ABSTRACT
Plants contain a complex array of genes capable of recognising invading pathogens and initiating active defence mechanisms. These genes typically operate as single dominant resistance genes and each resistance gene generally controls resistance to a single species of pathogen, and very frequently to only some isolates of that pathogenic species. Genetic analysis of host-pathogen interactions has shown that there is a ‘gene-for-gene’ interaction between each resistance allele and a corresponding avirulence gene in the pathogen that leads to the recognition and resistance response (Flor, 1971). This relationship suggests that resistance genes may encode receptors that recognise the direct or indirect products of pathogen avirulence genes (van den Ackerveken et al., 1993; Matthieu et al., 1994; Yucel et al., 1994).
