© 2007 Heron Publishing—Victoria, Canada
Cold hardiness of interspecific hybrids between Pinus strobus and P. wallichiana measured by post-freezing needle electrolyte leakage
Pengxin Lu (1, 2), Stephen J. Colombo (1) and Robert W. Sinclair (1)
1. Ontario Ministry of Natural Resources, Ontario Forest Research Institute, Sault Ste. Marie, Ontario P6A 2E5 / 2. Corresponding author (pengxin.lu@mnr.gov.on.ca) / Received January 4, 2006; accepted January 29, 2006; published online November 1, 2006
Summary
Interspecific hybrids between eastern white pine (Pinus strobus L.) and Himalayan blue pine (P. wallichiana A. B. Jacks.) were developed in Ontario, Canada, to introduce blister rust (Cronartium ribicola Fisch.) resistance genes to P. strobus. There is concern that introducing blister rust resistance has resulted in reduced cold hardiness of the progeny compared
with non-hybridized eastern white pine. To test the efficacy of backcrossing with P. strobus to improve cold hardiness, 1-year-old seedlings from hybrid crosses differing in P. strobus genome composition were artificially freeze-tested. In Experiment 1, unhardened seedlings were allowed to acclimate to progressively
lower temperatures in a growth room, whereas in Experiment 2, seedlings were hardened outdoors under natural weather conditions
in Sault Ste Marie, Ontario. Needle cold injury was determined by calculating relative electrical conductivity based on post-freezing
electrolyte leakage. Results indicated that needle fascicles from unhardened seedlings of all genotypes in the greenhouse
tolerated –5 °C for 3 hours with little or no injury. Cold hardiness increased in parallel with declining growth room minimum
temperature over the 7-week period of hardening. Cold hardiness was improved for hybrid crosses with increased Pinus strobus genome composition in Experiment 2, but the results were less conclusive in Experiment 1.
Keywords:
blister rust resistance, Cronartium ribicola, Himalayan pine, white pine.
