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

The research, carried out by Keyvan Pourrashid, Zohreh Jabbarzadeh, and Jafar Amiri at the Department of Horticultural Science, Faculty of Agriculture, Urmia University in Iran, was designed as a factorial experiment under a completely randomized design. The team foliar-applied silica dioxide nanoparticles at four concentrations: 0, 50, 100, and 200 milligrams per liter. These were crossed with three putrescine concentrations: 0, 1.5, and 3 millimolar. That twelve-treatment matrix allowed the researchers to separate the effects of each compound individually from the interactive effects of applying them in combination, a distinction that matters because biostimulants frequently behave differently in mixtures than they do on their own.

Silica nanoparticles have attracted growing attention in plant science over the past decade. Silicon is not classified as an essential element for most plants, yet abundant evidence shows that it strengthens cell walls, improves mechanical stability, and helps plants cope with environmental stress. Shrinking silicon down to the nanoscale changes the game further: nanoparticles offer an enormous surface-area-to-volume ratio, can adhere to and penetrate leaf surfaces more effectively than bulk particles, and may release silicon in a form that plant tissues can readily use. Previous work has shown benefits in crops as varied as sorghum under drought, maize under deficit irrigation, and ornamentals including roses, gerbera, carnation, and marigold, where silicon sprays have been linked to longer flowering periods and better postharvest performance.

Putrescine belongs to an entirely different family of molecules. It is a polyamine, a class of small nitrogen-rich compounds that participate in a startling range of plant processes, from cell division and DNA stabilization to flowering, fruit development, and responses to heat, salt, and drought stress. Polyamines carry positive charges that let them bind to negatively charged molecules such as DNA, RNA, and membrane phospholipids, which is one reason they help stabilize cellular structures under stress. They also crosstalk with major plant hormones, modulating the actions of auxins, gibberellins, and abscisic acid. Exogenous putrescine sprays have previously improved chlorophyll metabolism in tomato seedlings, salt tolerance in zinnia flowers, and postharvest quality in gerbera and alstroemeria cut flowers.

The rationale for combining the two was straightforward: silica nanoparticles and putrescine support plant performance through largely independent mechanisms, so their effects might add up or even multiply. What was missing, the authors note, was any systematic information about how the two interact in stock, an economically important ornamental whose commercial value depends almost entirely on vegetative vigor, floral quality, and vase life. The new experiment fills that gap with a full factorial design, meaning every nanoparticle concentration was tested against every putrescine concentration, including untreated controls for both.

The results were unambiguous in their overall direction. Compared with untreated plants, foliar application of silica nanoparticles and putrescine, particularly at appropriate concentrations and in combination, improved vegetative growth, biomass accumulation, floral quality, and vase life. But the standout treatment was not the highest dose of either compound. The best performance across most evaluated traits came from combining 1.5 millimolar putrescine with just 50 milligrams per liter of silica nanoparticles, the lowest nanoparticle concentration tested. That finding carries a practical message: in biostimulant science, more is not always better, and moderate doses can outperform aggressive ones, both in terms of plant response and in terms of cost and environmental loading.

The biochemical data help explain why the winning combination worked. Plants receiving the optimal treatment showed increased contents of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids, the pigment suite that drives photosynthesis. More chlorophyll means greater capacity to capture light energy and fix carbon, which in turn supports the vegetative growth and biomass gains the researchers recorded. Carotenoids do double duty as accessory pigments and as antioxidants that quench reactive oxygen species generated during photosynthesis, so their elevation suggests the treated plants were not only photosynthesizing more but also protecting their photosynthetic machinery more effectively.

The treatment also raised levels of soluble sugars, proteins, and anthocyanins. Soluble sugars are the currency of plant metabolism and a critical determinant of cut flower longevity, since a detached flower survives largely on the carbohydrate reserves it carried at harvest. Higher sugar content at the moment of cutting translates directly into more fuel for respiration and petal maintenance in the vase. Elevated protein content points to a more active metabolic state, while increased anthocyanins, the pigments responsible for red, purple, and blue coloration in plant tissues, indicate enhanced secondary metabolism and potentially better visual quality and stress resilience. Taken together, the biochemical profile suggests that the combined treatment improved the photosynthetic capacity and overall metabolic status of the plants before harvest, setting them up for a longer postharvest life.

The interactive nature of the effect is arguably the study’s most interesting scientific contribution. In a factorial design, an interaction means the response to one factor depends on the level of the other. Here, the fact that the best outcome came from a specific pairing rather than from either compound alone indicates genuine synergy or at least complementary action. One plausible mechanistic picture is that silica nanoparticles reinforce the physical infrastructure of leaves and stems while putrescine tunes the biochemical and hormonal environment inside cells, with the two effects converging on the same outcome: plants that grow better, flower better, and hold up longer after cutting. The authors suggest that this interactive strategy may represent a promising biostimulant approach for enhancing the commercial quality of ornamental plants more broadly.

For the floriculture industry, the implications are tangible. Stock is grown in greenhouses under tight schedules, and every extra day of vase life adds value for wholesalers, retailers, and consumers alike. A foliar spray protocol that combines a low dose of silica nanoparticles with a moderate dose of putrescine could, if validated at commercial scale, offer growers a relatively simple preharvest intervention to raise quality without genetic modification or heavy pesticide use. The study also adds to a fast-growing literature on silicon-based nanomaterials in sustainable agriculture, where researchers are exploring everything from nanoparticle uptake and translocation pathways to their roles in stress mitigation and nutrient management. Questions certainly remain, including how the treatment performs across different stock genotypes, seasons, and growing systems, and what the long-term environmental fate of engineered silica particles in greenhouse operations might be. But the core finding stands: two well-studied biostimulants, applied together at the right doses, can measurably improve how a flower grows, how it looks, and how long it lasts in the vase, and that combination may soon find a place in the greenhouse toolkit.

Subject of Research: Interactive effects of foliar-applied silica nanoparticles and putrescine on growth, biochemistry, and vase life of stock (Matthiola incana)

Article Title: Interactive effects of silica nanoparticles and putrescine on morphophysiological and biochemical performance in stock (Matthiola incana L. ‘Pilaster White’)

Article References: Pourrashid, K., Jabbarzadeh, Z., & Amiri, J. (2026). Interactive effects of silica nanoparticles and putrescine on morphophysiological and biochemical performance in stock (Matthiola incana L. ‘Pilaster White’). The Science of Nature, 113(6), Article 123. https://doi.org/10.1007/s00114-026-02177-1

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02177-1

Keywords: silica nanoparticles, putrescine, stock, Matthiola incana, ornamental horticulture, vase life, chlorophyll, biostimulants, floriculture, plant physiology, nanotechnology, greenhouse production

The research team, led by Sachin Naik and Michelle Jones, drew on a curated collection of 1,044 rhizobacterial isolates originally recovered from ornamental greenhouse crops grown in peat-based substrates. Rather than relying on the traditional tricalcium phosphate assays that dominate the phosphate-solubilizing bacteria literature, the team targeted iron phosphate directly, reasoning that the calcium-focused screens used in most prior studies may miss the strains most relevant to soilless production. Peat substrates contain significant intrinsic iron, much of it bound to organic matter, and under the mildly acidic to near-neutral conditions typical of greenhouse containers, phosphorus is progressively sequestered into stable iron phosphate precipitates that resist conventional fertilizer corrections.

To find bacteria that could liberate this trapped nutrient, the researchers deployed a high-throughput malachite green colorimetric assay. Each isolate was grown in triplicate in minimal medium containing iron phosphate dihydrate as the sole phosphorus source, and after four days of incubation the soluble phosphorus released into the culture supernatant was quantified spectrophotometrically. The results revealed a strikingly stratified microbial landscape: nearly 70 percent of the isolates showed minimal solubilization below 8 percent, about 28 percent displayed moderate activity, and only 24 isolates, a mere 2.3 percent of the collection, exceeded the 25 percent threshold set for high performers. Notably, Bacillus velezensis, the phosphate-solubilizing strain included as a commercial reference from the biostimulant Lalrise Vita, showed almost no activity against iron phosphate, solubilizing less than 3 percent.

Whole-genome sequencing of the top performers revealed a taxonomically diverse guild dominated by the genera Pantoea, Bacillus, Priestia, Paenibacillus, Pseudomonas, and Stenotrophomonas. Average nucleotide identity analysis confirmed species-level assignments for most strains, and the isolates proved remarkably cosmopolitan in origin, having been recovered from zinnia, vinca, petunia, geranium, and coleus. This broad host distribution suggests these bacteria are not tightly host-specific but instead occupy shared rhizosphere niches across taxonomically diverse plant families, a property that could make them useful in the mixed plantings and crop rotations common in commercial greenhouse operations.

The critical question, of course, was whether laboratory solubilization would translate into real plant benefit. Twenty-seven candidate strains were tested in a high-throughput greenhouse experiment using French marigold ‘Durango Yellow’ grown in peat-perlite substrate adjusted to pH 7.0, a deliberately severe phosphorus-limiting condition. After seedling establishment, insoluble iron phosphate served as the sole phosphorus source, and bacterial treatments were applied as weekly substrate drenches for four weeks. A laser-based digital phenotyping platform measured plant biomass, leaf area, and spectral reflectance indices that track chlorophyll content, canopy greenness, and senescence. Five strains emerged as clear winners: Pantoea communis C3A8, Pantoea formicae C8D10, Pseudomonas sp. C6E7, Pseudomonas sp. C9D1, and Priestia megaterium C3F10.

Intriguingly, two of those five, strains C3F10 and C9D1, had shown only about 3 percent solubilization in the in vitro assay, yet they ranked among the top performers in the greenhouse screen. This disconnect between biochemical activity in a flask and plant growth promotion in a pot carries an important lesson for biofertilizer development: in vitro solubilization percentage alone does not reliably predict in planta performance. The researchers deliberately included low and mid-range solubilizers in their greenhouse trials to test this very question, and the answer was unambiguous. Success in the rhizosphere depends on far more than raw solubilizing chemistry, encompassing colonization ability, stress tolerance, and the competitive exploitation of root-derived carbon.

A second, more rigorous validation experiment with 30 replicate blocks confirmed the greenhouse results at pH 6.5. Pantoea communis strain C3A8 delivered the strongest overall response, significantly increasing shoot digital biomass and 3D leaf area while boosting the green leaf index and shifting canopy color composition toward healthier green hues. Most tellingly, plants inoculated with C3A8 accumulated significantly more phosphorus in their shoot tissue than controls. Because iron phosphate was the only phosphorus supplied during the treatment period, this tissue analysis provides direct evidence that the bacterium released plant-available phosphorus from the insoluble iron phosphate pool. The authors believe this is the first report of phosphate solubilization ability in P. communis, expanding the known functional diversity of a genus previously represented mainly by P. agglomerans in this literature.

The genomic analysis explains why these strains differ so markedly in performance. Pantoea communis C3A8 and Pantoea formicae C8D10 each carry three copies of the gcd gene, which encodes glucose dehydrogenase, the central enzyme in gluconic acid-mediated inorganic phosphate solubilization, along with the pqqF and pqqL genes needed to synthesize its pyrroloquinoline quinone cofactor. Both also harbor extensive arsenals of phosphatase genes for mineralizing organic phosphorus, complete phosphate transport systems, and hundreds of genes for iron acquisition and root colonization. The Pseudomonas strains took a different genomic route, pairing single gcd copies with multiple pqqL copies, three copies of phoD and ppx in C6E7, and elevated counts of nitrogen acquisition and volatile synthesis genes. Priestia megaterium C3F10, remarkably, lacks gcd entirely and may instead rely on intracellular polyphosphate accumulation and controlled release, driven by five copies of the phosphoenolpyruvate synthase gene and multiple phoR regulatory copies.

Rhizosphere competence genes added another layer of ecological insight. The Pantoea strains carry multiple gene clusters for trehalose and mannitol catabolism, pathways linked to osmoprotection and persistence under the fluctuating moisture conditions of container substrates, while C3A8 uniquely encodes an inositol catabolic cluster, a trait shown in other bacteria to be essential for rhizosphere colonization. Priestia megaterium C3F10 carries gene clusters for sucrose and levan metabolism, which in other systems support biofilm formation and root surface attachment, along with the 3-oxoadipate pathway for degrading aromatic compounds derived from lignin and phenolic root exudates. The authors are careful to note that these genomic signatures generate hypotheses about mechanism rather than demonstrated links, and that direct substrate-level measurements of water-extractable phosphorus and rhizosphere enzyme activity will be needed to confirm which solubilization pathways operate in situ.

The practical implications extend well beyond ornamental horticulture. Greenhouse production depends almost entirely on fertigation, and the limited substrate volume and low cation exchange capacity of soilless containers routinely drive fertilizer runoff, phosphorus leaching, and environmental contamination. Growers frequently over-apply phosphorus to compensate for its rapid immobilization, a practice that wastes resources, disrupts micronutrient balance, and can even induce iron deficiency in crops. The five validated strains, with their complementary mechanisms spanning gluconic acid-mediated dissolution, organic phosphorus mineralization, nitrogen acquisition, and polyphosphate dynamics, suggest that microbial consortia could deliver synergistic benefits exceeding those of any single inoculant. If follow-up work confirms performance across diverse ornamental species and substrate types, these iron phosphate solubilizers could form the basis of biofertilizer formulations that let growers cut synthetic phosphorus inputs while maintaining crop quality, turning a stubborn chemistry problem into a biological opportunity.

Subject of Research: Iron phosphate solubilizing bacteria for sustainable phosphorus management in soilless greenhouse crop production

Article Title: High-throughput screening and genomic characterization of iron phosphate solubilizing bacteria for sustainable greenhouse production

Article References: Naik, S., Quijia-Pillajo, J., Chapin, L. J., & Jones, M. L. (2026). High-throughput screening and genomic characterization of iron phosphate solubilizing bacteria for sustainable greenhouse production. Plant and Soil. https://doi.org/10.1007/s11104-026-09134-x

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09134-x

Keywords: phosphate solubilizing bacteria, iron phosphate, greenhouse production, soilless substrate, plant growth promoting rhizobacteria, Pantoea communis, Pseudomonas, Priestia megaterium, whole genome sequencing, phosphorus availability, biofertilizer, controlled environment agriculture