Genomic approaches to accelerate American chestnut restoration

Over a century after two introduced pathogens killed billions of American chestnuts, introgression of pre-adapted resistance alleles from Chinese chestnuts has contributed to recovering of self-sustaining populations. However, progress has been slow because of the complex genetic architecture of resistance. To better understand blight resistance, we compared reference genomes, gene expression responses, and stem metabolite profiles of the resistant Chinese and susceptible American chestnut species. To accelerate resistance breeding, we conducted large-scale phenotyping and genotyping in hybrids of these species. Simulation and inoculation experiments suggest that significant resistance gains are possible through selectively breeding trees with an average of 70% to 85% American chestnut ancestry. The resources developed here are foundational for breeding to create diverse restoration populations with sufficient disease resistance and competitive growth.