Pigment-producing Kocuria spp. isolated from soil ameliorate systemic drought stress in wheat

Abstract

Drought stress severely limits crop yield, quality, and productivity by restricting water and nutrient availability. To enhance wheat growth under water-limited conditions, six bacterial isolates obtained from rhizosphere soil samples from Mumbai Metropolitan Region, India were screened for plant growth-promoting traits, including indole-3-acetic acid production, nitrogen fixation, phosphate and potassium solubilization, and siderophore production. Drought tolerance of the isolates was evaluated by growth in polyethylene glycol (PEG-6000)-supplemented medium, and cell viability was assessed using a resazurin-based assay. Ultraviolet (UV) resistance was further examined by prolonged UV exposure followed by viability estimation using the drop count method. Promising isolates were inoculated onto surface-sterilized germinated wheat seeds, and growth-promotion was evaluated using agar butts supplemented with PEG-6000, as well as soil-based pot experiments. Plant growth-promotion was assessed by measuring root and shoot length, fresh weight, leaf width, chlorophyll content, antioxidant activity (1,1-diphenyl- 2-picrylhydrazyl assay), total polyphenol (Folin–Ciocalteu assay), and flavonoid content (AlCl3 assay), along with reactive oxygen species (ROS) accumulation using DCFDA (2’,7’-dichlorofluorescin diacetate) staining. Among the tested isolates, the two pigment producers, Kocuria turfanensis and Kocuria rosea, demonstrated significant increases (p < 0.05) in individual root length, fresh biomass, and leaf width compared to untreated controls. They exhibited better antioxidant and ROS activity, along with significantly enhanced wheat growth under drought stress. The dual stress tolerance (osmotic and UV) exhibited by these pigment-producing strains suggests a link between pigment biosynthesis and drought-stress protection. These findings emphasize the potential of Kocuria spp. as effective bioinoculants for improving wheat performance under drought stress.