Preliminary overview of the first extensive rust resistance screening tests of Pinus flexilis and Pinus aristata

Limber pine ( Pinus flexilis James) and Rocky Mountain bristlecone pine (P. aristata Engelm.; hereafter referred to as bristlecone pine) are the dominant pines that occupy high elevation habitats of the southern Rockies. Bristlecone pine is primarily a subalpine and tree-line species while limber pine in the southern Rocky Mountains grows from 1600 m in the short grass steppe to over 3300 m elevation near the continental divide (see Schoettle 2004). These trees provide many ecosystem services including food for corvids, bears and squirrels, watershed protection, and picturesque gnarled tree forms on exposed sites. Both species are susceptible to infection by Cronartium ribicola J. C. Fisch., the non-native fungal pathogen that causes the lethal disease white pine blister rust (WPBR). WPBR has been present on limber pine since the 1970's in southern Wyoming and was first detected in northern Colorado in 1998 (Johnson and Jacobi 2000) and was discovered in southern Colorado infecting limber pine and bristlecone pine in 2003 (Blodgett and Sullivan 2004). The origin of the inoculum for the southern Colorado infection center is unclear, as it is over 200 km from the nearest known WPBR infections.