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Physiological and biochemical leaf and tree responses to crop load in apple
Jens N Wünsche1, Dennis H Greer, William A Laing
1HortResearch, Hawke's Bay Research Centre, Private Bag 1401, Havelock North, New Zealand.
Tree Physiology
|August 4, 2005
Summary
Flower thinning in apple trees impacts fruit quality and tree physiology. Lower crop loads improve fruit size and maturity, but reduce leaf photosynthesis due to carbohydrate accumulation.
Area of Science:
- Horticulture
- Plant Physiology
- Pomology
Background:
- Fruit crop load significantly influences individual fruit characteristics and overall tree performance.
- Understanding the physiological responses of apple trees to varying crop loads is crucial for optimizing fruit production and quality.
Purpose of the Study:
- To investigate the effects of different crop loads on fruit quality attributes in 'Braeburn' apple trees.
- To assess the impact of crop load on leaf photosynthetic rates and carbohydrate accumulation in apple trees.
Main Methods:
- Apple trees (Malus x domestica Borkh. cv. 'Braeburn') on M.26 rootstock were subjected to flower thinning to create four distinct crop loads (0, 100, 225, 400 fruits/tree).
- Fruit quality parameters including mass, maturity indicators (background color, starch/iodine score), soluble solids, flesh firmness, and dry matter were measured.
- Leaf photosynthetic rates, stomatal conductance, and nonstructural carbohydrate concentrations were monitored throughout the season.
Main Results:
- Fruit mass decreased significantly with increasing crop load.
- Fruit maturity, soluble solids, flesh firmness, and dry matter content were enhanced in trees with lower crop loads.
- Leaf photosynthetic rates were reduced in non-cropping and lightly cropping trees, correlating with increased leaf starch concentrations.
- Photosynthetic activity was positively related to stomatal conductance, suggesting end-product inhibition.
Conclusions:
- Flower thinning is an effective method to improve individual fruit quality and advance maturity in 'Braeburn' apples.
- Reduced photosynthetic efficiency in low-crop-load trees is linked to carbohydrate accumulation, potentially inhibiting photosynthesis.
- Altered photoprotective mechanisms, including xanthophyll cycle carotenoids, were observed in non-cropping trees, impacting photochemical efficiency.
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