Ribes leaves infected with blister rust are distributed on wire mesh above seedlings in the inoculation chamber. Dorena Genetic Resource Center. Cottage Grove, Oregon.
Photo by: Richard Sniezko Date: September 18, 2003
Credit: USDA Forest Service, Region 6, Umpqua National Forest, Dorena Genetic Resource Center. Source: DRGC digital photo collection; courtesy Richard Sniezko, Cottage Grove, Oregon.
The following description of the inoculation process at Dorena is excerpted from pages 72 and 73 of the Whitebark Pine Restoration Strategy for the Pacific Northwest Region. 2009–2013 (available here: ecoshare.info/uploads/documents/WPB_Strategy_PNW_093008cl...): "The Dorena Genetic Resource Center (Dorena), a component of the regional genetics program of Pacific Northwest Region (and a partner with the regional Forest Health Protection group), has established protocols for blister rust resistance testing of whitebark pine. These protocols are based on those developed and successfully used for screening of western white pine (P. monticola) and sugar pine (P. lambertiana) over the past 5 decades (Danchok et al. 2003). Resistance testing involves inoculation of young (usually 2-year-old) seedlings with spores of C. ribicola and evaluation of seedlings for up to 5 years after inoculation. Inoculation usually takes place in late August or during September (which coincides with time of natural infection in the field). Seedlings are moved into a climate-controlled inoculation chamber. Temperature within the inoculation chamber is maintained at around 16.7° C (62° F) and relative humidity at 100 percent. Ribes spp. are the alternative host for C. ribicola, and spores from infected Ribes spp. are necessary to infect the pines. Ribes spp. leaves infected with C. ribicola at the telial stage are collected from forests in Oregon and Washington or from the Ribes garden at Dorena. The Ribes leaves are placed on wire frames above the seedlings, telial side down. Spore fall is monitored until the desired (target) inoculum density of basiospores is reached for each box; the Ribes leaves are then removed. After the target inoculum density is reached for the last box, the temperature is raised to 20° C, and the seedlings are left in the inoculation chamber for approximately 48 hours to ensure spore germination and infection of the pine needles. Following inoculation, the seedlings are transported outside. The seedlings are evaluated over a period of 5 years for the presence of disease symptoms and mortality. The first symptoms to develop are needle lesions, or ‘spots.’ These are typically assessed approximately 9 months and 1 year after inoculation. Presence and number of stem symptoms along with mortality is assessed annually for 5 years after inoculation."