Studies on mechanisms of adaptation of the blast fungus to rice resistance genes

Abstract

The genus Pyricularia is the causal agent of blast diseases of monocot species. The most familiar species are P. grisea pathogenic on crabgrass and P. oryzae pathogenic on cultivated gramineous plants. Pyricularia oryzae is composed of several host-specific subgroups such as Triticum isolates pathogenic on wheat, Panicum isolates pathogenic on common millet, Setaria isolates pathogenic on foxteil millet, Oryza isolates pathogenic on rice, and so on (Hirata et al. 2007; Kato et al. 2000). Rice-blast-resistant cultivars were first developed by introducing resistance genes and began to be cultivated widely in Japanese farmer’s fields in the early 1960s. Within a few years, however, the resistance broke down due to rapid adaptation of the pathogen; that is, new races evolved that overcame the introduced resistance genes. The question is, how do plant pathogens adapt to new resistance genes so quickly? To obtain clues toward answering this question, we focused on evolutionary processes of a subtelomeric avirulence effector gene, AVR-Pita (Orbach et al. 2000), which is involved in race-cultivar specificity and corresponds to the rice resistance gene Pita. Chromosomal location of AVR-Pita