Rhizosphere Bacteria Isolated from Medicinal Plants Improve Rice Growth and Induce Systemic Resistance in Host Against Pathogenic Fungus

Abstract

Sheath blight (ShB) disease is a major biotic stress that causes significant yield loss in rice. Plant growth-promoting rhizobacteria (PGPRs) have been found to suppress the adverse effect of disease on plants. In the present investigation, an attempt has been made to evaluate the effect of PGPR strains isolated from the rhizosphere soil of medicinal plants on rice under stress conditions. We isolated 158 morphologically distinct bacterial strains and tested them against R. solani under invitro conditions and found 52 promising strains with more than 50% antifungal activity. These strains were examined for their physiological and biochemical characteristics and further confirmed with 16S rDNA gene-specific markers. Strains that inflicted > 80% inhibition during in-vitro studies were selected for pot and field experiments. The results indicated that Bacillus velezensis, B. megaterium, and B. toyonensis registered significantly higher plant growth-promoting activities with enhanced germination, seedling vigor, and dry weight. In addition, applying these PGP strains exhibits the lowest disease incidence, relative lesion length, delayed sclerotia formation, and recorded maximum grain yield per pot. The field study further confirmed that B. toyonensis provided significant disease suppression with least disease incidence (PDI: 17.37 and 12.88), relative lesion length percent (27.71and12.88), area under disease progress curve (382.98 and 286.25) value (AUDPC), and highest grain yield (63.00 and 48 t ha− 1) in Tapaswini and CR Dhan 1014 varieties, respectively, followed by B. megaterium and B. velezensis. The PGPR-treated plants also showed enhanced activities of defense enzymes like polyphenol oxidase, superoxide dismutase, and catalase showing induced systemic resistance (ISR). Thus, these three PGPR strains from medicinal plants enhanced the tolerance of rice to ShB disease with improved crop growth. Integrating these PGPR in seed treatment, seedling root dip and foliar application will improve the rice yield and farmers’ livelihood.