Developing Durable Pathogen Resistance Through Inter-Specific Backcrossing in Hybrid Poplar

Hybrid poplar is the predominant woody perennial being developed for the bioeconomy as a purpose-grown source of cellulosic feedstock for the future bioeconomy. It also is a desired feedstock for existing hardwood pulping facilities and the wood pellet industry. Hybrids between P. deltoides and P. maximowiczii have shown the highest levels of biomass production combined with resistance against Melampsora leaf rust, the most important pathogen in the Pacific Northwest. In 2022 a new race of Melampsora leaf rust appeared in the region with virulence on the heretofore resistant commercial P. deltoides × P. maximowiczii F1 hybrids.This project's effort is to circumvent this recent change in Melampsora pathogenicity by moving breeding efforts from first generation hybridization (F1) to an innovative approach of first-generation backcross hybridization (BC1) to obtain genetic resistance from resistant parental breeding stock. This will capitalize on the past investment in developing the commercial F1 hybrids by producing BC1 hybrids that maintain the high productivity of the first-generation hybrids combined with durable resistance to new and future races of Melampsora.Phase I will determine the source of the recent change in Melampsora genetics and breed experimental P. deltoides × P. maximowiczii BC1 families. In Phase II, new hybrid selections will be made based upon within-family segregation rates for durable rust resistance. Ultimately, new commercial nursery operations of highly productive and Melampsora-resistant BC1 selections will be made available to feedstock growers for the emergent cellulosic feedstock, the ongoing pulp and paper, and the commercial wood pellet industries