© 1986 Heron Publishing—Victoria, Canada
Physiological, environmental and genetic variation in apical dominance as determined by decapitation in Triplochiton scleroxylon
R. R. B. Leakey and K. A. Longman
Institute of Terrestrial Ecology, Bush Estate, Penicuik, Midlothian EH26 OQB, UK / Received April 14, 1986
Summary
Patterns of lateral shoot growth following decapitation in 1-meter tall, rooted Triplochiton scleroxylon K. Schum. cuttings varied with clone and in response to a range of environmental conditions and growth regulator treatments.
Two phases of bud activity were identified, the Sprouting Phase, in which many buds were released from correlative inhibition,
and the Dominance Phase (starting 3–4 weeks after decapitation) in which uppermost laterals began to dominate and suppress
growth, and sometimes cause apical abscission of lower lateral shoots. Except in non-erect plants, the most distal lateral
to elongate became the new leading shoot. During the Sprouting Phase, the proportion of active buds was increased by removing
leaves from the upper part of the stem, and by reducing the photoperiod from 13–15 h to 11 h, particularly at 20 °C rather
than 25 °C. Conversely, the proportion of sprouting buds was decreased by injecting plant stems with NAA (250 μg/plant). During
the Dominance Phase, suppression of lateral shoot growth was hastened by stem injection with GA3 (200 μg/plant), especially when applied to the uppermost shoot at the end of the Sprouting Phase. Reimposition of dominance
was delayed, however, by (1) high rates of N:P:K fertilization, (2) low temperature (20 versus 25 °C) under relatively long
days (13 and 15 h), (3) low photon flux density (160 μmol m–2 s–1) and (4) severe defoliation.
Plant orientation had no effect on bud activity of decapitated plants, but affected the relative vigor and orientation of
new lateral shoots. High temperature (25 versus 20 °C) and injection with GA3 increased the erectness of newly developing lateral shoots.
