Growth and cold hardiness of intervarietal hybrids of douglas-fir.

Potentials for improvement of the interior variety of Douglas-fir (Pseudotsuga menziesii var. 'glauca') by hybridization with the coastal variety (P.m. var. 'menziesii') were explored. The primary objective was to assess possibilities for increasing growth potentials of the interior variety while maintaining adaptation to relatively cold inland environments. Seventy full-sib hybrid families and their half-sib parental lines were grown in two contrasting environments common to the interior variety. Nine traits related to growth, phenology, and freezing tolerance in 4-year-old trees were compared.For traits related to growth (height and diameter) in the inland environment, hybrids equaled the growth of the coastal variety and exceeded the interior variety by 40 percent. For traits related to adaptation (bud burst, bud set, frost damage, tree form, and freezing tolerance), hybrids were intermediate but approached levels characteristic of the interior variety. Survival of hybrids equaled that of the interior variety and was superior to that of the coastal variety.Hybrid characters could not be predicted reliably from those of parental lines. Yet, quantitative genetic analyses suggest that expression of characters related to growth depends on nonadditive genetic effects, but expression of those related to adaptation is somewhat dependent on additive effects.Realization of the tremendous potential of hybridization for improvement of the interior variety will require at least one backcross generation or additional crosses utilizing introgressed populations.