Impact of PGPR Seed Priming on Germination, Yield, and Metabolite Profile of Basil (Ocimum basilicum L.) and Sage (Salvia officinalis L.)

Abstract

This study evaluated the potential of plant growth-promoting rhizobacteria (PGPR) from the genera Bacillus and Actinomycetes to enhance growth and secondary metabolite production in basil (Ocimum basilicum L.) and sage (Salvia officinalis L.). Six isolates obtained from the rhizosphere of Urtica dioica, including three Bacillus spp. (Bac1-Bac3) and three actinomycetes (Act1-Act3), were morphologically and biochemically characterized and screened for physiological tolerance and plant growth-promoting (PGP) traits, identifying two isolates with strong PGP potential. The selected strains were further evaluated in in vitro seed inoculation assays and pot experiments under controlled conditions. Plant yield parameters were assessed alongside biochemical analyses of plant material including total phenolics, rosmarinic acid content, phenylalanine ammonia-lyase activity, and antioxidant capacity. Inoculation with selected strains significantly improved early seedling performance, including germination (Act1 up to 117% in sage), root elongation (Act1 up to 200%), and shoot elongation (Bac3 up to 175%). After six weeks, Act1 maximized sage fresh biomass (77.6%), while Bac3 enhanced basil dry matter (60% increase). Beyond growth promotion, PGPR treatments significantly increased phenolic content, rosmarinic acid concentration, phenylalanine ammonia-lyase activity, and antioxidant capacity (lower IC₅₀ values), indicating activation of the phenylpropanoid pathway. Molecular identification (16S rRNA sequencing) revealed Bac3 as Bacillus pretiosus (97.95% identity) and Act1 as Streptomyces ardesiacus (97.73% identity).