ABSTRACT
Despite the discovery of resistance genes (R genes) early in the twentieth century and of the host-pathogen gene-for-gene relationship before the middle of the twentieth century, most progress in our understanding of the nature and function of R genes has only recently been achieved. The first R gene involved in a gene-for-gene interaction to be cloned and characterised was the tomato Pto gene for resistance to bacterial speck disease caused by Pseudomonas syringae pv. tomato (Martin et al., 1993). Since then, there has been a rapid accumulation of R genes cloned from a diverse range of plant species, including both monocotyledons and dicotyledons, and conferring resistance to a diverse range of pathogens, including viruses, bacteria, fungi, oomycetes, nematodes and insects (Table 5.1).
