INOCULATION OF WESTERN WHITE PINE WITH BLISTER RUST 371 



These differences in susceptibility were quite remarkable, especially 

 when one considers that in intercepting basidiospores a 2-year-old seed- 

 ling presents 4 times the "target" of a 1-year-old. Possible explanations 

 of this higher resistance of older seedlings are that: (1) stem as well 

 as primary foliage infections may occur on 1-year-old plants (Van Arsdel , 

 1968) ; and (2) the primary needles lack a resistance mechanism known to 

 be present in the short shoot, or fascicle base, of secondary foliage 

 (unpublished data, this laboratory) . 



SUMMARY 



In the course of 15 years work at this laboratory we have artificially 

 inoculated more than a million P. monticola seedlings with C. ribicola. 

 We can say that our efforts to secure heavy infection have been quite 

 successful, but in the same breath we should admit that we are still far 

 from obtaining a degree of control of the inoculation process that will 

 permit us to secure uniform infection. Consistently we have obtained 

 heavy (average 85%) infection of control seedling lots. But the between- 

 block variation in inoculation and infection in these, or of the full-sib, 

 test-cross lots comprising the progeny test, is forcing us to use rela- 

 tively large numbers of seedlings per replicate, and large numbers of 

 replicates per progeny. Substantial savings are possible if we can con- 

 trol uniformity, as well as intensity, of inoculation. 



Seedling height is significantly associated with the frequency of 

 blister rust lesions on western white pine seedling needles, but except 

 for a small increment of seedling height due to seed weight, effects are 

 parent associated. Seedling age, as already reported for both P. stvobus 

 and P. monticola, has a strong effect on degree of infection. 



LITERATURE CITED 



Bingham, R. T. , R. J. Olson, W. A. Becker, and M. A. Marsden. 1969. 



Breeding blister rust resistant western white pine. V. Estimates of 



heritability , combining ability, and genetic advance based on tester 



matings. Silvae Genet. 18: 28-38. 

 Heimburger, C. 1958. Forest tree breeding and genetics in Canada, p. 



41-49. In Proc. Genet. Soc. Can. 3. 83 p. 

 Hirt, Ray R. 1935. Observations on the production and germination of 



sporidia of Cronartium ribicola. N. Y. State Coll. Forest. Bull. 8, 



No. 3. 25 p. 

 McDonald, Geral Irving. 1969. Resistance to Cronartium ribicola J. C. 



Fisch. ex Rabenh. in Pinus monticola Dougl. seedlings. Ph.D. Thesis, 



Wash. State Univ. 74 p. 

 Mielke, J. L., T. W. Childs, and H. G. Lachmund. 1937. Susceptibility to 



Cronartium ribicola of the four principal Ribes species found within 



the commercial range of Pinus monticola. J. Agr. Res. 55: 317-346. 

 Patton, R. F. 1961. The effect of age upon susceptibility of eastern 



white pine to infection by Cronartium ribicola. Phytopathology 51 : 



429-434. 

 Patton, R. F. and A. J. Riker. 1966. Lessons from nursery and field 



testing of eastern white pine selections and progenies for resistance 



to blister rust, p. 403-414. In H. D. Gerhold, et al. (ed.) Breeding 



pest-resistant trees. Pergamon Press, Oxford. 505 p. 

 Squillace, A. E., and R. T. Bingham. 1958. Localized ecotypic variation 



in western white pine. Forest Sci . 4: 20-34. 



