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Ponderosa pine is an important source of lumber in British Columbia and currently occupies the hottest and driest forested habitat in the province. The species’ niche is expected to be pushed northward by climate change, leading to an increased demand for climate change-resistant seeds. In response, a new breeding program is being established in BC to meet this demand, focusing on producing seeds that can withstand drought and climate stress.  

This project, led by researchers at Simon Fraser University in partnership with the BC Ministry of Forests, aimed to generate foundational genomic resources for Ponderosa pine breeding programs, enhance seed exchange and contribute to BC’s climate change adaptation strategy. 

To identify drought-tolerant trees and understand their underlying genetic variation, Ponderosa pine seedlings from BC’s only A-class seed orchard were planted in raised beds and subjected to either drought stress or watering. Results showed that trees growing well under drought stress had higher leaf water levels and their stress response genes were less activated. Furthermore, faster growing families managed to maintain growth better than slow growing families in drought conditions.  

Extensive sequencing from leaves, roots, stems and buds identified active genes involved in drought tolerance and genetic variability in drought resistance. These results reveal the physiology behind drought tolerance and provide useful information for selecting trees that can maintain productivity in drought conditions. 

In further laboratory experiments, fast-growing trees showed increased root growth in mild drought conditions. Based on these observations, the team hypothesized that rapid root growth under mild drought stress may allow plants to tap into underground water, enabling higher water levels and growth of the shoot system, a strategy known as drought avoidance. This is particularly important in seedling survival, which is a top priority for breeders. 

Identifying trees that maintain growth in drought conditions, and those which possess potential drought avoidance strategies, equips the BC ponderosa pine breeding program with valuable information to inform future selection criteria. Additionally, this project has generated the first genomic resources for Ponderosa pine, offering insight into gene expression for this species. This will enable the development of additional genomic resources for future breeding efforts.