Susceptibility of Ponderosa Pine 

 to Western Gall Rust Within the 

 Middle Columbia River System 



R. J. Hoff 



INTRODUCTION 



Western gall rust caused by Endocronartium harknessii 

 is a relatively minor disease of northern populations of 

 ponderosa pine (Pinus ponderosa var. ponderosa). Most 

 damage is to young trees and galls are frequently confined 

 to branches (Leaphart 1955; Peterson 1959). 



Thomas and others (1984) reported that ponderosa pine 

 from Idaho, eastern Washington and Oregon, and central 

 and western Montana were most resistant, and that popu- 

 lations from the Colorado plains and the Southern Rock- 

 ies were most susceptible to gall rust. A more detailed 

 study of central Idaho populations, using artificial inocu- 

 lation with high spore density, revealed many highly 

 susceptible populations (Hoff 1986). Infection among 

 populations ranged from 65 to 95 percent. 



The purpose of this paper was to assess variation pat- 

 terns in susceptibility to western gall rust in populations 

 of ponderosa pine from northeastern Washington, north- 

 ern Idaho, and western Montana. 



MATERIALS AND METHODS 



Seeds from 125 populations from northeastern 

 Washington, northern Idaho, and Montana west of the 

 Continental Divide, and covering the elevation range of 

 the species, were included in this test (fig. 1). Most 

 stands were represented by an equal volume of seed from 

 10 randomly chosen trees. Some collections were from 

 several squirrel caches. Diversity was assured in the 

 squirrel cache collections by selecting cones with a variety 

 of morphologies, sizes, and colors. The seeds were sown in 

 containers (8 in 3 ) and grown and overwintered in a shade- 

 house at the Forestry Sciences Laboratory at Moscow, ID 

 Gat. 46°44' N., long. 1170°0'W., elevation 2,650 ft). The 

 seedlings were watered and lightly fertilized, with the 

 objective of producing seedlings that were not stressed but 

 without accelerating their growth. 



The experimental design was: 125 populations, 10 seed- 

 lings per population per replication, three replications. 

 Seedlings were grown in row plots. Total seedlings were 

 1,250 per replication and 3,750 for the test. 



BRITISH COLUMBIA 



Figure 1 — Number and locations of 

 populations of ponderosa pine 

 stands that were included in this test. 

 Letters A to D locate elevation dines 

 presented in figure 4. 



1 



