© 1997 Heron Publishing—Victoria, Canada
Effect of crop load on fruiting and leaf photosynthesis of 'Braeburn'/M.26 apple trees
John W. Palmer (1), Rita Giuliani (2) and Heather M. Adams (1)
1. HortResearch, Nelson Research Centre, P.O. Box 220, Motueka, New Zealand / 2. Dipartimento Colture Arboree, Universita’ di Bologna, Italy / Received August 9, 1996
Summary
Four-year-old apple (Malus × domestica Borkh.) trees cv. ‘Braeburn’ on M.26 rootstock were thinned at full bloom to establish six crop loads ranging from a heavy
crop to a deflowered treatment. At harvest, mean yield per tree varied from 0 to 38 kg and mean fruit weight ranged from 225
g in the heaviest cropping treatment to 385 g in the lightest cropping treatment. Light cropping resulted in a significant
advance in fruit maturity as indicated by background color, starch/iodine score and soluble solids. There were small differences
in leaf photosynthetic rate among the treatments when shoot growth was active. However, in early January, coincident with
cessation of shoot growth and maximum rate of accumulation of fruit weight, leaf assimilation rate was reduced by as much
as 65% on the deflowered trees compared to the trees carrying the heaviest crop. Leaf assimilation rate showed a curvilinear
response to crop load at this time, with little increase in leaf assimilation when crop load exceeded 12 fruit m–2 leaf area.
Keywords:
assimilation rate, fruit maturity, fruit quality, Malus × domestica, yield.
