| Summary: | Thesis (MScAgric)--Stellenbosch University, 2013. === ENGLISH ABSTRACT: Fruit size and the integrity of the rind are key components that determine the value of a citrus
fruit. The application of 2,4-dichlorophenoxy acetic acid (2,4-D) to reduce splitting, a
physiological disorder which entails cracking of the rind as well as to increase fruit size was
conducted on three different split-susceptible mandarin and two split-susceptible orange
cultivars. Treatments were applied directly after the physiological fruit drop period, as well as
in January and February at 10 mg·L-1, alone or in combination with calcium (Ca), potassium
(K) or gibberellic acid (GA3). Application of 2,4-D directly after physiological fruit drop,
either alone or in a tank-mix with K, consistently reduced the number of split mandarin fruit,
with later applications in January and February generally being ineffective. Post
physiological fruit drop application of 10 mg·L-1 2,4-D significantly increased growth rate
(mm.day-1) of all the mandarin cultivars, resulting in increased fruit size. Differences in
sensitivity of cultivars to 2,4-D were evident, with the January application reducing the
splitting in ‘Midknight’ Valencia. However, all the 2,4-D treatments reduced the fruit growth
rate of the orange cultivars. The 2,4-D treatments, in terms of splitting, increased rind
thickness, -strength and -coarseness of ‘Marisol’ Clementine, throughout fruit development.
In addition fruit diameter and –length increased to such an extent that the fruit shape was
altered (reduced d/l-ratio), reducing the potential of the rind to crack and the fruit to split,
however rind coarseness of treated fruit was also increased. There were no major negative
side effects on internal and external fruit quality, except for a possible reduction in juice
content (%). Therefore, 10 mg·L-1 2,4-D can be applied directly after physiological fruit drop
on ‘Marisol’ Clementine and ‘Mor’ mandarin to reduce fruit splitting. === AFRIKAANSE OPSOMMING: Vruggrootte asook die integriteit van die skil is belangrike aspekte in die bepaling van ʼn
sitrusvrug se waarde. Die toediening van 2,4-dichlorofenoksie asynsuur (2,4-D) om vrugsplit,
'n fisiologiese defek wat tot die kraak van die sitrusskil lei, te verminder is getoets op drie
mandaryn- en twee lemoenkultivars. Hiermee saam is die potensiaal van 2,4-D om
vruggrootte te verbeter ook geëvalueer. Die 2,4-D behandelings is direk na die fisiologiese
vrugval periode toegedien, asook in Januarie en Februarie, teen 10 mg·L-1, alleen of in
kombinasie met kalsium (Ca), kalium (K) of gibberelliensuur (GS3). Al die
mandarynkultivars het ʼn vermindering in die totale aantal gesplete vrugte getoon indien die
2,4-D (enkel of in kombinasie met K) toegedien was direk na fisiologiese vrugval.
Suksesvolle behandelings het ook 'n toename in vruggrootte tot gevolg gehad. Toediening
van behandelings in Januarie en Februarie was oor die algemeen oneffektief. Verskille in
kultivar sensitiwiteit teenoor 2,4-D is gevind, met vrugsplit in ‘Midknight’ Valencia wat
verminder was deur die Januarie toediening van 2,4-D. Al die 2,4-D behandelings het
vruggrootte van die lemoenkultivars verlaag. Daar is bevind dat die 10 mg.L-1 2,4-D, enkel of
in kombinasie met K, ‘n toename in beide skildikte en –sterkte van ‘Marisol’ Clementine
teweeg bring asook ʼn growwer skil. Behandelings met 2,4-D het vrugdeursnee en –lengte laat
toeneem, wat ʼn verandering in vrugvorm tot gevolg gehad het, tot so ʼn mate dat vrugte
minder geneig was om gesplete te wees. Behalwe vir ʼn moontlike verlaging in die sapinhoud
(%) van vrugte, was daar geen noemenswaardige negatiewe effekte op interne en eksterne
vrugkwaliteit nie. Die toediening van 10 mg.L-1 2,4-D direk na fisiologiese vrugval kan dus
aanbeveel word op mandaryn kultivars wat geneig is tot vrugsplit. === The Citrus Academy
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