Abstract
Populus species are currently being domesticated through intensive time- and resource-dependent programs for utilization in phytoremediation, wood and paper products, and conversion to biofuels. Poplar leaf rust disease can greatly reduce wood volume. Genetic resistance is effective in reducing economic losses but major resistance loci have been race-specific and can be readily defeated by the pathogen. Developing durable disease resistance requires the identification of non-race-specific loci. In the presented study, area under the disease progress curve was calculated from natural infection of Melampsora ×columbiana in three consecutive years. Association analysis was performed using 412 P. trichocarpa clones genotyped with 29,355 SNPs covering 3,543 genes. We found 40 SNPs within 26 unique genes significantly associated (permutated P<0.05) with poplar rust severity. Moreover, two SNPs were repeated in all three years suggesting non-race-specificity and three additional SNPs were differentially expressed in other poplar rust interactions. These five SNPs were found in genes that have orthologs in Arabidopsis with functionality in pathogen induced transcriptome reprogramming, Ca2+/calmodulin and salicylic acid signaling, and tolerance to reactive oxygen species. The additive effect of non-R gene functional variants may constitute high levels of durable poplar leaf rust resistance. Therefore, these findings are of significance for speeding the genetic improvement of this long-lived, economically important organism.
Highlights
Rust fungi cause some of the most important crop and tree diseases worldwide
In Populus species, leaf rust disease is caused by several species of Melampsora
M. 6columbiana, we performed association analysis on 412 unrelated P. trichocarpa genotypes from a North American provenance trial ranging from Alaska to Oregon
Summary
Rust fungi cause some of the most important crop and tree diseases worldwide. In Populus species (poplar trees), leaf rust disease is caused by several species of Melampsora. Severe poplar leaf rust infections decrease photosynthetic capacity, reduce biomass, and increase susceptibility to additional pathogens [1]. In North America, hybridization of rust species, M. occidentalis and M. medusae, has produced a new rust pathogen, M. This hybrid rust has demonstrated high pathogenic diversity. In an initial collection 13 pathotypes (race with unique virulence to specific hosts) were identified. Host resistance loci to pathotypes Mxc and Mxc map to unique chromosomes in poplar and are race-specific [3,4]
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