Genetic variation and phenotypic stability among three elevational sources of coastal Douglas-fir from southwest Oregon

Graduation date: 1988This study had three objectives: (1) to determine the degree to which within-source genetic variation and genetic correlations differ among elevational sources of Douglas-fir [Pseudotsuga menziesii (Mirb). Franco var. menziesii]; (2) to ascertain the degree to which phenotypic stability differs among and within elevational sources; and (3) to compare the relationships among four measures of stability (variance, regression slope coefficient, deviation from regression and ecovalence). To accomplish the objectives seeds were collected from 10 parent trees in three populations from each of three elevations. Nine traits were measured on two-year-old seedlings grown in four test environments that factorially combined heated and unheated air and soil. Results support the hypothesis that the magnitude of within-source genetic variation is homogeneous among elevations. However1 genetic correlations between growth and phenological traits varied by elevation. For example, increased height was positively and moderately correlated with late budset at the middle elevation, while in trees from low and high elevations, there was no correlation between height and budset. Because of the increased possibility of early summer drought and early fall frosts at the low and high elevations, respectively, cessation of the growing season may be under stronger selective pressure at these elevations, compared with the middle elevation. Middle elevation trees may be able to grow later in the growing season, resulting in a positive correlation between budset and height. For a majority of the traits in which mean phenotypic stability varied significantly by elevation, there was a trend towards highest stability of middle elevation families, and lowest stability of low elevation families. There were few cases of significant variation among families within elevation for three out of four stability measures. Nevertheless, in eight of nine of the seedling traits measured ecovalence varied significantly among families in at least one elevation. Thus. it may be possible to breed for ecovalence and develop broadly adapted genotypes. However, future experiments will need to include large numbers of test environments and genotypes in order to obtain precise estimates of stability measures. The only consistently strong and positive phenotypic correlation between the four stability measures was between ecovalence and deviation from regression