Rust infection and survival of 49 Pinus monticola families at a field site six years after planting

Abstract

This field trial evaluates white pine blister rust resistance of 49 families of Pinus monticola from Oregon and Washington. The Optical site had 93% of the trees infected six years after planting, but rust mortality is currently low. Families ranged between 31 to 100 percent infected and the number of stem symptoms ranged between three and eighteen. Families with R-gene resistance (HR) from the Cr2 gene were highly susceptible at Optical due to the presence of a virulent race of rust (vcr2). Families without Cr2 and with moderate to high frequencies of canker-free or bark reaction ('Q' families) in seedling screening at Dorena Genetic Resource Center (DGRC) were the most resistant at Optical with higher bark reaction and lower percent infection, mortality, and number of stem symptoms. Another subset of the families were inoculated in a seedling trial at DGRC using rust strains not containing vcr2. The Cr2 families had predictable levels of resistance and Q families also showed moderate levels of resistance in the DGRC seedling trial. Percent stem symptom and bark reaction traits were positively correlated between screening and field trials. Also the number of needle lesions in artificial screening was positively correlated with the number of stem symptoms at Optical.