MATERIALS AND METHODS 



Between 1950 and 1970, first-generation selfings were attempted on about 200 western 

 white pines in natural stands of northern Idaho. Seed and Si seedling lines were pro- 

 duced from more than 150 of these selfs, but seedlings of only about 50 Sj lines remained 

 after blister rust resistance testing. The resistant S^ seedlings were transplanted 

 into the blister rust resistance arboretum, where in 1972 they ranged from 8 to 21 years 

 of age. The trees below age 18 so far have fruited very infrequently, however. There- 

 fore, only 109 S^ trees in the 18- to 21-year-old age bracket, one to 18 trees in each 

 of 22 S^ lines, constitute the inbred materials covered in this paper. At present only 

 72 of these S^'s in 18 different lines survive. Some S^'s in 17 of the 18 surviving 

 Si lines have fruited. Outcrossed materials for comparison consist of over 1,000 sur- 

 viving trees in 158 lines. All outcrossed trees are lialf-sibs of the Sj trees, and of 

 the same ages. These half-sib trees occur in 140 full-sib and 18 wind-pollinated 

 progenies of the same 22 mother trees, and there are from 4 to 235 trees in each of 

 the 22 mother-tree lines. 



Female strobilus production on Sj's began in 1960, when single 9-year-old S^ trees 

 of two lines produced one or two strobili. Although pollinated, none of the three 

 strobili developed beyond that juvenile stage. The first mature cones and filled seeds 

 on Si trees were produced on 11-year-old Si's in 1962, from 1961 pollinations. Male 

 strobilus production on Si's was delayed until 1966, and then occurred only on a single 

 13-year-old tree. By 1972, however, some Si lines were producing large volumes of 

 pollen (up to 35,000 male strobili), and one Si line had produced male strobili every 

 spring for 6 years. Complete records on both female and male strobilus production were 

 maintained on all trees in the arboretum through 1966. Thereafter, because female 

 fruiting became so general and abundant, only male strobilus counts were continued. 



Over the 13 years since female strobilus production commenced on Si trees, many 

 kinds of inbred matings have been attempted on the Si's or on their half-sibs. Before 

 Si pollens became available, the Si's that bore female strobili were backcrossed to 

 their natural-stand parents or outcrossed to other natural-stand parents, using stored 

 pollens. Then, as the related but outcrossed half-sibs began producing pollen, the 

 Si's were mated with these in half-sib crosses, or the related half-sibs were themselves 

 crossed in half- and full-sib, backcross, self, or outcross matings. Finally, and 

 mainly in the last 5 years after Si male strobilus production attained substantial 

 proportions, S2 crosses. Si full-sib crosses. Si backcrosses, and single crosses between 

 Si's of two different lines were attempted. Thus, cone and seed yields from inbreds 

 representing a range of levels of inbreeding [F = 0.125 to 0.750) can be compared. 

 These inbred yields can also be compared with those from the outcross population of 158 

 related half-sibs. 



The various first- and second- generation inbred crosses compared may be more 

 clearly understood from examples of their pedigrees (table 2) . In calculating the 

 inbreeding coefficients, original parents were assumed not to be inbred. 



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