Survival, growth and wood specific gravity of interspecific hybrids of Pinus strobus and P. wallichiana grown in Ontario

Interspecific hybrids between eastern white pine (Pinus strobus L.) and Himalayan blue pine (P. wallichiana A.B. Jacks.) were created in Ontario, Canada, to introduce blister rust (caused by Cronartium ribicola Fisch.) resistance genes to the former. In this paper, we report the survival, growth, and wood specific gravity of these interspecific hybrids from field trials established between the 1970s and 1990s. Results indicate that while P. wallichiana generally performed poorly due to insufficient cold hardiness, progressive improvement in survival and growth was evident for the first generation hybrids (F1) and backcrosses (B1) to P. strobus, with a trend of better performance with increasing parentage of P. strobus. In southern Ontario, where climatic conditions were relatively mild, some interspecific hybrids outperformed P. strobus in 20- to 40-year-old trials. In northern Ontario, insufficient cold hardiness seemed to limit the survival and growth of the interspecific hybrids. Measured wood specific gravity was highest for P. wallichiana and lowest for P. strobus, with that of the interspecific hybrids being intermediate. Implications of the field trial results to breeding for increasing blister rust resistance of eastern white pine are discussed.