Changes in the pattern of genetic variability over time in American sycamore and the implication for early selection

Height, volume, and stem canker symptom data were collected at ales 3, 5, 7, 10, 13, and 15 years in three genetic tests of American sycamore (Platanus occidentalis L.) planted in Texas and Louisiana. Five provenances from Texas, Arkansas, and Louisiana were represented in the tests. Data were subjected to analysis of variance; heritabilities, coefficients of genetic prediction, and variance components were calculated. Provenance had no significant effect on height and volume; however, northern provenances tended to be more susceptible to stem canker. Significant family effects occurred for height and volume at all ages, and family heritabilities were moderate to high for all traits. Coefficients of genetic prediction between age 3 height and age 15 volume and canker rating were large and positive, suggesting that early selection to improve 15-year volume and canker resistance in sycamore would be possible. Over the course of this study, the additive variance for height and volume growth gradually increased. The variance attributed to the plantation X family interaction was generally small and nonsignificant. Changes in height and volume individual tree heritabilities overtime were due to changes in the magnitude of the between-plot and within-plot error terms and their impact on phenotypic variance. This appeared to be caused by differential timing and severity of stem canker infection in the tests.