© 2005 Heron Publishing—Victoria, Canada
Physiological and biochemical leaf and tree responses to crop load in apple
Jens N. Wünsche (1, 2, 3), Dennis H. Greer (4), William A. Laing (5) and John W. Palmer (6)
1. HortResearch, Hawke’s Bay Research Centre, Private Bag 1401, Havelock North, New Zealand / 2. University of Hohenheim, Department of Special Crop Cultivation and Crop Physiology, 70599 Stuttgart, Germany / 3. Corresponding author (jnwuensche@uni-hohenheim.de) / 4. School of Wine and Food Science, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia / 5. HortResearch, Mt. Albert Research Centre, Private Bag 92 169, Auckland, New Zealand / 6. HortResearch, Nelson Research Centre, P.O. Box 220, Motueka, New Zealand / Received July 30, 2004; accepted January 28, 2005; published online August 1, 2005
Summary
Seven-year-old apple (Malus × domestica Borkh.) trees cv. ‘Braeburn’ on rootstock M.26 were flower-thinned to establish four crop loads, resulting in final mean
fruit numbers per tree of 0, 100, 225 and 400. Mean fruit mass decreased by about 35% with each decrease in cropping density.
Fruit from light-cropping trees had significantly advanced maturity as indicated by the harvest management criteria of background
color and starch/iodine score, and other fruit quality characteristics such as soluble solids. Flesh firmness and dry matter
also increased with decreasing crop load. Compared with fruiting trees, mean leaf photosynthetic rates of non-cropping trees
were significantly lower (40%) between 75 days after full bloom (dafb) and fruit harvest, with a maximum reduction of almost
60% at 118 dafb. Photosynthetic activity decreased linearly with increasing concentration of leaf starch, but was positively
and significantly related to stomatal conductance. Consequently, the accumulation of nonstructural carbohydrates in leaves
of light-cropping or non-cropping trees may have led to end-product inhibition of photosynthesis. Increases in xanthophyll
cycle carotenoids mediated non-radiative thermal energy dissipation in non-cropping trees, providing increased capacity for
photoprotection but reducing photochemical efficiency.
Keywords:
chlorophyll fluorescence, fruit quality, leaf carbohydrates, leaf photosynthesis, leaf pigments.
