effect of Mutant strain F2-M18-8-4 on peanut pests in field.The control effect of mutagenic strain F2-M18-8-4 on A.medicaginis,F.occidentalis and grubs was evaluated,the effect of leaf conservation and yield increase of peanut were assessed.The results showed that 3 days later the control effect of F2-M18-8-4 to A.medicaginis and F.occidentalis was lower than 25%imidacloprid wettable powder,25%thiamethoxam water dispersant and 60g/L spinosad suspending agent,then the control effect on peanut pest increased,on the 15th day the control effects of F2-M18-8-4 to peanut aphid and F.occidentalis was 83.33%and 79.52%respectively,which were higher than those of three pesticides.The effect of protecting peanut leaves reached 63.58%on the 15th day.The yield reaching 5780.80kg/hm2 after using F2-M 18-8-4(300 trillion/hm2)with the increasing production was 16.55%.It is equivalent to commercial M.anisopliae insecticide CQMal28 emulsion powder.To sum up,UV mutagenesis can improve the virulence of M.anisopliae M18-8-4.It can improve the biological characteristics of M.anisopliae and increase protease and chitinase activities.Mutant strain F2-M18-8-4 has good control effect on peanut field pests.