Nonhost resistance to Phytophthora: novel prospects for a classical problem

Members of the oomycete genus Phytophthora are the most devastating pathoge ns of dicot plants. Recent developments in the study of these organisms hav e led to improved understanding of their phylogenetic relationships and tre nds in their evolution. Molecular analyses of nonhost (species-level) resis tance offer exciting prospects for disease management. A model that evokes a complex interplay of several layers of specific resistance, mediated by a set of ancient broad-spectrum R-gene loci. is sufficient to explain existi ng cellular and molecular data on nonhost resistance to Phytophthora.