The number of families required in a regional planting area, i.e., breeding zone 

 or adaptive provenance, is difficult to predict. Alfalfa breeders, who are working 

 with a species that has high genetic variations, and who have gone through several 

 generations of breeding, suggest 75 nonrelated individuals per planting area (Hanson 

 and others 1972). Because white pine also contains high genetic variation (Steinhoff 

 1979) we recommend 100 families per regional planting unit. 



There is very little variation in inland western white pine that is associated 

 with latitude, longitude, or elevation (Steinhoff 1979), meaning that there is only 

 one regional planting unit or breeding unit. And only one seed orchard is needed for 

 the entire inland area of white pine. 



With 3,000 families to start with and with inclusions of 100 families in the seed 

 orchard, only 1 out of 30 of the candidate trees need to be saved. One-hundred 

 families with the highest combinations of horizontal resistance would be chosen. 

 Individual seedlings with the various vertical resistance types will be chosen from 

 within these families. 



We recommend that the level of resistance imparted by the vertical resistance 

 genes be in the range of 50-60 percent. This will provide trees within the population 

 upon which the fungus can grow, but because these trees will by chance also contain 

 genes for horizontal resistance, they will not all die. Although there is much 

 argument in the agronomic field, it is possible that permitting the "old" races to 

 survive will have a stabilizing effect on the rust, i.e., the rust is not apt to 

 develop a new race to survive. 



Natural Selection — An Alternative Breeding Method 



There are probably at least 20-30 genes that control blister rust resistance in 

 western white pine. There are many genes that cause the death of the fungus and there 

 are many more genes that slow the epidemic or slow the fungus growth so that fewer 

 trees die. With this kind of genetic variation, we could just let nature run its 

 course. The only real drawback is nature's way takes too long. But what could be 

 done is to manage white pine stands to speed up nature's process. 



UTILIZATION OF RESISTANCE - HAZARD MAPPING 



In the previous section of this paper we recommended that the production of a 

 variety of western white pine contain moderate levels of complete resistance (50-60 

 percent) on a base of horizontal resistance. A variety with this level of resistance 

 would be planted throughout the inland range of white pine. However, at this time 

 and for a decade or two in the future, there will not be enough seed to fill the 

 planting needs. 



More seed would be available if the level of resistance was matched to the 

 degree of hazard: the intensity of blister infection. The degree of hazard faced by 

 white pines depends on the temperature, moisture, and wind conditions during periods 

 of basidiospore release. The seasonal weather pattern influences the multiplications 

 of the rust on the ribes patches as does the species of Ribes. The point is, that 

 various features of weather, ribes species, and distribution and topography can be 

 measured to produce hazard maps (McDonald and others, in press). Then seed with 

 varying levels of resistance can be matched to each site. For example, on the 

 highest hazard sites, seedlings with the best resistance would be planted, on less 

 hazardous sites seed could be collected from candidate trees (level of resistance 25- 



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