TITLE:
Apple Peel Biochemical Changes after Foliar Application of Combined Boron and Calcium II. Photosynthetic Pigments, Total Peroxides and Photochemical Efficiency
AUTHORS:
A. Mwije, E. W. Hoffman, E. Lötze
KEYWORDS:
Carotenoids, Chlorophyll, Total Peroxides, Malus domestica, ‘Cripps Pink’
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.6,
June
30,
2020
ABSTRACT: Understanding of the physiological effect of
post-full-bloom foliar boron combined with calcium (B+Ca) on apple (Malus domestica) peel tissues is envisaged to give way to the unknown
mode-of-action by which these mineral regimens suppress fruit sunburn-browning
incidence in orchards. Promotion of this mineral approach among growers, as a
certainly cheaper alternative to mitigate fruit sunburn-browning incidence in
apple orchards necessitates clear elucidation of its mode-of-action. This study
investigated peel photosynthetic pigments and total peroxides (as a measure of
oxidative stress) in three apple cultivars, ‘Cripps Pink’, ‘Golden
Delicious’ and ‘Granny Smith’ which were treated with
four B+Ca treatments varying in levels of B and Ca as well as inclusion of zinc
(Zn) in one treatment. Randomized complete block design experiments with five
replications were conducted at commercial farms in Western Cape, South Africa.
Significant (p 0.05) treatment effect for major pigment
aspects and total peroxides occurred in all cultivars, but with strong influence
of cultivar and fruit age. For instance, effect of varying B, Ca and possible B+Ca
duet-effect on photosynthetic pigments occurred in ‘Cripps Pink’, whereas the Zn-treatment was mainly responsible for significant
treatment effects in both ‘Golden
Delicious’ and ‘Granny Smith’ apples. Significant treatment
effect for total peroxides occurred in ‘Cripps Pink’ and ‘Granny
Smith’, yet
significant interaction effect occurred with ‘Golden Delicious’, however, these significant results did not yield
meaningful peel oxidative stress differences among the treatments. Foliar
treatment differences in photochemical efficiency (Fv/Fm) were not significant. The
study concludes with firm evidence that foliar B+Ca treatment composition has a significant effect on
apple peel photosynthetic pigments depending on cultivar, and Zn is not
desirable in the formulation of these treatments.