Early expression of apical control regulates length and crotch angle of sylleptic shoots in peach and nectarine

Syllepsis is the predominant mode of branching in young peach and nectarine trees [Prunus persica (L.) Batsch]. Cultivars differ considerably in expre ssion of apical control of sylleptic shoots. This has practical implication s regarding tree training. Four cultivars were selected for increasing apic al control by the central shoot axis, viz., 'Zaigina', 'Mayglo', 'Fiesta Re d' (all nectarines), and 'Oom Sarel' (clingstone peach), respectively. Youn g, actively growing shoots mere harvested when approximate to 300 mm in len gth, at a time when development of sylleptic shoots (laterals) had begun. L ength, crotch angle, and position (as distance from the apex) of the latera ls were recorded. When length of the laterals was plotted against their pos ition, two zones were observed. The gradient of length vs. position was sha llower in the distal than in the proximal zone. Autonomy in lateral shoots can be described as their ability to grow independently of apical control b y the apex of the branch. Autonomy of laterals near the branch apex increas ed with their length. In 'Zaigina' this was established via a more distal s tart of the second zone, and in 'Mayglo' via an increased gradient in the s econd zone. The early loss or maintenance of apical control regulates archi tecture in sylleptically branched peach and nectarine shoots. Crotch angle widening of laterals appears to be largely dependent on position, but in so me cultivars, such as 'Mayglo', other factors are also involved. The data p rovide evidence of correlative phenomena between actively growing shoots.