INTRODUCTION 



Investigations of the effects of inbreeding in western white pine {Pinus montioola 

 Dougl.) have been underway at this Station since 1950 (Bingham and Squillace 1955). 

 Over 150 seedling lines have been developed, each usually produced along with four 

 full-sib outcrossed seedling lines of the same mother tree (i.e., half-sibs of the 

 S^'s). Sj's and their outcrossed half-sib seedlings (hereafter called half-sibs) have 

 been artificially inoculated with the white pine blister rust fungus {Cronartium 

 ribiaola J. C. Fisch. ex Rabenh.), and seedlings that survived the rust exposure 

 (ranging from to 20 S^'s and 5 to 30 half-sibs) have been established in a blister 

 rust resistance arboretum at Moscow, Idaho. ^ The oldest of these resistant seedlings 

 are now 21 years of age. There has been substantial fruiting of the half-sib seedlings 

 for about 10 years, but only sporadic fruiting of the seedlings for about 5 years, 

 with the first substantial fruiting in 1972. 



Blister- rust-inoculated Si seedling lines have been of immediate value for support- 

 ing hypotheses on the presence of recessive resistance genes in western white pine 

 (McDonald and Hoff 1971). Now that the Sj lines are reaching reproductive maturity, 

 however, they are becoming useful for assessing possibilities and limitations of classi- 

 cal inbreeding methods (Shull 1910; Jones and Singleton 1935) for improvement of growth 

 and other traits . 



This paper considers the feasibility of an inbreeding program in western white pine, 

 its likely timing and promise. Data presented here are mainly restricted to cone and 

 seed bearing following controlled crossings on 18- to 21-year-old S\ trees in 18 differ- 

 ent lines. Second-generation inbred cone yields and seed progenies discussed include 

 those from selfing Sj trees (S2 crosses), S^ full-sib crosses, S^ backcrosses, single 

 crosses (between unrelated S^'s), and other inbred crosses of the second and first 

 generation. Descriptions and examples of these inbreds are given in "Materials and 

 Methods," starting on page 5. 



■^Progress reports on breeding for blister rust resistance in western white pine 

 include Bingham and others 1953, 1960, 1969, and 1972. 



