title: Post-pruning shoot growth increases fruit abscission and reduces stem carbohydrates and yield in macadamia.
abstract: OBJECTIVE
  There is good evidence for deciduous trees that competition for carbohydrates from shoot growth accentuates early fruit abscission and reduces yield but the effect for evergreen trees is not well defined. Here, whole-tree tip-pruning at anthesis is used to examine the effect of post-pruning shoot development on fruit abscission in the evergreen subtropical tree macadamia (Macadamia integrifolia, M. integrifolia × tetraphylla). Partial-tree tip-pruning is also used to test the localization of the effect.
  
  
  METHODS
  In the first experiment (2005/2006), all branches on trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R treatment) and shoots were removed from others (NR treatment). Fruit set and stem total non-structural carbohydrates (TNSC) over time, and yield were measured. In the second experiment (2006/2007), upper branches of trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R) and shoots were removed from others (NR). Fruit set and yield were measured separately for upper (pruned) and lower (unpruned) branches.
  
  
  RESULTS
  In the first experiment, R trees set far fewer fruit and had lower yield than NR trees. TNSC fell and rose in all treatments but the decline in R trees occurred earlier than in NR trees and coincided with early shoot growth and the increase in fruit abscission relative to the other treatments. In the second experiment, fruit abscission on upper branches of R trees increased relative to the other treatments but there was little difference in fruit abscission between treatments on lower branches.
  
  
  CONCLUSIONS
  This study is the first to demonstrate an increase in fruit abscission in an evergreen tree in response to pruning. The effect appeared to be related to competition for carbohydrates between post-pruning shoot growth and fruit development and was local, with shoot growth on pruned branches having no effect on fruit abscission on unpruned branches.
authors.affiliation: Industry and Investment NSW, Centre for Tropical Horticulture, Alstonville, NSW 2477, Australia.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: McFadyen
authors.forename: David
authors.initials: D
authors.lastname: Robertson
authors.forename: Margaret
authors.initials: M
authors.lastname: Sedgley
authors.forename: Paul
authors.initials: P
authors.lastname: Kristiansen
authors.forename: Trevor
authors.initials: T
authors.lastname: Olesen
mesh_terms: D050260:Carbohydrate Metabolism; D005638:Fruit / Q000254:growth & development* / Q000378:metabolism; D039106:Macadamia / Q000254:growth & development* / Q000378:metabolism / Q000502:physiology; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D018547:Plant Stems / Q000378:metabolism; D012038:Regeneration