Genetics of resistance and parasitism

Abstract

Cyst forming nematode pests of several major crops are controlled wholly or partly by the use of resistant cultivars (see chapter 12). These have been developed from naturally occurring plants in which particular cyst nematodes cannot reproduce. Such cultivars are grown, generally integrated with other methods of control, to prevent or reduce nematode multiplication, exploiting genetic interactions between plant and nematode. Reviews (Jones, Parrott and Perry, 1981; Sidhu and Webster, 1981; Cook and Evans, 1987; Triantaphyllou, 1987; Cook, 1991; Trudgill, 1991) emphasize that the genetic inheritance of plant resistance is better understood than that of nematode parasitism. Plants have many genes involved in defence responses and the recognition of potential parasites. Biotrophic, cyst-forming nematodes have a corresponding genetic complement involved in host recognition and parasitism. None the less, simply inherited resistance, identified by its major impact on nematode reproduction, has been used to breed successful resistant cultivars. Such cultivars, often with a single dominant resistant gene, have led to the emergence of ‘resistance-breaking’ nematode populations. Information about the genetics of nematode virulence is mostly assumed from the gene-for-gene hypothesis. In the case of potato cyst nematode Globodera rostochiensis Woll. and a dominant resistance gene in potato, it has been shown that the inheritance of virulence agrees with the predictions of this hypothesis (Janssen, Bakker and Gommers, 1991).