NOTES Genetics of cold hardiness in a cloned full-sib family of coastal Douglas-fir1

Abstract: Variation in cold-hardiness traits, and their extent of genetic control and interrelationships, were investigated among individuals (clones) within a single large full-sib family of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) from Oregon. Cold injury to needle, stem, and bud tissues was evaluated in fall 1996 and spring 1997 following artificial freeze testing of detached shoots collected from 4-year-old ramets (rooted cuttings). Variation among clones in cold-injury scores was significant (p < 0.01) for all shoot tissues in both fall and spring and averaged about three times the magnitude previously observed among open-pollinated families of this species. Thus, improving cold hardiness by within-family selection appears to hold much promise. Striking similarities in relative magnitudes of heritability estimates and genetic correlations in the full-sib family, compared with breeding populations, support the following hypotheses about the quantitative genetics of cold hardiness in this species: (i) heritability of cold hardiness (both broad-and-narrow-sense) is stronger in the spring than in the fall; (ii) cold hardiness of different shoot tissues in the same season is controlled by many of the same genes; and (iii) genetic control of fall cold hardi-ness is largely independent of cold hardiness in the spring. Résumé: La variation entre individus pour les caractères associés à la tolérance au froid, ainsi que le degré de con-trôle génétique et d’inter-relations, ont été étudiés sur des clones appartenant à une seule grande fratrie de douglas (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) côtier originaire de l’Oregon. Les dommages au froid observé