Occupancy of Flavonoids in Plants, Pathogen, and Opportunistic Fungi Interactions

Flavonoids are secondary metabolites found in plants that have antioxidant properties and pigments that give fruits and vegetables their vivid hues. They improve heart health, fight cancer, and infections and reduce inflammation. They are vital in plant disease prevention and fungi–plant relationships. Plants develop secondary metabolites like flavonoids to fight diseases. They are synthesized in metabolic pathways activated by PAMPs and defense-related genes. Chorismate is synthesized, and then transformed into flavonoid precursors such as chalcones and flavanones that later produce different flavonoids such as epigenin, epicatechin, naringenin, etc. against the plant pathogens and harmful fungi. Researchers have prioritized the significant role of flavonoids due to their higher antifungal activity, protective functions, and resistance to degradation. They can also act as an antioxidant to protect plants from UV radiation and other environmental stresses. Additionally, flavonoids can act as a phytoalexin, which are antimicrobial compounds secreted by plants in response to infection. Moreover, these are natural pesticides that reduce the ability of pathogens to colonize and penetrate the plant, reduce oxidative stress, protect crops from damage caused by fungi, reduce the growth of fungi, and increase resistance to disease. The aim of this chapter is to describe the role of flavonoids between the opportunistic fungi, plants, and pathogens and also highlights the role of flavonoids in plant–environment interaction and pathogen defense.