The Race to Find Eco-Friendly Ways to Tackle Phytophthora Infestans and Other Plant Pathogens

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by Jorge Luis Alonso with ChatGPT

The EU has decreased its use of chemical pesticides in response to environmental and health concerns. This shift has led to an increased focus on alternative pest control strategies, such as biological control. Biological control involves using living organisms to directly or indirectly control plant pathogens. One such pathogen is Phytophthora infestans, which causes potato and tomato late blight, resulting in significant food loss and economic damage.

To find effective biocontrol agents against P. infestans, researchers use in vitro assays because of their lower costs and greater experimental control. However, these assays may not identify agents that are effective for field use, and the knowledge gained from them may not be practical for practitioners. Therefore, more applied studies, such as greenhouse and agricultural field studies, are necessary to bring about meaningful change in pest management practices.

The Swedish University of Agricultural Sciences (SLU) has reviewed recent developments in the search for sustainable biological control of late blight. They discussed progress in understanding mycoparasite-prey interactions and the challenges of practical disease control in Europe. The literature on potential biocontrol agents for P. infestans, including Trichoderma, Pythium oligandrum, Bacillus, Pseudomonas, and Streptomyces, was reviewed, and their mechanisms of action and knowledge gained from in vitro studies were discussed. Research has also evaluated biological control agents (BCAs) in detached leaf assays and whole plant greenhouse bioassays to test biostimulation and direct disease control.

To control potato late blight in agriculture, Trichoderma species have been tested in field trials, with some studies showing significant effects on late blight incidence. Other fungal BCAs, such as C. globosum Cg-6 and Pythium oligandrum, have also demonstrated significant yield increases and foliar protection against late blight in field trials.

The development of biocontrol solutions to combat P. infestans poses several challenges and limitations. Regulatory processes involved in registering BCAs can be difficult and expensive, particularly in the EU where the approval process is lengthy due to more extensive regulations than in other parts of the world. Formulating microbial BCAs is also a major challenge because it is difficult to produce formulations that can be sprayed efficiently and remain viable over a long period. Environmental fate, toxicity, and resilience of the BCA are also factors that slow down the EU registration process.

Few of the BCAs presented in this review have been commercially formulated for late blight control, which may leave practitioners reliant on larger agrochemical companies to formulate and register BCAs. Nonetheless, studies have shown that applications of non-pathogenic microorganisms into the environment have not generated situations where the released organisms became overwhelming and the dominating species within the habitat. The integration of biocontrol into Integrated Pest Management (IPM) strategies presents a promising prospect for the future, and further research is necessary to address the challenges and limitations of the development and use of BCAs in pest management.

After reviewing the literature, SLU has identified several key findings about the search for efficient and sustainable biological control of late blight in agriculture:

• Large-scale in vitro screening approaches have had some success in identifying biological control agents (BCAs) that can reduce late blight disease severity in agriculture, but these successes are often limited
• Although in vitro approaches are useful for identifying the modes of action of BCAs, new studies should focus on testing BCAs in agroecosystems to understand their disease control and environmental survival.
• A better understanding of the interactions between BCAs and the soil microbiome can provide valuable ecological risk data and allow better formulations of existing BCAs.
• Microbiome studies have the potential to identify new BCAs adapted to the potato rhizosphere or that live endophytically in close association with potatoes.
• Instead of screening thousands of microbes, scientists should screen microbes for their production of secondary metabolites and cell wall-degrading enzymes, as well as their evolutionary potential in the agroecosystem, to identify new BCAs with traits adapted to the same environment as the pathogen.
• Utilizing well-characterized BCAs as cell factories to bioengineer effective formulations of secondary metabolites as biopesticides is a promising direction for the sustainable control of late blight disease.
• Practitioners should use BCAs as soil amendments before or at planting, to allow the establishment of healthy rhizosphere soil, like the use of probiotics and prebiotics to support human health.

Source: Hashemi, M., Tabet, D., Sandroni, M., Benavent-Celma, C., Seematti, J., Andersen, C. B., & Grenville-Briggs, L. J. (2022). The hunt for sustainable biocontrol of oomycete plant pathogens, a case study of Phytophthora infestans. Fungal Biology Reviews, 40, 53–69.

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