Association Analysis Identifies Melampsora xcolumbiana Poplar Leaf Rust Resistance SNPs

Populus species (aspen, cottonwood, and poplar) are currently being domesticated to maximize digestible biomass for conversion to biofuels. Severe infections of poplar leaf rust disease caused by Melampsora species leads to decreased photosynthetic capacity, reduced biomass and fiber volume, and increased susceptibility to additional pathogens. While genetic resistance has been the most efficient means to reduce economic losses, major resistance loci have been race-specific and can be readily defeated by the pathogen. A key step to developing more durable disease resistance is identifying non race-specific loci. We performed association analysis for area under the disease progress curve (AUDPC) on 412 unrelated P. trichocarpa genotypes in a common garden experiment representing the species’ natural range. Association analysis was performed using pre-selected SNPs and principal components representing population structure. A total of 45 SNPs in 27 genes achieved experiment-wide significance at P < 1.45× 10^-5 across the three years. These genes are signaling components of the early defense response associated with Melampsora resistance. Furthermore, five SNPs were validated through repetition in time or expression. In this long-lived organism, these associated loci further our understanding of poplar: rust interactions and lay the foundation for more efficient breeding of durable disease resistance.