Phase change in loblolly pine:Shoot development as a function of age

The growth behavior of grafted scions from 1‐, 4‐, 8‐ and 12‐year‐old ortets representing five half‐sib loblolly pine families was observed over a two‐year period (three for strobilus production) following grafting. Significant, persistent decreases in total number of cycles produced, height and diameter increment, number of branches produced, foliar surface area and total scion biomass were observed with increasing age. Needle length, diameter, and ability to form male and female strobili increased with increasing scion age. The persistence of these differences is not a function of size since the scions were the same length at grafting. The significance of these results to the establishment of breeding orchards, early genetic evaluation, and the nature of phase change is discussed.