Judelson, H. S. 2007. Molecular strategies for identifying determinants of oomycete pathogenicity. In: Molecular Mechanisms of Plant and Microbe Coexistence (P. Dion and C. Nautiyal, eds.). Springer, Heidelberg, in press.

Oomycetes are a diverse group of fungus-like eukaryotes encompassing both saprophytes and pathogens of plants and animals. Of the approximately 500 known species, those with the greatest human impact are the plant pathogens. These infect a wide range of crops, ornamentals, and native species, resulting in tens of billions of dollars of losses annually. Understanding factors required to be successful pathogens is a priority in oomycete research, since these may be targets for crop protection chemicals or plant-based resistance strategies. As illustrated in Fig. 1, such features may include the processes used to form the major infective propagules (spores), to breach physical barriers of the host (such as appressoria and hydrolytic enzymes), to acquire nutrients (transporters), and to alter the physiology of the plant (cytoplasmic effectors). The aim of this chapter is to describe the approaches used to study oomycetes and progress in understanding the molecular bases of their pathogenicity. In particular, genomics and proteomics-based strategies have recently become feasible for several oomycetes, adding to traditional methods of gene cloning and classical genetics. Some of these resources have existed for years in other pathogens such as the ascomycete and basidiomycete "true" fungi, but their impact on the oomycete field is relatively new. These advances will be addressed after introducing the reader to the taxonomy, biology, and pathology of oomycetes.