Isolation and Identification of antifungal metabolite producing endophytic Bacillus subtilis (S17) and its in vitro effect on Colletotrichum falcatum causing red rot in sugarcane

Abstract

Red rot, a threatening disease of sugarcane caused by fungal pathogen Colletotrichum falcatum Went adversely affect the yield and quality of crop. Therefore, it is important to explore such methods of protection which are organically safe especially with the use of bioagents. Currently, usage of endophytic bacteria as biocontrol agent have been focussed in the field of biological control and enhancement of crop productivity. Hence, this study was centred on endophytic bacteria Bacillus subtilis isolate S17 (identified by 16S rRNA analysis) isolated from the sugarcane stalk tissues. The in vitro study indicated that isolate S17 inhibited the mycelial growth of C. falcatum by 76.22 ± 2.34% in dual-culture antagonism assay. Scanning electron microscopy (SEM) revealed the distortion and destruction in the hyphae of the fungal pathogen by isolate S17. Further investigations proved that the hyphal disorientation was by the secretion of various enzymes (chitinase, β-1,3 glucanase, protease, pectinase, and amylase), inhibitory substances viz., siderophore, ammonia, hydrogen cyanide (HCN) and other volatile as well as diffusible metabolites. The volatile and diffusible metabolites exhibited strong inhibition (74.57 ± 1.45% and 81.86 ± 2.36%) against C. falcatum, respectively. Similarly, cell-free culture supernatant that contains extracellular metabolites exhibited mycelial inhibition (70.52 ± 0.95%) against C. falcatum. Thus, the present finding revealed that different metabolites as well as various exo-enzymes produced by B. subtilis (S17) inhibit red rot pathogen besides mechanism of the antagonism.