Phage4Crops will unite European scientists, farmers, regulators and industry to develop bacteriophage biocontrol against bacterial crop diseases.

Phage4Crops is a four year COST Action running from 13 October 2026 to 12 October 2030. The official memorandum does not assign a single research budget to the project because COST Actions primarily finance scientific networking rather than laboratory experiments, salaries, equipment or field trials. COST funding typically supports conferences, training schools, Short Term Scientific Missions, interlaboratory exchanges, communication activities and participation grants. Based on standard COST funding levels, the networking budget may be expected to fall in the approximate range of €690,000 over four years, although the final amount can vary depending on participation and annual implementation. Experimental work, including the planned cross country greenhouse and field validation studies, will require additional external funding. Phage4Crops aims to isolate at least 200 phages infecting plant pathogenic bacteria, genetically characterise more than 100 of them, establish a European phage repository, coordinate at least three agricultural validation trials and train more than 200 young researchers.

Researchers, students, plant pathologists, microbiologists, bioinformaticians, agronomists, companies, farmers and regulatory stakeholders can apply to join the Action through its official COST page. Participation is generally organised through the Working Groups, which cover phage discovery, biological characterisation, agricultural application, and regulatory and societal dimensions. Applicants must create an e COST profile and use the application option available under the Working Groups and Membership section. Membership of the Management Committee follows a separate national nomination procedure. Official page and application portal: https://www.cost.eu/actions/CA25147/

Europe has approved a major new scientific network dedicated to one of the least developed but potentially transformative applications of bacteriophages: the biological control of bacterial diseases in crops.

The COST Action Phage4Crops, formally designated CA25147 and entitled “Bacteriophages for Crop Protection: Discovery, Exploration, Application & Society”, was approved in Brussels on 19 May 2026. Its objective is not simply to collect new phages or demonstrate bacterial killing under laboratory conditions. The initiative is designed to construct the scientific, technological, regulatory and social infrastructure needed to make phage based crop protection a credible component of European agriculture.

Phage4Crops begins from a simple but increasingly urgent observation. Bacterial plant diseases cause substantial losses in crops, yet farmers often have access to very few effective curative treatments. In many agricultural systems, disease management still depends on prevention, sanitation, resistant plant varieties and repeated applications of copper based products or other chemical agents. These strategies can slow disease progression, but they do not always provide durable control and may generate environmental costs, including the accumulation of copper in agricultural soils and the selection of less susceptible bacterial populations.

Bacteriophages offer a fundamentally different approach. These viruses infect bacteria with a degree of specificity that can potentially allow pathogenic populations to be targeted while limiting broader disruption of beneficial microorganisms. Once a susceptible host is encountered, a lytic phage can inject its genome, redirect bacterial metabolism, produce new viral particles and lyse the infected cell. When the target bacterium disappears, the phage population is also expected to decline because it can no longer replicate.

This biological precision makes phages attractive for integrated crop protection, but it also creates scientific and operational complexity. Agricultural environments are far less controlled than laboratory plates. Sunlight, ultraviolet radiation, temperature changes, desiccation, rainfall, soil chemistry, plant surfaces and microbial competition can all influence phage survival and activity. A preparation that performs well in vitro may lose much of its effectiveness after application to leaves, roots, seeds or soil.

Phage4Crops was created to address this gap between experimental promise and agricultural reality.

From fragmented research to a European infrastructure :

Research on medical phage therapy has expanded rapidly over the past decade, supported by growing phage collections, genomic databases, compassionate use programmes and clinical trials. Agricultural phage research remains comparatively underdeveloped. The Phage4Crops memorandum highlights a pronounced imbalance between the two fields. Medicine benefits from extensive phage collections and increasingly detailed molecular studies, while agriculture still has relatively few characterised phages, limited evolutionary data, few large field trials and major gaps in the understanding of plant associated viral communities.

The problem is not a complete absence of expertise. Scientists across Europe are already studying bacteriophages, bacterial plant pathogens, microbial ecology, plant physiology, genomics and biological control. The difficulty is that many of these activities remain disconnected, confined to individual laboratories, national initiatives or short term projects.

Plant pathogens do not respect national borders. Bacteria can move through infected planting material, seeds, insects, irrigation systems, agricultural equipment and international trade. A disease that is currently restricted to one region may represent a serious future threat elsewhere. Responding effectively therefore requires shared collections, comparable methods, accessible data and coordinated surveillance.

Phage4Crops intends to bring together researchers in bacteriophage biology, bacterial genomics, metagenomics, bioinformatics, agronomy, epidemiology, microbial ecology, plant pathology, plant physiology, biotechnology and social sciences. Farmers, regulatory experts, industry representatives and public authorities are also expected to participate.

The initial network described in the project documentation already includes 87 proposers representing 55 laboratories across 25 COST countries. International partners from Africa, Asia, Oceania, North America and South America are also involved, giving the Action a scope that extends well beyond the European Union. The consortium includes academic groups, private sector participants, young researchers and experts in both fundamental and applied science.

This multidisciplinary structure is essential because an agricultural phage product cannot emerge from virology alone. Its development requires the identification of a relevant bacterial pathogen, the isolation of active phages, genomic safety assessment, host range analysis, formulation, ecological testing, field validation, production at scale and approval within a plant protection regulatory framework.

Building a European collection of agricultural phages :

One of the most ambitious objectives of Phage4Crops is the isolation and characterisation of at least 200 bacteriophages infecting phytopathogenic bacteria. At least 100 of these phages are expected to undergo genetic characterisation, with their metadata curated in a public database.

This would represent a major step for a field in which many economically important plant pathogens remain poorly represented in public phage repositories. Medical phage programmes often maintain collections targeting species such as Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Comparable resources for agricultural pathogens remain far less developed.

Phage4Crops plans to establish a European repository dedicated to bacteriophages infecting plant pathogenic bacteria. The repository would be linked to an open access database connecting bacterial hosts, phage genomes and phenotypic information. Such a resource could allow researchers to compare phages isolated in different countries, identify shared genetic modules and design cocktails using more rational biological criteria.

This is particularly important because a phage genome alone cannot fully predict agricultural performance. Researchers need to know which bacterial strains are infected, whether the infection is productive, how efficiently the phage adsorbs, how quickly bacterial killing occurs and how frequently resistance emerges. Information on bacterial receptors, defence systems, prophages and ecological fitness may also determine whether a candidate remains useful outside the laboratory.

A well constructed repository could eventually support the rapid selection of phages against an emerging plant disease. Instead of beginning every project with environmental sampling and isolation, researchers could search a shared collection, compare candidate genomes and test already characterised phages against newly collected bacterial isolates.

The design of durable phage cocktails :

Agricultural phage products will probably require combinations of several phages rather than dependence on a single isolate. A cocktail can broaden the range of susceptible bacterial strains and reduce the probability that one resistance mechanism will eliminate the entire treatment.

However, combining phages is not simply a matter of placing several active isolates in the same formulation. Two phages that appear different may use the same bacterial receptor, meaning that one mutation could generate cross resistance to both. Some combinations may interfere with one another, while others may produce complementary effects by targeting distinct surface structures or overcoming different bacterial defence systems.

Phage4Crops intends to generate integrated knowledge on plant, bacterium and phage interactions, including the study of prophage content and anti phage defence systems in phytopathogenic bacteria. Genomic approaches will be used to investigate CRISPR Cas systems and other defence mechanisms that could limit productive infection.

This emphasis reflects an important change in phage biology. Host range is no longer understood solely as a question of whether a phage can attach to the bacterial surface. Successful infection depends on multiple sequential barriers. The phage must encounter the pathogen, bind to an accessible receptor, inject its genome, escape restriction systems and other intracellular defences, reproduce under the physiological conditions of the plant environment and complete lysis before bacterial stress responses or abortive infection mechanisms interrupt the cycle.

Agricultural pathogens may also differ significantly between regions, plant species and seasons. A phage cocktail developed against a small reference collection may fail when confronted with genetically diverse field isolates. The database and repository proposed by Phage4Crops could help developers design cocktails from geographically and biologically representative collections rather than relying on a few laboratory strains.

Priority pathogens and economically important crops :

Phage4Crops will initially focus its scientific activities on at least four groups of bacterial plant pathogens selected according to scientific, economic and regulatory criteria. The final priorities will be informed by surveys of researchers and stakeholders, as well as recommendations from the European and Mediterranean Plant Protection Organization.

The project documentation identifies a broad range of candidate pathogens affecting major European crops.

Erwinia amylovora, the causative agent of fire blight, threatens apple and pear orchards. Pseudomonas syringae includes pathovars responsible for diseases in tomato, bean, melon and stone fruit trees such as cherry, apricot and plum. Members of the Ralstonia solanacearum species complex can cause destructive vascular wilts in potato and tomato. Xanthomonas species affect a wide range of crops, including cabbage, carrot, lettuce, pepper, tomato, strawberry, hazelnut and walnut.

Other potential targets include Acidovorax citrulli in cucurbits, Agrobacterium tumefaciens across numerous perennial and horticultural plants, Clavibacter michiganensis in tomato and pepper, Curtobacterium flaccumfaciens pathovars affecting bean, soybean, beet, onion and tulip, soft rot Pectobacteriaceae in vegetables and potatoes, Pantoea species in cabbage and melon, and Xylella fastidiosa in olives, grapevines and other perennial hosts.

These bacteria cause very different diseases and occupy distinct ecological niches. Some remain on plant surfaces before entering wounds or natural openings. Others colonise vascular tissues, roots or underground organs. This diversity means that there will be no universal agricultural phage treatment.

A phage preparation for a seed borne pathogen will require a different formulation and application strategy from one intended for a bacterium living in the xylem of a mature tree. The biology of the pathogen, the crop, the climate and the infection route must all shape product design.

From seed treatment to vascular delivery :

The Phage4Crops proposal describes several points in the agricultural production chain where phages could be applied.

Seed and nursery treatments could prevent bacterial infections at an early stage, before pathogens become established across a field. Soil and rhizosphere applications could reduce populations of soil borne bacteria while preserving or potentially supporting beneficial microbial communities. Foliar sprays and drip irrigation could deliver phages to leaves, stems or roots in greenhouse and field systems.

For high value perennial crops, more direct approaches may be needed. Vascular injection or other delivery systems could theoretically be explored for pathogens that colonise internal plant tissues, including Xylella fastidiosa infections in olives or other woody hosts.

Each route creates distinct formulation challenges. Phages applied to leaves can be rapidly damaged by ultraviolet radiation and drying. Those introduced into soil may adsorb to particles, become trapped in organic material or lose access to the bacterial host. Irrigation systems may expose phages to variable pH, temperature and water chemistry. Internal delivery must account for movement through plant vascular tissues and potential interactions with plant defence responses.

The project therefore places considerable emphasis on formulation and field persistence. Encapsulation approaches involving alginate beads, chitosan nanoparticles, liposomes and biodegradable polymers are among the strategies identified in the technical annex. These systems could protect phages from ultraviolet light, desiccation and temperature stress while enabling gradual or targeted release.

The effectiveness of these technologies will need to be measured under realistic conditions. A formulation that prolongs phage survival may also reduce the speed at which particles are released or limit contact with the bacterial host. Agricultural product development will require a balance between protection, accessibility, biological potency, cost and ease of application.

Testing phages beyond the laboratory :

One of the strongest commitments in the Phage4Crops programme is the validation of phage efficacy in controlled and agricultural settings. The Action aims to coordinate at least three cross country validation trials in greenhouses or field relevant systems, although the trials themselves will require financing outside the COST networking budget.

Candidate pathosystems mentioned for these studies include Erwinia amylovora, Pseudomonas syringae and Ralstonia solanacearum.

Cross country validation is particularly valuable because environmental variability is one of the central uncertainties in agricultural phage biocontrol. Temperature, humidity, light exposure, crop varieties, soil composition and local bacterial populations can change treatment performance. Repeating experiments in several regions can reveal whether an apparent effect is robust or dependent on one local set of conditions.

These trials should also help move the field beyond simple measurements of bacterial reduction. Relevant outcomes may include disease incidence, symptom severity, crop yield, phage persistence, development of bacterial resistance, effects on non target microorganisms and compatibility with existing agricultural practices.

Agricultural success will not necessarily mean complete eradication of the pathogen. A treatment that reduces disease sufficiently to protect yield, delays epidemic development or lowers the required quantity of copper based products may already provide substantial value.

The project intends to transform these findings into standardised protocols and best practice guidelines for phage formulation, application and regulatory compliance. Such guidance is urgently needed because experimental methods vary considerably between laboratories, making results difficult to compare.

Why phages could complement rather than replace other controls :

The scientific appeal of phages should not lead to the assumption that they will replace every existing plant protection strategy. Their most realistic role may be within integrated pest management systems.

Phages could be combined with resistant cultivars, crop rotation, sanitation, biological control organisms, disease forecasting, microbiome management and carefully reduced chemical treatments. Some combinations may be synergistic, while others may be incompatible and will require experimental evaluation.

Phage resistance is also likely to occur. Bacteria can modify surface receptors, activate intracellular defence systems or alter physiological states in ways that reduce susceptibility. In agriculture, however, resistance does not always mean complete treatment failure.

When a bacterial surface structure is required both for phage infection and for plant colonisation or virulence, resistance may carry an ecological cost. A receptor mutation could make the bacterium less able to attach to plant tissues, move through the host, acquire nutrients or compete with other microorganisms. Understanding these evolutionary trade offs will be essential for the rational selection of phages and cocktails.

Phage4Crops therefore aims to connect molecular biology with ecology and evolutionary modelling. The objective is not merely to identify the strongest bacterial killer in a laboratory assay, but to select phages that remain useful within a changing biological system.

Regulation may be as important as discovery :

The limited commercialisation of agricultural phages in Europe cannot be explained by technical barriers alone. Regulatory uncertainty remains one of the main obstacles to market access.

Phages are biological entities that replicate only in susceptible bacteria. Their composition may need to be updated as pathogen populations evolve. These characteristics do not fit comfortably within frameworks originally designed for conventional chemical plant protection products with stable and precisely defined active substances.

Developers must still demonstrate product identity, efficacy, manufacturing consistency, environmental safety and acceptable effects on non target organisms. They may also need to explain how phage cocktails will be modified over time and how biological variation will be controlled.

Phage4Crops plans to engage directly with the European Food Safety Authority, the European and Mediterranean Plant Protection Organization, national regulatory authorities, committees of the European Parliament and other stakeholders involved in plant protection policy.

The Action will not itself authorise commercial products, but it could provide the common scientific language needed for future regulation. Standardised methods, transparent databases, field evidence and agreed quality criteria could reduce uncertainty for both developers and evaluators.

The consortium also intends to address biosafety, intellectual property and public perception. Releasing biological control agents into the environment can raise legitimate questions, even when those agents are naturally present viruses of bacteria.

Public acceptance will depend on clear communication about what phages are, how they are selected, how their host specificity is evaluated and how environmental effects are monitored. The project recognises that scientific performance alone will not guarantee adoption.

Training the next generation of agricultural phage scientists :

Phage4Crops is also designed as a major training initiative. The network plans to train more than 200 young researchers and innovators across Europe and beyond.

Training schools and workshops are expected to cover phage isolation from agricultural samples, genome analysis, host range testing and practical applications. At least 40 Short Term Scientific Mission grants are planned to support exchanges between laboratories, allowing young scientists to learn specialised techniques and helping institutions standardise experimental workflows.

The project also aims to involve approximately 60 trainees in dedicated hands on schools and to generate open access guidelines that reduce barriers for laboratories entering the field.

This capacity building component may become one of the Action’s most durable achievements. Agricultural phage research requires scientists who can move between microbiology, genomics, plant pathology, ecology, formulation and regulation. Training researchers within isolated disciplines will not be sufficient.

Phage4Crops also proposes closer alignment with the Marie Skłodowska Curie Actions and may explore the creation of a future doctoral network involving academic and non academic partners.

The programme therefore offers opportunities not only for established laboratories but also for students, doctoral candidates and early career researchers interested in the intersection of virology, agriculture and sustainable biotechnology.

A bridge between research, farmers and industry :

Phage4Crops is not intended to remain an academic network. Its success will depend on whether its outputs are useful to farmers, plant health professionals, regulators and companies.

The project plans to engage at least 100 stakeholders through surveys, workshops, consultations and dissemination events. National clusters and contact points are expected to help identify local needs and connect groups that may be working on similar problems without knowing one another.

Farmer feedback will be particularly important. A biologically sophisticated treatment will have little agricultural value if it is too expensive, unstable, difficult to store or incompatible with standard equipment. Application timing, preparation, shelf life and integration into existing work routines can determine whether a product is adopted.

Industry participation will also be necessary for scale up, formulation, bioprocess development, quality control and distribution. The project notes that only a small number of European companies are currently active in agricultural phage biocontrol, despite increasing commercial interest worldwide.

By connecting companies with academic collections and biological data, Phage4Crops could help shorten the path from phage isolation to product development. It may also support new European proposals under future Horizon programmes related to agriculture, biodiversity and Farm to Fork objectives.

A One Health strategy for crop protection :

The project is explicitly inspired by the One Health concept. This is significant because antimicrobial resistance and microbial disease are often discussed primarily in the context of hospitals and human medicine.

Agriculture is part of the same biological system. Plant disease threatens food production, can increase dependence on chemical control and affects economic stability in rural communities. The health of crops, soils, animals, humans and ecosystems cannot be separated completely.

Phages may contribute to this broader strategy by reducing selected bacterial pathogens without the broad activity of many chemical agents. Their biodegradability and dependence on specific bacterial hosts could make them valuable tools for more targeted crop protection.

However, specificity is both their strength and their limitation. Effective use requires detailed knowledge of pathogen diversity, ecological conditions and application timing. Phages should not be presented as simple natural substitutes for pesticides. They are dynamic biological agents that must be understood, formulated and deployed with precision.

This is why Phage4Crops matters. The Action does not promise an immediate universal solution. Instead, it seeks to create the evidence, shared infrastructure and trained community required to determine where agricultural phages can genuinely work.

From isolated experiments to a European strategy :

Several previous European projects have already explored phages in crop protection, including VIROPLANT, PhageFire, EuroXanth and BeXyl. Phage4Crops is designed to connect experience from these initiatives while expanding the field into a broader and more permanent network.

Its planned outputs are concrete. The consortium aims to isolate at least 200 phages, sequence and annotate more than 100 phage genomes, establish a European repository, coordinate cross country validation studies, produce best practice guidelines, train more than 200 young researchers and generate collaborative publications, datasets and protocols.

The deeper ambition is institutional. Europe currently possesses many of the scientific components required for agricultural phage biocontrol, but they remain distributed across separate laboratories, disciplines and national systems. Phage4Crops seeks to assemble these components into a coherent research and innovation ecosystem.

If successful, the project could make it easier to identify promising phages, compare results between countries, design durable cocktails, evaluate formulations under realistic conditions and communicate reliable evidence to regulatory authorities.

It could also help redefine the place of bacteriophages in agriculture. Rather than being viewed as experimental curiosities or highly specific tools for exceptional situations, phages could become part of a broader portfolio of biological strategies for protecting crops while reducing dependence on environmentally problematic chemicals.

The next four years will show whether Europe can convert the extraordinary natural diversity of bacteriophages into practical, safe and accessible tools for agriculture. Phage4Crops provides the network through which that transition may begin.

Source :

The scientific objectives, proposed deliverables, target pathogens, network structure and implementation strategy described in this article are based on the official Memorandum of Understanding and Technical Annex for COST Action CA25147, Bacteriophages for Crop Protection: Discovery, Exploration, Application & Society, approved in Brussels on 19 May 2026.

https://e-services.cost.eu/files/domain_files/CA/Action_CA25147/mou/CA25147-e.pdf