Effect of geographic variation and jack pine introgression on disease and insect resistance in lodgepole pine

Incidence of western gall rust (Endocronartium harknessii (J.P. Moore) Y. Hiratsuka), stalactiform blister rust (Cronartium coleosporioides Arth.), needle cast (Lophodermella concolor (Dearn.) Darker), and sequoia pitch moth (Synanthedon sequoiae (Hy. Edwards) (Lepidoptera: Sesiidae)) attacks were investigated in a lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) provenance-family test plantation located at Red Rock Tree Improvement Station, Prince George, British Columbia. This plantation contains 778 wind-pollinated families from 53 provenances in British Columbia, Alberta, and the Yukon Territory. Pest incidence was assessed in 1993 when the plantation was 21 years old. Provenance had a significant effect on resistance to the four disease and insect attacks. Regression models using latitude, longitude, and elevation as predictors accounted for 38% to 80% of the provenance variation in pest incidence. Geographic patterns of genetic variation in pest resistance essentially followed longitudinal and elevational clines. The most interesting finding is the strong relationship between pest incidence and provenance distance to the western limit of the natural range of jack pine (Pinus banksiana Lamb.): the closer a lodgepole pine provenance is to the edge of jack pine distribution, the higher is its resistance to the pests. We hypothesize that jack pine introgression may have played a significant role in the evolution of pest defense in lodgepole pine. Effective selection and breeding for pest resistance in lodgepole pine may have to look beyond the intraspecific gene pool.