ISHS Acta Horticulturae 636: XXVI International Horticultural Congress: Key Processes in the Growth and Cropping of Deciduous Fruit and Nut Trees
EFFECT OF KAOLIN APPLICATIONS ON APPLE FRUIT QUALITY AND GAS EXCHANGE OF APPLE LEAVES |
| Authors: | M. le Grange, S.J.E. Wand, K.I. Theron |
| Keywords: | carbon assimilation, Malus domestica Borkh., particle film technology, PPFD, sunburn |
| Abstract:
Sunburn is a major problem in the apple industry in South Africa, with damage amounting to as much as 50% of the crop culled in the orchard. During the 1998/99 growing season M-97-009 (100% kaolin) was evaluated for its efficacy to control sunburn on ‘Royal Gala’, ‘Fuji’ and ‘Granny Smith’ apples. It reduced sunburn on all three cultivars, although not significantly on ‘Granny Smith’. During the 1999/00 growing season Surroundä WP (95% kaolin) was applied to ‘Cripps’ Pink’ apple trees in the Western Cape and no significant reduction in sunburn was observed. The effect of these foliar applications on canopy light conditions, net CO2-assimilation rate (A), leaf photosynthetic response to varying light levels, stomatal conductance and transpiration rate in ‘Cripps’ Pink’ trees was also determined. The particle film significantly reduced A in the inner canopy under both moderate and high leaf-to-air vapour pressure deficit (VPD) but reduced A in the outer canopy only under moderate VPD when stomatal conductance was high. Apparent quantum yield of leaves on the outer canopy of treated trees was reduced, possibly indicating that coated leaves reflect more light, and thus have less light available for photosynthesis than uncoated leaves under the same external light intensity. | |
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