Mechanism Of Emamectin Benzoate Posion Bursaphelenchus Xylophilus

Pine wood nematode（Bursaphelenchus xylophilus）is a worldwide dangerous forestry pest.In our country,B.xylophilus was found in Nanjing in 1982.So far,it has caused extremely serious economic and environmental harm to China.With the frequent use of chemical control,B.xylophilus gradually develops drug resistance.It is urgent to screen low toxicity and efficient environment-friendly agents.At the same time,the research on the interaction mechanism between B.xylophilus and drugs is not enough.In this paper,the screening of chemicals and the toxicity to B.xylophilus and host Pinus.koraiensis were determined,and the transcriptome was sequenced.To explore the mechanism of killing B.xylophilus by emamectin benzoate,so as to provide a theoretical basis for the chemical control of B.xylophilus.The specific research contents and main results are as follows:1.By comparing the biotoxicity of emamectin benzoate,organophosphorus pesticide thiazoline,plant essential oil Jiang Huang essence oil,aromatic ginger flavone,citrinone,1,8-eucalyptus,β-Caryophyllene,α-cypermene 9 kinds of nematicides against the B.xylophilus.The results showed that among the 9 nematicides,emamectin benzoate was the most toxic to B.xylophilus,followed by thiazoline;2.The two-year-old branches of P.koraiensis were treated with emamectin benzoate and thiazoline respectively,and the toxicity of the two agents to the branches of P.koraiensis was observed.The results showed that emamectin benzoate was non-toxic to the branches of the host plant.Through the determination of metabolome and the diffusion of emamectin benzoate in the trunk of P.koraiensis in the forest,it is known that emamectin benzoate can diffuse in the body of P.koraiensis.3.B.xylophilus was inoculated into the branches of P.koraiensis by skin grafting method.The inoculated branches of P.koraiensis were treated with emamectin benzoate,and the symptoms of P.koraiensis branches were observed without emamectin benzoate as the control.The results showed that the symptoms of P.koraiensis branches treated with emamectin benzoate were significantly weaker than those in the untreated group.At the same time,the recovery treatment group and the control group found that emamectin benzoate could significantly reduce the population of B.xylophilus in P.koraiensis branches,thus affecting the incidence of P.koraiensis branches4.When B.xylophilus was treated with LC₂₀ emamectin benzoate,it was found that B.xylophilus had suspended death,and the number of suspended death decreased with time.Among them,the false death rate of B.xylophilus was the highest when treated with emamectin benzoate for 30 minutes,the mortality of B.xylophilus reached 20%at 5 hours,and the mortality would not increase with the increase of time within 24 hours.Therefore,B.xylophilus treated with emamectin benzoate for 30 min and 5 h were selected for transcriptome sequencing.A total of 97 differentially expressed genes up-regulated at the two time points were screened by transcriptome data analysis.The results of KEGG enrichment analysis showed that 4 genes are short-chain dehydrogenase（SDR）related genes.According to the analysis of transcriptome data,SDR may play a role in the resistance of B.xylophilus to emamectin benzoate,but it is not sure whether SDR related genes regulate the resistance of B.xylophilus to emamectin benzoate,and experiments need to be carried out to verify its mechanism.5.The B.xylophilus was soaked in si RNA and the SDR related gene Bx-sdr of B.xylophilus was silenced.The gene silencing efficiency was detected by real-time fluorescence quantitative PCR.The results showed that the expression of Bx-sdr gene in B.xylophilus treated with RNAi decreased significantly.The B.xylophilus treated with RNAi was treated with LC₂₀ emamectin benzoate.The results showed that the mortality of nematode was higher than 20%at 5 hours.The above results show that emamectin benzoate is a biogenic pesticide with good toxicity to B.xylophilus and no toxicity to P.koraiensis.After treating B.xylophilus with LC₂₀emamectin benzoate,the expression of Bx-sdr-1 gene of B.xylophilus increased,regulated the SDR in B.xylophilus for metabolic detoxification,and promoted the resistance of B.xylophilus to emamectin benzoate.