Resistance to and Tolerance of Plant Parasitic Nematodes in Plants

Resistant cultivars have several advantages over other methods of reducing nematode populations: their use requires little or no technology and is cost effective; they allow rotations to be shortened and best use to be made of the land; and they do not leave toxic residues. In contrast, nematic ides are uneconomic on many lower-value crops and when used on high-value crops are applied at relatively high rates with the consequential risk of toxic residues (16). Resistant cultivars also need to be tolerant; those that are intolerant will suffer extreme damage if grown in heavily infested soil. Equally, tolerant cultivars that are not resistant tend to increase nematode population densities to damagingly high numbers. The purpose of this review is to outline the mechanisms and principles governing nematodelplant interactions and to consider some of the useful parallels between nematodes and other plant pathogens, especially fungi. Terminology, which often differs between branches of plant pathology (51), is briefly discussed. These differences arise because many plant pathologists are concerned with the expression of disease in whole crops in the field and the epidemiology of mobile pathogens capable of explosive population in-