Role of terpenes in plant defense to biotic stress

Terpenes constitute a highly diverse class of chemical compounds produced by the plant and playing a role in many functions, both physiological and ecological. Plants constantly interact with other organisms, from beneficial to detrimental, and evolved sophisticated regulatory mechanisms to control these interactions. The role of terpenes, or more in general of terpenoids, as preformed or induced chemical deterrents to herbivores is known since long, and their complex role in plant defense against pathogens is increasingly present in the scientific literature. The synthesis of terpenes is one of the responses to attack in numerous plant-pathogen binomials, where terpenes act as specialized or generalized pathogen inhibitors. In this chapter, the involvement of terpenes and terpenoids in resistance to plant pathogens, such as fungi, bacteria, and viruses, and, where relevant, their vectors, is described.