© 2005 Heron Publishing—Victoria, Canada
Root-zone temperatures affect phenology of bud break, flower cluster development, shoot extension growth and gas exchange
of ‘Braeburn’ (Malus domestica) apple trees
Dennis H. Greer (1, 2), Jens N. Wünsche (3), Cara L. Norling (4) and Harry N. Wiggins (4)
1. School of Wine and Food Sciences, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia / 2. Corresponding author (dgreer@csu.edu.au) / 3. HortResearch, Private Bag 1401, Havelock North, New Zealand / 4. HortResearch, Private Bag 11-030 Palmerston North, New Zealand / Received January 4, 2005; accepted May 9, 2005; published online October 3, 2005
Summary
We investigated the effects of root-zone temperature on bud break, flowering, shoot growth and gas exchange of potted mature
apple (Malus domestica (Borkh.)) trees with undisturbed roots. Soil respiration was also determined. Potted ‘Braeburn’ apple trees on M.9 rootstock
were grown for 70 days in a constant day/night temperature regime (25/18 °C) and one of three constant root-zone temperatures
(7, 15 and 25 °C). Both the proportion and timing of bud break were significantly enhanced as root-zone temperature increased.
Rate of floral cluster opening was also markedly increased with increasing root-zone temperature. Shoot length increased but
shoot girth growth declined as root-zone temperatures increased. Soil respiration and leaf photosynthesis generally increased
as root-zone temperatures increased. Results indicate that apple trees growing in regions where root zone temperatures are
≤ 15 °C have delayed bud break and up to 20% fewer clusters than apple trees exposed to root zone temperatures of ≥ 15 °C.
The effect of root-zone temperature on shoot performance may be mediated through the mobilization of root reserves, although
the role of phytohormones cannot be discounted. Variation in leaf photosynthesis across the temperature treatments was inadequately
explained by stomatal conductance. Given that root growth increases with increasing temperature, changes in sink activity
induced by the root-zone temperature treatments provide a possible explanation for the non-stomatal effect on photosynthesis.
Irrespective of underlying mechanisms, root-zone temperatures influence bud break and flowering in apple trees.
Keywords:
flowering, photosynthesis, root respiration, shoot growth.
