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Comparative Analysis of Populus trichocarpa Resistance to Melampsora spp. Leaf Rust Disease
J. LA MANTIA (1), J. Klápště (1), Y. A. El-Kassaby (1), S. D. Mansfield (1), C. J. Douglas (1), R. C. Hamelin (2). (1) University of British Columbia, Vancouver, BC, Canada; (2) The University of British Columbia, Vancouver, BC, Canada

<i>Populus trichocarpa</i> is a native natural resource to the Pacific Northwest; providing fast-growing woody biomass for utilization in wood and paper industries and biofuels production. Poplars co-evolve with native <i>Melampsora </i>spp; however, hybrid poplar breeding and international trade has introduced an exotic rust species to North America, <i>Melampsora larici-populina</i>. Moreover, a new hybrid rust; <i>M. </i>×<i>columbiana</i>, has enhanced pathogenicity and has become the principal leaf rust in the Pacific Northwest. In the presented study, 407 and 397 <i>P. trichocarpa </i>genotypes were screened for resistance to <i>M. larici-populina</i> and <i>M. </i>×<i>columbiana</i> in independent trials of inoculated leaf disks, respectively. A total of 29,355 SNPs in 3,543 genes were used for association analysis to compare host resistance mechanisms. Resistance to each species displayed a continuous range from complete resistance to upwards of 40 pustules per leaf disk at 14 days post inoculation. Final number of pustules and area under the disease progress curve were significantly correlated amongst 378 common poplar genotypes R2 = 16.0% at <i>p</i> < 0.01 and R2 = 12.0% at <i>p</i> < 0.05, respectively. A total of 13 SNPs were significant at <i>P </i>< 3.30 × 10-5. Associated SNPs were located in genes regulating ROS, auxin signaling, and anthocyanidin biosynthesis revealing the first non-R gene resistance loci. No SNP was associated in both analyses, but more in-depth SNP coverage may results in non-species specific rust resistance.

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