TIME TRENDS IN GENETIC-CONTROL OVER HEIGHT AND DIAMETER IN MARITIME PINE

Height and diameter of 257 twenty-year-old maritime pine (Pinus pinast er Ait.) trees, originating from a factorial mating design, were subdi vided in annual height increments (AHI) and annual diameter increments (ADI). Cumulative and annual data of both traits were compared using two different genetic models. The two traits exhibited very different genetic expressions. For cumulative data, the heritability increased s teadily with age for height and was very stable for diameter. For annu al data, this evolution did not reveal any particular trend for AHI bu t appeared much more stable for ADI. Different effects seemed to be in volved in the variation of annual increments: year and residual effect s were 5 and 2.5 times more important for AHI than for ADI, respective ly; in contrast, family and individual effects were 10 and 15 times mo re important for ADI than for AHI, respectively. Serial correlations c alculated at the full-sib family mean level also showed different patt erns: low values and rapid decrease of correlations for successive AHI , and high values and a linear decrease for successive ADI. As trees a ged, the genetic expression of height growth appeared to be more unsta ble than for diameter growth. Interpretations about these expressions and their consequences for early selection are discussed.