Elucidating the Role of Flavonoids in Countering the Effect of Biotic Stress in Plants

In constantly changing environmental conditions, plants are exposed to a lot of biotic as well as abiotic stresses that have an adverse effect on their growth and production. Biotic stressors that include pests and pathogens cause several diseases in plants, deteriorate their health, and lower their produce. In order to have a grip on these stresses, some secondary metabolites are produced by plants that confer resistance against various pathogenic microorganisms. Among those secondary metabolites are flavonoids that represent a class of plant phenolic compounds. Flavonoids are spectacular, low-molecular-weight, structurally diverse group of phenylpropanoids that are found in flowers, stems, roots, vegetables, fruits, grains, etc. These naturally occurring phenolic compounds are further categorized into various subgroups like flavone, isoflavone, flavanone, flavanonol, flavonol, anthocyanidin, flavanol, etc. They play defensive roles in plants against a wide variety of disease-causing microorganisms like bacteria, fungi, nematodes, viruses, and insect pests. Plants are endowed with biosynthetic machinery to produce these secondary metabolic compounds and consist of various transporters for translocating them to different parts where they provide protection against pathogens and pests. The present chapter personifies a comprehensive elucidation of the biogenesis, transport, and protective role of flavonoids against biotic stressors in plants.