ABSTRACT
Plants have developed a broad array of responses to pathogens, which are categorized into three distinct groups. This chapter briefly discusses the nature of disease resistance in plants and then focuses specifically on the role of pathogenesis-related (PR) proteins in disease resistance. It mainly concentrates on the current research in the authors' laboratory in three plant-pathogensystems. The chapter also focuses on the research conducted to elucidate the possible role of chitinases in disease resistance, and related studies on these threeplant-pathogen systems. Manifestation of disease generally occurs through visual symptoms which may range from mild to severe. In a compatible interaction, the host response to pathogenic attack maybe delayed or may not occur at all. Under certain conditions, however, a compatible interaction can be converted to an incompatible one through the activation of latent defensive responses. This phenomenon is called "induced systemic resistance" (ISR) or "systemic acquiredresistance" (SAR).
