Genetic Improvement of Sawtimber Potential in Loblolly Pine

Progeny from 48 elite parents of loblolly pine (Pinus taeda L.) were bred in a disconnected diallel mating design and were planted at four sites across the lower coastal plain of the southeastern United States. Height, dbh, volume, fusiform rust incidence (caused by the fungus Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme), stem forking, stem sweep, branch angle, branch diameter, branch frequency, and a sawtimber potential score were measured after six growing seasons. There were significant differences among families for all traits measured. Individual-tree narrow-sense heritability estimates ranged from 0.06 to 0.22 and half-sib family-mean heritability estimates ranged from 0.73 to 0.98. Height and volume were the traits most highly correlated with the sawtimber potential score of individual trees. From multiple regression, 79% of the variation in sawtimber potential breeding values can be attributed to variation in volume, rust incidence, stem sweep, and forking breeding values. The potential dollar value of loblolly pine was increased as much as 162% over local checks when both volume and sawtimber potential were used to select the 10 best parents from the population. Implementation of a selection index on currently measured traits is a promising opportunity to make gains in the proportion of sawtimber produced from improved germplasm of loblolly pine in the southeastern United States. FOR. SCI. 58(2):168-177.