Seed inhabiting bacterial endophyte Bacillus amyloliquefaciens (SS7) defends sorghum Sudan grass seedlings from a phytopathogen Rhizoctonia solani.

Seeds naturally harbour bacterial endophytes that act as primary symbionts of plants. This study aimed to isolate and characterise seed inhabiting bacterial endophytes of sorghum sudan grass and evaluate the most active endophyte, Bacillus amyloliquefaciens-SS7 for protecting seedlings against Rhizoctonia solani infection. Seven bacterial endophytes (SS1-SS7) were isolated from surface sterilized sorghum sudan grass seeds and identified via 16 S rRNA sequencing. All isolates were screened for plant growth promoting and antifungal activities. B. amyloliquefaciens-SS7 exhibited the highest siderophore production and strong antifungal activity. Gene screening confirmed the presence of antifungal lipopeptide genes (Iturin A and Bacillomycin D) in B. amyloliquefaciens. Extracted lipopeptides from B. amyloliquefaciens strongly inhibited R. solani in disc diffusion assays. Bright field and fluorescence microscopy revealed that lipopeptides caused structural deformations and cell death in R. solani. Microcosm assays demonstrated significant protection of seedlings inoculated with B. amyloliquefaciens from Rhizoctonia infection. Histological studies confirmed overproduction of superoxide ions and cell death in seedlings infected with R. solani. Biochemical analysis showed increased levels of phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD), and peroxidase (POX) in treated seedlings compared controls. Infections caused by R. solani targeted the collar region of seedlings, causing damping-off in those lacking the endophyte B. amyloliquefaciens. This study concludes that sorghum sudan grass seeds contain bacteria like B. amyloliquefaciens-SS7, which are crucial in protecting seedlings from R. solani. This research is the first to report on the role of seed endophytic bacteria (SEB) in the protecting sorghum sudan grass against R. solani.