Submitted to: Acarology International Congress Proceedings
Publication Type: Book / Chapter
Publication Acceptance Date: September 17, 2003
Publication Date: N/A
Interpretive Summary: Losses sustained from root diseases are estimated at $4 billion each year in the US. This book chapter provides an overview of root diseases and root parasites, life cycles of soilborne pathogens, and defenses that plants mount against these pathogens. Many root pathogens cause tissue death that leads to root rot. Whereas some plants have effective resistance to nematodes, parasitic plants, and pathogens that cause wilting, they generally lack resistance to pathogens that cause root rot. Two plant hormones, jasmonic acid and ethylene, have been shown to provide marginal protection against such pathogens. Naturally-occurring metabolites and morphological traits have also been implicated in root defenses. Current knowledge of these defense mechanisms is discussed.
Technical Abstract: pathogens, including Phytophthora, Pythium, Fusarium, and Bipolaris are primarily semi-biotrophic or necrotrophic fungi with wide host ranges. The hypersensitive response and apoptotic cell death, oxidative mechanisms that limit biotrophic pathogens, act to exacerbate disease symptoms in the case of necrotrophic pathogens. Although pathogenesis-related proteins can be induced in roots during pathogen challenge, effective resistance is not obtained. However, jasmonic acid and ethylene have been found to mediate parallel as well as synergistic defense pathways that confer partial tolerance to root necrotrophic pathogens, as is the case for foliar necrotrophs. Components of signal transduction pathways identified in model plant-microbe interactions, root-pathogen signaling, and host-dependent factors and traits that can impact root-pathogen interactions are discussed.