LIMITATIONS AND ADVANTAGES OF CONIFERS, VS. AGRONOMIC CROPS, 

 AS RESISTANCE BREEDING MATERIALS 



John IV. Duffield 



School of Forest Resources, North Carolina State University 

 Raleigh _, North Carolina, U.S.A. 



ABSTRACT 



The space and time extension of trees, the biology of conifers, 

 and the nature of forestry are discussed in relation to the 

 strategy and tactics of breeding for blister rust resistance. 

 The virtual immortality of tree genotypes, achievable by 

 cloning, the longevity and abundance of conifer seed and pollen, 

 and the relative ease of maintaining the identity of large trees 

 are seen as advantages offsetting, in part, the disadvantages of 

 long breeding and test cycles. These features, plus ecotypic 

 diversity and an hypothesis regarding the history of relations 

 between white pines and blister rust are used to support an 

 argument for basing white pine breeding strategies on a very 

 large gene pool. 



This title, thoughtfully suggested by our Director, sounds like one 

 of those riddles that starts: "What's" the difference between...?" In 

 fact the title leads into one facet of the larger question, "What are the 

 differences between forestry and agriculture?" Unless one is expert in 

 both agriculture and forestry, he is likely to produce answers based on 

 misapprehension of at least one of these activities. I can modestly 

 claim that my ignorance of agriculture is much more extensive than the non- 

 stocked areas of my knowledge of forestry. Therefore I will talk mostly 

 about conifers and very little about agronomic crops. 



Most of the tree-breeders in the audience are accustomed to a certain 

 attitude toward their vocation held by the breeders of annual and other 

 ephemeral and unimpressive plants. The attitude appears to be a compound 

 of incredulity, sympathy, and perhaps a tinge of the kind of bewildered 

 admiration we feel for lion-tamers, astronauts, submariners, and university 

 presidents. As I analyze the grounds for this attitude, they seem to con- 

 sist of the special features of trees in general, of conifers in particular, 

 and of forestry. Moreover, white pine forests and forestry have special 

 features worth noting. I hope to dispel some of the incredulity of our 

 earth-bound colleagues, inform their sympathy, and sustain whatever 

 admiration they may feel. 



The single word that seems to epitomize the special features of trees 

 is extension. Trees are markedly extended in space and time. Their exten- 

 sion in time is perhaps their most impressive feature to the plant breeder, 

 for it suggests impossibly long breeding and test generations. With no 



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