Stress-adapted endophytic Pseudomonas strains isolated from unmanaged lupin promote potato growth and suppress verticillium wilt through complementary biocontrol and plant growth-promoting mechanisms

Verticillium wilt, primarily caused by Verticillium dahliae, is among the most destructive soil borne diseases impacting global potato production. Fungal propagules remain viable in soil for extended periods, and conventional control measures often show limited efficacy. These challenges underscore the necessity for sustainable disease management strategies. We evaluated two stress adapted endophytic Pseudomonas strains, B18 and B14, isolated from unmanaged wild Lupinus roots in Quebec, Canada, for their plant growth promoting and biocontrol potential against Verticillium wilt in potato. Both isolates exhibited multiple plant beneficial traits. B18 demonstrated strong phosphate solubilization, indole 3 acetic acid production, putative nitrogen fixation related activity, siderophore production, and hydrogen cyanide production. These traits correlated with enhanced plant growth promoting effects, including stimulation of seed germination and radicle growth. In contrast, B14 primarily exhibited antagonistic activity against Verticillium species through similar plant beneficial mechanisms, indicating complementary activities between the strains. The cell free supernatants of B18 further supported its biostimulant activity, suggesting a significant role for its extracellular metabolites. Greenhouse experiments using the Verticillium susceptible potato cultivar Russet Burbank, inoculated with either strain, showed enhanced plant growth and reduced disease severity compared with pathogen only controls. Under pathogen challenge, plants treated with plant growth promoting rhizobacteria (PGPR) exhibited up to 62% greater shoot height and approximately double the leaf production. Additionally, these plants produced 4.2 times more tubers than pathogen only plants. Disease progression, measured as the area under the disease progress curve (AUDPC), was reduced by 84 to 92% following bacterial inoculation. While individual strains effectively suppressed disease, the combined B18 plus B14 strains resulted in the most substantial improvements in growth, biomass, root development, and tuber production. These findings demonstrate that stress adapted endophytic Pseudomonas strains from wild Lupinus can contribute to sustainable potato production. The B18 plus B14 consortium, when combined with two-strain inoculation, demonstrated the most significant effects. These findings emphasize the potential of functionally complementary microbial inoculants for the integrated management of Verticillium wilt and other persistent soil-borne diseases in potatoes.