GENETIC-VARIATION AND PRODUCTIVITY OF POPULUS-TRICHOCARPA AND ITS HYBRIDS .9. PHENOLOGY AND MELAMPSORA RUST INCIDENCE OF NATIVE BLACK COTTONWOOD CLONES FROM 4 RIVER VALLEYS IN WASHINGTON

A common-garden study of Populus trichocarpa Torr. and Gray was initia ted in 1985 when material from 128 trees was collected along two mesic (Hoh and Nisqually) and two xeric (Dungeness and Yakima) river valley s. In spring 1986 cuttings were used to establish two replicate planta tions, at Puyallup and at Wenatchee, WA. For 2 years trees were assess ed for timing of spring flush, autumn budset and leaf fall, and incide nce of Melampsora occidentalis leaf rust. Seasonal patterns varied wit h trait, plantation, year, and origin of clones. Significant differenc es were found mainly between clones from the lower and upper elevation s of the Nisqually (LN, UN) and Yakima (LY, UY). At both plantations, clones from the cooler UN flushed later than those from the LN. In con trast, cool canyon climates of some sites along the LY resulted in lat er spring flush of lower than upper clones. Factors affecting patterns of autumn phenology differed between trees from those river valleys. Later budset in LN vs. UN trees was again related to cold affecting th e growing season length, but earlier budset and leaf fall in LY than U Y clones at Puyallup was brought about by higher rust infection. The g reater rust susceptibility of LY material likely reflects lower rust p ressure in the more arid lower Yakima valley, Soil moisture deficit an d the presence/absence of rust at the plantations also contributed to autumn phenology patterns. Genetic variances were large for all traits at Puyallup. In Yakima trees, the large group component of the geneti c variance (elevational group, clone) in leaf fall and rust points to a steep selection gradient along the Yakima. A similarly steep gradien t seems also to influence spring flush along the Nisqually. Heritabili ties indicate moderately to very strong genetic control in these trait s. The patterns of genetic variation have implications for short-rotat ion intensive-culture forestry and management of natural populations.