Strawberries native rhizobacteria as PGPR and biocontrol agents against root rot caused by Pythium irregulare in strawberry plants

Abstract

Strawberry ( Fragaria × ananassa ) cultivation is increasingly threatened by root rot caused by Pythium irregulare , an aggressive soilborne pathogen with limited sustainable control options. This study aimed to explore the potential of native rhizobacteria from strawberry soils as plant growth-promoting rhizobacteria (PGPR) and biocontrol agents against P. irregulare . A total of 150 bacterial isolates were screened in vitro , from which eleven exhibited strong antagonism, with inhibition rates exceeding 80 % in some cases. Microscopic examination revealed pathogen hyphal deformation, swelling, and cytoplasmic leakage when co-cultivated with selected isolates. Indirect mechanisms, including volatile organic compounds and cell-free filtrates, further suppressed mycelial growth, with isolates FR18, V3, and EH36 showing inhibition above 70 %. Biochemical assays confirmed multiple PGPR traits, including nitrogen fixation, phosphate solubilization, ammonia secretion, IAA and siderophore production and synthesis of hydrolytic enzymes. Molecular screening detected genes associated with lipopeptide biosynthesis (iturin, surfactin, bacillomycin), providing a genetic basis for biocontrol potential. Greenhouse trials validated the protective role of six isolates, with EH36, FR18, CM16, and SB6 significantly reducing disease severity to levels comparable to the non-inoculated control. Field experiments confirmed that bacterial inoculation enhanced canopy development, biomass accumulation, and chlorophyll content, while stabilizing growth responses across replicates. Overall, this work provides the first evidence that strawberry-native rhizobacteria can effectively suppress P. irregulare while enhancing plant growth under both controlled and field conditions. These findings highlight the promise of locally adapted bacterial isolates as eco-friendly alternatives to chemical fungicides and open pathways for developing bioinoculants to support sustainable strawberry production. • Eleven rhizobacterial isolates showed strong in vitro antagonism against P. irregulare. • The most effective isolates (FR18, V3, V4) inhibited pathogen growth by over 80 %. • Microscopy revealed hyphal deformation, vacuolization, and cytoplasmic leakage. • Greenhouse assays confirmed reduced root rot severity, with protection up to 65 %. • Field trials demonstrated enhanced strawberry growth and yield after inoculation.