Pine Breeding in the United States 



THE SOUTHEASTERN AND SOUTH- 

 ERN STATES have four principal tim- 

 ber pines all used in hybridization 

 work. None of the crosses so far made 

 have resulted in conspicuous hybrid 

 vigor comparable to that found in the 

 white pine crosses, but some of them 

 combine desirable properties of the 

 parent species in such a way as to be of 

 great interest to timber growers. The 

 cross between shortleaf and loblolly 

 pines is generally superior to shortleaf 

 pine in form and growth rate and gives 

 some promise of growing in areas out- 

 side the natural range of loblolly pine, 

 notably in eastern Texas and Arkansas. 



Loblolly and shortleaf pines have 

 both been crossed with slash pine, per- 

 haps the most productive pine in the 

 region for both timber and naval stores. 

 Slash pine would contribute much 

 more to the economy of the South if 

 it were not comparatively restricted in 

 its distribution; it is to be expected 

 that crosses with loblolly and shortleaf 

 pines can be made that will consider- 

 ably extend the range of slash pine 

 without sacrificing productivity. The 

 natural hybrid between longleaf and 

 loblolly pines has been known for some 

 time, and a number of second-genera- 

 tion hybrids have been tested at the In- 

 stitute of Forest Genetics. Some of 

 these show strikingly good form and 

 rapid growth under conditions wholly 

 unfavorable to longleaf pine. 



FOR THE LAKE STATES two im- 

 portant timber pines have been used in 

 crosses, which have shown remarkable 

 vigor. The first of these, eastern white 

 pine, has already been discussed under 

 the northeastern region. The second, 

 jack pine, has been crossed with lodge- 

 pole pine of western United States to 

 give a hybrid as vigorous as jack pine 

 and as much as 79 percent taller than 

 lodgepole pine of the same age. So 

 far, this cross has been made only 

 with the lodgepole pine of the high 

 Sierra Nevada, which is a relatively 

 slow-growing tree at medium to low 

 altitudes. 



It is quite possible that lodgepole 



pine from lower elevations in the Pa- 

 cific Northwest or in the Rocky Moun- 

 tains may be used with a selected local 

 race of jack pine to produce even better 

 hybrids. This cross should have great 

 appeal to the pulpwood growers and is 

 comparatively easy to produce. 



Preliminary experiments at the In- 

 stitute of Forest Genetics have shown 

 that jack pine cuttings can be rooted 

 rather easily, thus opening up the pos- 

 sibility of establishing clonal seed-par- 

 ent blocks of this species that can be 

 mass-pollinated with lodgepole pine 

 pollen to produce hybrids at relatively 

 low cost. The scheme is especially 

 practicable for jack pine, which nor- 

 mally produces sound seeds at an ear- 

 lier age than most other pine species. 



WESTWARD, in the northern Rocky 

 Mountain and Pacific Northwest re- 

 gions, the same hybrids that show 

 promise in the Lake States are likely 

 to succeed. Recent work by T. T. 

 Munger shows that at the Wind River 

 Arboretum in southern Washington, 

 eastern white pine equals the western 

 white pine in growth and form. Thus 

 it is reasonable to expect that hybrids 

 that have shown superior growth in 

 tests in California and Massachusetts 

 will thrive in the Northwest. Although 

 neither of the parent species is gener- 

 ally resistant to blister rust, it is be- 

 lieved that resistance can eventually be 

 introduced from resistant species such 

 as Balkan and Himalayan pines or from 

 resistant individuals of eastern white 

 pine. No doubt some resistant trees of 

 western white pine will eventually be 

 found and brought into the breeding 

 program. 



For the central and southern Rocky 

 Mountains, the Southwestern States, 

 and California, a number of the hybrids 

 have been produced. Monterey pine of 

 the mild California coast has been 

 crossed with knobcone pine, which is 

 generally found in locations with much 

 lower winter temperatures and more 

 extreme summer drought than occur 

 in locations where Monterey pine has 

 survived. It is a typical combination 



