Abstract: To explore the excellent biocontrol resources for Codonopsis pilosula root rot, a biocontrol strain LC36 with antagonistic activity was screened from Codonopsis pilosula rhizosphere soil using dilution coating method and plate confrontation method. Strain LC36 was identified as Paenibacillus polymyxa based on morphological characteristics, physiological and biochemical features and multi-gene phylogenetic analysis. The abilities of strain LC36 to secrete cellulase, protease, chitinase and IAA were determined by Congo red chromogenic method, transparent circle method and Salkowskis colorimetric method. The results showed that strain LC36 could secrete cellulase, protease and IAA, but couldn't secrete chitinase. The cellulase activity, protease activity and IAA content were quantitatively determined using DNS method, Folin phenol method and Salkowskis colorimetric method, respectively. The cellulase activity, protease activity and IAA content were 11.38 U/mL, 15.86 U/mL and 18.65 mg/L, respectively. Based on single factor experiment, the fermentation conditions were further optimized by Plackett-Burman experiment and steepest ascent experiment. Three important fermentation factors (pH, temperature and rotation speed) were screened out. The optimal fermentation conditions were as follows: sucrose 20 g/L, peptone 20 g/L, sodium chloride 1.5 g/L, glycerol 10 mL/L, dipotassium hydrogen phosphate 1.5 g/L, pH 7, inoculum 7%, liquid volume 100 mL, temperature 32 ℃, and rotation speed 167 r/min. After treatment with fermentation broth of strain LC36, the disease incidence and lesion diameter were significantly lower than those of the control group. The control effect of strain LC36 on C. pilosula root rot reached to 57.63%. In summary, strain LC36 has good biocontrol potential to C. pilosula root rot, and could be considered as an excellent biocontrol strain with high development and utilization value.

Key words: Codonopsis pilosula root rot, biocontrol bacteria, screening and identification, fermentation conditions, control effect