r RESISTANCE OF WHITE PINES IN EASTERN NORTH AMERICA 265 



screening for climatic adaptation and resistance to blister rust, in a 

 similar manner to what seems to be the case with some P. peuce in Finland. 

 The most promising population thus far is W.P. 139, reasonably stable 

 5 years after inoculation and showing good adaptation and vigorous growth. 

 Some trees of this population have begun flowering and are being used for 

 breeding purposes. 



P. montiacla Dougl .--The results of tests with seedlings of this 

 species, raised from seeds obtained in the Interior of British Columbia, 

 are presented in Table 6. All 5 populations tested were eliminated by 

 blister rust infection 6 to 8 years after inoculation. Poor adaptation 

 to climate was also quite evident. In addition, there are 3 populations, 

 not shown in the table. These have been subjected to natural infection 

 by blister rust only. Two are still represented by 9 and 2 surviving 

 seedlings, respectively. These seedlings have been grafted for further 

 resistance tests. Because of the remarkable resistance of P. montioola 

 materials to attacks by the white pine weevil, Pissodes strobi Peck, 

 additional new materials have been obtained from British Columbia of the 

 most promising provenances, as shown by former tests. The resulting 

 seedlings will be screened for resistance to blister rust on a fairly 

 large scale, prior to testing for weevil resistance. About 15 years ago 

 seeds of some of R. T. Bingham's resistant selections were received at 

 Maple. The 7 resulting seedling lots have all perished in about 6 years 

 because of poor climatic adaptation. 



P. parvi flora Sieb. £ Zucc .--The results with one population raised 

 from seeds received from Nagano Prefecture, Honshu, Japan, are shown in 

 Table 6. Five consecutive inoculations with blister rust have caused no 

 infection. The losses are due entirely to other causes, mainly poor 

 climatic adaptation. Seedlings of this species show very slow growth 

 initially and many perish from frost heaving. It has not been possible to 

 keep this population growing on its own roots. Since 1960 all the more 

 vigorous seedlings have been grafted on P. strobus , resulting in a very 

 satisfactory growth rate and few losses thereafter. No blister rust has 

 been observed on these materials nor on any other grafts of P. parviflora 

 and P. pentaphylla Mayr subjected to natural infection. It must be con- 

 cluded that at least this population is highly resistant, if not immune, 

 to blister rust. The same is the case with P. koraiensis Sieb. £ Zucc. , 

 where only occasional needle spots of no further consequence have been 

 observed after natural infection. 



P. strobus x P. pentaphylla . --The blister rust infection of 5 seedling 

 populations from this and the reciprocal cross with a single P. pentaphylla 

 from Rochester, New York, is shown in Table 7. All populations show 

 infection and one was eliminated 3 years after inoculation. Three of the 

 remaining populations became infected 1 year after inoculation, while the 

 fourth required 4 years for this. In all cases the populations continued 

 to segregate susceptible seedlings for 1 to 5 years, i.e., they were 

 unstable in this respect as are most hybrids with P. strobus. The results 

 indicate that the susceptibility of P. strobus is incompletely dominant to 

 the supposed resistance of P. pentaphylla. The resistant selections of 

 P. strobus from Wisconsin and Pointe Platon in some cases yield progenies 

 with somewhat higher proportions of rust-free seedlings than unselected 

 P. strobus and have as yet not been eliminated by blister rust. 



