Seedling cold and drought hardiness in half-sib families of submaritime Douglas-fir




Darychuk, Nicole T.

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The submaritime zone of British Columbia experiences summer drought and spring and fall frosts which cause high mortality of seedlings planted for reforestation. Seedlings of half-sib Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) families were studied at 3 test sites in the coast mountains of British Columbia, and in a complementary pot trial on southern Vancouver Island from 2007-2008, with the aim of studying physiological traits related to cold and drought hardiness. These families originated from British Columbia's submaritime zone, and had a range of breeding values. This allowed for comparison of growth and stress resistance traits among progeny with expected differences in performance. In the field trial, spring and fall cold hardiness were assessed using chlorophyll fluorescence after controlled freezing. Growth and mortality data, shoot water potential and carbon isotope discrimination were recorded as measures of drought stress and water use efficiency. In the pot trial, a subset of families was grown under 3 drought levels to study drought hardiness characteristics. Growth, biomass allocation, date of vegetative bud burst, gas exchange, shoot water potential, and chlorophyll fluorescence were measured. Means comparisons between families, treatments and study sites were performed, narrow-sense heritabilities were calculated, and physiological traits were compared using correlation analyses. Family, field site and drought treatment had significant effects on many physiological parameters. Wild stand families tended to have greater field survival and fall cold hardiness than seed orchard families. Field height was negatively correlated with survival and spring cold hardiness. Shoot water potential and water use efficiency showed positive correlations with leader growth in the field. These data have relevance to the selection of families for the BC submaritime Douglas-fir tree breeding program. They can also help further our understanding of how growth and stress resistance traits interact, and provide information on inherent genetic control of these traits.



Douglas fir, Seedling, British Columbia