Predicted genetic gains and testing efficiency from two loblolly pine clonal trials

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Abstract
Clonal field trials were established at two sites using rooted cuttings from 450 clones of eight full-sib families of loblolly pine (Pinus taeda L.). Height, survival, fusiform rust infection (caused by Cronartium quercuum (Berk) Miyabe ex Shirai f.sp. fusiforme), bole straightness, and diameter were measured after four growing seasons. There were significant differences among full-sib families and among clones within families for all traits studied. Moderately high within-family repeatabilities of clone means (0.50 to 0.75) for growth traits and a very high within-family repeatability of clone means (0.94) for fusiform rust infection were estimated. When the best eight clones were selected regardless of family structure, the volume yield was 52% greater than that of the unimproved seedlings at two sites. Selection of the best two clones from each of four families produced only slightly lower estimated genetic gains than the above scenario. The probability of fusiform rust infection ranged from 0.08 to 0.93 among clones at the South Carolina site. Predicted genetic gain for rust resistance was relatively insensitive to selection intensity, as there were numerous clones with high apparent resistance. The number of ramets per clone necessary to reliably characterize performance on one site was estimated to be between four and six. These results contribute to estimates of the gains available from clonal forestry and will help guide clonal testing and selection programs. Implementation of clonal forestry and cost issues are discussed.