Department of Horticulture

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Acclimation of apple peel to light and temperature and the effect thereof on red colour development and tolerance to sunburn
(Stellenbosch : Stellenbosch University, 2017-12) Barasu, Prince Dogbeda; Midgley, S. J. E.; Schmeisser, M.; Steyn, Willem Jakobus; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
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.
Active modified atmosphere packaging, postharvest physiology, quality attributes and shelf life of minimally processed pomegranate arils (cv. Wonderful)
(Stellenbosch : Stellenbosch University, 2015-03) Banda, Kalenga; Opara, Umezuruike Linus; Caleb, Oluwafemi James; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Minimally processed fresh products have a short shelf life and marketable period and could therefore benefit from active modified atmosphere packaging (MAP) technology because it allows earlier establishment of suitable equilibrium atmospheres than passive MAP. However, there are limited studies that have explored the application of active MAP in minimally processed pomegranate arils. This study, therefore, investigated the effects of active MAP and storage conditions on postharvest physiology, quality attributes and shelf life of pomegranate arils (cv. Wonderful). In the first part of the study, the effects of storage temperature (5, 10 and 15 °C), relative humidity (76, 86 and 96%) and citric acid pre-treatment on transpiration rate (TR) of minimally processed pomegranate arils were investigated. In addition, the effects of storage temperature (5, 10, 15 and 20 ± 2 °C, and 90 ± 2 % RH) on respiration rate (RR) and quality attributes of citric acid treated and non-treated arils were determined in order to establish best storage conditions. Citric acid pre-treatment was only effective in reducing aril RR at 15 and 20 °C. Aril RRs were lowest at 5 °C throughout the 5 d storage duration and declined from 4.75 to 2.86 mL CO2 kg-1 h-1 and 4.86 to 2.7072 mL CO2 kg-1 h-1 for citric acid treated and non-treated arils, respectively. About twofold increase in RR was observed with increase in storage temperature from 5 to 15 °C and threefold when increased to 20 °C. Storing arils under low temperature condition (5 °C and 96 % RH) maintained the lowest transpiration rates (TR), with arils under these conditions suffering negligible moisture loss (~1%) after 9 d compared to 7 and 12% moisture loss for those stored under 86 and 76 % RH, respectively. The study further showed that citric acid pre-treatment had no significant effects on TR of arils at all the temperature and RH combinations. The effects of active MAP on postharvest physiology, quality attributes and shelf life of minimally processed pomegranate arils at 5 °C and 90 % RH were investigated using two independent experiments. In experiment 1, arils were packed in low barrier bi-axially oriented polyester (BOP) polymeric film under two active MAPs (5% O2 + 10% CO2 + 85% N2; 30% O2 + 40% CO2 + 30% N2), passive MAP and clamshell containers as control. In experiment 2, a high barrier polyethylene polymeric film (polylid) was used with arils packed in three active MAPs (5% O2 + 10% CO2 + 85% N2; 30% O2 + 10% O2 + 60% N2; 100% N2) and passive MAP as the control. Respiration rate, physico-chemical attributes, antioxidant properties (total anthocyanin, total phenolic and ascorbic acid content, and radical scavenging activity), microbial quality and sensory attributes were monitored every third day over a 12 d storage period. Equilibrium O2 (16-18%) and CO2 (7%) atmospheres were established after 3 d in the low barrier BOP in experiment 1; however, the recommended levels of gas composition (2-5 % O2 and 10-20% CO2) for MAP of minimally processed pomegranate arils were not reached. In contrast, O2 levels decreased and CO2 increased continuously, in pomegranate arils packaged in high barrier polylid film in experiment 2. Respiration rate of arils in both low barrier BOP film and high barrier polylid film were significantly affected by MAP and increased significantly (p < 0.05) with storage duration. Arils in clamshell containers maintained lower RR than other MAP treatments, while passive MAP had the highest in experiment 1. Arils in active MAPs with low O2 (5% O2 + 10% CO2 + 85% N2), high O2 (30% O2 + 10% CO2 + 60% N2) and passive MAP in the high barrier polylid film generally maintained similar RR levels throughout the 12 d storage duration. In contrast, RR of arils in 100% N2 was about 40% lower than that in other MAP treatments from day 6 until the end of storage. Furthermore, MAP with 100% N2 was effective in supressing ascorbic acid oxidation from day 6 until the end of storage. Total anthocyanin content (TAC) of arils fluctuated with storage duration across all the MAP treatments. At the end of 12 d storage duration, anthocyanin content of arils in experiment 1 was highest in clamshell packages (30.7 ± 0.9 mg C3gE/ 100ml) and lowest in passive MAP (26.7 ± 1.8 mg C3gE/ 100 ml). In the high barrier polylid film in experiment 2, arils in 100% N2 maintained higher TAC levels than other MAP treatments from day 9 until the end of storage. Similarly, radical scavenging activity of arils in the high barrier polylid film in experiment 2 was highest in 100% N2 while that in passive MAP was lowest from day 6 until the end of storage. Arils in in 100% N2 and high O2 atmospheres in both experiment 1 (30% O2 + 40% CO2 + 30% N2) and 2 (30% O2 + 10% CO2 + 60% N2) maintained lower aerobic mesophilic bacteria counts than other MAP treatments throughout the storage duration. However, shelf life was limited to 9 days for arils in 100% N2 based on overall acceptability and off-odour sensory scores, while arils in active MAP with high O2 scored above the acceptable limit by day 9. Arils in passive MAP in both films also remained acceptable until day 9, while those in clamshell packages were not acceptable beyond day 6.
An advanced evaluation of prohexadione-calcium on apple, pear, plum and nectarine trees
(Stellenbosch : Stellenbosch University, 2004-03) Meintjes, Jacobus Johannes; Theron, K. I.; Stassen, P. J. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: The control of excessive vegetative growth is important in deciduous fruit orchards. Currently the plant growth regulator prohexadione-calcium (p-Ca) is used to control apple shoot growth in the Untited States of America and some European countries. The effect of P-Ca on the shoot and fruit growth of apples (Malus domestica B.), pears (Pyrus cummunis L.), plums (Prunus sa/icina L.) and nectarines (Prunus persica L.) was evaluated. Inhibition of shoot growth can effect fruit growth. Therefore I did a literature review on the fruit growth of pome- and stone fruit. Split pit, a physiological disorder associated with an increased fruit growth rate in stone fruit, was also investigated. During the course of the 2001 / 2002 season two trials were conducted in the Villiersdorp area of the Western Cape on 'Golden Delicious' and 'Granny Smith' apple trees. Single and multiple applications of P-Ca at different rates, with and without the surfactant Dash®, were applied. One of these trials was continued during the 2002 / 2003 season. In the 2001 / 2002 season, P-Ca reduced shoot growth in both trials on 'Golden Delicious'. The shoot growth of 'Granny Smith' was reduced in both trials where PCa was applied three or four times. There was an improvement in the fruit size of 'Golden Delicious' in both trials, but there was no improvement in the fruit size of 'Granny Smith'. In the 2002 / 2003 season, the single P-Ca application did not reduce shoot growth. Unfortunately 'Golden Delicious' was harvested before any data were obtained. Once again P-Ca had no effect on the fruit size of 'Granny Smith'. Dash® did not improve the effect ofP-Ca. In the 2002 / 2003 season we replicated one trial on five different pear cultivars in the Wolsely area of the Western Cape. Single and multiple applications of P-Ca at different rates were compared to a girdling treatment (2 weeks after full bloom). 'Early Bon Chretien', 'Rosemarie', 'Flamingo', 'Forelle' and 'Packham's Triumph' pear trees were used and Dash®was added to all 0f the treatments. P-Ca reduced shoot growth in all of the pear cultivars. Girdling reduced shoot growth only in 'Forelle'. P-Ca increased fruit set of 'Early Bon Chretien', 'Rosemarie' and 'Forelle', however, this was associated with a reduced fruit size of 'Early Bon Chretien' and 'Rosemarie'. Girdling did not increase fruit set, but increased fruit size of 'Flamingo' and 'Early Bon Chretien'. P-Ca reduced return bloom of 'Packham's Triumph' and 'Forelle', whereas girdling increased return bloom in all the cultivars except 'Packham's Triumph'. In the 2002 / 2003 season, trials were also conducted on 'Pioneer' and 'Songold' plums and 'May Glo' nectarine in the Wemmershoek and Stellenbosch area of the Western Cape. Single applications at different rates of P-Ca were applied. Dash® was added to all of the treatments. The higher rates of P-Ca reduced the shoot growth of 'Pioneer'. P-Ca only reduced shoot growth of 'Songold' initially and but did not reduce shoot growth of 'May Glo'. P-Ca had no influence on fruit size of 'Pioneer', 'Songold' or 'May Glo'. P-Ca did not aggravate the occurrence of split pit. In conclusion, P-Ca reduced shoot growth in apples and pears when applied at the appropriate rates. Although P-Ca reduced shoot growth of 'Pioneer' plum, more research needs to be done on stone fruit to optimise timing and rate of P-Ca applications.
Advances in design and performance evaluation of fresh fruit ventilated distribution packaging : a review
(Publishers version, 2020-02-17) Mukama, Matia; Ambaw, Alemayehu; Opara, Umezuruike Linus
This review was initiated to realise the state-of-the art in optimising the ventilation and structural requirements of corrugated packaging carton design. Researchers have been using computational methods: computational fluid dynamics, particularly, the finite volume method, to analyse the airflow and heat transfer performances, and computational structural dynamics, particularly, the finite element method, to analyse the loss of compression strength due to vent-holes. Models are validated using actual testing: wind tunnel based forced air cooling system to study the produce cooling kinetics and box compression test machine for the package industry to study the structural dynamics. Studies on the rate and uniformity of produce cooling and the loss of structural strength in corrugated cartons as a function of size, shape, and location of vent-holes are reviewed. Based on experimental data, results show that the loss in strength can range between 10–40 % on addition of vent and hand holes on cartons, and reasonable increase in cooling rates is only achieved with increase in carton face ventilation area only up to 7–8 %. With regards to internal packaging components, increasing awareness of consumers to the environmental degradation of especially disposable plastic packaging means packers and suppliers must devise means to cut back and eventually eliminate plastic packaging from fruit and vegetables.
Advancing full production and increasing yield in young 'Triumph' persimmon orchards
(Stellenbosch : University of Stellenbosch, 2010-03) Scheepers, Stephanus Jacobus; Steyn, Willem J.; Theron, K. I.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Persimmon production is new to South Africa with about 700 ha planted to the dioecious, parthenocarpic Triumph cultivar since 1998. Little local expertise is available to assist growers in achieving high yields of high quality fruit and previous research has shown that recipes that are followed in Israel, from where ‘Triumph’ was introduced to South Africa, do not necessarily have any beneficial effect in South Africa. ‘Triumph’ orchards in South Africa are often late in reaching full production. Persimmon trees are generally vigorous and prone to excessive fruit drop, partly due to excessive vegetative growth, especially when young and grown on the very vigorous Diospyros lotus seedling rootstock. The first objective of this study was to evaluate the use of growth retardants and various severities of girdling to increase flower formation, fruit set and yield in vigorous, young ‘Triumph’ orchards. Scoring and girdling improved fruit set and yield in two such orchards and are recommended as tools to improve yield in ‘Triumph’ in South Africa. Strapping, prohexadione-Ca (P-Ca) and paclobutrazol (PBZ) did not increase yield whereas 5 mm bark removal was too severe a treatment and decreased fruit quality in the current season and yield in the following season. None of the treatments had an effect on flower formation or decreased vegetative growth. PBZ, especially as foliar spray, appears to advance fruit maturity. P-Ca at 125 mg L-1 and 250 mg L-1 induced phytotoxicity symptoms and decreased yields in both orchards. However, further research is required before P-Ca and PBZ are completely discarded as treatments to manage vigor in ‘Triumph’ persimmon in South Africa. In contrast to the negative effect of excessive vigor on fruit production, the profitability of orchards is dependent on the rapid growth of trees after planting in order to fill the allotted canopy volume and achieve full production as quickly as possible. Hence, the second objective of this study was to determine optimum levels of irrigation and fertilizer application rates to attain early, high yields in newly planted ‘Triumph’. Fertigation was applied at three levels, viz. ½X, 1X and 2X with 1X being the commercial standard application rate. Irrigation was also applied at these levels without addition of fertilizer. In addition, fertilizer was applied at 0X, ½X and 1X at 1X irrigation level. Tree size increased with an increase in water application rate. Yield also increased linearly with an increase in water application rate due to a linear increase in fruit size. Fertigation and ½X water as well as an increase in fertilizer application rate at 1X irrigation substantially delayed fruit ripening. Hence, careful management of fertilizer and water application rate could be used to extend the harvesting period and, therefore, the marketing window of South African ‘Triumph’. We recommend that the trial be continued for a further few seasons so that the effect of water and fertilizer application rates on fruit quality and storability can be assessed. Fruit set may also be affected as trees reach their mature size with a concomitant increase in shading.
Advancing harvest maturity and improving storability of ‘Triumph' persimmons
(Stellenbosch : Stellenbosch University, 2012-03) Bill, Malick; Steyn, Willem J.; Theron, K. I.; Ungerer, S. F.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: ‘Triumph’ persimmon production in South Africa is export driven and the profitability of the industry is largely dependent on consumer demand and supermarket shelf space in the European market. In order to realise high returns, it is important to advance harvest maturity to attain early fruit that arrives on the market prior to European summer fruits. In addition, market feedback suggests that fruit picked during the second half of the harvesting period stores poorly and rapidly softens during shelf life. It is important to establish whether this is the case. The effect of paclobutrazol (PBZ) application rate on fruit maturity and keeping quality, return bloom and vegetative growth was investigated over two seasons. Advanced harvest maturity was attained at a compromise of reduced fruit storage quality and stunted growth with the severity of the compromise increasing with increasing PBZ application rate. To advance harvest maturity while maintaining acceptable keeping quality, PBZ application at 0.75 ml per plant is recommended although effects on harvest maturity will not persist into the subsequent season as found at higher application rates. Prohexadione-calcium (P-Ca) as an alternative for PBZ in advancing harvest maturity was evaluated over two seasons. A positive response to three foliar applications of P-Ca at 200 mg·L-1 was noticed in the first season. In the second season, a single application of P-Ca at 300 mg·L-1 two weeks before harvest significantly advanced harvest maturity. Due to the rapid metabolism of P-Ca in the plant, it is unlikely that growth in the subsequent season will be affected. Based on these results, the persimmon industry will undertake commercial trials in the 2012 season to further assess the efficacy of P-Ca application in advancing harvest maturity. The effect of various rest breaking agents (RBAs) on bud break, flowering, fruit maturity and quality as well as vegetative growth was assessed for one season. RBAs did not increase or advance bud break and flowering. Consequently, yield and harvest maturity were unaffected by the treatments. The ineffectiveness of the RBAs could be due to the low application rates used or the fulfilment of the chilling requirement prior to treatment application. An experiment was carried out to determine whether storability and shelf-life differ between “early” and “late” production areas in South Africa as well as between orchards within these areas. The data indicated that fruit colour is a good maturity parameter and indicator of fruit storability. However, “late” fruit were about 1 kg softer than “early” fruit at the same colour chart value. We therefore recommend that fruit from late regions are harvested at colour chart values of 5 and 6 (yellow-green) instead of 3 and 4. Fruit from “late” orchards as well as GA3-treated fruit with a colour chart value of 3 and less should be culled due to the high propensity (>20%) of these fruit to become soft during storage and shelf life. A delay in 1-MCP treatment and interruption of the cold chain considerably increased fruit softening during storage and shelf-life. Further research is required to verify this result.
Alternative postharvest technologies for the maintenance of ‘Parthenon’ broccoli quality during export and domestic marketing.
(Stellenbosch : Stellenbosch University, 2022-04) De Beer, Tarryn; Crouch, E. M.; Crouch, Ian; Theron, K. I.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Broccoli is prized for its nutritional quality. The green colour and a compact head symbolise freshness. Export and domestic marketing of broccoli is limited by its high perishability. The aim of this study was to investigate the use of two 1-methylcyclopropene (1-MCP) application methods in combination with packing to maximise broccoli storage life under different temperature regimes typically found in the export and domestic handling chains. Under simulation of domestic handling chains, optimal temperature storage (0 °C) of broccoli (cv. Parthenon) in combination with 1-MCP and packaging [Xtend™ modified atmosphere packaging (MAP) or macro-perforated high-density polyethylene (HDPE) liners] resulted in a maximum storage duration of 30 days. In a second season, optimal temperature storage with MAP (RipeLock™) allowed for 42 days storage. Storage at suboptimal temperatures (viz. 7.5 °C or 12 °C), in mixed loads with ethylene is, however, common during domestic handling. Under such environments 1-MCP prevented broccoli (cv. Parthenon) yellowing that occurred with increasing storage temperature from 0 °C-7.5 °C and 7.5 °C-12 °C. Furthermore, 1-MCP alone or in the presence of ethylene extended shelf-life of broccoli (cv. Parthenon) compared to controls, at both temperatures. This research showed how an in-box treatment system of 1-MCP can be used as a viable alternative to the traditional, bulk, in-room application method, having a similar effect in reducing yellowing compared to controls. Sensory quality of broccoli was maintained in MAP (RipeLock™) at 0 °C and 7.5 °C. At 12 °C, where sensory quality was the poorest, 1-MCP reduced the perception of ‘sulphur odour’ compared to untreated and ethylene exposed broccoli. Dimethyl trisulphide (DMTS), an off-odour related volatile, was the most abundant volatile measured at all storage temperatures. The oxidative state of broccoli increased with an increase in storage temperature from 0 °C to 7.5 °C to 12 °C. Ascorbic acid and glutathione were oxidized with an increase in storge temperature. Glutathione, however, had a consistently higher percentage oxidation compared to ascorbic acid. Under simulated export conditions, broccoli was stored at 0 °C in various MAP types with or without 1-MCP. 1-MCP was either applied in-room before packaging or in-box during packaging. Results showed that extended storage without packaging is not recommended due to excessive weight loss. Across two seasons variations in shelf-life were noted. In the first season, a maximum storage duration of 25 days was realised with broccoli stored in Xtend™, or a generic HDPE MAP film with 1-MCP. In the second season, the maximum storage duration was 35 days, irrespective of MAP type or 1-MCP treatment. Here, the limiting factor for shelf-life was sensory quality. At optimal temperature volatiles related to off-odour were negligible, indicating that sensory deterioration was not related to fermentation in the MAP environment. In the second season it was reported that if good quality broccoli is stored at 0 °C, RipeLock™ or Xtend™ MAP in combination with 1-MCP should yield no benefit over untreated broccoli in non-specific, generic liners bags (15 μm HDPE).
Anaerobic digestion of dairy manure wastewater, food and fruit waste, a sustainable source of bio-energy and waste management
(Stellenbosch : Stellenbosch University, 2016-03) Sakeus, Kafula; Lotze, Elmi; Raffrenato, Emiliano; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: The potential for anaerobic co-digestion (AD) organic waste streams such as dairy manure waste water, fruit and food waste is a well-established process. A pilot study, utilizing a new constructed 40.248 m3 plug-flow, three chamber anaerobic reactor was conducted to determine the effects of temperature, electrical conductivity (EC), pH, organic loading rate (OLR) over a 20 day hydraulic retention time (HRT) on biogas yield, waste volume reduction, water soluble minerals, reduction of pathogenic microorganisms (Escherichia coli O157:H7), phytotoxcity and anaerobic microbial population dynamics. The reactor was equipped with a build-in temperature sensor which allowed for the internal temperature to be recorded from the circulation of water via an 8L biogas geyser. The reactor was also fitted with three ports connected to the three individual chambers, from which samples for EC and pH were lifted for analysis. Dairy manure wastewater had a total soluble (TSS) concentration (2.59 g/l) which was considerably lower than the anticipated 10% TSS. This meant the reactor had an OLR of 2.59 kg/m3reactor/day (Total suspended solids) and 1.97 kg/m3reactor/day volatile suspended solids (VSS). To maintain an organic retention time (ORT) equivalent to HRT, co-digestion of fruit and food waste was than calculated based on the TSS and VSS content of dairy manure wastewater. The results validated that the reactor’s temperature plays an important role in the production of biogas and reduction of pathogenic microorganisms of the digestate. Due to the low temperatures during the trial period, no viable biogas yields were detected using the current water displacement system and thus no biogas quality analysis were conducted. Temperature data confirmed that at temperatures below 20 °C, there was no linear relationship between the salinity indicator, EC and temperature. In addition, these low psychrophilic temperatures at a HRT of 20 days had no comparable impact on the reduction of pathogenic microorganisms. However, a 97% reduction in TSS entering the reactor was observed in all digestates. Water soluble minerals entering the reactor through feedstock were comparable to the soluble mineral concentrations the digestate. Although, the digestates contained high concentrations of mineral nutrients such as ammonium which were above the legal limit of waste water to be discharged in the environment. At concentrations below 75% none of the digestates showed significant phytotoxicity effects quantified with tomato seed germination. While, the data also seem to suggest that OLR had a noticeable influence on microbial population dynamics. Overfeeding the reactor induced an instant decreased on pH and also increased the microbial population species that colonize the different chambers. Under current sub-operating conditions compounded by low OLR, the AD reactor was not competitive enough to replace the current composting operation.
Anthocyanins in selected Proteaceae
(Stellenbosch : Stellenbosch University, 2002-12) Schmeisser, Michael; Jacobs, G.; Holcroft, D. M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Trials were conducted to follow colour development during the growth season of the commercial Leucadendron cultivar 'Siivan' Red', as well as the Protea cultivars 'Ivy', 'Carnival' and 'Sylvia'. HPLC analysis showed that pigments responsible for red colour in Leucadendron and Protea cultivars are anthocyanins. Initial extraction of anthocyan ins from freeze-dried and finely ground Leucadendron leaves, using 5% formic acid in methanol, resulted in the precipitation of gel-like compounds, making the extracts impossible to filter for HPLC. Trials were conducted to determine the optimum extraction solvent and extraction time for anthocyanin quantification in Leucadendron, using 'Safari Sunset' (Leucadendron sa/ignurn x L. /aureo/urn) as reference material. Acetone, 80% acetone, 5% formic acid in water and 5% formic acid in methanol were added to freeze dried leaf samples and allowed to extract for one hour. Extracts were analysed by reverse-phase HPLC. Extractions with methanol and water yielded extracts with a high content of pectin-like compounds, making them difficult to purify for HPLC. 80% acetone proved to be the most efficient extraction solvent, yielding the highest anthocyanin concentration, and showing the least amount of insoluble compounds. Optimal extraction time was determined for 80% acetone by testing 1, 6 and 24-hour extractions respectively. Although 6 hour extraction showed a slightly higher yield, a 1-hour extraction should suffice for quantification of anthocyanin changes over time, as trends will clearly be evident. 'Siivan Red' shoots meeting export quality can generally be harvested from mid February to mid April (late summer to autumn). The harvesting period ends as the colour of the distal leaves forming the flower head change from red to green. Anthocyanin, chlorophyll and carotenoid fluctuations were investigated in 'Siivan Red' during the 2000 growth season. The observed red colour loss is the result of the net degradation of anthocyanins and appeared to be correlated to the phenological development of the shoot. Although a positive correlation was noted between anthocyanin content and average daily temperature and mean daily sunlight hours, it appears unlikely that they are the causal factors for the observed colour change. Anthocyanin degradation started during conditions of long exposure to high light intensities and continued during a period of low temperature (autumn), both which are known to favour anthocyanin synthesis rather than its degradation. Therefore it appears that colour development in 'Silvan Red' is developmentally regulated. The Leucadendron cultivar 'Safari Sunset' with the same parentage as 'Siivan Red', is noted for its more intense red-purple colouration, which it does not lose during its development. The more intense colouration of 'Safari Sunset' has been ascribed to the higher total anthocyanin concentration, which was almost double that encountered in 'Siivan Red'. 'Safari Sunset' was shown to contain the same major types of anthocyanins, and hence the purple colouration (not seen in 'Siivan Red') can not be explained in terms of different types of anthocyanins being present. However, the ratio between the two major anthocyanins present in both 'Safari Sunset' and 'Siivan Red' were significantly different in that 'Safari Sunset' showed a considerably higher concentration of peak 1, which is most likely responsible for the observed purple colouration. High anthocyanin concentrations have been noted to buffer against visual changes in colour, which is the most probable reason that a colour loss is not observed in 'Safari Sunset'. Colour development of the innermost involucral bracts of three Protea cultivars was followed from an initially selected inflorescence size to commercial harvest (when flowers have opened slightly). 'Ivy', 'Carnival' and 'Sylvia' show a light pink, dark pink and red colouration respectively, which has been ascribed to differences in total anthocyanin concentration. Colour development in 'Carnival' showed a quadratic trend with time, with the highest rate of anthocyanin synthesis occurring a week prior to harvest. Colour development in 'Ivy' and 'Sylvia' were shown to be linear with time. As inflorescences are closed during their development and anthocyanin synthesis in the innermost involucral bracts occurred in darkness, light does not appear to have a major influence on colour development. Temperature did not appear to have a significant effect on flower colour, as flowers developing later in the season, when ambient temperatures were lower, showed no significant differences in anthocyanin concentration to those harvested earlier. Hence, it appears that colour development in all three cultivars is developmentally regulated.
Apple tree and fruit responses to shade netting
(Stellenbosch : University of Stellenbosch, 2007-03) Smit, Armand; Midgley, S. J. E.; Steyn, Willem J.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticulture.
The production of high quality fruit that meet international standards is of vital importance to the South African fruit industry. Detrimental climatic conditions are forcing producers to examine alternate production methods. In this study the effect of protective netting on apple tree (Malus domestica) physiology, microclimate and fruit quality was investigated to determine the potential of apple production under netting in the Western Cape Province of South Africa. The influence of 20% black shade netting on the photosynthetically photon flux density, leaf and fruit surface as well as air temperature was measured on four blush apple cultivars over a two year period in the Koue Bokkeveld area, in the Western Cape, South Africa. Measurements were also taken on leaf gas exchange, including net CO2 assimilation rate under ambient and saturating CO2 conditions, stomatal conductance, and transpiration rate. A decrease in light conditions of 22 - 31% was measured under black netting thus reducing the amount of light available to the plant significantly. Leaves under the netting were cooler by 1.7 – 3.9°C on a milder day (11 January 2005) and by 4.3 – 6.2°C on a hot day (28 February 2005) than control leaves. Fruit surface temperature under the netting was cooler by 0.7 - 2.9°C on milder days, and by 4.0 - 5.3°C on a hot day (28 February 2005) than control fruit. Significant increases in CO2 assimilation, stomatal conductance and transpiration were found under the netting. Netted treatments also showed a lower leaf vapour pressure deficit and tended to be less water stressed having higher leaf water potential than the control treatments. Differences in leaf nitrogen were not significant between treatments except for ‘Cripps’ Pink’ where non netted treatments had higher leaf nitrogen levels than the netted treatments during the 2004 season. Heat tolerance and the ability to recover after exposure to different temperatures for different lengths of time, was evaluated for the same four blush apple cultivars grown under protective netting. The results showed that fruit taken from the netted treatments had a higher incidence of injury based on chlorophyll fluorescence measurements, and did not recover well at temperatures higher than 45°C. The higher tolerance of the non-netted fruit at 45°C could be due to better acclimation to high light and heat levels than the fruit from the netted treatment. Fruit quality of ‘Royal Gala’, ‘Fuji’, Cripps’ Pink’ and ‘Braeburn’ was evaluated for netted and non-netted treatments as well as between five different crop loads as sun-treatments. It was found that cultivars reacted differently to the altered microclimate under the netting. Significant interaction between net and crop load treatments was found for fruit mass of ‘Royal Gala’ and ‘Fuji’. Fruit mass declined more rapidly with increased crop load under nets than in the open. The net treatment reduced sunburn significantly in all the cultivars except ‘Cripps’ Pink’. Ground colour was found to be positively influenced by netting on ‘Braeburn’ and during 2005 on ‘Royal Gala’. Blush colour was reduced under the netting for ‘Braeburn’ and ‘Fuji’ and unaffected for ‘Royal Gala’ and ‘Cripps’ Pink’. Fruit firmness, total soluble solids and titratable acidity, were reduced under nets for most of the cultivars. Netting thus seems to have a positive effect in reducing sunburn damage but a varying effect on other fruit quality parameters, which seem to be cultivar specific. The influence of black protective netting on vegetative growth was determined by measuring total prunings and trunk circumference. Reproductive bud development analysis was also done. An increase was found in summer prunings for ‘Fuji’ and ‘Cripps’ Pink’ which was most likely due to the topping of the trees to prevent them from growing into the netting. Seasonal trunk growth was affected significantly for ‘Braeburn’ with a higher percentage recorded under the netting. Reproductive bud development was higher for the netted treatments and on trees with lower crop loads. Photosynthetic photon flux density was reduced significantly in a ‘Granny Smith’ orchard at harvest by black, blue and grey type netting. Sunburn was significantly reduced under the black and blue netting. Fruit mass was higher under the netted treatments during the second season of measurements. Firmness and total soluble solids were lower under the netting. Blush colour was found to be significantly lower under the black netting. Seed viability, ground colour, titratable acidity, starch breakdown, stem end russet and the occurrence of Fusicladium pyrorum damage was unaffected by the netting.
Application of dynamic controlled atmosphere technologies to reduce incidence of physiological disorders and maintain quality of 'Granny Smith' apples
(MDPI, 2021-05-26) Kawhena, Tatenda Gift; Fawole, Olaniyi Amos; Opara, Umezuruike Linus
The efficacy of dynamic controlled atmosphere technologies; repeated low oxygen stress (RLOS) and dynamic controlled atmosphere-chlorophyll fluorescence (DCA-CF) to control superficial scald development on ‘Granny Smith’ apples during long-term storage was studied. Fruit were stored for 2, 4, 6, 8, and 10 months at 0 °C in DCA-CF (0.6% O2 and 0.8% CO2), regular atmosphere (RA)(≈21% O2 and 90–95% RH), and RLOS treatments: (1) 0.5% O2 for 10 d followed by ultra-low oxygen (ULO) (0.9% O2 and 0.8% CO2) for 21 d and 0.5% O2 for 7 d or (2) 0.5% O2 for 10 d followed by controlled atmosphere (CA) (1.5% O2 and 1% CO2) for 21 d and 0.5% O2 for 7 d. Development of superficial scald was inhibited for up to 10 months and 7 d shelf life (20 °C) under RLOS + ULO and DCA-CF treatments. Apples stored in RLOS + ULO, RLOS + CA, and DCA-CF had significantly (p < 0.05) higher flesh firmness and total soluble solids. The RLOS phases applied with CA or ULO and DCA-CF storage reduced the development of superficial scald by possibly suppressing the oxidation of volatiles implicated in superficial scald development.
Application of gum arabic and methyl cellulose coatings enriched with thyme oil to maintain quality and extend shelf life of “Acco” pomegranate arils
(MDPI, 2020-12-01) Kawhena, Tatenda Gift; Tsige, Alemayehu Ambaw; Opara, Umezuruike Linus; Fawole, Olaniyi Amos
The effects of gum arabic (GA; 1.5% w/v) and methyl cellulose (MC; 1% w/v) enriched with thyme oil (TO; 0.25 and 0.5% v/v) on the quality of “Acco” pomegranate arils were studied. Coating treatments, namely, MC, MC + TO0.5%, MC + TO0.25%, GA, GA + TO0.5% and GA + TO0.25% were applied on arils by dipping, and evaluations were made on physicochemical and microbiological quality, phytochemicals and antioxidant capacity of arils stored (5 ± 1 ◦C, 95 ± 2% RH) for 16 days. Dipping arils in GA or MC, both containing TO (0.5% v/v) significantly (p < 0.0001) reduced weight loss and enhanced antioxidant activity (FRAP) (p = 0.0014). However, dipping arils in GA combined with TO (0.25% v/v) had the highest influence on reducing aril respiration rate compared with other treatments. Overall, results showed that application of coatings (GA + TO0.5% and GA + TO0.25%) reduced total yeast and mould and total plate counts and maintained quality up to 8 days of storage. These findings suggest that either GA + TO0.5% or GA + TO0.25% coatings have the capability to extend storage life of “Acco” pomegranate arils.
An architectural analysis of pear cultivars grown under South African conditions and the relevance to local maintenance pruning strategies.
(International Society for Horticultural Science -- ISHS, 2005) Cook, Nigel C.; Du Plooy, Pierre
To quantify the growth habit of locally important pear varieties, initially, 2- year-old pear branches were classified into groups based on the length and position of lateral shoots. Four groups were formed that ranged from cultivars with a spurred growth habit and strong apical control, to cultivars with a spreading growth habit and weak apical control. Secondly, the development of fruiting branches was observed for up to five years by observing the five developmental alternatives of the terminal buds of laterals, i.e., dormant, vegetative, reproductive without fruit, reproductive with fruit, and abortion. Under local conditions two general problems were observed. A large proportion of buds remain vegetative giving rise to poor flowering, and many buds remain dormant, probably due to the use of vigorous rootstocks and inadequate winter chilling. Local training systems address these shortcomings through the use of rest-breaking agents, girdling, and winter pruning techniques. Winter pruning strategies for locally important cultivars can be split into two broad approaches. In one approach spurs are renewed within spur systems primarily via bourse shoots. In the other approach spurs are renewed via year-old shoots. The motivation for the use of these systems is discussed in light of the above architectural findings.
Aroma profiles and non-destructive determination of quality parameters of Japanese plums (Prunus salicina Lindl.)
(Stellenbosch : University of Stellenbosch, 2011-03) Louw, Esme Denise; Theron, K. I.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Plums with good taste, aroma and eating quality lead to repeat purchases and sustained demand. Taste includes non-volatile compounds, e.g. sugars and acids, and has been well researched to meet the consumers’ preferences. Plum aroma, however, has not enjoyed the same attention. Limited literature is available on the aroma of Japanese plums and none could be found on the effects of relatively long cold storage on the profiles. The main aim of this study is to investigate the changes in aroma compounds of Japanese plums throughout maturation and ripening and the effects of commercial cold storage regimes. Near infra-red (NIR) spectroscopy was also evaluated as a non-destructive method to determine plum quality parameters aimed at minimising sample variability. In Paper 1, NIR spectroscopy was used to develop prediction models for total soluble solid (TSS), total acidity (TA), sugar-to-acid ratio, firmness and weight in three cultivars (Pioneer, Laetitia and Angeleno) and a multi-cultivar model. Samples were collected for seven consecutive weeks and repeated over two seasons. TSS results showed excellent predictability (R2 = 0.817-0.955; RMSEP= 0.453-0.610 % Brix) but the TA models did not perform well. The sugar-to-acid ratio models had results comparable to that of TSS. Both the firmness and weight models had acceptable results. The models of ‘Pioneer’ and ‘Laetitia’ had a better predictability capacity than the ‘Angeleno’ model. Although the multi-cultivar models outperformed the single cultivar models on R2 values it had higher prediction errors. The robustness of all the TSS, TA and firmness models is high in terms of seasonality, range and cultivar. Papers 2 and 3, the main focus of the study, are concerned with the aroma profile dynamics of Japanese plums. HS-SPME was used in both papers to extract the aroma compounds followed by GC-TOFMS for separation and identification. In Paper 2, the aroma volatile compounds of three cultivars (Pioneer, Laetitia and Angeleno) were determined for a seven week period including samples from three maturity stages (immature, harvest and tree-ripe). A total of 35 compounds were identified of which ten were generic. Each cultivar had five unique compounds resulting in different aroma profiles for each of the maturity stages and distinct separation patterns using discriminant analysis. The study was extended in Paper 3 where the aroma volatile compounds of six cultivars (Pioneer, Sapphire, Laetitia, Songold, Larry Anne and Angeleno) and one plumcot (Flavor King) were determined at three functional stages (commercial harvest, tree-ripe fruit and cold stored fruit). A total of 62 compounds were identified and classified into three groups (‘unique’ (31), ‘generic’ (11) and ‘frequent’ (20)) based on their frequency of occurrence. The aroma profiles of ‘Larry Anne’ and ‘Flavor King’ are the most affected by cold storage conditions and ‘Pioneer’ appears to be the least affected. All the cultivars have significantly different aroma profiles at all three of the functional stages with ‘Sapphire’, ‘Larry Anne’ and ‘Flavor King’ showing the largest differences. ‘Flavor King’, a plumcot, presented a ripe aroma profile that was much diverged from that of the true plums.
Aspects of fruit size and quality in citrus
(Stellenbosch : Stellenbosch University, 2002-12) Mzini, Loyiso L.; Rabe, E.; Theron, K. I.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Sciences.
ENGLISH ABSTRACT: Fruit size can be a problem in 'Clementine' mandarin and 'Valencia' orange in the Western Cape region of South Africa. Small fruit is not only unacceptable to the consumer but is also more difficult and expensive to harvest. Means of alleviating this problem is to manage the crop load. Hand thinning trials were conducted to evaluate the effect of timing and severity thereof in enhancing fruit size. The benefits of enhancing large fruit size was obtained by a heavy-thinning (60% fruitlet removed) treatment, but the actual benefits were offset by a reduction of total yield. Yield was reduced up to 30% when heavy thinning treatments were applied. No effect on early or late treatments were obtained since the trial was conducted rather late (4 to 6 weeks after the physiological fruit drop period) to obtain the desirable results. However, better packouts are expected with thinning treatments since blemished fruit are also removed. The effect of multiple 2,4-dichlorophenoxy propionic acid (dichlorprop) sprays were also evaluated on 'Nules Clemetine' mandarin. Comparing multiple sprays with a single spray, it was observed that more than one spray was no better in improving fruit size. The use of multiple dichlorprop sprays resulted in no additional yield reduction, while internal fruit quality was also not affected. The best results were obtained with dichlorprop at 50 mg. L-1 • The use of dichlorprop with different surfactants was evaluated in both 'Clementine' mandarin and 'Valencia' orange. The fruit size was increased from 50 mg. L-1 up to 100 mg. L-1 • Yield was usually not affected but, where reductions were experienced, yield of large fruit (>55 mm) was not significantly affected. In the 'Valencia' orange trials, during the first year, dichlorprop was sprayed relatively late (fruit diameter: 19 mm). No fruit size, yield and internal fruit quality effects were observed. The following year, when early and late sprays (fruit diameter at spray time = 8 and 12 mm, respectively) were evaluated, it was observed that late sprays had no effect on fruit size, whereas fruit size (48 fruit per carton) was significantly increased by early sprays. This implies that the dichlorprop effect on fruit size is during the early stages of fruit development, just after or during the late stage of the physiological fruit drop period. Yield was drastically reduced by up to 35%, which affected the actual kilograms of large fruit adversely in some treatments. Juice percentage was inconsistent and tended to be reduced by dichlorprop application. Dichlorprop tended to increase TSS slightly in year one and significantly so in year two, but did not affect the TSS:TA ratio. The use of Orchex mineral oils as surfactant at 150 mL. 100 L-1 was effective and seemingly allowed lower rates of dichlorprop to be used. Therefore, surfactants seemed to show potential in enhancing dichlorprop efficiency to reduce the application cost. The dichlorprop-sprayed fruit was used to measure carotenoid content of the rind during the later stage of fruit development. Observations indicate that dichlorprop-sprayed fruit at 50 mg. L-1 obtained better carotenoid content in both 'Clementines' mandarin and 'Valencia' orange. Also, fruit exposed to light had higher carotenoid levels as compared to fruit shaded with brown paper bags. However, dichlorprop-sprayed fruit at 100 mg. L-1 , even though exposed to light did not show significant differences with unsprayed in both shaded and exposed conditions. Therefore, no consistent effect of dichlorprop was established on total carotenoid content of the rind.
Aspects of mineral nutrition affecting fruit quality of ‘Nadorcott’ mandarin
(Stellenbosch : Stellenbosch University, 2017-12) Marais, Helen; Cronje, Paul Jacobus Robbertse; Hoffman, L. (Lynn) (Horticulturalist); Zacarias, Lorenzo; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH SUMMARY: Mineral nutrition of Citrus is one of the key controllable factors influencing fruit quality. The mineral nutrients known to have the greatest impact on Citrus fruit quality, in order of magnitude of effect, are nitrogen (N), potassium (K) and phosphorous (P). The timing of application together with the amount of fertiliser applied is of critical importance in determining the impact it will have on Citrus fruit quality, including any possible long-term effects on tree growth, development and phenology. Three experiments were conducted to study fruit quality of ‘Nadorcott’ mandarin, taking both these above-mentioned considerations into account. The first experiment explored the known influence of P on decreasing citric acid content of Citrus fruit. In production areas with cold winters, harvest dates can be delayed by high fruit acid content, to such an extent that flowering is detrimentally impacted and hence also the fruit yield of the following season. Results obtained indicated that the citric acid content of fruit was significantly decreased by mono-ammonium phosphate (MAP) sprays, applied at seven and/or eight weeks after full bloom (WAFB). The second and third experiments concentrated on the influence of late N application on ‘Nadorcott’ fruit quality when studied in combination with different irrigation regimes and under different climatic conditions, respectively. The second experiment showed that, when the influence of N is considered in combination with irrigation, it has a more pronounced effect on Citrus fruit quality than exerted by N alone. Over-irrigation can have the most serious negative effect on fruit quality when all the factors studied were considered, therefore it is proposed that irrigation is likely to be the main determinant for success when managing N fertilisation. In the third experiment where the effect of late N in different forms on fruit quality was studied, the influence thereof was found to be insignificant. In addition, none of the N applications negatively affected rind quality, including that of colour development or the incidence of disorders. Beneficial effects on flowering for the following season were, however, also not recorded. Currently it can be concluded that since the application of late N had negligible effects on fruit quality in this study it may be used in an orchard with a known N deficiency, later in the season, subject to the prerequisite that the orchard is not over-irrigated. This study confirmed the complexity of mineral nutrition in citriculture, based on the large number of factors that influence fruit quality. Future research should attempt to establish the ideal time of MAP application, also taking different concentrations and production areas into account. Late N application trials should be expanded to an in-depth study of the effect of the N status of the tree on flower initiation, whilst establishing the production conditions under which this practice should be recommended.
Berry abscission in vitis vinifera L. cv. Waltham Cross : changes in abscission-related factors during berry development
(South African Society for Enology and Viticulture, 2005) Burger, D. A.; Jacobs, G.; Huysamer, M.; Taylor, M. A.
During the 1999 season, changes in total soluble solids (TSS), titratable acids (TA), pedicel diameter, berry diameter, berry mass and fruit removal force (FRF) were determined at biweekly intervals from 27 until 111 days after full bloom (DAFB) for Waltham Cross table grapes. In addition, at each assessment stage, grape bunches were detached and held in the dark at about 25°C for 80 h. Thereafter, moisture loss, FRF, berry abscission potential as well as percentage berry abscission were determined. During stages I and II of fruit growth (27 to 54 DAFB), TSS did not change significantly, while TA increased. FRF increased significantly during this early stage of berry development, indicating a strengthening of the abscission zone tissue. During stage III (after 54 DAFB), a decline in FRF occurred, which coincided with a perceptible increase in TSS and a decrease in TA. Berry mass increased significantly from 27 to 111 DAFB. Pedicel diameter only increased significantly for the period 27 to 41 DAFB, while berry diameter increased significantly for the period 27 to 97 DAFB. Grapes sampled at 27 DAFB had a significantly lower FRF and significantly higher levels of berry abscission and moisture loss after the 80-hour period in the dark, compared with grapes sampled at a later stage. At 27 DAFB, the abscission zone developed between the pedicel and the rachis, thereafter it developed between the pedicel and the berry. Although FRF did not change significantly as berries ripened (from 83 to 111 DAFB), abscission potential and percentage berry abscission were significantly higher for grapes harvested at 83 DAFB at a TSS of 12.3°Brix than for grapes harvested more mature, at a higher TSS. Moisture loss correlated significantly (P<0.0001) with berry abscission, with a correlation coefficient of 0.84. Berry abscission also correlated significantly (P<0.0001) with abscission potential, pedicel and berry diameter, FRF (at sampling), FRF (after 80 h) and berry mass, but not with TSS or TA.
Bestuiwing- en bevrugtingstudies by verskillende druifvarieteite
(Stellenbosch : Stellenbosch University, 1963-03) Kriel, A.; Theron, C. J.; Orffer, C. J.; De Waal, C. T.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science.
ENGLISH ABSTRACT: no abstract available
Browning and watercore disorders in 'Fuji' apples explored by means of X-ray computed tomography (CT)
(Stellenbosch : Stellenbosch University, 2020-12) Chigwaya, Kenias; Crouch, E. M.; Crouch, Ian; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: The Fuji apple cultivar occupies 9% of land under apple production in South Africa. To ensure all year-round fruit availability, ‘Fuji’ apples are stored for extended durations. However, ‘Fuji’ apples are prone to internal browning (IB) during storage. IB is characterized by patches of brown flesh in the apple tissue, which makes fruit unmarketable and causes financial losses. Browning symptoms that have been identified in apple cultivars include radial browning, diffuse browning, combination browning, CO2 damage and core-flush. Techniques such as X-ray computed tomography (CT) that can evaluate IB disorders non-destructively are important. This study aimed to explore IB types and watercore in ‘Fuji’ apples quantitatively and qualitatively using X-ray CT. Exposure of fruit to high CO2 conditions for 3 days after harvest at 21 °C induced IB in the core region of fruit. The construction of porosity maps for intact fruit enabled characterization of tissue structure before and after disorder development. Porosity distribution of ‘Fuji’ was higher in the cortex region compared to the core region. High-resolution X-ray CT scans performed on IB affected and unaffected fruit tissue showed differences in microstructural properties such as porosity, pore size distribution and pore connectivity. Fruit size had a significant effect on the susceptibility of ‘Fuji’ apples to CO2 stress-induced IB. Radial porosity profiles did not differ significantly between fruit that developed IB and fruit that did not develop IB. However, porosity along the axial profile was generally higher for fruit that did not develop IB, particularly in the region between the calyx end and the core region. This was the first X-ray CT study carried out on South African ‘Fuji’ apples to evaluate how fruit microstructural properties relate to the IB types identified under different storage conditions. A further study was done to determine microstructural properties of watercore affected fruit tissue and the effects on storability of ‘Fuji’ apples. X-ray CT scans showed that fruit tissue with watercore had a significantly low porosity and connectivity of pores. This may have a negative impact on respiratory gas diffusion in the fruit and could increase susceptibility to IB during storage. Furthermore, watercore affected tissue had significantly smaller cells due to plasmolysis. For long-term storage experiments, it was found that regular atmosphere (RA) stored fruit had a significantly higher incidence of core-flush compared to fruit from controlled atmosphere (CA) and delayed controlled atmosphere (delayed CA) storage. Although CA and delayed CA were effective in reducing core-flush incidence, they both resulted in a significantly higher incidence of radial browning. Fruit with CO2 damage and cavities were also evaluated in this study. CO2 damage was associated with cell damage and increased pore sphericity. All IB types evaluated resulted in an increased tissue porosity and altering of pore sphericity, anisotropy and pore size distribution. IB after short-term exposure to CO2 stress occurred only in the core region while IB types observed after long-term storage occurred in all fruit tissue regions. This study provided unique insights into the microstructural properties of different IB types occurring in ‘Fuji’ apples.
Ca-metalosate as an alternative Ca formulation for decreasing Ca related disorders in fruit trees
(Stellenbosch : Stellenbosch University, 2018-03) Le Roux, Eugene; Lotze, Elmi; Stander, J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Generally, calcium (Ca) foliar applications are used to improve the Ca status of fruit and control the incidence of Ca-related disorders, viz. bitter pit (BP) in apples and albedo breakdown (AB) in citrus. The main aim of the study was to determine whether Ca-metalosate as an alternative Ca formulation is effective in decreasing Ca-related disorders in fruit trees. Firstly, the role of formulation of Ca and boron (B) foliar applications to improve fruit quality in ‘Golden Delicious’ apples was quantified. Secondly, evaluation of pre-harvest foliar applications of a chelated Ca and B combination to reduce AB in citrus was carried out. Thirdly, xylem functionality in developing fruitlets of different apple cultivars was determined, as it impacts on Ca transport into the fruit. Ca concentration of fruit 80 days after full bloom (dafb), was significantly increased by Ca nitrate [Ca(NO3)2] foliar applications compared to Ca-metalosate and the control. The incidence of BP was also significantly reduced by Ca(NO2)3 foliar applications compared to the control, but not compared to Ca-metalosate. Results indicated that Ca foliar applications with a nitrate carrier, higher Ca concentration (active), lower point of deliquescence and molecular weight/size are more effective at increasing Ca concentration of fruitlets and reduce BP incidence in ‘Golden Delicious’ apples. This confirms previous findings that formulation has an effect on the efficiency and penetration of Ca foliar applications. B-metalosate in combination with Ca-metalosate failed to significantly reduce the incidence of AB in both sweet orange cultivars (Turkey and Cara Cara). Further research under South-African conditions, with an amended protocol, including five or more Ca-metalosate foliar applications, starting from 81 dafb, is suggested to determine if metalosates can successfully reduce the incidence of AB. This protocol differs from the one used in this study, but was successful when applied as salt formulation foliar application. Ca-metalosate and control indicated lower Ca (%) in the albedo tissue of creased fruit compared to non-creased fruit, indicating that Ca plays a role in AB. At ±49 dafb, a steady decline in xylem functionality was observed in all six apple cultivars evaluated, supporting recommendations that additional Ca foliar applications should start before 40 dafb to decrease the incidence of Ca-related disorders in fruit trees. Less susceptible apple cultivars showed an earlier decline of xylem functionality (42 dafb) compared to susceptible apple cultivars (49 dafb). This is in contrast to previous findings. A relationship between Ca-related disorders and loss of xylem functionality early in the season could not be established in this trial. A slight recovery of xylem functionality in all six apple cultivars evaluated was observed later in the season, under both climatic areas and this has not been reported previously in apples. Further research on xylem functionality under South African conditions should continue. Studies should commence earlier, starting at 28 dafb, and continue until harvest, to determine whether apple cultivars experiencing an earlier loss of xylem functionality are more prone to Ca-related disorders and whether xylem functionality slightly increases later in the season. By including microscopy studies during this period, the physical disruption of xylem bundles should be confirmed.

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