FAMILY VARIATION FOR FALL COLD-HARDINESS IN 2 WASHINGTON POPULATIONS OF COASTAL DOUGLAS-FIR (PSEUDOTSUGA-MENZIESII VAR MENZIESII (MIRB) FRANCO)

In order to assess the genetics of fall cold hardiness in coastal Doug las-fir (Pseudotsuga menziesii var. menziesii (Mirb.) France), shoot c uttings were collected in October from saplings (9-year-old trees) of open-pollinated families in two progeny tests in each of two breeding zones in Washington, one in the Coast range (80 families) and one on t he west slope of the Cascade Mountains (89 families). Samples from ove r 5500 trees were subjected to artificial freezing and visually evalua ted for needle, stem and bud tissue injury. The extent to which cold i njury is genetically related to tree height and shoot phenology (timin g of bud burst and bud set) was also evaluated. Significant family var iation was found for all cold hardiness traits; however, individual he ritability estimates were relatively low (ranging from 0.09 to 0.22). Significant family-by-test site interaction was detected for needle in jury in the Cascade breeding zone, but not in the coastal zone. Geneti c correlations (r(A)) among needle, stem and bud tissues for cold dama ge were weak (0.16 less than or equal to r(A) less than or equal to 0. 58) indicating that genes controlling fall hardening are somewhat diff erent for different tissues. Timing of bud burst and bud set were only weakly correlated with cold injury (r(A) less than or equal to 0.49). Thus, bud phenology is a poor predictor of fall cold hardiness in thi s species. There was no consistent relationship between tree height an d cold injury in the coastal zone. In the Cascade zone, taller trees a ppeared to be more susceptible to cold injury, but the association was weak (mean r(A) = 0.38, range 0.20-0.72).