Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Effect of a feedback control by early secondary xylem formation on the outcome of competition between leafy shoots in apple (Malus x domestica Borkh.). | 209s Ann. Sci. For. 1989 46 suppl. 209s-212s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Effect of a feedback control by early secondary xylem formation on the outcome of competition between leafy shoots in apple Malus X domestica Borkh. A. Jebari and J. Crabbe Morphogenèse Végétale Appliquée Faculte des Sciences Agronomiques Gembloux Belgique Introduction From bud break onwards a developing shoot induces within its bearing stem a strand of secondary xylem which progressively expands basipetally along the stem and spreads tangentially around it. The rate of this process and the differentiated wood characteristics . frequency and width of vessels depend upon the rate of shoot elongation Jebari and Crabbe in preparation . The varying conducting capacity resulting from these early events affects the outcome of shoot competition and plays a part in the complex control of the apical dominance syndrome in woody plants. Materials and Methods On 1 yr old apple trees cv. MM 106 the unique axis was pruned at ca 60 cm high before bud burst and debudded except for the 2 uppermost buds designated as buds shoots 1 and 2 1 being the most distal and when stated bud 4 or 5 located on orthostichies next to bud 1 or 2 respectively. All shoots present were periodically measured. The degree of dominance between the 2 upper shoots is evaluated by the ratio of their lengths . Furthermore anatomical investigation was carried out in order to evaluate initiation and expansion of cambial activity new secondary xylem characteristics and their variations. The experiment was limited to the spring growth flush . from bud break to late June. Results On a pruned woody axis the outcome of competition between the 2 uppermost shoots is very uncertain. When a large population of plants is pruned as stated above a continuum is generally observed between 2 extreme habits strong dominance of shoot 1 on one side and forking due to subequal elongation of both shoots on the .
