PARENT SESSION
Symposium #34: The Rapid Decline of White Pine Ecosystems of the West: Causes, Consequences, and Restoration Strategies.
Organized by: DF Tomback, AW Schoettle, and GI McDonald
Friday, August 9. 9:00 AM to 12:00 PM. Turquoise Ballroom, TCC.
Genetic interactions between the blister rust fungus and white pines: resistance as a foundation for restoration.
ZAMBINO, PAUL*,1, MAHALOVICH, MARY2, 1 USDA Forest Service, Moscow, ID2 USDA Forest Service, Moscow, ID
ABSTRACT- Multiple mechanisms of resistance to white pine blister rust have been identified in North American five-needle pines. For successful utilization in restoration they must minimize host damage after normal rust exposure, have reasonable heritability, and be effective against variable rust populations. Major gene resistance (MGR), is conferred by different dominant genes in sugar pine (SP) and coastal western white pine (WWP). Hypersensitive needle spots are the only visible damage. However, as predicted by gene-for-gene theory, virulent (V) races occur that infect MGR-resistant SP (V1, 2 California locations), WWP (V2, scattered eastern Oregon locations), and both hosts (V1V2, one California location), limiting deployment of MGR by itself. Restricted colonization of branch and bole after needle colonization, e.g., "needle spots only", "bark reaction", "slow canker growth" and "tolerance" phenotypes, forms the basis of most selection in five-needle pines. Phenotypes may in part be a pleiomorphic expression of common mechanisms with complex inheritance, as mixed phenotypes may occur within families and symptoms can vary depending on environment. Resistance from restricted colonization appears to be more stable against rust evolution than MGR. Frequencies of resistant progeny phenotypes within and among families determine selection of parent trees for collections of seed for planting and scions for developing breeding or seed orchards. Progeny with superior resistance are also selected for orchards. Strategies have not been developed to utilize putative ontogenic (mature tree) and induced resistance mechanisms.
KEY WORDS: Cronartium ribicola , Pinus monticola , Pinus lambertiana , resistance mechanisms