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, a prevalent soil-borne disease affecting potato crops, is caused by the fungus Verticillium dahliae. Conventional control methods often prove ineffective due to the persistence of fungal spores in soil. This highlights the need for sustainable disease management practices. Researchers investigated two stress-tolerant endophytic Pseudomonas strains, labeled B18 and B14, sourced from wild Lupinus plants in Quebec, Canada, to assess their potential for promoting plant growth and combating Verticillium wilt in potato crops.

Both strains exhibited beneficial traits for plants, such as the ability to solubilize phosphate, produce indole-3-acetic acid, fix nitrogen, generate siderophores, and produce hydrogen cyanide. These traits contributed to enhanced plant growth, including improved seed germination and root development. Conversely, B14 primarily displayed antagonistic effects against Verticillium species through similar plant-beneficial mechanisms, indicating that the strains complement each other's activities.

The cell-free supernatants of B18 further supported its biostimulant properties, suggesting the importance of its extracellular metabolites. In greenhouse trials, potato plants (Russet Burbank cultivar) inoculated with either strain showed increased growth and diminished disease severity compared to uninfected plants. Inoculated plants exhibited up to 62% greater shoot height and twice the number of leaves when challenged by the pathogen.

Moreover, plants treated with the beneficial bacteria produced 4.2 times more tubers than those only exposed to the pathogen. Disease progression was substantially reduced by 84 to 92% following bacterial inoculation. While both strains individually provided effective disease control, the combined use of B18 and B14 yielded the most significant improvements in plant growth, biomass, root development, and tuber production.

These findings suggest that stress-tolerant Pseudomonas strains from wild Lupinus can play a vital role in the sustainable management of potato crops, particularly in the integrated control of Verticillium wilt and other persistent soil-borne diseases.