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

[摘要] ENGLISH SUMMARY: Sunburn is the biggest abiotic quality defect affecting apple orchards in South Africa. In blushedcultivars, inadequate red colour development at harvest is of similar importance as sunburn asquality defect. The presence of these two quality defects negatively affects profitability of SouthAfrican apple orchards. This study was undertaken to assess the response of apple peels from treeson different rootstocks of differing vigour to photothermal stress. Rootstocks are purported toproduce different microclimatic conditions to developing fruit depending on their vigour. Theobjective was to identify whether previous acclimation to light and temperature affected thesensitivity of 'Rosy Glow' (RG) and 'Golden Delicious' (GD) apple peel from a range ofrootstocks, to damage (photosystem and visible peel damage) under induced natural photothermalstress and whether such acclimation affected the ability of 'Rosy Glow' apples to colour underdifferent 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 thefive-day period. Duration of exposure to the stress condition, the recovery period, and canopyposition were identified as the dominant influences on damage and recovery of RG photosystemswith 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 positionwere 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. Fruitfrom the different canopy positions acclimated differently which showed in their response to thephotothermal stress. Slightly lower peel sensitivity occurred in fruit from trees on the rootstockG3007 and a higher sensitivity in M793.To ascertain the effect of rootstock on the colouring potential of RG apples, fruit peel discs weresubjected to six temperature treatments. The effect on red colour development of RG apples underlab conditions is rootstock related and not related to vigour. Although fruit colour developmentvaried between different rootstocks under different temperatures, results indicate differentoptimum 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 colourdevelopment 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 ofmodifying fruit microclimate) on the red colour response of 'Cripps' Pink' (CP) apples at harvestwas evaluated. The cooling treatments applied showed different responses on change in hue of CPapples at harvest, but all cooling treatments were beneficial to red colour development. Latecooling treatment from mid-February to mid-March was more effective in decreasing hue of CPapples at the end of the trial.

[发布机构] Stellenbosch University