Genetic Variation in Response to Herbicide and Fertilization Treatments for Growth and Form Traits in Loblolly Pine

The effects of imposed silvicultural treatments and genetics on growth and form traits were investigated in a 15-year-old loblolly pine (Pinus taeda L.) trial in southwestern Georgia, USA. The trial consisted of four treatment combinations and 25 open-pollinated first- and second-generation families. Average individual-tree stem volume ranged from 185.2 dm(3) in the combined fertilization and herbicide plots to 91.2 dm(3) in the control plots. Variation among treatment combinations was significant for height, volume, sweep, and forking defect but was not significant for branch angle and fusiform rust disease incidence (caused by the fungus Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme). Family effects were significant for all traits across treatments. Individual-tree heritability values ranged from 0.10 (stem sweep) to 0.39 (branch angle). Corresponding family-mean heritability values had a range of 0.60 (stem sweep) to 0.90 (branch angle). Genetic correlations between growth (height and volume) and other traits (rust, branch angle, stem forking, and stem sweep) were low and not significant. The lack of important culture x genetics interactions in the study indicates a low risk of losing value due to suboptimal matching between genetic material and silvicultural prescriptions.