Susceptibility of Pinus contorta Pinus banksiana complex to Endocronartiumharknessii: host-pathogen interactions

Lodgepole (Pinus contorta Dougl. ex Lound.) and jack (Pinus banksiana Lamb. ) pines occur sympatrically and hybridize in central and northwestern Alber ta, providing opportunities for studying unique ecological and evolutionary interactions. We conducted a greenhouse inoculation experiment to investig ate interactions between 40 populations of lodgepole and jack pines and the ir 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 h eight were assessed when the seedlings were 6 months and 1 year old. Lodgep ole pine and the hybrids were significantly more susceptible to the rust in fection than jack pine. Jack pine grew significantly faster than the hybrid s and lodgepole pine. In addition, the seedlings infected with spores from lodgepole pine grew significantly slower than those with spores from jack p ine. While the overall rust scores indicated that spores from lodgepole pin e was more virulent to the hosts than those from jack pine, both spore sour ces were better adapted to their own host species, causing significant spor e source host group interactions. However, such host specificity in the wes tern gall rust is far from stabilized (equilibrium)because of continued gen e exchanges among the two parental species and their hybrids.