212 HOWARD B. KRIEBEL 



P. peuce hybrids, though not exceptionally vigorous, are of special 

 interest because of the excellent form, rust resistance and possible 

 weevil resistance of this species (Wright and Gabriel, 1959; Heimburger, 

 1958, 1963). At least 7 different crosses between P. peuae, P. strobus, 

 and their hybrids have been made successfully, mostly at Maple, Ontario. 

 The hybrid P. peuce x strobus was considered by Fowler and Heimburger 

 (1958) to be of doubtful value to forestry because of its intermediate 

 growth rate, but valuable for back crossing to P. strobus to introduce 

 resistance to blister rust and weevil damage. Successful crosses have 

 also been made between P. montiaola and P. peuae , and between P. montiaola 

 and the hybrid P. peuae x strobus (Wright , 1959) . 



Korean white pine hybrids with sugar pine P. lambertiand) are con- 

 sidered by Heimburger {unpublished notes') to be worth further study from 

 the standpoint of weevil resistance as well as blister rust resistance. 

 Kriebel found that the barrier to hybridity in crosses of P. strobus x 

 koraiensis is a problem of embryo inviability rather than gametic incom- 

 patibility. The same situation exists in the crosses P. strobus x aembra. 

 P. strobus x flexilis (Kriebel, 1968), and probably also P. peuae x aembra 

 (Hagman and Mikkola, 1963) . Because some cell differentiation is possible 

 in the zygote, there is a possibility of finding ways to obtain new and 

 very useful hybrids. 



SUMMARY 



In addition to eastern white pine, several European and Asiatic 

 species of white pines appear to be useful in North America because of 

 their vigor or pest resistance. The high degree of crossability of some 

 of these species offers the attractive possibility of developing vigorous 

 hybrids on a large scale, and of introducing insect and disease resistance 

 into the native P. strobus. The white pines, in f act , seem to be particu- 

 larly well suited to the application of interspecific hybridization as a 

 technique for forest tree improvement J Prior to mass production, how- 

 ever, is the most urgent need for the scientific study of variation 

 within each of the potential parent species by cooperative international 

 testing, and the subsequent selection, within the areas of potential use, 

 of superior genotypes to be used for the breeding of hybrids. 



LITERATURE CITED 



Andresen, J. W. 1964. The taxonomic status of Pinus ahiapensis. 



Phytologia 10: 417-421. 

 Aughanbaugh, J. E., H. R. Muckley, and 0. D. Diller. 1958. Performance 



records of woody plants in the Secrest Arboretum. Ohio Agr. 



Forest. Dep. Series 41. 90 p. 

 Barnes, B. V., and R.- T. Bingham. 1962. Juvenile performance of hybrids 



between western and eastern white pine. U.S. Dep. Agr. Forest Serv. , 



Intermountain Forest £ Range Expt. Sta. Res. Note 104. 7 p. 

 Bingham, R. T., A. E. Squillace, and R. F. Patton. 1956. Vigor, disease 



resistance, and field performance in juvenile progenies of the hybrid 



Pinus montiaola Dougl. x Pinus strobus L. Z. Forstgen. u. Forstpf 1 . 



5: 104-111. 

 Brown, H. P., A. J. Panshin, and C. C. Forsaith. 1949. Textbook of 



wood technology. McGraw-Hill, New York. 652 p. 

 Critchfield, W. B., and E. L. Little, Jr. 1966. Geographic distribution 



of the pines of the world. U.S. Dep. Agr. Misc. Publ. 991. 97 p. 



