Genetic basis of susceptibility to Diplodia sapinea and Armillaria ostoyae in maritime pine

Forest ecosystems are increasingly challenged by extreme events, e.g. pest and pathogen outbreaks, causing severe ecological and economical losses. Understanding the genetic basis of adaptive traits in tree species is of key importance to preserve forest ecosystems. Adaptive phenotypes, including susceptibility to two fungal pathogens ( Diplodia sapinea and Armillaria ostoyae ) and an insect pest ( Thaumetopoea pityocampa ), height and needle phenology were assessed in a range-wide common garden of maritime pine ( Pinus pinaster Aiton), a widespread conifer in the western Mediterranean Basin and parts of the Atlantic coast. Broad-sense heritability was significant for height (0.497), needle phenology (0.231-0.468) and pathogen symptoms (0.413 for D. sapinea and 0.066 for A. ostoyae ) measured after inoculation under controlled conditions, but not for pine processionary moth incidence assessed in the common garden. Genetic correlations between traits revealed contrasting trends for pathogen susceptibility to D. sapinea and A. ostoyae . Maritime pine populations from areas with high summer temperatures and frequent droughts were less susceptible to D. sapinea but more susceptible to A. ostoyae . An association study using 4,227 genome-wide SNPs revealed several loci significantly associated to each trait. This study provides important insights to develop genetic conservation and breeding strategies integrating tree responses to pathogens.