Genetic variation in mountain hemlock (Tsuga mertensiana Bong.): quantitative and adaptive attributes

Patterns of genetic variation for adaptive and quantitative attributes in m ountain hemlock (Tsuga mertensiana (Bong.)) seedlings from British Columbia were examined at the population (provenance) and family levels. The popula tion and family levels were represented by 12 provenances and 10 families f rom a single location, respectively. The adaptive attributes were related t o gas exchange (net photosynthesis, transpiration rate, intercellular-to-am bient CO2 concentration ratio, mesophyll conductance, stomatal conductance, and photosynthetic water use efficiency) and the quantitative traits were related to biomass allocation (height, root collar diameter, root dry weigh t, shoot dry weight and harvest index). Univariate and multivariate analyse s of the studied attributes indicated the presence of significant differenc es at both, the population and family levels. Although the populations diff ered significantly in all studied traits, a relatively small portion (5-15% ) of the total variation was attributed to among populations. On account of the observed large intra-population variation, no trends between the studi ed traits and geography were detected when data from individual seedlings w ere used; however, significant trends were detected on population means for the majority of gas-exchange attributes. Population-level analyses indicat ed lack of appreciable relationship between the quantitative and adaptive a ttributes. Intra-population analyses produced high narrow-sense heritabilit ies for the majority of the attributes studied. The observed high intra-pop ulation variation that is accompanied with high genetic control over the st udied attributes present an opportunity for genetic improvement. On the oth er hand, the observed significant differences among populations represent a challenge for gene conservation efforts as well as to the methods deployed to exploit these variations. (C) 1999 Elsevier Science B.V. All rights res erved.