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MULTIPLE TRAIT SELECTION IX fcHITE PIXE BREEDING SYSTEMS: 

 BLISTER RUST RESISTANCE, WEEVIL RESISTANCE, TIMBER YIELD ! 



Henry D. Gerhold 



School of Forest Resources , Pennsylvania State University , 



University Park, Pennsylvania, U.S.A. 



ABSTRACT 



A white pine variety with improved resistance to both white 

 pine blister rust and white pine weevil would be useful in 

 certain regions of North America. Some form of multiple trait 

 selection in a fairly complex breeding system would be required 

 to produce it. Forest and nursery environments are used as 

 examples in discussing the efficiency of selection and possi- 

 bilities of bias due to interference between methods of 

 evaluating growth, rust incidence, and weevil damage. The 

 advantages of using index selection rather than independent 

 culling levels or tandem selection are considered, as well as 

 some potential disadvantages. Interactions of the two pests 

 on their common host in different environments are likely to 

 introduce bias into estimates of means and genetic variances. 

 Mortality caused by rust and weevils may be another source of 

 bias, and may also restrict opportunities for index selection. 

 In order to reduce complexity and to maximize genetic progress 

 without excessive risks, separate selection and testing for 

 resistance to the two pests is suggested at first. Initial 

 goals would be to find two sets of parents each having superior 

 breeding values for resistance to one of the pests, and to 

 estimate parameters for two separate selection indices. 

 Ultimately a single selection index may be developed which 

 includes blister rust resistance, weevil resistance, and other 

 traits related to economic timber yield. 



INTRODUCTION 



Numerous white pine breeding programs in North America focus on 

 genetic improvement in Pinus strobus L., P. monticola Dougl . , and ?. 

 larhertiana Dougl. Most of the programs have existed less than 10 years, 

 and few of them for as long as 20 years. Their improvement objectives, 

 being related to different environmental and economic conditions, vary 

 in several respects. In some regions the damage caused by white pine 



1 Research on white pine weevil resistance has been supported by 

 Forest Service, USDA, Grant #1 and by Northeast Regional Research Project 

 NE 27, USDA. Authorized on July 28, 1969, as Paper No. 3634 in the 

 Journal Series of the Pennsylvania Agricultural Experiment Station. 



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