Population-dependent selection strategies needed for 2-year-old black cottonwood clones
Riemenschneider, D.E. | McMahon, B.G. | Ostry, M.E.
We conducted a study to determine whether genotypic and phenotypic covariances among important traits differed between collections of black cottonwood (Populus trichocarpa Torr. & Gray) from British Columbia and northern Idaho. We also determined how differences in estimated covariances could affect various multiple-trait clonal selection strategies. The experimental design consisted of 166 clones from British Columbia and northern Idaho intermixed at random in two replications of three-tree row plots. Measurements made during the second growing season included tree height, frequency and number of sylleptic branches, number of leaves, and the lengths and areas of leaf plastochron index 5, 10, and 15 leaves at the end of the growing season. The severity and extent of Melampsora leaf rust and Septoria leaf spot were also evaluated. We found high heritability for tree height, phenology, leaf morphology, and resistance to damaging agents. However, no advantage to using leaf morphology to improve genetic selection for tree height was demonstrable. Restricted selection indices had high potential utility for controlling increases in damaging agents. However, the relation between tree height and leaf diseases varied between the British Columbia and northern Idaho collections of black cottonwood, and between black cottonwood and an adjacent experimental population of balsam poplar (Populus balsamifera L.). Such population-related variation in intertrait covariances suggests that selection strategies involving disease resistance may need to be evaluated on an individual population basis.
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