Nematodes play an important role as parasites of humans, animals, and plants. In agriculture the economic losses caused by plant-parasitic nematodes worldwide are estimated to amount to ~U.S.$77 billion a year (1). Typically, plant-parasitic nematodes have a highly diversified range of plant parasitism (2,3). Some spend their whole life cycle outside the root, feeding on the surface (browsing ectoparasites) or deeper tissues (sedentary ectoparasites); others have evolved the capability to invade the root and to feed from cortical (migratory endoparasites) or stelar cells (sedentary endoparasites). Economically most relevant are sedentary endoparasites of the genera Heterodera and Globodera (cyst nematodes), and of the genus Meloidogyne (root-knot nematodes). They represent the most advanced level of root parasitism as they induce and maintain specific nurse cell structures as a continuous source of food for development and reproduction. Agronomically important species of the cyst nematodes, common mainly in temperate regions of the world, are G. rostochiensis and G. pallida on potato, H. glycines on soybean, H. schachtii on sugar beet, and H. avenae on cereals. In contrast, root-knot nematodes, with M. incognita as one of the most important representative, have a very broad host range and are adapted to warm and hot climates.