| Entomopathogenic fungi is a kind of insect pest pathogens, which have been extensively used to control agricultural and forestry pests and show a great potential application in IPM( Integrated Pest Management) system. It is necessary ,as a microbial insecticide, to be effective, cheap, convenient for use and innoxious to environment. For entomopathogenic fungi, to get a strain which bears high and stable virulence and can be applied in all kinds of climates is more significative.Nomuraea rileyi, an entomopathogenic fungus, is a cosmopolitan species in infecting many economically important pests, especially noctuids such as Helicoverpa arnigera,Spodoptera exigua,Trichoalusia ni and is capable of causing epizootic death in fields. In this article, the producing condition and properties of chitinase secreted by N. rileyi, relationship between enzymatic activity and pathogenicity of N.rileyi under different temperatures and effects of some factors on the pathogenicity of N.rileyi were studied.The results are as followings:1.Culture medium formulation for the production of chitinase secreted by N. rileyi was conducted by comparision of the effects of different carbon sources, nitrogen sources and other factors on the yield of this enzyme. The results showed that the optimal conditions for the stain to produce chitinase are 6 days of 28℃with the initial pH 6.0, and the liquid medium containing 2.0% glucose as its carbon source and 0.6% peptone plus 0.6% beef extract as nitrogen source after inoculating dosage 2mL suspension of conidia (1×10~7/mL).The highest enzymatic activity was 21.53U/mL and that was 8 times the initial enzymatic activity;2.The optimal temperature and pH for enzyme activity is 50℃and 6.0, respectively. The enzyme activity is stable under 40℃and in pH range of 5.5-6.5. The enzyme activity descends obviously when temperature was above 60℃and was completely inhibited when the enzyme was treated at 80℃. Besides, the activity can be enhanced by Tween-80 and inhibited by SDS;3.The experimental results showed that the chitinase activity increased as cultural time went on in each temperature (except 35℃, its activity was 0 in first and second day); And at 17℃, 20℃, 23℃, 26℃, 30℃, 35℃, enzymatic activity of chitinase was 8.148U/mL,9.481 U/ mL,10.96 U/ mL,12.44 U/ mL,6.518 U/ mL,2.667 U/ mL, respectively. These indicated that enzymatic activity of chitinase from N.rileyi was affected by the temperature;4.The determination of pathogenicity of N.rileyi was conducted at different temperatures. The results showed that temperature had evident effect on the pathogenicity of N.rileyi, especially when the temperature was high. At 17℃,20℃,23℃,26℃, the pathogenicity was high and the rectified mortality was 64.44%,87.78%,95.56%,83.33%, respectively. But at 30℃,35℃, the rectified mortality was either 0%;5.Hyphal bodies in hemocoel represented distinct discrepancy by microscope inspection in vitro when silkworms were infected at different temperatures. The hemocoel of larvae infected by N.rileyi was fully filled with hyphal bodies at 17℃, 20℃, 23℃. The hyphae were dense, tenuous and short at 17℃while they were a little broad, long at 20℃and 23℃. In addition, hyphae were sparse at 26℃compared with temperatures mentioned above. The were no hyphae at 30℃and 35℃;6.Pathogenicity of entomopathogenic fungi is always affected by many factors such as temperature, humidity, etc. The experimental results showed the pathogenicity of N.rileyi was high in temperature range of 17℃-26℃and the highest mortality of larvae was 95.56% at 23℃.The mortality rate of larvae enhanced with humidity increasing. The lethal effect was higher when relative humidity was above 70%, but it descended evidently as the relative humidity was less than 70%. In addition, the low instar larvae were easily infected and the denser suspension of conidia was, the higher motality. was resulted in.
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