Plant growth-promoting rhizobacteria and biocontrol agents triggered plant defence responses against phytopathogenic fungi and improved rice growth

This study examined the antifungal activity and plant growth-promoting (PGP) traits of 30 beneficial bacterial strains isolated from Brassica campestris (L.) rhizosphere in rice. Among these, the PRB-8 strain exhibited potent antifungal activity against rice pathogens and produced a robust biofilm and a variety of PGP compounds. Based on our results, the PRB-8 showed distinct antifungal activity against fungal pathogens such as Rhizoctonia solani (75 %) > Alternaria alternata (74.5 %) > Sclerotium rolfsii (70 %) > Macrophomina phaselina (68 %) > Fusarium oxysporum (67 %). The isolate PRB-8 also increased the germination efficiency and length of rice seedlings under in-vitro conditions. The isolate PRB-8 was identified as Klebsiella pneumoniae (accession no. MT672588) and the absence of a hydrolysis zone on sheep blood agar plate suggests that PRB-8 is non-pathogenic. Inoculation of PRB-8 to R. solani and F. oxysporum-infected rice seedlings promotes length, dry biomass, and photosynthetic pigments and decreases the disease index in rice. Furthermore, PRB-8 potentially enhanced the defense responses in rice by increasing phenylalanine ammonia-lyase (PAL), beta-1,3 glucanase, polyphenol oxidase (PPO), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), which play a significant role in protecting plants from phytopathogens. Thus, it can be concluded that the use of the PRB-8 strain enhances rice growth and resistance to phytopathogens while simultaneously offering agroecosystems and environmentally friendly choices. Shortly, natural antagonistic PGPR may be used as biocontrol agents to sustainably enhance biotic stress tolerance and global food production.