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Summary: Understanding the genetic basis of how plants defend against pathogens is important to monitor and maintain resilient tree populations. Swiss needle cast (SNC) and Rhabdocline needle cast (RNC) epidemics are responsible for major damage of forest ecosystems in North America.Here we investigate the genetic architecture of tolerance and resistance to needle cast diseases in Douglas‐fir (Pseudotsuga menziesii) caused by two fungal pathogens: SNC caused by Nothophaeocryptopus gaeumannii, and RNC caused by Rhabdocline pseudotsugae.We performed case–control genome‐wide association analyses and found disease resistance and tolerance in Douglas‐fir to be polygenic and under strong selection. We show that stomatal regulation as well as ethylene and jasmonic acid pathways are important for resisting SNC infection, and secondary metabolite pathways play a role in tolerating SNC once the plant is infected. We identify a major transcriptional regulator of plant defense, ERF1, as the top candidate for RNC resistance.Our findings shed light on the highly polygenic architectures underlying fungal disease resistance and tolerance and have important implications for forestry and conservation as the climate changes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Climate change will impact reforestation strategies. [•] We assess impacts to Pinus ponderosa and Pseudotsuga menziesii varieties. [•] Few populations should remain adapted to the 2060 climate of their provenance. [•] High proportions of forested lands will need species or climatype conversion. [•] Conservation programs of P. menziesii in Mexico are of urgent need. [Copyright &y& Elsevier]

Highlights: [•] We model the climate niche of Pinus ponderosa and Pseudotsuga menziesii varieties. [•] Classification errors were less than 5% and were mostly false positives. [•] Niche space was mapped for the decade surrounding 2060 using GCM ensemble output. [•] Projected impacts were more severe for P. ponderosa than for P. menziesii. [•] Projections were dire for the varieties occurring in Mexico. [Copyright &y& Elsevier]

Tree improvement programs have generally relied on testing families in open light environments. With increased interest in multiaged silvicultural systems, some people have questioned whether families selected in the open are appropriate for planting in the shade. We grew Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) families from two climatically distinct seed sources for 2 years under four levels of shade. The response to shade differed for several traits between the two populations and among families within populations. The magnitude of variation associated with the interaction, however, was small compared with the overall effects of genetic selection or of shade. Families selected based on performance in an open light environment resulted in nearly the same response to selection when grown under shade as families selected based on performance in the shade. We conclude that seedlings from families selected in an open light environment are appropriate for use in the low-light environments of alternative silvicultural systems and that use of such genetically selected stock may compensate for the less favorable growing conditions. Genetic selection may contribute importantly to meeting multiple objectives, including the production of significant amounts of wood as well as the efficient and timely creation of large stand structures neededfor other forest values. [ABSTRACT FROM AUTHOR]