Fruit split and fruit size studies on Citrus

Stander, Ockert Petrus Jacobus (2013-03)

Thesis (MScAgric)--Stellenbosch University, 2013.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/79933
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