New rhizobacteria strains with effective antimycotic compounds against rhizome rot pathogens and identification of genes encoding antimicrobial peptides

Bacterial strains were isolated from turmeric rhizosphere and 18 of them exhibited plant growth promoting traits and ability to solubilize mineral. They also showed the ability to concurrently suppress the growth of multiple fungal phytopathogens under in vitro assay. An isolate of Bacillus safensis, produced indole 3-acetic acid, NH3, HCN, siderophore, and cell wall degrading enzymes (cellulase, protease and pectinase) and exhibited remarkable suppression of various fungal pathogens infecting turmeric viz., Pythium myriotylum, P. aphanidermatum, Colletotrichum gloeosporioides, C. capsici, Macrophominaphaseolina and Fusarium oxysporum under in vitro conditions. In a subsequent greenhouse experiment, turmeric was inoculated with these fungal pathogens and in treatments with B. safensis the Disease Index (DI) was significantly reduced compared to the fungicide treatment. The greenhouse trials evidently demonstrated that the rhizome rot incidence in turmeric treated with B. safensis decreased by 84.61%, compared to fungicide treatments. We searched for the presence of biosynthetic genes that encode for the production of antimicrobial peptides (AMP) in the shortlisted rhizobacterial strains and the B. safensis strain, with the most biocontrol efficiency showed the presence of the genes encoding bacillomycin, surfactin and iturin. The dominance of putatively encoded biosynthetic genes reaffirmed the robust biocontrol potential of this strain for protection against a broad array of fungal phytopathogens. Our findings indicated that the growth promotional and antifungal potential of B. safensis strain, IISR-TB4 (NCBI- MT192800) could be further exploited to reduce the dependence on fungicides for sustainable turmeric cultivation.

Automated summary

Bacterial strains isolated from turmeric rhizosphere, specifically B. safensis, exhibited plant growth promoting traits, ability to solubilize minerals, and concurrent suppression of multiple fungal phytopathogens. This strain, when used in greenhouse experiments, significantly reduced the incidence of root rot in turmeric. Presence of genes encoding antimicrobial peptides further reaffirmed the biocontrol potential of B. safensis. These findings suggest that this strain can be effectively used in sustainable turmeric cultivation, reducing the reliance on fungicides.