Bacillus velezensis LABIM40 AS A POTENTIAL BIOCONTROL AGENT TO REDUCE Fusarium HEAD BLIGHT OF MAIZE AND WHEAT

Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe (teleomorph Gibberella zeae [Schwein.] Petch) is a critical fungal disease in maize (Zea mays L.) and wheat (Triticum aestivum L.) in southern Brazil. It causes reduced grain yield and grain contamination with mycotoxins, especially deoxynivalenol, which inhibits protein biosynthesis, and zearalenone, an estrogenic mycotoxin. Moreover, the rotation of maize with wheat in combination with favorable weather conditions for FHB can result in an accumulation of inoculum, which can enhance mycotoxins content in both cultures. There is an urge to discover new alternatives to control the disease, once only one commercial product is registered in the country (Firmeza®). In this context, Bacillus species hold the potential of being used as biocontrol agents of many fungal diseases because they can produce biologically active compounds against soil-borne and post-harvest pathogens, such as bacteriocin-like substances, lipopeptides, surfactin, fengycin and several other active compounds. Therefore, the aim of this study was to verify the potential of Bacillus velezensis LABIM40 in controlling the fungus under in vitro conditions by evaluating fungal growth inhibition through the dual culture assay and well diffusion with cell-free culture (CFC) sterilized by autoclaving, in which the concentration of 200µL/mL of CFC was used. After verifying fungal growth reduction by the bacteria, the minimum inhibitory concentration at which 50% of the replicates were inhibited (MIC50) was determined by the plate diffusion method. All the experiments were carried out three times and MIC50 essay had concentrations of 600, 500, 400, 200, 100, 50, 25, 12,5 and 6,25μL/mL as well as one control (fungus growth in the absence of bacterial metabolites), with 4 replicates each. The measurements of mycelial growth inhibition halos were done at the closing of the control plates, 6 days after starting the tests. Statistical analysis was performed by the software GraphPad Prism version 6.0. Analysis of Variance (ANOVA) showed no significant differences among the four lowest concentrations. Linear regression analysis determined MIC50 as 415,3μL/mL. These data corroborate the antifungal ability developed by Bacillus species showing the capacity of LABIM40 strain being further developed and used as a commercial biocontrol agent in both pathosystems.