ISO 



Yearboo^ of Agriculture 1949 



might more appropriately be called 

 shotgun methods in their present state 

 of development. They include the in- 

 duction of gene mutations and chromo- 

 some rearrangements by X-ray and 

 other types of radiation, heat treat- 

 ments, and cold shocks. The doubling 

 of chromosome numbers by treatment 

 of seeds or growing points with col- 

 chicine, acenaphthene, or other chem- 

 icals was once regarded as promising 

 for making pine hybrids true-breeders. 

 This hope has faded somewhat in the 

 face of a number of failures of this 

 type of experimentation, and at pres- 

 ent such work is placed in the category 

 of pure research, which, given sufficient 

 time and effort, may yet produce valu- 

 able tools for the practical tree breeder. 



What has been accomplished by 

 these methods and how and where can 

 the accomplishments be put to use? 



Perhaps the best way to answer is to 

 make a tour of the forest regions of this 

 country, stopping long enough in each 

 to see what the breeders have to offer. 



IN THE NORTHEASTERN STATES, the 

 eastern white pine is most interesting 

 to the tree breeder because of its great 

 commercial value and because of the 

 challenge offered by its susceptibility 

 to the attacks of two major pests, the 

 white-pine weevil and the white pine 

 blister rust. This pine belongs to a 

 group of closely related species, which 

 includes the western white pine of the 

 northern Rockies as well as the Pacific 

 Northwest, Himalayan white pine, and 

 the Balkan pine of Yugoslavia and 

 Greece. The last two pines are of par- 

 ticular interest because they exhibit 

 some resistance to blister rust. 



Several pine breeders have made hy- 

 brids within this group. Workers at the 

 Arnold Arboretum of Harvard Uni- 

 versity and at the Institute of Forest 

 Genetics have found that hybrids be- 

 tween eastern white pine and western 

 white pine, between western white pine 

 and Himalayan white pine, and be- 

 tween Himalayan white pine and east- 

 ern white pine are all more vigorous 

 than the parent species. During the 



first 7 years of growth, the hybrid just 

 about doubles the height growth of the 

 parents. 



L. P. V. Johnson and G. Heimburger 

 of Canada have crossed eastern white 

 pine with the Balkan pine. C. Syrach- 

 Larsen in Denmark also has made this 

 cross and has grown hybrid seedlings 

 that are already producing pollen. 



Some of this pollen has been used 

 in crosses with the western white pine 

 at the Institute of Forest Genetics. By 

 this means we hope to introduce the 

 blister rust resistance of the Balkan 

 and Himalayan pines into a cross that 

 exhibits hybrid vigor. The work of 

 A. J. Riker and associates at the Uni- 

 versity of Wisconsin has shown that in 

 areas heavily infected with blister rust 

 a rare tree may be found to have a high 

 degree of resistance. These trees are 

 now being used to produce stock that 

 can be tested for resistance to blister 

 rust. Dr. G. Heimburger is emphasiz- 

 ing both blister rust resistance and re- 

 sistance to white-pine weevil attack in 

 his breeding work with the white pines. 



The practical value of all hybrids de- 

 pends on their adaptation to the 

 climate in which they are planted. 



Some of the hybrids mentioned are 

 of unknown hardiness in the Northeast, 

 but we can be confident that others will 

 thrive because both parent species are 

 known to be hardy. This applies espe- 

 cially to the eastern-western white pine 

 hybrid and to a less certain degree to 

 the hybrids involving the Balkan white 

 pine. The Himalayan pine is known to 

 be hardy in Philadelphia, and there- 

 fore hybrids involving this species 

 should thrive at least that far north. 



Pitch pine, which is currently of 

 minor importance in the Northeast be- 

 cause of its poor form and slow growth, 

 has been successfully crossed with 

 loblolly and shortleaf pines to yield 

 hybrids that surpass pitch pine in form 

 and rate of growth. The hardiness of 

 these hybrids has not yet been tested 

 in the more northerly region inhabited 

 by pitch pine, but it is reasonable to 

 expect that the hybrids will be at least 

 intermediate in cold resistance. 



