| In this paper,the entomogenous fungi of diseased grubs were isolated,purified and identified,and the biological indexes such as colony morphology,growth rate,sporulation and germination rate were studied.The pathogenicity and virulence of this strain to several important agricultural pests were determined by bioassay.Orthogonal experiment was used to determine the optimum medium and conditions for solid culture of the strain.The main research results of this thesis are as follows:(1)An entomopathogenic fungus was isolated and purifiedA strain was isolated and purified from zombie grub,and its morphological characteristics were observed by microscopy with glasspiece culture.The strain was identified as Eumycota,Deuteromycotina,Hyphomycetales,Moniliales,clusteriaceae,Moniliaceae and Beauveria,Beauveria bassiana,named Bb170428.(2)Determination of several biological indicators of Beauveria bassiana Bb170428The colony color of beauveria bassiana Bb170428 on PDA medium was white,the matrix color was light yellow,and the colony was powdery,loose,thinner and the edge was radial.On the 15 th day,the colony diameter was 25.52±0.99 mm,and the daily average growth was 1.70 ±0.07mm/d.After 15 days of culture,the average sporulation was 8.65×109/dish,and the germination rate in PDA liquid medium was 87.02%.On the SDAY medium,the matrix color was yellow-brown,and the colonies showed dense and fluffy,and the colonies were thickness and uneven.On the 15 th day,the colony diameter was 20.17±0.41 mm,the daily average growth was 1.34±0.03mm/d;After 15 days of culture,the average sporulation yield was 8.55×109/dish;the germination rate in SDAY liquid medium was 90.70%.(3)The pathogenicity and virulence of Beauveria bassiana Bb170428 to several important agricultural pests was determined.The results of bioassay showed that Beauveria bassiana Bb170428 was pathogenic to Colaphellus borzoringi,Chilo suppressalis,Ostrinia furnacalis,Agrotis segetum,Mythimna separata and white grubs and the pathogenicity to different pests was different.It has the strongest pathogenicity to A Ostrinia furnacalis and Chilo suppressalis,and is significantly higher than other pests.The virulence of the same pest to the higher instar larvae is greater than that of the low instar larvae,but the virulence of the Ostrinia furnacalis and Chilo suppressalis is not significant.The virulence of the higher instar larvae of the Agrotis segetum and Mythimna separata is significantly greater than that of the low instar larvae.The virulence of the Colaphellus borzoringi adult is significantly higher than that of the larvae.The corrected mortality rates of Beauveria bassiana Bb170428 against Colaphellus borzoringi,Chilo suppressalis,Ostrinia furnacalis,Agrotis segetum,Mythimna separata and white grubs were 85.00%,94.55%,94.64%,80.00%,54.76%,and 67.86% respectively.The LC50 of Bb170428 infecting the 2nd instar larvae of Colaphellus borzoringi,Chilo suppressalis,Ostrinia furnacalis,Agrotis segetum,Mythimna separata respectively were 2.26×1012 spores/m L,6.01×106 spores/m L,3.06×106 spores/m L,1.20×109 spores/m L,7.75×1011 spores/m L on the 15 th day;The LC50 of Bb170428 infecting Colaphellus borzoringi adult and the 5th instar larvae of Chilo suppressalis,Ostrinia furnacalis,Agrotis segetum,Mythimna separata respectively were 1.64×106 spores/m L,1.25×106 spores/m L,1.20×106s pores/m L,7.72×106 spores/m L,2.63×109 spores/m L on the 15 th day;on the 30 th day,the LC50 of infected the 3rd instar of white grubs was 1.57×108 spores/m L.(3)The optimum solid medium and culture condition of beauveria bassiana Bb170428 were optimizedThrough the best nutrients and best filler selection,respectively,to determine the best nutrients are maize flour and rice,and the best fillings are peanut hull powder and wheat bran.Orthogonal experimental design was used to optimize the ratio of four components of maize flour,rice,peanut hull powder and wheat bran.The optimal solid medium formula was selected as the mass ratio of maize flour: rice: peanut shell: wheat bran =2:2:3:1.At this time,the unit sporulation was the largest,reaching 9.96×109 spores/g.Based on the determination of the best solid medium,the effects of culture temperature,solid medium water content and inoculum size on sporulation were studied.The L2556 orthogonal combination test design method was used to optimize the screening of the five levels of the above culture conditions.The optimal culture conditions for Beauveria bassiana Bb170428 were determined as the temperature was 26?,water content was 40%,and the inoculum size was 14 m L/100 g.The maximum sporulation under this condition was 14.51×109 spores/g.The range analysis showed that the influence of each factor on the unit sporulation was the temperature>inoculation size>water content,and the influence of each factor on the sporulation of the strain reached a significant level. |
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