28 Plant-parasitic Nematodes

Abstract

Plant-parasitic nematodes are a major problem in modern agriculture and cause diseases in all crops of economic importance. Worldwide, yield losses are estimated to run into tens of billions of dollars per year. In general, symptoms of nematode infestation in the field are patches of poorly growing plants, often accompanied by wilting. In roots, symptoms depend on the nematode species and may involve galling, stunted root growth, and necrosis. To prevent the buildup of unacceptably high population densities, farmers tend to use integrated pest management systems, which combine the use of nematicides, crop rotation, and, if available, resistant cultivars. Nematicides are the most expensive and toxic pesticides that are in widespread use in modern agriculture and evoke increasing opposition for environmental reasons. This is illustrated by the drastic reductions in the use of nematicides that are proposed by the European Community for the next decade. A large-scale ban on nematicides will further increase the agronomic problems that result from these pests. Since only a limited number of resistance traits are available for use in breeding programs, genetic engineering of nematode resistance may provide crucial alternatives for germ plasm improvement. Compared to fungal and bacterial phytopathology, our knowledge of plant/nematode interactions is limited and progressing slowly (Sijmons et al. 1994). The long and complex life cycle of these obligate parasites poses a major limitation for experimental approaches under laboratory conditions. There are no protocols available for axenic growth, and only a few species have been reported to grow on undifferentiated callus...