Toxicological Bioassay of Fungal Metabolite Against Plant Pathogenic Bacteria

Toxicological bioassay used in this research was performed as per the standard procedure (Bahroun et al., 2018). The pure pathogenic identified cultures of Bacillus subtilis, Bacillus mycoides, and Staphylococcus sp. strains were obtained from the Bioresource Institute for Health Utilization, Zunyi Medical University, Zunyi, China, for antibacterial study of fungal metabolite. A fresh culture of these selected pathogenic strains was transferred into 1 ml of sterile H₂O, and a 100-μl portion was spread over solidified PDA plates. Five-millimeter-diameter filter paper disks immersed in fungal metabolite were placed at equal distances on the inoculated PDA plates. All bacterial isolations were done in triplicate and transferred to an incubator for 1 h incubation at 4°C to ensure diffusion of compounds from the fungal metabolite disks. Then, the test plates were incubated at 25°C for 24 h in a bacteriological incubator. The size of the bacterial growth inhibition zone was calculated in millimeters (mm). The standard formula (Balouiri et al., 2016) was applied to the inhibition zone size.

Inhibition zone = average diameter of the colony−5 mm (diameter)