Clarateta Sudafrica

CREASING STUDIES IN CITRUS

BY
ZANELE PENELOPE PHIRI

Dissertation presented for the degree of Master of Science in Agriculture at Stellenbosch University

Supervisor:

Dr. J.S. Verreynne
Citrus Research International
Dept. of Horticultural Science

Co-supervisor:

Dr. P.J.R. Cronjé
Citrus Research International
Dept. of Horticultural Science

March 2010

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DECLARATIONBy submitting this dissertation electronically, I declare that the entirety of the work contained therein
is my own, original work, that I am the owner of the copyright thereof (unless to the extent explicitly
otherwise stated) and that I have not previously in its entirety or in part submitted it for obtaining any
qualification.

Date : . . . . . . . . . . . . . . . . . .

Copyright © 2010Stellenbosch University
All rights reserved

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ABSTRACT
Creasing, also known as albedo breakdown, is a preharvest disorder that affects the albedo of
citrus fruit causing creases on the surface of the fruit. It is a recurrent problem in Navel and
Valencia oranges and can cause individual orchard losses which often exceed 50%. Although the
contributing factors are known, thephysiological basis of creasing development is unresolved and
the current control measures do not prevent creasing satisfactory. Hence, better control measures
and further understanding of the physiology of creasing development is required.

The objective of this two-year study was to determine if the position of fruit in a tree, light and
carbohydrate manipulation techniques, and albedo mineralnutrients influence creasing
development. Furthermore, the most effective application timing of gibberellic acid (GA3) with
the least negative effect on fruit rind colour development and the effectiveness of cytokinins,
other products and different root biostimulants to reduce creasing incidence were evaluated.

The position of fruit in the tree and light influenced the development of creasing andthe
distribution of mineral nutrients in the albedo. Creasing incidence was higher on the south side
than on the north side of the tree and fruit from the inside sub-sectors had a greater creasing
incidence compared to fruit from the outside sub-sectors. The shady part of outside fruit was
more creased compared to the sunny part of the fruit and covering fruit with brown paper bags
increasedcreasing severity. The light manipulation techniques used on the leaves and fruit
increased the nitrogen (N), phosphorus (P), potassium (K) and manganese (Mn) concentrations in
the albedo and differences in the albedo mineral nutrients amongst the sub-sectors evaluated were
observed, but creasing severity or creasing incidence was not significantly correlated with the
albedo mineralconcentrations at harvest. Albedo mineral concentrations earlier in the season may
play a role in creasing development, as creasing severity was significantly correlated with copper

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(Cu), K, and Mn concentrations in the albedo during stage II of fruit development. Creasing
incidence and albedo mineral concentrations were not affected by any of the carbohydrate
manipulation techniques used inthis study.

The incidence and severity of creasing was significantly reduced, with a minor negative effect on
fruit rind colour development, by the application of GA3, from mid November to mid January.
Localised fruit application of CPPU [N-(2-chloro-4-pyridyl)-N-phenylurea], MaxCel (6Benzyladenine) and CPPU in combination with calcium after physiological fruit drop reduced the
incidence andseverity of creasing, although creasing incidence was not significantly different
from the control. The application of Messenger®, AVG (aminoethoxyvinylglycine) and different
root biostimulants did not reduce creasing incidence. The results showed that cytokinins could
reduce creasing incidence and justify further studies on application and uptake efficiency. The
use of different root...