MASS PRODUCTION' OF IMPROVED FOREST TREE PLANTING STOCK 



THROUGH SYNTHETIC VARIETIES 



Ernst J. Schreiner 

 Northeastern Forest Experiment Station, Forest Service 3 

 'J.S. Department of Agriculture 3 Durham, New Hampshire, USA 



ABSTRACT 



Mass breeding methods for multiple-trait improvement of forest 

 planting stock are discussed, with emphasis on rust resistance 

 in Virtus. Varieties with super, overall genetic fitness are a 

 good objective, but will require both populational and individual 

 buffering. 



Advantages and disadvantages of (1) single- or multiple-cross 

 hybrids, (2) varietal blends, (3) multilineal varieties, (4) 

 synthetic varieties, and (5) multiclonal hybrid varieties for 

 mass production of improved planting stock are discussed. 



INTRODUCTION 



This paper is an attempt to evaluate mass breeding methods for 

 multiple-trait improvement of forest planting stock with emphasis on pest 

 resistance, particularly rust resistance in Finns. Practically all 

 forest tree species need improvement in more than one trait. For example 

 rust resistance in Pinus strobus L. would be of very little value in the 

 Northeastern Region without white pine weevil resistance and rapid growth, 

 and for upland planting of rapid-growing hybrid poplars, rust resistance 

 without a wide range in site adaptability would have very limited 

 practical value. 



BREEDING FOR FITNESS IN FOREST TREES 



The overall object of forest tree breeding should be the creation of 

 varieties with a high degree of fitness. Fitness is generally defined as 

 the relative ability of an organism to survive and transmit its genes to 

 the next generation (King, 1968) , and variability in fitness is defined 

 as the variability under different environments (Pfahler, 1964). Adapta- 

 bility to the widest possible environmental variation, including field 

 resistance to diseases and insects, will require well-buffered varieties 

 with a broad adaptive norm. 



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