Bacterial canker, caused by the pathogen Clavibacter michiganensis, is notoriously difficult to control, particularly in greenhouse production systems where conditions favor disease spread and where growers have limited options once an infection takes hold. The disease can cause significant production losses, affecting yield and fruit quality, and it has long been a source of frustration for commercial tomato growers. Because chemical treatments against the pathogen are limited in their effectiveness and increasingly constrained by regulatory and environmental pressures, the search for sustainable alternatives has become a priority for the agricultural sector. The INRS study was designed specifically to address this gap, drawing on a library of bacterial strains previously isolated from fields growing a variety of crops.

The screening process, led by Professor Éric Déziel of the INRS Armand-Frappier Santé Biotechnologie Research Centre, evaluated hundreds of candidate strains for their ability to combat the pathogen and support plant health. From this large-scale effort, the researchers identified three particularly promising bacterial strains. One of these delayed the appearance of disease symptoms by up to seven days in tomato plants exposed to Clavibacter michiganensis while also significantly reducing disease severity. In plant pathology, a delay of that magnitude can be commercially meaningful, giving crops a longer productive window and reducing the overall disease burden within a growing cycle. The two other strains also demonstrated the ability to protect plants while simultaneously promoting their growth.

Nasim Sedighian, an environmental microbiology researcher and first author of the study, who conducted the work during her postdoctoral fellowship at INRS, emphasized the significance of the dual function observed in the strains. “We identified bacteria capable of protecting plants against a major disease while also enhancing their growth. This dual function represents a highly promising opportunity for more sustainable agriculture,” she said. The combination of biocontrol and growth promotion in a single organism is what makes the finding especially attractive from a practical standpoint, since growers would not need to deploy separate products to achieve disease protection and improved plant vigor.

Beyond the immediate agricultural implications, the study produced an intriguing taxonomic finding. Genomic analyses revealed that two of the strains studied may belong to a previously unrecognized lineage within the Pseudomonas marginalis group, a cluster of bacteria known for their close associations with plants. This observation opens new avenues of research into beneficial plant-associated microorganisms and suggests that the diversity of useful bacteria in agricultural soils and crop environments may be greater than currently appreciated. Understanding the evolutionary relationships and functional capabilities of these newly recognized lineages could help researchers identify additional strains with valuable biocontrol or growth-promoting properties in the future.

The research did not emerge in isolation. It was conducted in collaboration with Agro-100 Ltd., a long-standing partner of the Déziel laboratory, and was shaped by challenges identified directly by greenhouse tomato growers. This partnership-based approach reflects a growing trend in agricultural science, in which academic laboratories work closely with industry to ensure that laboratory discoveries can be translated into products and practices that meet the real-world needs of producers. For more than two decades, Professor Déziel’s laboratory has developed recognized expertise in beneficial microorganisms and their agricultural applications, building the strain collections and screening infrastructure that made the current study possible.

“This research highlights the importance of partnerships between academia and industry in addressing real-world challenges facing the agricultural sector. In the long term, these microorganisms could provide growers with new tools to protect their crops more sustainably,” said Déziel, who holds the Canada Research Chair in Fundamental and Applied Sociomicrobiology. His remarks underscore the practical orientation of the project, which from its inception aimed at developing biological solutions adapted to the realities of the greenhouse sector rather than pursuing purely fundamental questions about plant-microbe interactions.

The technical basis for how such beneficial bacteria operate is an active area of investigation in plant microbiology. Beneficial strains can protect plants through a variety of mechanisms, including competitive exclusion of pathogens, stimulation of the plant’s own immune responses, and the production of antimicrobial compounds that inhibit pathogen growth. Growth promotion, meanwhile, can result from improved nutrient acquisition, hormone modulation, or enhanced stress tolerance. While the published study documents the protective and growth-promoting effects of the three strains in tomato plants exposed to Clavibacter michiganensis, further work will be needed to characterize precisely which mechanisms underlie the observed benefits and how those mechanisms perform under the variable conditions of commercial production.

According to the research team, further testing under commercial growing conditions will be required to confirm the effectiveness of the bacterial strains and to determine how they can be used most effectively. Greenhouse environments differ from laboratory settings in temperature, humidity, light, and microbial community composition, and a strain that performs well in controlled experiments may behave differently at scale. Establishing application protocols, dosing strategies, and compatibility with existing growing practices will be essential steps on the path from discovery to deployment. The involvement of an industry partner such as Agro-100 positions the team to navigate this transition, and the study was supported financially by Agro-100, CRIBIQ, and the Natural Sciences and Engineering Research Council of Canada (NSERC).

The broader significance of the work lies in its contribution to the movement toward reduced chemical inputs in agriculture. As regulators and consumers push for lower pesticide residues and more environmentally friendly production methods, biological control agents derived from naturally occurring microorganisms have attracted growing interest. The INRS findings demonstrate that a systematic screen of existing strain collections, guided by clear industry needs, can surface organisms with the potential to address major crop diseases. If subsequent commercial-scale trials confirm the laboratory results, tomato growers could gain a new tool against bacterial canker that protects yields while supporting more sustainable farming systems, and the previously unrecognized Pseudomonas lineage identified along the way may yield further discoveries in the years ahead.

Subject of Research: Beneficial bacteria for tomato growth promotion and biocontrol of bacterial canker

Article Title: Beneficial bacteria protect tomatoes and promote plant growth

Article References: Beneficial bacteria protect tomatoes and promote plant growth. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: beneficial bacteria, tomato, bacterial canker, Clavibacter michiganensis, biocontrol, plant growth promotion, Pseudomonas marginalis, greenhouse production, sustainable agriculture, INRS, biological solutions, Applied and Environmental Microbiology