Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2010. / ENGLISH 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, the physiological 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 mineral nutrients 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 and the
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
increased creasing 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 mineral concentrations at harvest. Albedo mineral concentrations earlier in the season may
play a role in creasing development, as creasing severity was significantly correlated with copper (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 in this 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 (6-
Benzyladenine) and CPPU in combination with calcium after physiological fruit drop reduced the
incidence and severity 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 biostimulants are not recommended, but it is suggested that treatment effects
may be more pronounced over a longer period. / AFRIKAANSE OPSOMMING: Kraakskil is ‘n vooroes abnormalitiet wat die albedo van sitrusvrugte affekteer, deur krake op die
oppervlak van vrugte te veroorsaak. Dit is ‘n algemene probleem in Navel en Valencia lemoene
en kan boordverliese van tot 50% of soms hoër veroorsaak. Alhoewel die bydraende faktore
bekend is, is die fisiologiese basis van kraakskil ontwikkeling onopgelos en die beskikbare
beheermaatreëls is nie bevredigend nie. Dus, beter beheermaatreëls en ‘n beter begrip van die
fisiologie van kraakskil ontwikkeling is nodig.
Die doel van die twee-jaar studie was om te bepaal of die posisie van vrugte in ‘n boom, lig en
koolhidraat manipulasie tegnieke en minerale elemente in die albedo, kraakskil ontwikkeling
beïnvloed. Die mees effektiewe toedieningstyd van gibberelliensuur (GA3) sonder ‘n negatiewe
effek op vrugkleur is bepaal en die effektiwiteit van sitokiniene, ander produkte en verskillende
wortel biostimulante om kraakskil voorkoms te verminder, is geëvalueer.
Die posisie van vrugte in ‘n boom en lig het kraakskil ontwikkeling en die verspreiding van
minerale element in die albedo beïnvloed. Kraakskil voorkoms was hoër aan die suidekant van
die boom as aan die noordekant en vrugte in die binnekant van die boom het ‘n groter kraakskil
voorkoms as vrugte in die buitekant van die boom gehad. Die skadukant van buitevrugte het meer
kraakskil gehad as die sonkant en die toemaak van vrugte met ‘n bruin papiersak het die graad
van kraaksil verhoog. Die lig manipulasie tegnieke wat op die blare en vrugte gebruik is, het die
stikstof (N), fosfaat (P), kalium (K) en mangaan (Mn) konsentasies in die albedo verhoog en
verskille in die albedo minerale elemente tussen sub-sektore is waargeneem, maar betekenisvolle
korrelasies is nie tussen die graad en voorkoms van kraakskil en die albedo minerale element
konsentrasies by oestyd waargeneem nie. Albedo minerale element konsentrasies vroeër in die
seisoen mag ‘n rol speel by kraakskil ontwikkeling, omdat die graad van kraakskil betekenisvol gekorreleer was met albedo koper (Cu), K, en Mn konsentrasies tydens fase II van
vrugontwikkeling. Kraakskil voorkoms en albedo minerale element konsentrasies is nie deur
enige van die koolhidraat manipulasie tegnieke geaffekteer nie.
Die voorkoms en graad van kraakskil is betekenisvol verlaag, met ‘n geringe negatiewe effek op
vrugkleur, deur die toediening van GA3 vanaf mid November tot mid Januarie. Gelokaliseerde
vrugtoedienings van CPPU [N-(2-chloro-4-piridiel)-N-phenielureum], MaxCel (6-
Bensieladenien) en CPPU saam met kalsium na fisiologiese vrugval het die voorkoms en graad
van kraakskil verlaag, alhoewel kraakskil voorkoms nie betekenisvol van die kontrole verskil het
nie. Die toediening van Messenger®, AVG (amino etoksievinielglisien) en veskillende wortel
biostimulante het nie kraakskil voorkoms verlaag nie. Die resultate het getoon dat sitokiniene
kraakskil voorkoms kan verlaag en verdere studies op die toediening en opname effektiwiteit
word aanbeveel. Die gebruik van verskillende wortel biostimulante word nie aanbeveel nie, maar
die effek behoort meer sigbaar te wees na ‘n langer periode van behandeling.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4219 |
| Date | 03 1900 |
| Creators | Phiri, Zanele Penelope |
| Contributors | Verreynne, J. S., Cronje, P. J. R., University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 116 p. : ill. |
| Rights | University of Stellenbosch |
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