‘Granny Smith’ (GS) is the most widely planted apple cultivar in South Africa, accounting for 25% of apple plantings in 2008 (Deciduous Fruit Producers’ Trust, 2009). However, the total area of GS planted in South Africa has decreased by almost 15% during the last 15 years as a result of competition from more lucrative blushed cultivars. Apart from realizing lower returns, the proportion of Class 1 fruit from GS trees is lower compared with other cultivars as a result of zero tolerance for red blush, sunburn blemishes, and whitening of the peel. Fruit with sunburn or red blush are downgraded to Class 3 and will not pass for export. Although older GS orchards are being replaced with more profitable cultivars, GS will remain an important component of the South African industry for the time being. Hence, ways have to be found to increase the yield of Class 1 fruit.
In South Africa, sunburn and red blush may decrease Class 1 fruit by 35% and 20%, respectively (Griessel, personal communication). These blemishes occur in high light environments (Tustin et al., 1988; Warrington et al., 1996), where high light in combination with low or high temperatures initiates the synthesis of red anthocyanins or yellow carotenoids, respectively. Sunburn necrosis occurs as a result of thermal death of epidermal and subepidermal cells that leads to formation of a necrotic spot and is caused by extreme fruit surface temperature (52 ± 1 °C), whereas sunburn browning is a result of high fruit surface temperatures (46 to 49 °C) in the presence of light (Schrader et al., 2008). Photo-oxidative browning can occur at much lower peel temperatures (less than 30 °C) when fruit peel is suddenly exposed to high irradiance resulting in photobleaching followed by necrosis (Felicetti and Schrader, 2008). Chlorophyll levels decreased as a result of sunburn in all apple cultivars studied (Felicetti and Schrader, 2009). Red blush in GS is formed when anthocyanin synthesis is stimulated by low night temperature and mild days in combination with high irradiance (Reay, 1999), conditions that occur mostly during early fruit development in spring or during fruit maturation in the fall.
Peel whitening occurs under extremely low irradiance (Hirst et al., 1990) and may decrease Class 1 fruit in South Africa by ≈10% (Griessel, personal communication). The problem usually worsens with storage. A perception is increasing among fruit importers that South African GS is less green than GS of competing countries (Griessel, personal communication). To deal with this problem, fruit are shipped to lower-value markets, which has a negative effect on net profits achieved by producers. There is currently no coordinated effort to develop cultural practices to address this problem. To increase GS Class 1 fruit by decreasing sunburn, red blush, and peel whitening, it is necessary to have a sound understanding of green color development in apple peel and how it is affected by the light environment.
The main objective of this research was to relate GS fruit position in the canopy and the respective light environments to external fruit quality in terms of peel color, sunburn, and red blush development under commercial fruit-growing conditions in South Africa. The peel color of fruit at different canopy positions was measured at regular intervals from fruit set until harvest and related to irradiance level and peel temperature. Our hypothesis was that fruit from partially shaded canopy positions exposed to high levels of diffuse light but with limited exposure to direct sunlight would show less shading-related whitening as well as less high radiation-related yellowing and red blush development during fruit development. We also considered that irradiance level during early fruit development has a major effect on final fruit color. Results obtained would provide a basis from which to reassess the current planting systems used for GS and to devise pruning strategies for improving fruit color and increasing the percentage of Class 1 fruit in existing GS orchards.
Bergh, O., Franken, J., van Zyl, E.J., Kloppers, F. & Dempers, A. 1980 Sunburn on apples—Preliminary results of an investigation conducted during the 1978/79 season Decid. Fruit Grow. 30 8 22
Chen, L., Li, P. & Cheng, L. 2008 Effects of high temperature coupled with high light on the balance between photooxidation and photoprotection the sun-exposed peel of apple Planta 228 745 756
De Jong, T.M. & Doyle, J.F. 1985 The effect of row orientation on light distribution in hedgerow peach tree canopies Acta Hort. 173 159 166
Felicetti, D.A. & Schrader, L.E. 2008 Photooxidative sunburn of apples: Characterization of a third type of apple sunburn Int. J. Fruit Sci. 8 160 172
Felicetti, D.A. & Schrader, L.E. 2009 Changes in pigment concentrations associated with sunburn browning of five apple cultivars. I. Chlorophyll and carotenoids Plant Sci. 176 78 83
Ferree, D.C. & Schupp, J.R. 2003 Pruning and training physiology 319 344 Ferree D.C. & Warrington I.J. Apples: Botany, production and uses CABI Publishing Oxfordshire, UK
Gindaba, J. & Wand, S.J.E. 2005 Comparative effects of evaporative cooling, kaolin particle film, and shade net on sunburn and fruit quality in apples HortScience 40 592 596
Griessel, H.M., Rabe, E. & Srydom, D.K. 1992 The effect of harvest date on the chlorophyll concentration of ‘Granny Smith’ apples Decid. Fruit Grow. 42 456 458
Hirst, P.M., Tustin, D.S. & Warrington, I.J. 1990 Fruit colour respones of ‘Granny Smith’ apple to variable light environments N. Z. J. Crop Hort. Sci. 18 205 214
Izso, E. & Larsen, F. 1990 Fruit quality development of ‘Granny Smith’ apples in response to tree canopy light microclimate HortScience 25 1134 1135 (abstract).
Jackson, J.E. & Palmer, J.W. 1972 Interception of light by model hedgegrow orchards in relation to latitude, time of year and hedgerow configuration and orientation J. Appl. Ecol. 9 341 357
Knee, M. 1971 Anthocyanin, carotenoid, and chlorophyll changes in the peels peel of ‘Cox's Orange Pippin' apples during the ripening on and off tree J. Expt. Bot. 23 84 96
Lancaster, J.E., Lister, C.E., Reay, P.F. & Triggs, C.M. 1997 Influence of pigment composition on skin color in a wide range of fruit and vegetables J. Amer. Soc. Hort. Sci. 122 594 598
Li, P. & Cheng, L. 2008 The shaded side of apple fruit becomes more sensitive to photoinhibition with fruit development Physiol. Plant. 134 282 292
Ma, F. & Cheng, L. 2004 Exposure of the shaded side of apple fruit to full sun leads to up-regulation of both the xanthophyll cycle and the ascorbate–glutathione cycle Plant Sci. 166 1479 1486
Middleton, S. & McWaters, A. 2001 Increasing the yield and fruit quality of Australian apple orchards Horticulture Australia Ltd Sydney, Australia
Mierowska, A., Keutgen, N., Huysamer, M. & Smith, V. 2002 Photosynthetic acclimation of apple spur leaves to summer-pruning Scientia Hort. 92 9 27
Miller, S.S. 1982 Regrowth, flowering, and fruit quality of ‘Delicious’ apple trees as influenced by summer pruning J. Amer. Soc. Hort. Sci. 107 975 978
Mussini, E., Correa, N. & Crespo, G. 1985 Evolucion de pigmentos en frutos de manzanas ‘Granny Smith’ Phyton. 45 79 84 (abstract in English).
Parchomchuk, P. & Meheriuk, M. 1996 Orchard cooling with pulsed overtree irrigation to prevent to solar injury and improve fruit quality of ‘Jonagold’ apples HortScience 31 802 804
Reay, P.F. 1999 The role of low temperatures in the development of the red blush on apple fruit (‘Granny Smith’) Scientia Hort. 79 113 119
Reay, P.F., Fletcher, R.H. & Thomas, V.J. 1998 Chlorophylls, carotenoids and anthocyanin concentrations in the skin of ‘Gala’ apples during maturation and the influence of foliar applications of nitrogen and magnesium J. Sci. Food Agr. 76 63 71
Robinson, T.L. 2003 Apple-orchard planting systems 345 407 Ferree D.C & Warrington I.J. Apples: Botany, production and uses CABI Publishing Oxfordshire, UK
Schrader, L., Sun, J., Zhang, J., Felicetti, D. & Tian, J. 2008 Heat and light-induced apple skin disorders: Causes and prevention Acta Hort. 772 51 58
Tustin, D.S., Hirst, P.M. & Warrington, I.J. 1988 Influence of orientation and position of fruiting laterals on canopy light penetration, yield, and fruit quality of ‘Granny Smith’ apple J. Amer. Soc. Hort. Sci. 113 693 699
Warrington, I.J., Stanley, C.J., Tustin, D.S., Hirst, P.M. & Cashmore, W.M. 1996 Light transmission, yield distribution, and fruit quality in six tree canopy forms of ‘Granny Smith' apple J. Tree Fruit Prod. 1 27 54