Multifaceted Plant Growth Promoting Traits and Abiotic Stress Resistance Abilities Exhibited by Chrysanthemum Rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) boost plant growth and agricultural sustainability in an ecologically friendly way. The cultivation of chrysanthemum, a globally significant flower crop, has relied heavily on substantial agrochemical inputs that have detrimental impact on the environment. To assess the potential of chrysanthemum rhizobacteria to reduce this reliance, bacterial strains were retrieved from the plant rhizosphere and subjected to an assessment of various plant growth-promoting traits. Out of the 34 rhizobacterial isolates, 21 demonstrated the production of the plant growth hormone auxin, 21 had phosphate solubilization ability, 22 were capable of nitrogen fixation, and 21 could produce ammonia. Based on these findings, seven preeminent PGPR strains, characterized by multifaceted plant growth-promoting traits, were selected for subsequent studies and identified as species belonging to Acinetobacter, Bacillus, Pantoea, Serratia and Staphylococcus. The selected strains were systematically analyzed for their capacity to endure an array of abiotic stresses. A majority of these strains demonstrated adaptation under osmotic stress ranging from -0.15 to -0.49 MPa, temperatures of 20°C and 30°C, and salt stress within the range of 3 to 7% NaCl, which suggests their potential to promote plant growth across diverse environmental conditions. Additionally, the secretion of hydrolytic enzymes such as protease, pectinase and amylase was examined, and only the Staphylococcus hominis PGPR-12 strain demonstrated the ability to produce all three extracellular hydrolases. These findings underscore the potential application of multiple isolates possessing promising plant-probiotic properties to enhance plant growth across various conditions, thereby necessitating further exploration through pot and field assays.