Research On Persistence Dynamics Of Metarhizium Spp. In Tobacco Soil And The Control Effect Against Tobacco Pest

Metarhizium.spp is a kind of entomopathogenic fungi,widely be used to control many species of pest,and it can not only infect insects,but also be in the soil of persistent,continue to control pests.Tobacco?Nicotiana tabacum?is an economically important crops in Guangdong Province,but the insect pests pose serious threat to tobacco production.In this thesis,Metarhizium strains virulent to tobacco pest have been screened as research objects.The persistence dynamics of Metarhizium strains in the soil of green house and tobacco field were studied to select strains with good persistent ability.The chemical pesticides that had no effect on the growth of Metarhizium were screened and were mixed with Metarhizium.Then select compatible pesticides at lower levels to been applied to field experiment to determine the control effect,which provided scientific basis for the study and improvement of the application value and practical control effect of Metarhizium.The results were shown as following:1.The persistence dynamics of Metarhizium spp and Beauveria bassiana in tobacco soil in Gguangdong Province.The germination dynamics of 5 different isolate Metarhizium and 1 isolate Beauveria bassiana in green house soil were compared.The germination rate decreased significantly after treatment for 60 days,and there was a slight decrease after treatment for 180 days.The sporulation of most entomopathogenic fungi fell below 50%except rhe strains Ma05,Ma09,Ma19,Ma22 and Ma24,Beauveria bassiana consistently showed a downward trend,and the germination rate of it was only 15%after a year.The sporulation was decreased rapidly at 32°C,the store temperture was 4°C.The soil water content has a significant influences on sporulation.The CFU?Colony forming unit?of 5 isolate Metarhizium and1 isolate Beauveria bassiana were decreased rapidly at the first month and then had rebounded.The quantity of CFU the upper layer of 3cm depth all decreased rapidly and had not been detected after 150 days.The quantity of the upper layer of 30cm depth were all decreased rapidly but also can been detected after one years.The soil environment of three area in Guangdong Province were all suitable for Metarhizium survival and persistence could last for a year.2.The correlational analyses about enzyme activity of extracellaluar proteases and chitinase with virulence.Virulence regression equation about 19 isolate Metarhizium was built based on cumulative mortality and times of Spodoptera litura Fabricius.The enzyme activity of extracellular proteases was tested and analyzed with cumulative mortality and LT₅₀.The correlation index were 0.9209 and 0.7318 separately,which was positively associated with cumulative mortality and had no correlation with LT₅₀.The correlation index of chitinase and cumulative mortality were 0.4747 and 0.3718,separately,which had no correlation with anyone.Finally Ma09 was selected as the highest virulent strain for production3.The compatibility of Metarhizium and chenmical pesticidesThe influence of 20 pesticides to the Metarhizium were tested.The most pesticides can suppress the Metarhizium growing,but some pesticides with lower concentration could promote the production of Metarhizium.Screen three kinds of compatibility pesticides by comparing growth inhibition ratio.Inhibition of germination and sporulation.The pesticides were:Deltamethrin Chlorantraniliprole and Bacillus thuringiensis.They all can be use for mixture with Metarhizium.4.The study of the control effect of Metarhiziium against the tobacco pest.The control effect of the using metarhizium granules?5×10⁶ spore/g?with base fertilizer could reached 78.67%in the field,under the dose of 100g/plant.It could been used for control soil dwelling pests.1g conidial powder added into 1L water,which could dip roots of 150 tobacco,The control effect was more than 90%.The control effect was65.58%by dropping 500mL spore suspension,that concentration was 3.34×10⁵ spore/mL.Spraying with spore suspension,that concentration was 1.25×10⁸ spore/mL,the control effect was only 32.29%.The control effects of inoculation and root dipping were the best,followed by the rooting method,and the spraying method was the worst by comparing the effects of four treatments on the control of underground pests.The control effect of Metarhizium on Myzus persicae and Spodoptera litura was low by testing five different formulations and it was not suitable for field application.The effects of emulsion and oil formulations against Spodoptera litura were 34.11%and 36.06%,respectively.The effects of emulsion and oil formulations against the aphids were 81.18%and 70.86%,respectively.It could be used to control the aphids.The mixture was best for tobacco pest control and the effects of mixture against Myzus persicae and Spodoptera litura were91.99%and 83.16%,respectively.