Pine Breeding in the United States 



149 



narrowed the scope of its work to the 

 genetic improvement of the timber 

 pines. John Barnes, W. C. Gumming, 

 and W. G. Wahlenberg pioneered in 

 the development of pollination tech- 

 niques. F. I. Righter joined the sta- 

 tion staff in 1931 and, with W. G. 

 Gumming, perfected the techniques 

 and used them to demonstrate the 

 great possibilities for genetic improve- 

 ment that could be realized through 

 species hybridization in the pines. At 

 about this time, Philip G. Wakeley, 

 also of the Forest Service, made a num- 

 ber of crosses between the timber-pine 

 species of the Southeastern States. 



Much of the pioneer work in pine 

 breeding thus is behind us. 



THREE GENERAL METHODS are avail- 

 able to the tree breeder today. Two of 

 them selection and hybridization 

 consist of using and recombining he- 

 reditary variations already existing 

 among trees. The third method can be 

 used to create hereditary variations 

 through physical or chemical treat- 

 ments. 



Selection becomes much more effec- 

 tive when it is combined with other 

 techniques, such as progeny testing, 

 vegetative propagation, or hybridiza- 

 tion. Progeny tests of self-pollinated 

 plants help determine which parents to 

 select for the best offspring. But since 

 the pines are predominantly cross-pol- 

 linated, a progeny test in which only 

 the seed parent is known tells only half 

 of the story. Vegetative propagation, 

 which is used by fruit growers to mul- 

 tiply selected trees, has not yet reached 

 a stage of development for pines which 

 would permit economical propagation 

 of forest planting stock except in New 

 Zealand, where it is practiced with 

 Monterey pine. Great progress has been 

 made, however, by workers in South 

 Africa and Australia; by K. W. Dor- 

 man and his associates, who have been 

 working with turpentine pines in the 

 southeastern part of the United States ; 

 and by N. T. Mirov, of the Institute of 

 Forest Genetics in California. 



This work has resulted in techniques 



by which the clones from selected pines 

 may be vegetatively propagated for re- 

 search purposes or for establishment of 

 seed-producing plantations. Members 

 of a clone are merely parts of a single 

 tree, made to produce roots and be- 

 come self-supporting or supplied with 

 roots by grafting. Numerous experi- 

 ments have shown that pines and many 

 other forest trees can produce few seed 

 as a result of self-pollination; usually 

 the few seedlings so produced are weak. 

 Pollination between members of the 

 same clone is equivalent to self-pollina- 

 tion. For that reason, mixing several 

 clones in a seed-producing plantation 

 is necessary to insure cross-pollination 

 and satisfactory seed production. Such 

 plantations in Sweden contain from 6 

 to 12 selected clones, all from a single 

 local race to insure adaptability. When 

 two selected trees or clones are cross- 

 pollinated, there is no certainty that 

 the offspring will be better than the 

 average for the species, but when half 

 a dozen or more selected clones are al- 

 lowed to interpollinate the chance for 

 average superiority of the offspring is 

 increased. Only by controlled pollina- 

 tion can it be determined which pairs 

 of clones will consistently produce su- 

 perior offspring. Perhaps the most 

 promising field for selection work with 

 pines is the search for trees resistant to 

 disease and insect attack. 



The methods and benefits of pine 

 hybridization were discussed in an ar- 

 ticle on hybrid forest trees in the 1943- 

 1947 Yearbook of Agriculture. 



Briefly, the benefits to be expected 

 are hybrid vigor, the combination of 

 desirable characters in a single plant, 

 and the uncovering by hybrid segrega- 

 tion of hitherto unsuspected characters 

 in the offspring derived from breeding 

 within a hybrid population. Naturally, 

 hybridization can be expected to be 

 most effective if the parents are se- 

 lected rather carefully. 



As to the third method available to 

 tree breeders, most of the techniques for 

 initiating new hereditary variations are 

 barely out of the laboratory and as yet 

 cannot be consciously directed they 



