Screening, fermentation condition optimization, and field control effect evaluation of an antagonistic bacterium against Ralstonia solanacearum

Abstract:

[Background] Tomato bacterial wilt is a soil-borne bacterial disease caused by Ralstonia solanacearum, which severely restricts the production of tomato. [Objective] To screen out an antagonistic bacteriumand apply it to biocontrol of tomato bacterial wilt. [Methods] We used the inhibition zone method and agar diffusion method to screen the bacterial strains with strong antagonistic effect against R. solanacearum from the rhizosphere soil of healthy tomato plants in a field with bacterial wilt in Hengyang, Hunan. The strain was identified by the observation of morphological characteristics, physiological and biochemical tests, and sequence analysis of 16S rRNA gene and gyrA gene. The fermentation conditions were optimized by single factor test and orthogonal test. The control effect was investigated by field experiment. [Results] Strain TR-1 with a significant antagonistic effect against R. solanacearum was screened out and preliminarily identified as Bacillus velezensis. The optimized medium for TR-1 was composed of 20.0 g/L soluble starch, 10.0 g/L soybean peptone, and 5.0 g/L K₂HPO₄. The optimum fermentation conditions:pH 6.0-7.0, 30-33℃, 160 r/min, and 48 h. The inhibition zone of the sterile fermentation supernatant of TR-1 cultured under the optimized conditions against R. solanacearum showed a diameter of 2.95 cm, which was about twice the size before. TR-1 showed the control effect of 60.30% in the field experiment. [Conclusion] The optimization of fermentation conditions greatly improves the inhibition effect of TR-1 fermentation broth. The strain has a good control effect on tomato bacterial wilt in the field experiment and demonstrates the potential to be applied in the biocontrol of this disease.