THE AUTHOR 



R. J. HOFF is principal plant geneticist with the Intermountain 

 Research Station's Forestry Sciences Laboratory in Moscow, 

 ID. He received a B.A. degree in biology from Western 

 Washington State University and a Ph.D. in botany from 

 Washington State University. 



RESEARCH SUMMARY 



Ponderosa pine from the middle Columbia River system 

 proved to be highly resistant to western gall rust. Only 28 

 percent of the seedlings that were inoculated at the beginning 

 of their second growth year were infected 39 months after 

 artificial inoculation. Three major resistant reactions were 

 observed: trees that expressed no symptoms, trees that had 

 visible bark reactions, and trees in which the fungus causing 

 the initial infection later died. 



The degree of infection increased with elevation, with 

 15 percent of the variation accounted for. A stepwise multiple 

 regression used a combination of elevation, azimuth, distance 

 from inoculum source, and southwest departure to account 

 for 26 percent of the variation. This analysis also indicated 

 that the populations that were nearest to the inoculum source 

 were most susceptible. 



My conclusions were: (1) Most of the variation in suscepti- 

 bility to western gall rust was random. (2) There was a 

 moderate association with elevation and geographic area. 

 (3) Three distinct resistance reactions were operating. 



This information should be useful to forest managers in 

 selecting stands for collecting seed and for selecting superior 

 seed trees for reforestation and tree improvement. 



Intermountain Research Station 

 324 25th Street 

 Ogden, UT 84401 



