Pathogenesis of Nematode-Infected Plants

In this review, an attempt is made to bring together recent developments in under­ standing pathogenesis in nematode-infected plants. As in other disease situations, one must consider factors that affect the attraction between the host and parasite within a given environment. Once in contact with the roots, nematodes may feed either on the surface of roots as ectoparasites or internally after penetration of roots as migratory or sedentary endoparasites. Studies on the feeding processes of ec­ toparasitic nematodes have provided valuable information that can be applied to studies of the sedentary endoparasitic forms where direct observations on feeding are difficult. The developmental processes of pathogenesis are related to the way that nematodes adversely affect the host-either as superficial feeders or as endoparasites that induce syncytia or giant cells. Some nematodes cause extreme galling. In many cases, nematodes act alone as primary pathogens, but in other cases they interact with other organisms in disease complexes or serve as vectors for viruses. This review covers some information discussed in other reviews in the specific areas of nematode-induced plant pathogenesis. Studies on the biochemical and physiological aspects of pathogenesis by root-knot nematode have been omitted since they were reviewed recently by Dropkin (22) and Bird (11).