RELATIVE BLISTER RUST RESISTANCE OF NATIVE AND 

 INTRODUCED WHITE PINES IN EASTERN NORTH AMERICA 



C. Heimburger 



(Retired) Southern Research Station, Research Branch, 



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



ABSTRACT 



The main results at Maple, Ontario, Canada, with blister rust 

 inoculation of seedling populations of Pinus peuce, P. peuce 

 x strobus, P. griffith%i s p, griffithii x strobus, P. 

 monticola, P. zzr~;i flora, P. strobus x pentaphylla and ?. 

 strobus are presented. 



Some P. peuce, P. griffithii and ?. parviflora populations 

 show high proportions of resistant seedlings and are of promise 

 for further resistance breeding. Two P. strobus, differing in 

 susceptibility, were used to identify good resistance trans- 

 mitters in P. peuce. Several P. griffithii x P. strobus natural 

 hybrid populations contain high proportions of resistant seed- 

 lings and indicate that their female parents may be good 

 resistance transmitters. One P. pentaphylla was used to 

 indicate somewhat higher resistance in Wisconsin and Canadian 

 ?. strobus selections than in unselected ?. strobus. Breeding 

 for resistance at the intraspecies level in P. strobus has thus 

 far not been as promising. 



The resistance of white pines to blister rust, caused by Cronartium 

 ribicola J.C. Fisch. ex Rabenh. , discussed in the following is resistance 

 just to the races of blister rust introduced to both eastern and western 

 North America from Europe and probably does not represent resistance to 

 all possible races. It is probable that the blister rust in North .America 

 has undergone only slight changes in virulence since its introduction at 

 about the turn of the century. It encountered very susceptible hosts, 

 both in the pines and in some of the Ribes . Hence, the information about 

 resistance of the white pines obtained in western Europe and in eastern and 

 western North America should be quite comparable. Differences in infection 

 frequency and intensity would be due more to differences in susceptibility 

 of the hosts and conditions for infection than to possible differences in 

 rust virulence. 



Observations on resistance of the different white pines are thus far 

 based only on very small samples of the total range of their variation. 

 This applies particularly to observations on resistance of exotic species. 

 Spaulding (1925), Hirt (1940), Childs and Bedwell (1948) and Patton 

 (1966) have found the resistance of several Asiatic species to be higher 

 than the resistance of the native Pinus strobus L. and ?. monticola Dougl . 



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