Geographic variation in susceptibiity of Alberta lodgepole pine to western gall rust

Seedlings from 291 open-pollinated families of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) from three breeding regions (B1, B2, and C) in west-central Alberta were evaluated in the greenhouse during 1992-1994 for their response to infection by western gall rust (WGR) (Endocronartium harknessii (J.P. Moore) Y. Hiratsuka). Region C is a foothill outlier whereas the two western regions are under strong cordilleran influence in the Rocky Mountains. Significant variation in WGR resistance was found among and within regions. A general east-west trend was observed, with western and high-elevational families being more susceptible to WGR infection. Regression of WGR resistance on geographic origins of families accounted for up to 25% of the among-family variation. However, the among-family variation in region C could not be predicted by any geographic variables. Canonical discriminant analysis of WGR resistance and geographic variables could discern families in region C from those in regions B1 and B2. While the widespread introgression from jack pine (Pinus banksiana Lamb.) could contribute to WGR resistance in lodgepole pine, the observed geographic variation could also be a selection gradient induced by regional patterns of geoclimatic conditions for WGR development.