Acclimation of apple peel to light and temperature and the effect thereof on red colour development and tolerance to sunburn

Barasu, Prince Dogbeda (2017-12)

Thesis (MScAgric)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: Sunburn is the biggest abiotic quality defect affecting apple orchards in South Africa. In blushed cultivars, inadequate red colour development at harvest is of similar importance as sunburn as quality defect. The presence of these two quality defects negatively affects profitability of South African apple orchards. This study was undertaken to assess the response of apple peels from trees on different rootstocks of differing vigour to photothermal stress. Rootstocks are purported to produce different microclimatic conditions to developing fruit depending on their vigour. The objective was to identify whether previous acclimation to light and temperature affected the sensitivity of ‘Rosy Glow’ (RG) and ‘Golden Delicious’ (GD) apple peel from a range of rootstocks, to damage (photosystem and visible peel damage) under induced natural photothermal stress and whether such acclimation affected the ability of ‘Rosy Glow’ apples to colour under different temperature conditions. We found that damage to peel photosystems occurred at all exposure periods in both cultivars, with peels under one hour exposure showing general indications of progressive recovery over the five-day period. Duration of exposure to the stress condition, the recovery period, and canopy position were identified as the dominant influences on damage and recovery of RG photosystems with duration of exposure and recovery period being the dominant influences on GD photosystems. Likewise, duration of exposure, the length of the evaluation period together with canopy position were the dominant influences on visible peel damage observed on both RG and GD apples. However, rootstock plays a role in the visible peel damage observed on RG apples in 2016. Fruit from the different canopy positions acclimated differently which showed in their response to the photothermal stress. Slightly lower peel sensitivity occurred in fruit from trees on the rootstock G3007 and a higher sensitivity in M793. To ascertain the effect of rootstock on the colouring potential of RG apples, fruit peel discs were subjected to six temperature treatments. The effect on red colour development of RG apples under lab conditions is rootstock related and not related to vigour. Although fruit colour development varied between different rootstocks under different temperatures, results indicate different optimum temperature ranges for different rootstocks in the red colour development of RG apples. Geneva rootstocks G222 and G3007 rootstocks showed the highest potential for good colour development following a cold front under warm late-season conditions on par with the current industry standard M793. In our final experiment, the effect of fruit cooling (as a means of modifying fruit microclimate) on the red colour response of ‘Cripps’ Pink’ (CP) apples at harvest was evaluated. The cooling treatments applied showed different responses on change in hue of CP apples at harvest, but all cooling treatments were beneficial to red colour development. Late cooling treatment from mid-February to mid-March was more effective in decreasing hue of CP apples at the end of the trial.

AFRIKAANSE OPSOMMING: Sonbrand is die grootste abiotiese kwaliteitsdefek wat appelboorde in Suid-Afrika raak. In blos kultivars is onvoldoende rooi kleurontwikkeling by oes van soortgelyke belang as sonbrand as kwaliteitsdefek. Die teenwoordigheid van hierdie twee kwaliteitsdefekte beïnvloed winsgewendheid van Suid-Afrikaanse appelboorde negatief. Hierdie studie is onderneem om die reaksie van appelskil van bome op verskillende onderstamme van verskillende groeikragtigheid na foto-termiese stres te assesseer. Onderstamme lei tot verskillende mikroklimatiese toestande vir ontwikkelende vrugte, afhangende van hul groeikragtigheid. Die doel was om te identifiseer of vorige akklimasie tot lig en temperatuur die sensitiwiteit van 'Rosy Glow' (RG) en 'Golden Delicious' (GD) appelskil van 'n reeks onderstamme vir skade (fotosisteem en sigbare skilskade) beïnvloed, onder geïnduseerde natuurlike foto-termiese stres, en of sodanige akklimasie die kleurontwikkelingsvermoë van 'Rosy Glow' appels beïnvloed het onder verskillende temperatuurtoestande. Ons het bevind dat skade aan skil fotosisteme by alle blootstellingstydperke in albei kultivars plaasgevind het, maar skille onder een uur se blootstelling het algemene aanduidings van progressiewe herstel oor die vyf dae periode getoon. Die duur van stresblootstelling, die herstelperiode, en die blaardakposisie is geïdentifiseer as die oorheersende invloede op skade en herstel van RG fotosisteme, terwyl die duur van blootstelling en herstelperiode die dominante invloede op GD fotosisteme was. Net so was die duur van stresblootstelling, die herstelperiode, en die blaardakposisie die oorheersende invloede op sigbare skilskade wat op beide RG- en GDappels waargeneem is. Onderstamme speel egter 'n rol in die sigbare skil skade wat in 2016 op RG appels waargeneem is. Vrugte uit die verskillende blaardakposisies het verskillend geakklimatiseer, wat in hul reaksie op die foto-termiese stres getoon is. Effens laer skilsensitiwiteit het plaasgevind in vrugte van bome op die onderstam G3007 en 'n hoër sensitiwiteit in M793. Om die effek van onderstam op die kleurpotensiaal van RG appels te bepaal, is vrugskilskywe aan ses temperatuurbehandelings onderworpe. Die effek op rooi kleurontwikkeling van RG-appels onder laboratoriumtoestande was verwant aan die onderstam maar nie aan groeikragtigheid nie. Alhoewel vrugkleurontwikkeling verskil het tussen verskillende onderstamme onder verskillende temperature, dui resultate op verskillende optimum temperatuurreekse vir verskillende onderstamme in kleurontwikkeling van RG-appels. Geneva onderstamme G222 en G3007 het die hoogste potensiaal vir goeie kleurontwikkeling na 'n laatseisoen koue front getoon, soortgelyk aan die potensiaal van die huidige bedryfstandaard M793. In ons finale proef is die effek van vrugverkoeling (as 'n metode om vrugmikroklimaat te wysig) op rooi kleurontwikkeling van 'Cripps' Pink' (CP) appels by oes geëvalueer. Die verkoelingsbehandelings wat toegedien is het verskillende reaksies gewys op kleurverandering van CP appels by oes, maar al die behandelings was voordelig vir rooi kleurontwikkeling. Die laat verkoelingsbehandeling vanaf middel Februarie tot middel Maart was die effektiefste vir kleurontwikkeling van CP appels aan die einde van die proef.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102931
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