Physiological and biochemical leaf and tree responses to crop load in apple.
Seven-year-old apple (Malus x 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.
Wünsche
Jens N
JN
HortResearch, Hawke's Bay Research Centre, Private Bag 1401, Havelock North, New Zealand.
Greer
Dennis H
DH
Laing
William A
WA
Palmer
John W
JW
D050260:Carbohydrate Metabolism / Q000502:physiology; D002734:Chlorophyll / Q000378:metabolism; D005638:Fruit / Q000378:metabolism / Q000502:physiology*; D027845:Malus / Q000378:metabolism / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology*; D012621:Seasons; D014197:Trees / Q000378:metabolism / Q000502:physiology*
D002734:Chlorophyll