Exploring the potential of bacterial endophytes from Medicinal plant Gymnema sylvestre with plant beneficial traits and antimicrobial efficacy against phytopathogens.

Abstract

Gymnema sylvestre (Gudmar) is an important medicinal plant recognized for its diverse bioactive compounds, including antimicrobial and immune-stimulatory properties, and for its association with beneficial endophytic microorganisms. However, the plant growth-promoting and biocontrol potential of its bacterial endophytes remains poorly understood. The present study aimed to isolate and characterize bacterial endophytes from different tissues of G. sylvestre and evaluate their PGP attributes and antagonistic activity against major soil-borne phytopathogens. A total of 30 bacterial endophytes were isolated from leaf (n = 14), stem (n = 9), and root (n = 7) tissues. Screening for PGP traits revealed that 36.7% of isolates produced indole-3-acetic acid (IAA) (>20 μg/mL), 56.7% produced siderophores, 16.7% solubilized phosphate, and 20.0% solubilized zinc. In addition, 30.0%, 23.3%, 16.7%, and 16.7% of isolates exhibited DNase activity, nitrate reduction, urease production, and citrate utilization, respectively. Extracellular enzyme production was also recorded, with isolates showing amylase (36.7%), protease (30.0%), cellulase (23.3%), and lipase (40.0%) activities. An antagonistic assay against soil-borne fungal pathogens using a dual culture assay showed inhibition of fungal growth in 5, 5, and 3 endophyte isolates against Sclerotium rolfsii, Rhizoctonia solani, and Fusarium oxysporum, respectively with maximum zone of inhibition up to 67%, 67% and 62%, respectively against each pathogen. Based on combined PGP and antagonistic performance, six elite isolates were selected for in-planta validation and molecular identification using 16S rDNA sequencing. In-planta evaluation in chickpea demonstrated significant improvements in seed germination, plant growth, and biomass compared with the uninoculated control. Bacillus cereus strain NIBSM_GdR7 produced the greatest increase in plant height, whereas Bacillus cabrialesii strain NIBSM_GdL7 yielded the highest fresh and dry biomass. Under pathogen challenge, seed biopriming of chickpea with selected endophytes reduced disease incidence caused by S. rolfsii, providing 68.7-87.8% protection, with the highest protection observed for Bacillus proteolyticus strain NIBSM_GdL2. These results indicate that G. sylvestre harbors bacterial endophytes with promising plant growth-promoting and antifungal properties, and that selected Bacillus isolates can in future serve as candidate bioinoculants for sustainable crop improvement and disease suppression.