Abstract
Cloned progeny tests in forest tree breeding provide the ability to assess the same genotypes across multiple environments and partition observed phenotypic variance into additive and non-additive genetic effects. In this study, 2362 clones from 53 crosses of loblolly pine (Pinus taeda L.) were tested across eight locations in the Southern US. Alpha cyclic incomplete row-column design was used to accommodate a large number of clones in a replication. Tree stem volume (cubic decimeter) was assessed at age 6 using various variance-covariance structures of mixed models. Models with factor analytic additive genetic structures and spatially correlated residuals or polynomial fixed row and column effects efficiently captured heterogeneity in the data. The narrow-sense clone mean heritability estimate for stem volume was 0.41 for the simple compound symmetry additive genetic structure. The estimates were higher for more complex models, ranging from 0.56 to 0.61. Non-additive genetic variance for stem volume was about a fraction of the additive genetic variance, suggesting that the trait is mainly controlled by large number of genes each with small effect. The results suggested that for forest trees genetic field tests with large number of genetic entries, breeders should consider incomplete row-column designs to model micro-site heterogeneity in two directions. These designs allow spatial modeling using row and column information, which can efficiently account for heterogeneity in the environment, resulting in higher heritability estimates and more reliable ranking of varieties for selection.
Published Version
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