Susceptibility ofPinus contorta - Pinus banksianacomplex toEndocronartium harknessii: host-pathogen interactions

Abstract

Lodgepole (Pinus contorta Dougl. ex Lound.) and jack (Pinus banksiana Lamb.) pines occur sympatrically and hybridize in central and northwestern Alberta, providing opportunities for studying unique ecological and evolutionary interactions. We conducted a greenhouse inoculation experiment to investigate interactions between 40 populations of lodgepole and jack pines and their putative hybrids across this hybrid zone and two sources of the western gall rust fungus, Endocronartium harknessii (J.P. Moore) Y. Hiratsuka, one from lodgepole pine and the other from jack pine. Rust susceptibility and height were assessed when the seedlings were 6 months and 1 year old. Lodgepole pine and the hybrids were significantly more susceptible to the rust infection than jack pine. Jack pine grew significantly faster than the hybrids and lodgepole pine. In addition, the seedlings infected with spores from lodgepole pine grew significantly slower than those with spores from jack pine. While the overall rust scores indicated that spores from lodgepole pine was more virulent to the hosts than those from jack pine, both spore sources were better adapted to their own host species, causing significant spore source × host group interactions. However, such host specificity in the western gall rust is far from stabilized (equilibrium) because of continued gene exchanges among the two parental species and their hybrids.Key words: Pinus contorta - Pinus banksiana complex, western gall rust, natural hybridization, coevolutionary genetics.