Plant invasion by pathogens is a component of environmental change. Plant soil feedback refers to the process by which plants alter the physical, chemical and biological properties of soil through their activities, thus altering soil properties which in turn affect plant growth, population dynamics and community structure (Bever et al., 1997, Li and Shao 2025). Inhibitory and beneficial effect of soil biota on plant can accelerate or decelerate over time depending on the net effect on accumulating pathogenic or mutaualistic soil organisms (Reinhart and Callaway 2006). Plants interact with various microbes in different ways. The symbiotic relationships are divided into three categories based on whether the symbiont has beneficial, harmful or no effect on the host (Leung and Poulin 2008):
- Mutualism: The interaction where both the plant and the symbiont reciprocally benefit from the relationship.
- Commensal: The symbiont utilizes the host without benefiting or harming it.
- Parasitic/Pathogenic: The symbiont uses the host as a resource and cause harm to plant health, growth, and productivity.
Mutualistic plant microbe interaction benefits plant and microbe e.g. nitrogen fixing bacteria and mycorrhizal association, where the fungi extend the plant root system, increasing the surface area for nutrient absorption while plant supplies the fungi with carbohydrate (Li 2023). These relation mutualisms, commensalism and pathogenic are not fixed and are dynamic shifting between interaction modes in response to host physiology, microbial adaptation and environmental conditions. A microbe may function as mutualist in one host, but act as pathogen or commensal in another host (Osayande et al., 2025). The plant-pathogen outcome often emphasizes binary outcome such as virulent or avirulent (gene-for gene recognition) (Osayande et al., 2025).
In mutualistic associations, the plant and microbe communicate through molecular signaling. Recognition between the plant and the microbe triggers exchange of signals, leading to the establishment of symbiotic structures and the exchange of nutrients (Li 2023). Whereas in pathogenic interaction, pathogens produce virulence factors that enable them to infect and colonize plant tissues. Virulence factors include toxins, enzymes that degrade plant cell walls or proteins that suppress the plant immune response. On the other hand, plant has evolved defense mechanisms to recognize and respond to the pathogen attack (Li 2023).
Microbe-associated molecular patterns (MAMPs)-triggered immunity (MTI) is a known plants innate immune response to pathogens. Plants are inhabited by several species of commensal, many of which have beneficial effects on the host. These microorganisms often express the same immunogenic MAMPs that are found in pathogens. Commensals in plant microbiome have evolved a variety of strategies to interfere or bypass MTI to establish symbiosis (Teixeira et al., 2021; Zhang and Kong 2022). Root colonization by commensals is controlled by MTI which in turn can be modulated by specific members of bacterial root microbiota (Teixeira et al., 2021). Plants immune system has a role in microbiome assembly and control microbial homeostasis in response to environmental variation (Teixeira et al., 2019). The sensing of MAMPs by pattern recognition receptors (PRRs) initiates quantitative immune responses to control host-microbial load, whereas diversification of MAMPs and PRRs emerge as a mechanism that can locally shape microbial assemblages in plant populations (Hacquard et al., 2017). Root commensal may avoid host cell damage, a signal that enhances MTI in root tissue to prevent the activation of plant immunity during colonization (Zhou et al., 2020; Teixeira et al., 2021).
Coevolutionary selection pressure include environmental constraint and ecological interactions that bring about changes in plant and microbe growth and gene expression to affect fitness and survival. Depending on the pressure and constraints, host organisms or microbe may transition between antagonistic and beneficial association (Stengel et al., 2022). Antagonistic interactions, such as competition are expected to generate co-existing population that are stable to fluctuate in a predictable way. Symbiosis is considered as mutually beneficial associations and alternatives to antagonistic relationships such as parasitism (Douglas 2008). The conflict and antagonism are linked to the acceptance of original definition of symbiosis as any persistent association between different species and arises from the recognition that many real relationships are not invariably mutualistic or antagonistic. The impact of association on a organisms can vary with environmental conditions and with the genotype, age and condition of the partners, this variation can include organisms with effect that vary from beneficial to neutral to deleterious. (Douglas 2008). Examples: Fungal pathogen Colletotrichum species cause plant disease (Balendres 2025). Several pathogenic Colletotrichum species, expressed mutualistic or commensal lifestyle in plants not known to be a host. The mutualist may provide disease resistance, drought tolerance and/or growth enhancement to the host plant (Redman et al., 2001). Plant growth is stimulated by beneficial association of the mycorrhizal fungus but mycorrhizal fungus Glomus macrocarpum cause tobacco stunt disease (Modjo and Hendrix 1986). Pseudomonas syringae pv. tabaci is a leaf pathogenof oat causing death of the plant but it elevated plant growth and symbiotic association influencing overall dinitrogen fixation in legumes (Knight and Langston-Unkefer 1988; Knight et al., 1988; Saffo et al., 1992).
Plants are protected from pathogens not only by their own immunity but also by the colonizing commensal microbes (Shalev et al., 2022a). Commensal Pseudomonas can protect Arabidopsis thaliana from the effects of pathogenic Pseudomonas by reducing their growth within the plant(Shalev et al., 2022b). Changes in environmental condition can lead to modifying the interactions between plants and organisms either positively or negatively.
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BIOLOGICAL PROCESSES- A NATURE'S GIFT 