SUMMARY 



There are no reproductive barriers in western white pine restrictive enough to 

 preclude an inbreeding program. Filled seed yields following second-generation inbreed- 

 ing are low, but consistent, from a variety of matings. Hfficiency of the program can 

 be increased by proceeding only with Sj lines where seed yield is relatively high. 



Reproductive maturity of western white pine lines was attained at about 15 to 

 20 years of age, and the fruiting of S2 lines may be delayed even more. Meanwhile, 

 because of the length of inbred generations, and because the greatest increment of the 

 increase of homozygosity occurs in the first inbred generation, it seems expedient to 

 begin single crossing among the better Si lines immediately. Some success has accom- 

 panied similar "early" crossing in maize (cf. Lonnquist and Williams 1967) . Performance 

 of these single-cross progenies, and the level to which their reproductive vigor is 

 restored, will be critical information in the decision as to whether we should embark 

 on a practical inbreeding program in western white pine. 



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