<i>Populus</i><i>trichocarpa</i> × <i>Populus</i><i>deltoides</i> hybrids for short rotation culture: variation patterns and 4-year field performance

Abstract

Studies were conducted on the comparative growth and morphology of Populustrichocarpa (T), P. deltoides (D), F 1 hybrids (T×D), F 2 hybrids (TD × TD), and B 1 hybrids (T × TD, TD × T) at one nursery and two plantation sites in western Washington and Oregon. First coppice resprouts in the nursery showed intermediacy of the F 1 and F 2 between parentals in four of five morphological leaf traits measured, and intermediacy of B 1 values between F 1 and T in three. Amounts of variation generally conformed to the model of F 2 &gt; B 1 &gt; F 1 . The percent significant trait correlations were 11.6 for the F 1 , 8.7 for the B 1 , and zero for the F 2 . No simply inherited traits were identified. Growth in the first and successive coppices in the nursery was significantly greater in the F 1 than in the B 1 and F 2 generations. The same trend was observed in two field tests at Pack Forest, Washington and Westport, Oregon in which 691 and 381 clones from 60 and 42 families, respectively, gave a rank order in 4-year volume growth of F 1 &gt; B 1 &gt; T &gt; F 2 &gt; D. Several F 1 families and clones showed high rank consistency between years and locations. The results confirm earlier studies and are discussed in relation to the mechanisms that underlie T × D hybrid superiority.