154 



{P. albicaulis), southwestern white (P. stwbiliformii) , and bristlecone (P. aristata) pines 

 are subject to infestation from this pathogen (Hoffand Hagle 1989). 



Damage to eastern white pine has been comparatively less than damage to western 

 white pine populations. The majority of eastern white pines grow in low-rust-hazarf' 

 areas. In addition, the species is less susceptible to blister rust than western whitt 

 pine (Bingham 1983). Western white pine stands can have as high as 94 percent mor- 

 tality caused by the disease (Hirt 1948). 



Different approaches have been utilized to control blister rust. The alternate hosts 

 for Cronartium jibicola are species in the genus Kibes, eg., gooseberry, and blister rust 

 control prescriptions have recommended the removal or eradication of Biba bushes 

 since the early 1900s. This practice continues in eastern North America, as Ribei 

 removal has been shown to be a successful control mechanism in high-rust-hazard 

 areas (Ostrofsky et al. 1988). In the western forests of Washington. Idaho, Montana, 

 and Wyoming, almost 470 million Bibes bushes were removed from 1923 to 1965 

 (Hoff and Hagle 1989). This practice was discontinued, however, due to the limited 

 and, often, absence of success in controlling blister rust. Chemical control using 

 antibiotics was tried briefly, but was abandoned after limited success (cf. Bingham 

 1983). 



The damage to western white pine populations was so extensive that operational plant- 

 ing of the species had been generally discontinued by 1968 (Ketcham et al. 196&). 

 However, planting of western white pine has resumed using blister rust-resistant 

 seedlings. Forest geneticists identified resistant trees in natural populations of west- 

 ern white pine, as well as other white pine species, and instituted screening/breeding 

 programs (Riker el al. 1943, Bingham 1983). Genetic resistance to blister rust was 

 found to differ among species {cf. Garrett 1986). Blister rust resistance is polygenic in 

 eastern white pine, controlled by a single dominant gene in sugar pine, and at leasL 

 two separate, recessive genes confer resistance in western white pine. Tree improve- 

 ment programs have developed seed orchards for eastern and western white pines 

 that produce seed with blister rust resistance. 



Natural range of western whtte pinetn the Uruted :itaUs 



10 



