Impact of shade netting on internal and external quality of ‘Nadorcott’ mandarin fruit

Botes, Johane (2018-12)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: In the export-focused citrus industry of southern Africa, the production of high quality fruit i.e. good size, well-developed rind color, blemish-free fruit and good taste is of utmost importance to remain sustainable. Shade nets are a preharvest technique implemented to protect crops against excessive sunlight, wind and hail damage. Shade nets are effective in reducing sunburn, but inconsistent results from previous studies arise about fruit size, rind color and internal quality. Furthermore, the impact on postharvest fruit quality with regard to developing rind physiological disorders and to maintain the physical integrity of the rind as a protection layer against moisture loss and decay development, is not known. Three experiments were conducted to determine how 20% white permanent shade netting would influence, firstly the fruit quality development, secondly the postharvest behavior and lastly the rind physical properties of ‘Nadorcott’ mandarin fruit produced in Citrusdal, over two seasons (2016 and 2017). In the first experiment, results indicated that the fruit size, rind color and internal quality development patterns were similar for both shade-net exposed and control fruit. Shade netting, however, resulted in an increased fruit size over the 2017 development period, but with no influence on rind color or maturity. Sunburn incidence was effectively reduced by shade nets. During cold storage at 4 and -0.6 °C over a period of 34 days, storage duration did not influence the postharvest quality of shade net fruit differently compared to control fruit in terms of rind color, internal quality parameters and fruit weight loss. In addition, no negative effect of shade netting was evident for the above-mentioned parameters or the incidence of staining. In the third experiment inconsistency occurred with regards to the effect of shade netting on fruit rind strength at harvest. A higher firmness was recorded for shaded fruit in the first season. However, during cold storage, there was some indication that the shade net fruit was more susceptible to deformation and required a lower force over the whole storage duration to puncture the rind, compared to the control fruit. However, a lower force required may also be beneficial as it could be indicative that the fruit may be easier to peel. The firmness of shade net-produced fruit was differently influenced by cold storage in 2016, within the first 14 days of storage, compared to the control. In 2017, control fruit were recorded to have a higher firmness over the storage duration. Both results indicated that the control fruit possibly stored better than shade-net fruit. To conclude, shade net was effective in reducing sunburn without negatively affecting any external and internal quality parameters. The postharvest storage potential of fruit from shade netting did not differ from the control at both storage regimes. Results regarding the impact of shade netting on the physical properties of the rind provides some first guideline threshold force values required before damage is inflicted on the fruit. Knowledge of typical forces applied during the commercial harvest- and pack house processes is, however, required before these values can be compared to commercial practices to determine its importance. The use of shade-netting shows potential as a preventative technology ensuring high quality, unblemished fruit, but requires future studies taking into account the effect of various cultivars, tree age, bearing positions and the microclimatic effect on fruit production and postharvest storage behavior.

AFRIKAANSE OPSOMMING: Die produksie van hoë gehalte vrugte met die verlangde vruggrootte, goed ontwikkelde skilkleur, vlekkelose voorkoms en goeie smaak is van uiterste belang vir die uitvoer-gefokusde sitrusbedryf van suiderlike Afrika om volhoubaar te bly. Skadunette is ‘n voor-oes tegniek wat toegepas word om gewasse te beskerm teen oormatige sonlig-, wind- en haelskade. Skadunette is doeltreffend om sonbrand te verminder, maar teenstrydige resultate van vorige studies bestaan egter ten opsigte van vruggrootte, skilkleur, en interne kwaliteit. Optimale na-oes vrugkwaliteit moet ook volgehou word sonder dat fisiologiese skilafwykings ontwikkel, asook die behoud van die fisiese integriteit van die skil om sodoende vogverlies en verrotting te beperk. Drie eksperimente was uitgevoer om vas te stel hoe 20% wit permanente skadunet eerstens die vrugkwaliteit ontwikkeling beinvloed, tweedens die na-oes gedrag en laastens die fisiese eienskappe van die skil van ‘Nadorcott’ mandaryn vrugte soos geproduseer in Citrusdal oor twee seisoene (2016 en 2017) affekteer. In die eerste eksperiment het vrugte van beide behandelinge dieselfde ontwikkelingspatroon gevolg in terme van vruggrootte, skilkleur en interne kwaliteit. Skadunet het gelei tot ‘n hoër gemiddelde vruggrootte oor die ontwikkelingsperiode van 2017, maar met geen invloed op skilkleur of rypheid nie. Sonbrand was egter drasties verminder onder die net. Tydens koue opberging van vrugte oor ‘n tydperk van 34 dae by 4 en -0.6 °C onderskeidelik, was bevind dat die stoortydperk nie die skadunet geproduseerde vrugte anders beïnvloed het teenoor die kontrole vrugte in terme van skilkleur, interne kwaliteit parameters en die vogverlies van vrugte nie. Daarbenewens was geen negatiewe effek van skadunette sigbaar op bogenoemde vrugeienskappe sowel as met die teenwoordigheid van bevlekking (‘staining’) van vrugte nie. In die derde eksperiment was daar teenstrydige resultate met betrekking tot die skadunet-effek op die skilsterkte by oes. Vrugte blootgestel aan skadunet was fermer by oes in 2017. Tydens koue stoor, het resultate getoon dat die skadunet vrugte moontlik meer geredelik vervorm kan word en ‘n laer toegepaste krag benodig het om die skil te prik in vergelyking met die kontrole vrugte. ‘n Laer krag kan moontlik ‘n aanduiding wees dat dié vrugte makliker sal skil wat voordelig kan wees. Koue opberging het ‘n groter effek op die fermheid van skadunet geproduseerde vrugte gehad binne die eerste 14 dae van opberging in vergelyking met kontrole vrugte. In 2017 het kontrole vrugte weer ‘n hoër fermheid vertoon oor die opbergingsperiode, wat moontlik aandui dat kontrole vrugte opberging beter hanteer as skadunet geproduseerde vrugte. Die gevolgtrekking van hierdie studie was dat die skadunet effektief was om sonbrand te verlaag, sonder om egter die interne en eksterne kwaliteitseienskappe negatief te beïnvloed. Verder het skadunet geen effek gehad op die opbergingspotensiaal van vrugte by 4 en -0.6 °C nie. Resultate rondom die impak van skadunette op die fisiese eienskappe van die vrugskil was ‘n eerste rapportering en dien dus as ‘n riglyn van die drempelkrag wat toegepas kan word voordat vrugbeskadiging intree. Kennis van die kommersiële krag wat tydens die oes- en pakhuisproses van toegepassing is, word egter benodig om hierdie waardes te vergelyk met kommersiële waardes om die impak daarvan vas te stel. Die gebruik van skadunette toon potensiaal as voorkomende tegnologie wat hoë kwaliteit, vleklose vrugte verseker, maar verdere studies word vereis waar die effek van verskillende kultivars, boom ouderdom, draerposisies en mikroklimaat op vrug produksie en na-oes opbergingspotentiaal in ag geneem moet word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105141
This item appears in the following collections: