Characterization of pinus pinaster seedling growth in different photo‐ and thermoperiods in a phytotron as a basis for early selection

Seedlings of Pinus pinaster families exhibiting monocyclic or polycyclic adult growth patterns, were cultivated in climate chambers during two successive growth periods separated by a period of low temperature to satisfy the chilling requirement. Six treatments combining photoperiod and temperature factors were tested. The morphology of the apex was assessed and height and biomass measured. First season seedlings grown in continuous light varied in apex morphology from the typical juvenile rosette to the adult bud usually found outdoors on 2‐yr‐old plants. It seems possible to distinguish monocyclic and polycyclic populations at an early stage by characters related to development and growth height. The results indicate that special environmental conditions during seedling development may be used as a tool in the search for criteria for early selection.