As plant pathologists, we’re often trained to think in terms of the disease triangle: a susceptible host, a virulent pathogen, and a favorable environment. Soil usually appears in that framework as part of the environment—a background condition rather than a central actor. Yet, the more I read about soilborne diseases, the harder it became to accept that view. Across different pathosystems, researchers repeatedly reported similar observations: some soils naturally suppress disease, even when pathogens are present. Others remain highly conducive despite management interventions. In many cases, disease outcomes could not be explained simply by pathogen abundance.

This review began with a straightforward objective: to understand how soil properties influence the epidemiology of soilborne pathogens. Written together with Florabelle Castañeda, Leny Galvez, and Mark Angelo Balendres, what followed was an exploration that took us far beyond traditional pathogen-centered thinking. One challenge quickly became apparent. The literature on soil suppressiveness is enormous, but it is often fragmented. Studies may focus on microbial diversity, organic amendments, soil structure, microbial networks, or disease epidemiology, yet these topics are rarely discussed together. We wanted to build a conceptual bridge between them. As we worked through the literature, a recurring pattern emerged: the same soil could either facilitate pathogen persistence or constrain it through intense biological interactions. Gradually, this led us to a simple metaphor: soil can function as both a reservoir and a battlefield. In some situations, soil acts as a reservoir where pathogens accumulate, persist, and await opportunities to infect plants. In others, it resembles a battlefield populated by competing microorganisms, predators, antagonists, and complex ecological interactions that limit pathogen establishment and spread. Of course, real soils are neither purely reservoirs nor purely battlefields. They exist somewhere along a continuum, shaped by biological, chemical, and physical processes. This idea became the organizing framework for the review (Figure 1).

 Three soil components emerged as the central focus: microbial diversity, soil organic matter, and soil structure. We chose these three deliberately. Unlike factors such as soil pH or parent material, they are highly dynamic, deeply interconnected, and directly responsive to agronomic management. They are, in practical terms, the levers available to those who want to shift soil conditions from reservoir to battlefield.

One of the most interesting lessons was how difficult it is to separate cause from consequence in soil microbial ecology. High microbial diversity is frequently associated with lower disease incidence, but diversity alone is not a magic solution. The composition of the community, the functions it performs, the structure of the soil, and the availability of organic matter all interact to influence disease outcomes. The same increase in microbial diversity can suppress disease in one context and fail to do so in another. In some cases, high background diversity can even prevent introduced biocontrol agents from establishing, outcompeted before they can act.

Another insight was the importance of viewing disease suppression as an ecological process rather than a property of individual organisms. Beneficial microbes do not operate in isolation. Their effects depend on food webs, resource competition, environmental filtering, and the physical architecture of the soil itself. Even pore networks and aggregate structure can influence how pathogens move, survive, and encounter hosts—a reminder that soil physical integrity is not merely an agronomic concern, but also an epidemiological one.

Perhaps the most exciting aspect of writing this review was seeing how rapidly the field is evolving. Advances in metagenomics, synthetic microbial communities, ecological modelling, and high-resolution imaging are beginning to move the discipline beyond descriptive studies towards predictive frameworks. Instead of simply cataloguing microbes associated with healthy or diseased plants, researchers are increasingly asking why these relationships emerge and whether they can be manipulated to improve plant health. This review reinforced a simple but powerful idea: soil is not merely the stage on which plant disease develops; it is an active participant in the process.

If we want to understand, predict, and manage plant diseases more effectively, we need to think of soil as a living ecosystem whose biological, chemical, and physical components jointly shape pathogen dynamics. The tools to do this are finally emerging—from functional metagenomics and synthetic community experiments to high-resolution imaging of soil pore networks. The next challenge is to integrate them into frameworks that can forecast disease risk before symptoms appear. Ultimately, the future of soilborne disease management may depend less on eliminating pathogens and more on understanding the ecological conditions that determine whether soil functions as a reservoir for disease or a battlefield that keeps it in check.

Pires, D., Castañeda, F., Galvez, L. & Balendres, M.A. (in press). Soil as a battlefield and a reservoir: linking soil components to the epidemiology of soilborne plant diseases. Microbial Ecology, 89: 162. https://doi.org/10.1007/s00248-026-02810-6