The origin of rice-infecting populations of Magnaporthe oryzae.
Published: 2004
Language: eng
Number of pages: 215
Description: The main goal of this study was to identify the origin of rice-infecting populations of Magnaporthe grisea. Although M. grisea  has been reported from a wide range of host species, most of which are grasses, it appears to be composed of host-specific populations. For phylogenetic studies within M. grisea, ten polymorphic loci, located on five chromosomes, were identified: actin, BAC6, beta-tubulin, calmodulin, CH7-BAC7, CH7-BAC9, chitin synthase 1, translation elongation factor 1 alpha,  M. grisea hydrophobin-like protein, and a nitrogen regulatory protein.The Magnaporthe species responsible for rice-blast was delimited from within the M. grisea complex and described in the first phase of this thesis project. A new biological species,  M. oryzae, was segregated from M. grisea based on phylogenetic analysis of data from three loci (actin, beta-tubulin and calmodulin) and fertility testing. The newly described species, M. oryzae, causes rice blast and gray leaf spot of other grasses, while M. grisea  causes gray leaf spot of Digitaria spp.In order to identify the origin of rice-infecting populations, phylogenetic analysis of M. oryzae was performed on a sample of 497 isolates. This sample consisted of isolates both from culture collections and from contemporary population samples. When data from all ten loci were combined in a single analysis, thirty-seven distinct haplotypes were identified within  M. oryzae. Sequential phylogenetic analyses, using data from all ten loci with parsimony, distance, and Bayesian approaches, resolved both patterns of recombination and clonality in M. oryzae. The relationships among isolates from wheat, rice, Setaria spp. Leersia hexandra and Panicum repens were predominantly tree-like, consistent with a lack of recombination, while relationships among isolates from other hosts were reticulate, indicating a history of genetic exchange and recombination. All phylogenies support a single origin for the globally distributed M. oryzae lineage responsible for rice blast. The direction of host-shifts in M. oryzae  was resolved by rooting a network for the closely related haplotypes from rice and other grass hosts. The rice-infecting population originated as a result of a single host-shift from Setaria spp. Rice was also a source for at least two additional host-shifts to the common rice-field weeds, L. hexandra and P. repens.
Notes: Adviser:  Linda M. Kohn.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-05, Section: B, page: 2165.