Variation in needle morphology of blister rust-susceptible and resistant western white pine (Pinus monticola, Cronartium ribicola)

White pine blister rust, caused by the fungus Cronartium ribicola J. C. Fisch. ex Rabenh., is a devastating disease of western white pine (Pinus monticola Dougl.). The primary infection sites for the rust fungus are the stomata of secondary needles. Reports of large differences in infection levels of seedlings grown in two Idaho nurseries prompted us to investigate differences in needle traits that might be associated with infectability. We examined morphological traits and needle surface characteristics on current year needles from 2-year-old western white pine seedlings of the same genetic stock grown in three nursery environments and also compared morphological traits and needle surface characteristics of needles from seedlings of families which, when grown in the same nursery, varied in needle lesion frequency. In a separate study, we examined needle surface traits and infection levels on white pine seedlings grown for two growing seasons in three nurseries in northern Idaho and which were inoculated with basidiospores of C. ribicola in early September 1999.; Significant differences were observed in needle length and width, number of stomatal rows and stomata per row, total number of stomata per needle, adaxial surface area, stomatal density, major axes of stomata, stomatal shape and area, stomatal occlusion, epistomatal wax degradation and the contact angles of water droplets among seedlings of the same genetic stock grown in three nurseries.; Stomata on needles from rust susceptible families were larger and rounder than those from resistant families (P < 0.02). Needle traits of seedlings from bulked seed from the Moscow Seed Orchard were similar to those from the resistant families. Applied water droplets on needles from susceptible families had smaller contact angles than on resistant families. No significant differences were found among families in wax structure (degradation) and stomatal occlusion.; Infection efficiency following inoculation with basidiospores varied dramatically among seedlings grown in the three nurseries. The highest infection efficiency occurred on seedlings that were removed from cold storage just one month prior to inoculation and had actively growing tips and developmentally immature needles when they were inoculated. The relative effects of genetics, physiological condition, nursery environment, and growth regimes on the infectability of seedlings with blister rust were not resolved.