Resistance to oomycetes: a general role for the hypersensitive response?

Oomycete plant pathogens, such as Phytophthora, downy mildews and Pythium, have devastating disease effects on numerous crop and ornamental plants. Va rious types of genetic resistance to oomycetes occur in plants, and can be determined at the subspecific or varietal level trace or cultivar-specific resistance), or at the species or genus level (nonhost resistance). In addi tion, resistance might be a quantitative phenotype (partial resistance). Re sistance reactions are often associated with the hypersensitive response a programed cell death pathway. Recent advances in the genetic, biochemical a nd cytological characterization of disease resistance suggests that the hyp ersensitive response is associated with all forms of resistance to Phytopht hora and downy mildews. Identification of the resistance genes involved in nonhost and partial resistance to oomycetes remains an important challenge.