Biological control of plant pathogens is referred to as controlling disease causing organisms (pests) such as insects, mites, and weeds; using another beneficial organism. This is one of the best sustainable methods of plant disease management, instead application of agrochemicals.
The use of chemicals is a major practice of controlling pathogens in today’s world, to address the issue of losing crop quantity and quality due to plant diseases. Pesticides, insecticides, weedicides, and fungicides are the main types of agrochemicals used during crop cultivation and post-harvest management of food products. So far, chemicals have achieved a high rate of success in controlling plant pathogens, but it always comes at a cost.
Environmental problems and health related problems are the direct costs of using agrochemicals. Other than that, chemicals produce resistant pathogens making their control even more challenging.
This has created a requirement for sustainable disease control mechanisms to make sure that the present and the future of food production are in a safe zone, to feed the skyrocketing human population.
Fungus, bacteria, viruses, or a mixture of two or more microorganisms are used to control pathogenic organisms. Microbial biological control agents act via a range of modes of action in controlling pathogens.
Some microbial biological control agents compete with pathogenic microbes for nutrients, habitat, or optimum growth conditions. Obligate biotrophic pathogens infect living host cells and do not depend on nutrients from the outside environment. Necrotrophic pathogens kill the host tissues and utilize the available nutrients in them. Whereas some other pathogenic microbes depend on exogenous nutrients where they have to compete with other microbes. If the microbiome is already invaded by a biocontrol beneficial microbe with good genetical potential, the pathogen has to compete to colonize. Currently, recombinant DNA technology is used to develop such biological control agents with several beneficial characteristics.
Antagonists acting through hyper-parasitism and antibiosis directly interfere with the pathogen. Hyperparasites invade and kill mycelium, spores, and resting structures of pathogenic bacteria and fungi. Such interactions between pathogens and biological control agents are regulated through various metabolic functions. Compounds such as enzymes, different signaling molecules, antibiotics, and other antimicrobial metabolites are produced when the biocontrol agent interacts with the pathogen. Production of secondary metabolites with anti-pathogenic properties at low concentrations in situ supports biological control agents to obtain a competitive advantage to colonize, absorb nutrients, and thereby, spread their colonies.
Highly effective microbes against pathogens can be selected to culture them on artificial media to be utilized at a mass scale during the growing season once or several times. Biocontrol products that are manufactured commercially by companies sometimes contain living microbes. On the other hand, some biocontrol products only contain antimicrobial metabolites extracted by biological control agents. In most cases, antimicrobial metabolites are produced by antagonists directly on the spot where the pathogenic target is present, so screening such antimicrobial products can only be done when the correct target interacts with the biocontrol agent.
It is expected that complex chemical communication happens within and in between microbiomes and plants including the contribution of signaling by microbial biocontrol agents to the continuous chemical crosstalk between organisms in the environment. It helps in inducing resistance in plants (MAMP triggered immunity) so that the pathogen is defended with a selective pressure and the pathogen may have to overcome to cause the disease in the host plant.
The future of microbial biocontrol agents depends mostly on better screening assays for finding the next generation with more capabilities to address the issue of less productivity of polluted and chemically treated land. Biological remediation of dumped and polluted lands is the hope of not only microbial biocontrol agents, but also all the beneficial microbes. Multi-omics for a better understanding of complex events in the microbial world can make the use of microbes in a correctly defined manner so that maximum efficiency is obtained.
Reffernces
Teixidó, N., Usall, J. et al. (2022). Insight into a Successful Development of Biocontrol Agents: Production, Formulation, Packaging, and Shelf Life as Key Aspects. Horticulturae, 8(4), 305.
Velivelli, S. L., De Vos, P. et al. (2014). Biological control agents: from field to market, problems, and challenges. Trends in Biotechnology, 32(10), 493-496.
Lahlali, R., Ezrari, S. et al. (2022). Biological control of plant pathogens: A global perspective. Microorganisms, 10(3), 596.
Köhl, J., Kolnaar, R. et al. (2019). Mode of action of microbial biological control agents against plant diseases: relevance beyond efficacy. Frontiers in plant science, 845.
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