Identification and Culture Optimization of Effective Biocontrol Agent on Thosea senensis for Tea Plantations

  Objective  A biocontrol microbe on Thosea senensis Walker suitable for organic tea agriculture was identified and optimal culture conditions studied.

  Method  From the intestines of T. senensis died from disease in nature, microbes were cultured and screened by means of varying the temperature. Indoor virulence of the selected microbes on T. senensis was determined by immersion feeding and further identified by morphological, molecular biological, and phylogenetic tree analyses. Culture of the isolated strain was optimized by univariate and orthogonal experiments.

  Result  The endophytic strain X-11 with high efficacy in controlling the pest was isolated. The 3^rd instar larvae of T. senensis fed with a 2.56×10⁸ conidia·mL⁻¹ X-11 solution displayed a cumulative corrected mortality rate of 90.5% with a median lethal time LT₅₀ of 2.88 d on the 7^th day after treatment. Based on the 16S rDNA molecular identification and phylogenetic analysis, X-11 was determined to be Paenibacillus azoreducens. The optimized culture conditions for the bacterium included the use of 2% inoculum to culture for 60 h at 36℃ with a final count approaching 1.34×10⁹ conidia·mL⁻¹.

  Conclusion  The endophytic strain with high control efficacy on T. senensis larvae was identified as P. azoreducens. It could be cultured to be used as a bioagent for the pest control at tea plantations.