Optimum selection age for height in shortleaf pine

Genetic and phenotypic correlations for height were estimated for shortleaf pine (Pinus echinata Mill.) in Missouri from a single progeny test comprising 44 half-sibling families assessed at 3, 5, 7, 10, 17 and 25 years of age. The age-age genetic correlations for height ranged from 0.68 to 0.99, and phenotypic correlations from 0.28 to 0.84. Age-age phenotypic correlations for height had a strong linear relationship with logarithm of age ratio (R-2 = 0.89) but age-age genetic correlations had a weak linear relationship with logarithm of age ratio (R-2 = 0.27). Early selection efficiency for height was examined using the ratio of gain per year between indirect early selection and direct selection at age 25. When flowering age was assumed to be 10 years, optimum selection age was predicted to be 10 using either the genetic or the phenotypic linear model. When flowering age was assumed to be 3 years, optimum selection age was predicted to be 3 and 8 years based on the genetic and phenotypic linear models, respectively. The phenotypic linear model underestimated genetic gain at all ages, particularly at young ages.