20 JOHN W. DUFFIELD 



intention to be cynical, I note that the perennial habit of trees has not 

 appreciably inhibited the annual harvest of publications by tree breeders. 

 Longevity of trees has other consequences. It may cause the thoughtful 

 tree-breeder to ponder the question of climatic change and its possible 

 effects on such phenomena as fir die-back (Tannensterben) in central and 

 southern Europe. 



The tree breeder must indeed, in the words of Gifford Pinchot, "take 

 a long look ahead". But longevity has its advantages. A tree genotype 

 is available to a succession of breeders in the form of a single long- 

 lived individual or ortet, and is potentially immortal in the form of 

 the ramets of a clone. This is, of course, true of certain grasses as 

 well. Clonal propagation, rather readily accomplished for virtually all 

 trees, enables the breeder to extend biotypes indefinitely in space, time, 

 and number of individuals for testing and breeding. Moreover, it is of 

 special significance to the resistance breeder, for it enables him to 

 perpetuate by isolation biotypes susceptible to killing diseases, and 

 thus to have on the shelf stable biological reagents for the study of 

 races of pathogens or the identification of injurious agents such as air 

 pollutants (Berry and Hepting, 1964). 



The perennial habit of trees, considered apart from simple longevity, 

 makes things generally difficult for the tree breeder, for it usually means 

 that a tree is from 2 to 20 years old and correspondingly large before it 

 flowers. The size of reproductively mature trees makes environmental 

 control difficult and expensive and thus limits the tree breeder's ability 

 to control flowering time, to facilitate certain crosses and distribute 

 the pollination work load over time. We are gradually chipping away this 

 roadblock as our knowledge of flowering biology increases. 



Trees are obviously extended in space. To look on the bright side 

 first, this has the consequence of keeping tree-breeders fit, or in 

 practice as riflemen, or both. Tree breeders see many views denied to 

 others and, because people and birds are unused to finding people in 

 trees, tree-breeders who are not excessively single-minded have unusual 

 people- and bird-watching opportunities. The vertical and horizontal 

 extensions of a tree have the effect of placing the same organism in 

 several micro-climates simultaneously. This is especially significant to 

 the pathologist. In addition, the very size of a mature tree crown 

 aggravates the task of certifying a tree as being symptom-free. This is 

 especially true of white pine blister rust, with the size problem com- 

 pounded by time. For old infections may persist many years and remain 

 cryptic to all but the sharpest-eyed pathologist or the most perceptive 

 squirrel seeking succulent canker tissue to gnaw. I have discussed else- 

 where more fully the space-time problems in tree breeding and some 

 possible partial solutions (Duffield, 1963). 



Trees, in general, share with man a long history of non-domestication, 

 from the breeder's point of view. With a few exceptions like the date 

 palm, trees have managed, until Dr. Schreiner and very few predecessors 

 went to work, to remain above the brave new world of organisms genetically 

 remodeled by man. This means that, in general, trees have a store of 

 genetic variability that has been neither sorted out nor dissipated. 

 They therefore offer the resistance breeder both challenge and opportunity. 



Adequate seed production is a characteristic with high survival value 

 for trees, as for other plants. Crop plants, however, have in most cases 

 been rigorously selected for high seed production. Forest tree populations 



