LITERATURE REVIEW 



An extensive literature deals with effects of first-generation selfing in conifers, 

 especially Pinus . The summary by Franklin [1970) covers much of this literature through 

 1967, and adequately describes effects of inbreeding as reflected in S;^ cone and seed 

 yields, seed germination, and mortality and early growth of seedlings. His table 3 

 sums up these effects in Pinus, pointing out that in general, and in comparison to 

 outcrossing, neither cone yield nor total (filled plus hollow) seed yield are affected, 

 filled seed yield is reduced about one-third, hollow seed yield is increased about 2-1/2 

 times, seed germination is reduced about one-tenth, seed weight is little affected, 

 seedling mortality is about one-third higher, and seedling height is reduced about 

 one -fourth. 



These general conclusions are quite applicable to western white pine, except that 

 in young trees (18 to 21 years) cone yield may be reduced, if not in the older trees 

 (30 to 50 years) covered by Franklin. 



Several times in the past (Bingham and Squillace 1955; Squillace and Bingham 1958; 

 Barnes and others 1962) we have noted the wide variation in self- fertility of different 

 western white pine mother trees. Some trees are comparatively self-fertile, others 

 self-sterile, in respect to seed yield, as is shown in table 1. The self- fertile trees 

 like parent 58 are equal or better in filled S^ seed yield and give somewhat greater 

 hollow seed yield. The seat, manner of operation, and timing of the incompatibility 

 mechanisms are unknown, but the effect is strongly associated with the mother tree. 



In contrast, literature on second-generation inbred crossing is very sparse. Only 

 five reports of crossing of S^ trees have been found. Some of this inform.ation was 

 outlined by Franklin (1970), but is reviewed more completely in this paper, so that 

 sounder conclusions may be drawn as to the feasibility of continued inbreeding or the 

 likelihood of improvement of conifers by use of classical inbreeding methods. 



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