Apple Peel Biochemical Changes after Foliar Application of Combined Boron and Calcium I. Phenolics and Physico-Chemical Attributes
2020
Post-full bloom foliar applications of boron in
combination with calcium (B+Ca) suppress fruit sunburn-browning incidence in
apples (Malus domestica). However, the mode-of-action is not yet explained and
hence, protocols to exploit this seemingly cost-effective peel physiology
augmenting approach compared to usual methods (shade-netting, overhead cooling
and kaolin application which attenuate excess fruit heat-load), cannot be fully
developed or promoted justifiably among growers. Apple fruit sunburn-browning
disorders are rampant worldwide, partly because of climate change as well as
high cost and inefficacy of the established methods. However, knowledge of B+Ca
effect on apple peel physiology may unravel the mode-of-action, paving the way
for commercialization of this novel approach. In this study, B+Ca effect on
apple peel phenolics and selected fruit physico-chemical attributes was investigated,
using studies conducted at two farms for two seasons in Western Cape, South
Africa. Four foliar treatments varying in B, Ca and inclusion of zinc (Zn),
were applied on ‘Cripps Pink’, ‘Golden Delicious’ and ‘Granny Smith’ apples in 2014/15 (only ‘Cripps Pink’) and 2015/16 (all
cultivars) in randomized complete block design experiments with five
replications. Fruit peel samples for quantitative determination of total
phenolics and total flavonoids analyses were collected at different fruit
maturity stages. Significant (p ‘Golden Delicious’ and ‘Granny Smith’ only) and total flavonoids
(all cultivars). Physico-chemical attributes (fruit diameter, size and total
soluble solids) were only evaluated in ‘Golden Delicious’ and ‘Granny Smith’,
and no significant differences among treatments occurred. Since no clear
treatment differences in apple peel phenolic patterns were observed, other appropriate
biochemical aspects like photosynthetic pigments should be investigated among
such foliar B+Ca treatments.
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