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Hein J. Gerber, Willem J. Steyn and Karen I. Theron

The European fig cultivars Bourjasotte Noire, Col de Damme Noire, and Noire de Caromb were recently introduced to the Western Cape Province of South Africa. Producers struggle to implement effective commercial practices that will optimize yield of quality fruit. A phenological study was conducted to establish the optimum 1-year-old shoot length to maximize yield. The number of fruit, budbreak, and shoot growth on 1-year-old shoots comprising four length categories (‘Bourjasotte Noire’: 10 to 15, 25 to 40, 50 to 65, and 75+ cm; ‘Col de Damme Noire’ and ‘Noire de Caromb’: 10 to 20, 30 to 50, 60 to 80, and 100+ cm) were evaluated. In ‘Bourjasotte Noire’, all four categories seem to be suited for reproduction in the current season and also provide sufficient new shoot growth to ensure a fair yield the next season. In ‘Col de Damme Noire’, category four seems to be the best 1-year-old shoot length for reproduction both in terms of fruit number and fruit size. However, yield on these shoots may not be optimal the next season, because current-season shoots are too short. It seems that this cultivar will require pruning to stimulate strong new shoot growth that will ensure regular, high yields. In ‘Noire de Caromb’, category one shoots are very productive relative to their length. Categories two and three were also relatively productive, whereas category four was less productive but developed a large number of current-season shoots similar in length to category one that should be productive the next season. These results will allow us to develop pruning strategies to ensure an optimal balance between current-season yield and the development of new fruiting wood to ensure regular, high yields. It also suggests that the three cultivars studied will require differential application of horticultural practices to attain regular, high yields of large fruit.

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Brian Makeredza, Michael Schmeisser, Elmi Lötze and Willem J. Steyn

An experiment that entailed the manipulation of irrigation was carried out to assess the effect of water stress on sunburn development in ‘Cripps’ Pink’ apples. Normal irrigation, half irrigation, and no irrigation treatments were applied for 15 days starting on 14 Mar. 2010 (Southern hemisphere). Stem water potential, fruit surface temperature (FST), sunburn incidence, and sunburn severity were measured. Sunburn was also categorized into browning, necrosis, or bleaching sunburn types. Fully exposed fruit without prior sunburn symptoms were tagged for progressive sunburn assessments, whereas sunburn was also assessed at harvest for all fruit per tree. Soil moisture and stem water potential decreased, whereas FST, sunburn incidence, and severity increased linearly with a decrease in irrigation level. Sunburn necrosis increased with increasing water stress. In conclusion, water stress aggravates sunburn development under conditions conducive for its development by increasing FST.

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Willem J. Steyn, Samuel F. Ungerer and Karen I. Theron

The persimmon (Diospyros kaki Thunb.) cultivar Triumph is prone to poor fruit set, particularly in young orchards, in both Israel and South Africa where it is mostly grown. Two applications of 20 mg·L−1 gibberellic acid (GA3) at 30% and 70% full bloom (FB) are recommended as the industry norm to increase fruit set, but results obtained are often unsatisfactory. We conducted experiments during the 2005–06 and 2006–07 seasons in a young orchard (less than 5 years old) and a full-bearing orchard to determine the efficacy of GA3 application and scoring or girdling during FB to increase fruit set and yield in ‘Triumph’ persimmon. We also established the effect of 2005–06 treatments on return bloom in 2006–07. Although GA3 treatments were ineffective in increasing fruit set and reduced cumulative yield over the two seasons as a result of a reduction in return bloom, scoring increased the cumulative yield by 50% compared with the untreated control and by 92% compared with GA3 application in the young orchard. In the full-bearing orchard, scoring or girdling increased the cumulative yield over the 2005–06 and 2006–07 seasons by 52% compared with the industry standard GA3 application and by 22% compared with trees that received scoring/girdling in addition to GA3. Hence, scoring or girdling did not entirely offset the negative effect of GA3 application on return bloom. The increase in fruit numbers in response to fruit set treatment brought about a reduction in fruit mass. In conclusion, the ineffectiveness of GA3 in increasing fruit set and its negative effect on return bloom do not justify its further use to improve fruit set in young or full-bearing ‘Triumph’ orchards in South Africa. Either scoring or girdling can be used to increase yield but will need to be accompanied by pruning and thinning strategies to achieve adequate fruit size and to prevent the onset of alternate bearing resulting from overcropping.

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Jacques R. Fouché, Stephanie C. Roberts, Stephanie J.E. Midgley and Willem J. Steyn

The dark green apple cultivar, Granny Smith (GS), makes up 25% of the South African apple industry. However, production of GS is becoming unprofitable as a result of a high incidence of sunburn, red blush, and pale green fruit that decreases the proportion of Class 1 fruit that is suitable for export to more lucrative markets. This study was conducted to investigate the relationship between canopy position and external fruit quality with the ultimate aim to devise pruning and training strategies to maximize export yield. During early fruit development [26 days after full bloom (DAFB)], chlorophyll concentrations were the highest in fruit from higher light environments. Good green color at harvest relied on exposure of fruit to high irradiance at this stage because 50% shading between 14 and 56 DAFB significantly decreased dark green color at harvest. Exposed fruit from the northern side of east–west rows received the highest irradiance throughout the season [53% of full sun photosynthetic photon flux (PPF)] and had the highest fruit surface temperature (on average 5 °C above ambient). A high proportion of exposed fruit from either side of the row developed red blush. Only 22% to 39% of exposed fruit from the outer canopy did not develop sunburn or red blush. Partially shaded fruit from the southern side of east–west rows received ≈5% of full sunlight and had the highest chlorophyll concentrations and darkest green color at harvest. Deeply shaded inner canopy fruit received ≈2% of full sunlight, had low chlorophyll concentrations, and were lighter green in color. The 10% darkest green fruit received moderately high irradiance (25% to 45% of full sun PPF) during early fruit development (until ≈80 DAFB) but became progressively shaded (3% of full sun PPF) during the latter half of the season. Fruit that developed sunburn and the lightest green fruit were exposed to high (1300 μmol·m−2·s−1) and extremely low (50 μmol·m−2·s−1) light, respectively, throughout their development. In conclusion, maximum chlorophyll synthesis and dark green color require an open canopy during the first half of fruit development, whereas shading is necessary during the latter half of fruit development to avoid the occurrence of sunburn, red blush, and photothermal destruction of chlorophyll. GS may benefit significantly from the installation of shade netting if combined with rigorous pruning and vigor control.

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Brian Makeredza, Helen Marais, Michael Schmeisser, Elmi Lötze and Willem J. Steyn

Red color development toward harvest may conceal superficial blemishes such as sunburn browning in apple peel. Masking of sunburn may result in the underestimation of sunburn incidence in full red and blushed cultivars and may result in inaccurate assessments of sunburn susceptibility of various cultivars. However, anthocyanin accumulation may potentially also increase sunburn by decreasing the albedo and thereby increasing the fruit surface temperature (FST). Conversely, it has been proposed that anthocyanins may protect peel against photothermal stress. We assessed the effect of anthocyanin accumulation on the visible sunburn incidence in two trials. In the first trial, hue angle, blush coverage, sunburn incidence, and sunburn severity were assessed on fully exposed apples of the green cultivars, Granny Smith and Golden Delicious, as well as the blushed cultivars, Royal Gala, Fuji, Braeburn, and Cripps' Pink, and the full red cultivar Topred, a month before harvest and again at harvest. Increases in sunburn toward harvest were greater in green than in red and blushed cultivars. Accumulation of anthocyanins seemed to decrease the conspicuousness of sunburn browning, which is a superficial form of sunburn while sunburn necrosis, which manifests as sunken black spots, was not masked by anthocyanins. In the second trial, ‘Granny Smith’, ‘Fuji’, and ‘Cripps’ Pink’ apples with moderate sunburn browning, sunburn necrosis, or no sunburn were tagged 1 month before the expected harvest date. Sunburn browning was apparent and significantly increased in severity in ‘Granny Smith’ while the severity of visible sunburn browning symptoms decreased in ‘Fuji’. Sunburn severity increased at the same level in the control and sunburn browning ‘Cripps’ Pink’ fruit. Measurement of maximal photochemical efficiency of the originally undamaged apples and the sunburn browning treatment indicated comparable damage levels in the peel of the sunburn browning treatment in all three cultivars. No masking of sunburn necrosis occurred. Our data thus provide clear evidence that anthocyanin accumulation masks sunburn browning in blushed and red cultivars, but does not seem to increase the susceptibility or protect these cultivars from sunburn damage. The incidence of sunburn browning is likely to be underestimated in red and blushed cultivars, with compounding effects on comparative studies of sunburn susceptibility between cultivars and sunburn physiology.

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Esnath T. Hamadziripi, Karen I. Theron, Magdalena Muller and Willem J. Steyn

We hypothesized that the microclimate at different positions in the tree canopy may affect the appearance, eating quality, and consumer preference for apple fruit. Hence, the aim of this study was to evaluate the internal and external quality of inner and outer canopy apples in relation to consumer preference for the eating quality and appearance of these fruit. We determined peel color, flesh firmness, percentage starch breakdown, soluble solids concentration (TSS), titratable acidity (TA), and dry matter concentration (DMC) for inner and outer canopy ‘Starking’, ‘Golden Delicious’, and ‘Granny Smith’ from the Ceres region in South Africa in the 2009–10 and 2010–11 seasons. We also determined reducing sugars, total phenolics, and total antioxidant capacity in the 2009–10 season. A trained panel assessed the sensory characteristics of fruit while consumers were asked to indicate their liking for the eating quality and appearance of fruit. Outer canopy fruit of all three cultivars had higher antioxidant capacity, TSS, DMC, lower TA, and were generally sweeter than inner canopy fruit. Consumers could discern eating quality differences and generally preferred the eating quality of outer canopy fruit. The appearance of outer canopy fruit was not preferred in the “green” cultivars, probably as a result of the unfamiliarity of consumers with such fruit. Consumers did, however, prefer the redder outer canopy to the less red inner canopy ‘Starking’ fruit. The redness of ‘Starking’ fruit in this study can therefore be seen as a true signal of eating quality, i.e., the redder the fruit, the better the eating quality, and this would probably apply to other fully red and bicolored apple cultivars. Hence, the classification of red cultivars into different quality classes based on the extent of red color development seems justified from an eating quality perspective. In contrast, blushed outer canopy ‘Granny Smith’ and ‘Golden Delicious’ are culled for aesthetic reasons. It might be possible to develop a niche local market for these blushed fruit based on their better eating quality. Our data were generated in older orchards with trees planted at low density and with large canopies. Planer, two-dimensional canopies are likely to reduce the differences between inner and outer canopy fruit. Differences in macroclimate or in fruit maturity between seasons may also have an overbearing effect on fruit quality parameters compared with canopy microclimatic conditions.