Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/27/2007
Publication Date: 1/3/2008
Citation: Leong, S.A. 2008. The ins and outs of host recognition of Magnaporthe oryzae. In: Gufstason, J.P., Taylor, J., Stacey, G., editors. The Genomics of Disease. New York, NY: Springer Science+Business Media. p. 119-216.
Technical Abstract: Flor first proposed the gene-for-gene hypothesis to describe the relationship of races of the flax rust and cultivars of its flax host (Flor, 1955). In its simplest form, this hypothesis states that for every resistance gene in the host plant, there exists a complementary avirulence (cultivar specificity) gene in the pathogen that allows the host to recognize the pathogen and resist development of the diseased state. Since its first proposal, the gene-for-gene hypothesis has been found to be applicable to many host-pathogen interactions including that of the rice blast fungus Magnaporthe orzyae and its host Oryza sativa (e.g., Ellingboe, 1992; Leung et al., 1988; Silue et al., 1992a,b; Smith and Leong, 1994;Valent et al., 1991) as well as subspecific groups of M. orzyae and their respective hosts (Kato, 1983; Valent et al., 1986; Valent and Chumley, 1994). This fundamental relationship is of great practical interest as M. orzyae is rapidly able to overcome new disease resistances in rice soon after their deployment (Bonman et al., 1992). Moreover, M. oryzae and the closely related Magnaporthe grisea together exist as complex taxa with numerous subspecific groups that are sometimes interfertile but differ in their host range (Couch and Kohn, 2002; Kato et al., 2000; Valent et al., 1991). How these different subspecific groups interrelate evolutionarily is of great concern as some of these alternate hosts are frequently found growing in close proximity to or in rotation with rice, and M. orzyae isolates infecting these alternate hosts can sometimes also infect rice (Kato, 1983; Kato et al., 2000; Mackill and Bonman, 1986; Y. Jia, personal communication). In Japan, barley and rice are alternatively cultivated in the same field, and rice-infecting strains of M. orzyae also infect barley. Blast disease of barley is apparently minimized when M. oryzae infection is limited by cooler temperatures (Yukio Tosa, personal communication). With the advance of global warming, these environmental limitations of blast prevalence may soon disappear, as is already being seen with the emergence of blast in California. Pathogens and pests that were a problem only in more southern regions of the US are now becoming serious in northern US regions like Wisconsin (Judy Reith-Rozelle, personal communication).