Evaluating the Efficacy of the Fermentation Formula of Bacillus velezensis Strain Tcb43 in Controlling Cucumber Powdery Mildew

Abstract

Powdery mildew is a prevalent disease that affects cucumber crops, leading to yield reductions and declines in quality. Bacillus sp. strain Tcb43 culture medium was shown to be capable of inhibiting fungal spore germination in previous reports. In this study, the identification of the Tcb43 strain was updated to Bacillus velezensis by using whole-genome sequencing. The strain exhibited tolerance to a wide range of temperatures (12–40 °C), salinities (7–10%), and pH levels (ranging from 5 to 11). Additionally, Tcb43 demonstrated insensitivity to most tested fungicides. A new fermentation formula, Tcb43FBSO, was developed by adding 0.25% soybean oil to the fermented formula (Tcb43FB). This new formula exhibited a shelf life of up to 12 months with the decrease in bacterial count from 5.35 × 108 to 1.97 × 108 cfu/mL. Greenhouse assays showed that the treatment of potted cucumber plants with a 100-fold dilution (100×) of Tcb43FBSO for four weeks resulted in a significant reduction (64.64%) of cucumber powdery mildew compared to the mock group. In large-scale greenhouse trials, the treatment of cucumber plants with 200× of Tcb43FBSO for 5 weeks effectively suppressed powdery mildew disease, with a control rate that reached 76.6% compared to the mock group. These findings highlight the potential of Tcb43 as a biocontrol agent for managing cucumber powdery mildew and suggest its promising application in agriculture.