BREEDING OF WHITE PINE FOR RESISTANCE TO BLISTER RUST 

 AT THE INTERSPECIES LEVEL 



C. Heimburger 

 (Retired) Southern Research Station, Research Branch, 

 Ontario Department of Lands and Forests, Maple, Ontario, Canada 



ABSTRACT 



The results of interspecific hybridization of white pines at 

 Maple, Ontario, Canada, from 1956 to 1965 are presented. 

 Five species, Pinus griffithii (syn. P. wallichiana) , P. monticola, 

 P. parviflora, P. peuce and P. strobus , can be easily crossed 

 with each other but with reduced seed set and somewhat reduced 

 fertility in the F^'s and F2's, and backcrosses, including some 

 triple and multiple crosses, are reported also. Some precocious 

 flowering was observed in hybrid populations resulting from 

 crosses of P. peuce with all other members of this closely 

 related group. The use of this precocious flowering as a 

 means of reducing the time periods during gene transfer from 

 one species to another is discussed. 



A white pine breeding project was initiated at the Southern Research 

 Station of the Ontario Department of Lands and Forests at Maple, Ontario, 

 Canada, in 1946. The aim of this project was to develop new strains of 

 native white pine {Pinus strobus L.) having resistance to blister rust, 

 caused by Cronartium ribicola J. C. Fisch. ex Rabenh. , and other desirable 

 traits for growing in southern Ontario. Promising white pine materials 

 were assembled for breeding work at both the intraspecific and inter- 

 specific levels. The results with interspecific hybridization will be 

 discussed in this paper. 



Several exotic species, closely related to native white pine, namely 

 P. peuce Griseb., P. griffithii McClell. (syn. P. wallichiana A. B. Jacks.) 

 and P. parviflora Sieb. £ Zucc. (includes P. himekomatsu Miyabe & Kudo and 

 P. pentaphylla Mayr) are more resistant to blister rust than P. strobus 

 (Spaulding, 1925; Tubeuf, 1926, 1933). In addition, breeding materials 

 of several other white pine species were of interest because of their 

 largely unexplored breeding potentials. 



The work started from scratch on former farm land. It took about 

 10 years to establish a nursery and other propagating facilities, to 

 assemble a collection of breeding materials in the form of seedlings and 

 grafts, and to work out a reasonably satisfactory method of growing black 

 currants (Ribes nigrum L.) under the climatic conditions of this Station. 

 The first interspecific crosses were made on native older white pine at 

 the Station and in the vicinity; later, as grafts of the new acquisitions 

 began to flower more abundantly, most of the hybridization work was shifted 

 to tnese. 



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