Western gall rust resistance in pines: using genomics to discover resistance mechanisms and develop new tools for tree breeding

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A sustainable, predictable timber supply is vital to maintain competitiveness of Canada's forest industry. Measures that reduce losses to pests and diseases, which account for substantial annual losses of merchantable timber, can help improve forest productivity. Lodgepole pine, a major commercial species in British Columbia and Alberta, is particularly susceptible to Endocronartium harknessii, the causative agent of western gall rust. This pathogen, which is found across Canada, causes stunted growth, stem deformity and mortality. We have determined that western types of E. harknessii are more virulent than eastern types. Extensive pine regeneration that is occurring in the wake of the mountain pine beetle outbreak in British Columbia and Alberta is increasing the proportion of juvenile pines on the landscape, which are at greatest risk for western gall rust infection and mortality. Resistance to western gall rust is heritable, and planting of western gall rust-resistant stock has great promise to reduce yield losses to this pathogen. Western gall rust resistance has been identified as a priority for tree breeding by the Government of Alberta, which has the mandate for tree improvement in the province. Addressing this priority, the goal of this project is to discover genomic signatures of western gall rust resistance in lodgepole pine and lodgepole x jack pine hybrids, and translate these discoveries into genomic tools for tree breeding. We will identify pine genes associated with resistance by conducting genomic selection and association genetic analyses with a unique set of molecular marker and disease severity data for families of seedlings and mature trees. We will then identify molecular mechanisms of pine resistance and pathogen severity through combining genomic scale analyses of pine tree gene expression with genome comparisons of E. harknessii pathogen types that are more or less likely to cause disease. Outcomes from this research will be used to develop DNA markers and statistical models that predict western gall rust resistance for tree breeding programs. These genomic tools may be the first to be implemented in Alberta, and therefore have the potential to transform forest tree improvement for our partners.************