Exploiting Plant Innate Immunity to Protect Crops Against Biotic Stress: Chitosaccharides as Natural and Suitable Candidates for this Purpose

Abstract

1. Introduction One of the most innovative approaches for controlling plant diseases is through the enhancement of the plant's own defence mechanisms (induced resistance), which would not involve the application of toxic compounds to plants. It has been well established for over 100 years, that plants can defend themselves; however, in the last 20 years, a significant progress in our knowledge on plant immunity, has provided the understanding required to allow induced resistance to be used in practice. In this chapter we will discuss the bioactivity of chitosaccharides as pathogen associated molecular patterns and their potentiality in crop protection. 2. General remarks on chitosaccharides structure and availability The fungal kingdom is extremely varied in species and reproductive structures; however, the shape and integrity of a microorganism is determined by the mechanical strength of its cell wall. This complex cellular structure performs a broad range of crucial roles during the interaction with the environment. Despite the fact that its composition varies noticeably between species, it is composed typically of glucan, mannan, proteins and chitin (Dhume et al., 1993). Chitin is a lineal polysaccharide composed of 2-acetamide-2-deoxy-D-glucopyranoside (N- acetyl-D-glucosamine) residues ß-(1-4) linked (Figure 1) that can be also found in insect exoskeletons and crustacean shells but not in plants. Chitosan is the name used for low acetyl substituted forms of chitin and consequently, is a linear heteropolysaccharide composed of ß-1,4-linked 2-amino-2-deoxy-D-glucopyranose (D-glucosamine) and N-acetyl- D-glucosamine in varying proportions (Figure 1). Chitosan is commercially produced by