Beneficial bacterial inoculation modulates hormonal-redox responses associated with enhanced floral volatile biosynthesis in Rosa damascena.

Damask rose (Rosa damascena) is an economically important aromatic crop whose fragrance quality is largely determined by the biosynthesis of floral biogenic volatile organic compounds (BVOCs). Beneficial microorganisms have emerged as sustainable biostimulants for improving plant growth and stress tolerance; however, their influence on floral volatile composition remains insufficiently understood. This study evaluated the effects of inoculation with Bacillus pumilus, Bacillus thuringiensis, and the salt-tolerant bacterium Vibrio campbellii on plant growth, physiological responses, antioxidant-related metabolites, and floral BVOC composition in two R. damascena cultivars, Mon Klai Kangwon (MK) and Mon Dangprasert (MD), under normal and NaCl-treated conditions. B. pumilus significantly promoted vegetative growth and branching, increasing growth by 22.83% with 8.00 branches per plant in MK and by 17.66% with 5.33 branches per plant in MD. These responses were associated with increased indole-3-acetic acid and salicylic acid concentrations, reduced malondialdehyde accumulation, and higher phenolic, flavonoid, ascorbic acid, and proline levels. Under NaCl-treated conditions, V. campbellii reduced oxidative damage and maintained plant growth and antioxidant-related metabolites compared with NaCl-treated plants. GC-MS analysis revealed cultivar-dependent alterations in floral BVOC composition. B. pumilus increased the relative abundance of phenylethyl alcohol and key oxygenated monoterpenoids, including citronellol, citral, and neral, particularly in MK, whereas V. campbellii helped maintain major volatile compounds in MD under NaCl treatment. These findings indicate that beneficial bacterial inoculation was associated with coordinated changes in plant physiological status, antioxidant-related metabolism, and floral BVOC composition, highlighting its potential as a sustainable strategy for improving fragrance quality in aromatic crops.