ABSTRACT
Host plant resistance has been used extensively for disease control in diverse crop species. It is governed in many cases by the ‘gene-for-gene’ system, i.e., the specific recognition between pathogen aυr (avirulence) gene and its cognate plant disease resistance (R) gene. A plant displays a resistance phenotype when corresponding avr and R genes are present in the pathogen and the plant, respectively, or becomes susceptible if either is absent or inactive (for review see Dangl and Jones, 2001). However, in many cases, host plant resistance is not durable as a result of constant genetic evolution in pathogens, in particular, loss of avirulence genes (for review see Leach et al., 2001).
