Biocontrol of potato common scab is associated with high Pseudomonas fluorescens LBUM223 populations and phenazine-1-carboxylic acid biosynthetic transcript accumulation in the potato geocaulosphere

Biological control (biocontrol) is the use of live microorganisms to control disease caused by plant pathogens and is commonly viewed as a promising alternative to pesticide use in agriculture. Bacteria belonging to the Pseudomonas family are often used as biocontrol agents because they display a broad range of mechanisms to control plant diseases. We previously discovered a strain of Pseudomonas (LBUM223), which was able to reduce symptoms of common scab of potato in controlled and field experiments through its production of an antibiotic. In this study, we aimed to better understand how the soil populations of LBUM223 and the expression of a key gene involved in the synthesis of the antibiotic varied in our experiments in order to further explain how disease control occurred. Results obtained from controlled experiments showed that soil populations of LBUM223 significantly declined over 4 moths, unless the pathogen was present, which seemed to maintain populations at a higher level. Under field conditions, soil populations of LBUM223 followed a similar decline in time when a single dose was applied in spring but remained stable when re-applied every two weeks. An increase in LBUM223 populations also logically led to higher antibiotic gene expression and less disease symptoms. Taken together, our findings suggest that LBUM223 is able to, and must, colonize the soil surrounding potato at high levels in order to achieve disease control, which is important knowledge in order to further develop LBUM223 into a successful field treatment for common scab of potato.