Population divergence in the wheat leaf rust fungus Puccinia triticina is correlated with wheat evolution
M. Liu (1), J. KOLMER (2). (1) AAFC, ECORC, Ottawa, ON, Canada; (2) USDA ARS, St. Paul, MN, U.S.A.
As an obligate biotrophic parasite, <i>Puccinia triticina</i>, the wheat leaf rust fungus likely co-evolved with different forms and ancestors of wheat. To test this hypothesis, we generated <i>P. triticina</i> DNA sequence data from fifteen loci with different levels of polymorphism, and conducted phylogenetic (parsimony, Bayesian, maximum likelihood) and coalescence-based analyses. Four forms of <i>P. triticina</i> were determined that showed correlation with wheat type and geographic locations: 1. <i>P. triticina</i> from common hexaploid wheat found worldwide; 2. <i>P. triticina</i> from cultivated tetraploid durum wheat found worldwide; 3. <i>P. triticina</i> from tetraploid wheat from Ethiopia and 4. <i>P. triticina</i> from diploid <i>Aegilops speltoides</i> that has been found only in Israel. Phylogenetic and coalescence analyses indicated that <i>P. triticina</i> on diploid <i>A. speltoides</i>, the probable B genome donor of hexaploid wheat, diverged initially, followed by the Ethiopian durum wheat form and then by the common wheat form. <i>P. triticina</i> on worldwide cultivated durum wheat was the most recently coalesced form, which formed a clade nested within the common wheat form. By a relative time scale, the divergence of <i>P. triticina</i> forms as delimited by host specificity appears very recent. Significant reciprocal gene flow between the common wheat form and the durum wheat form, and from the common wheat form to Ethiopian durum form was detected.
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