Endophytic bacilli from medicinal-aromatic perennial Holy basil (Ocimum tenuiflorum L.) modulate plant growth promotion and induced systemic resistance against Rhizoctonia solani in rice (Oryza sativa L.)

Abstract

Among the twenty-one bacterial endophytes isolated from Holy basil (Ocimum tenuiflorum), eight were potentially inhibiting the growth of five plant pathogens. Percent suppression of Rhizoctonia solani, Sclerotium rolfsii, Alternaria alternata, Microphomina phaseolina, and Bipolaris sorokiniana radial growth was significantly higher by isolates BTL-4 (70.64%), BTL-1 (80.63%), BTL-1 (57.50%), BTL-5 (81.28%), and GTS-15 (73.81%), respectively. Based on 16S rRNA gene sequencing, these isolates were putatively identified as Bacillus altitudinis (BTL-1 and GTS-16), Bacillus tequilensis (BTL-4), Bacillus safensis (BTL-5), Bacillus haynesii (GTR-8), Bacillus paralicheniformis (GTR-11), Bacillus pacificus (GTR-12), and Bacillus siamensis (GTS-15). Selected endophytes were tested against R. solani in vivo and found to reduce sheath blight disease incidence to a varying extent. Rice plants challenged with R. solani and inoculated with Bacillus altitudinis GTS-16 exhibited the least value of percent infected tillers, recorded maximum induction of defense-related enzymes (phenyl ammonia lyase, peroxidase, and polyphenol oxidase), and enhanced dry matter accumulation. Confocal Scanning Laser Microscope imaging using LIVE/DEAD™BacLight™ bacterial viability staining has indicated trans-genera colonization of O. tenuiflorum endophytes in rice. Exploring the potential niches like the endosphere could open the vast arena of opportunity for developing newer strains of biocontrol agents.