GROWTH AND PHENOLOGY OF 1-YEAR-OLD MARITIME PINE (PINUS-PINASTER) SEEDLINGS UNDER CONTINUOUS LIGHT - IMPLICATIONS FOR EARLY SELECTION

Experiments were conducted in the Stockholm Phytotron to test continuo us light as a method to hasten the development of seedlings. Two sets of maritime pine (Pinus pinaster Ait.) families were grown under growt h-accelerating conditions in a controlled environment. The first set c omprised 18 open-pollinated families that were exposed to continuous l ight and 16-h photoperiod during the first growth period. The second s et comprised nine half-sib families that were exposed to two continuou s light treatments differing in their temperature regimes. In both cas es seedlings were exposed to a 16-h photoperiod during the second grow th period. All families were chosen according to their breeding values for height growth and polycyclism estimated in the oldest progeny tes ts of the maritime pine program. In both experiments, traits were foun d that correctly ranked the families for either growth or polycyclism during the second growth period. During the first growth period, bette r results were obtained under the most growth accelerating treatments. Yet, in the second experiment, consistency between phytotron and fiel d rankings was already achieved for both treatments in the first growt h period. It is suggested that more attention should be paid to the se edling development over the first years and that future retrospective tests should be conducted in a similar way in order to end controversi es.