Disease resistance in plants can involve any number of genes, from a single major gene to many loci determining resistance. Single-gene resistance mechanisms with large effects are more common in agricultural crops but only a few have been described in forest species, which reflects the greater genetic diversity of the host and pathogen populations in forest pathosystems . In forest species, resistance is typically polygenic and durable, with few examples of simply inherited disease resistance. This is likely due to the limited potential for Mendelian analysis in forest trees and complex life cycles of many forest pathogens . However, disease resistance is not exclusively polygenic in forest pathosystems. Examples of single qualitative resistance, include loblolly pine (Pinus taeda) resistance to the fusiform rust disease [41, 42], resistance to white pine blister rust in several species of pine [43, 44] and evidence for major gene resistance to weevil in Sitka spruce .