Genetic Variation of Stem Forking in Loblolly Pine
Forking defects were studied in loblolly pine (Pinus taeda L.) in 6-year-old genetic tests from the second cycle of breeding in the North Carolina State University Cooperative Tree Improvement Program. Data were available from 268 test series (each with two 6-parent half-diallel mating designs, with 12 parents, 30 crosses, and 144 progeny per cross) over six geographic regions. A subset of 123 series with average forking between 20 and 80% was used for genetic analysis. Forking differed significantly among regions, with the highest in the Upper Gulf Coastal Plain (24%) and the lowest in the Georgia‐Florida Coastal Plain (12%). The individual-tree heritabilities were low (0.06), but the half-sib (0.76), narrow-sense full-sib (0.59), and broad-sense full-sib (0.71) family-mean heritabilities were moderately high. This result suggests that forking is partially under genetic control at the family level, but at the individual tree level, it is mostly determined by the environment. Genetic gain was estimated for half-sib family selection with a selection differential of 20%. Gain ranged from 12 to 23% reduction in forking across different regions. A weak unfavorable genetic correlation (0.18) was found between forking and height, suggesting that selection for growth alone will negatively affect forking in loblolly pine. A favorable genetic correlation (0.33) was found between forking and straightness.
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Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
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