Biological Control of Potato Fusarium Dry Rot Using Trichoderma asperellum and Bacillus subtilis: Mechanisms, Applications and Future Perspectives
In the context of food security, the potato (Solanum tuberosum L.,) is one of the most important staple crops for human consumption, being the third most important one after food grains and oilseeds. Although potato is an agronomic and nutritional important crop, potato production and post-harvest preservation are significantly challenged by biotic factors and among them, Fusarium dry rot is considered as a highly destructive post-harvest disease. Dry rot is caused by a complex of Fusarium soil and tuber borne fungi which cause significant economic losses during storage, transit and seed multiplication, sometimes reducing up to 60% of the total harvest in long-term storage. Synthetic chemical fungicides have been traditionally used by management. This high-intensity chemical approach is now being called into doubt however, because of the ability of pathogen strains to rapidly become fungicide resistant, environmental toxicity, chemical residue in food and the global regulatory ban on the use of conventional synthetic fungicides. Biological control with microbial antagonists is an environmentally safe, very successful approach to synthetic chemistry. Of the various types of biological control agents (BCAs), the filamentous fungus, Trichoderma asperellum and the endospore-forming bacterium, Bacillus subtilis have proven to be particularly promising. They have a variety of multi-targeted mechanisms of action such as direct mycoparasitism, competition for nutrients and space, inhibition by a wide range of volatile organic compounds and non-ribosomal antimicrobial metabolites produced. Importantly, these BCAs also trigger systemic resistance (ISR) responses in the potato host, which activate the plant's innate defence mechanisms to resist the next attack. This review gives an overview of the biological control of potato dry rot caused by Fusarium species, including the taxonomy and epidemiology of the pathogens; details the molecular and biochemical mechanism of action of T. asperellum and B. subtilis; and investigates the synergistic effects of their co-cultivation and consortium formulations. Lastly, we discuss physiological, formulation and environmental factors that affect the efficiency of biocontrol; we list the existing challenges for commercialization and registration of biopesticides and forecast a future scenario where synthetic biotechnology, nanotechnology, CRISPR-based strain engineering and AI-based screening platforms will form the cornerstone of robust, climate-friendly biopesticide systems.