RESEARCH SUMMARY 



Potential gains from tree improvement of ponderosa pine in 

 southern Idaho were assessed after 16 years of field testing. 

 From a comparison of progenies of 258 half-sib families from 37 

 populations growing at four test locations, genetic gains in 16- 

 year height were related to (1) seed collections within seed zones, 

 (2) seed collections from selected populations within seed zones, 

 and (3) seed orchards developed after family trials. 



Analysis of popuHation differentiation provided bases for re- 

 evaluation of seed transfer guidelines. In general, seed for 

 reforestation may be transferred from the collection area (1) 

 + 750 ft (230 m) elevation, (2) + 50 miles (0.7 degrees) latitude, 

 and (3) +60 miles (1.2 degrees) longitude. In addition, a gain 

 of about 4 percent in 16-year height can be expected from seed 

 collections in populations of highest mean performance. 



Quantitative genetic analyses provided estimates of the 

 additive genetic variance and phenotypic variance required for 

 predicting gains in 16-year height after seed orchards are 

 developed from family trials. Depending on the intensity of 

 family selection and individual selection within families, genetic 

 gains of 8 to 14 percent can be expected from seed orchards. 

 Realization of these gains requires seed orchards to be composed 

 of less than 150 genotypes. 



CONTENTS 



Page 



INTRODUCTION 



1 



MATERIALS AND METHODS 



1 



RESULTS AND DISCUSSION 



3 



Population Differentiation 

 Quantitative Genetics 



3 

 6 



PUBLICATIONS CITED 



9 



