TITLE:
Apple Peel Biochemical Changes after Foliar Application of Combined Boron and Calcium I. Phenolics and Physico-Chemical Attributes
AUTHORS:
A. Mwije, E. W. Hoffman, E. Lötze
KEYWORDS:
Flavonoids, Malus domestica, Sunburn
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.6,
June
30,
2020
ABSTRACT: 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 0.05) interaction (treatments and fruit
maturity stages) effect was observed for total phenolics (‘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.