Application of Bacillus subtilis B2-GFP to Promote Growth of Sweet Pepper Seedlings

  Objective   Effects of applying Bacillus subtilis B2-GFP culture broth on the growth and physiology of sweet pepper seedlings were studied.

  Methods  In a pot experiment, seedlings of sweet pepper Shuoyuan 808 were treated with B. subtilis B2-GFP culture broths at the concentrations of 1×10⁵ CFU·mL⁻¹ (T1), 1×10⁶ CFU·mL⁻¹ (T2), 1×10⁷ CFU·mL⁻¹ (T3), and 1×10⁸ CFU·mL⁻¹ (T4), along with non-treatment control (CK). The transplanted sweet pepper seedlings were given 5 mL 1×10⁶CFU·mL^₋₁ B2-GFP culture broth every 7 d for 3 times. Growth index, biomass accumulation, leaf photosynthesis, and chlorophyll fluorescence parameters as well as antioxidant enzyme activities, morphological formation, and root vitality of the plants were monitored at 21 d.

  Results  Application of the B2-GFP culture broth increased the plant height and biomass as well as the leaf area and chlorophyll content over CK. The greatest effect was observed under T2, which also accentuated the leaf transpiration rate (T_r), stomatal conductance (G_s), maximum fluorescence (F_m), photosystem II potential Activity (Ф_PSⅡ), and photochemical fluorescence quenching coefficient (qP) as well as the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) in the roots but reduced the intercellular CO₂ concentration (C_i) and chlorophyll basic fluorescence (F_o).

  Conclusion   When the transplanted sweet pepper seedlings were given 1×10⁶ CFU·mL⁻¹ B2-GFP culture broth, all monitored indicators on the plant growth and root development including leaf photosynthetic parameters and biomass and root antioxidant enzymes activities and vitality were significantly improved in 3 weeks.