Objective Control efficacy of Bacillus subtilis Bv17 against gerbera root rot and effects on cut flower quality and yield as well as rhizosphere soil microbial communities were analyzed.

Methods In an indoor experiment, two varieties of gerbera were grown in pots of blank control free of root rot disease (CK1) and control with root rot-infected soil and irrigated with either water (CK2) or treatments of B. subtilis Bv17 suspensions in varied concentrations (T1, T2, T3, and T4). Indicators of root rot disease and control efficacy on the gerbera plants were monitored. Microbial diversity in soil was determined by high-throughput sequencing. Meanwhile, cut flower yield per plant and pedicel length and thickness of the gerbera plants were recorded as well.

Results Compared to CK2, the root-irrigation with Bv17 suspensions in various concentrations significantly reduced the disease index on the gerbera plants. T3 that applied the bacterial agent at 5×10⁷ cfu·mL⁻¹ rendered the greatest efficacy of 91.87% against root rot on Daxueju and 90.79% on Linglong. With Bv17 additions, the microbial alpha diversity and relative beneficial species abundance in the soil rose significantly, and the microecological environment optimized as well. Meanwhile, the cut Daxueju flower yield per plant increased by 85.71% and Linglong by 88.24%. The commercial value of the cut flowers was thus improved with 11.47cm longer and 1.13mm thicker pedicels on Dasueju and 10.64cm longer and 1.46mm thicker pedicels on Linglong.

Conclusion Irrigation with B. subtilis Bv17 water suspensions not only effectively mitigated the root rot appearance on gerbera plants but also optimize the rhizosphere microecological environment and enhance the soil microbial diversity boosting yield and quality of the cut flowers.