Masters Degrees (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.
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.
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.
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.
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
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.
Calcium uptake and distribution in relation to periods of active white root growth in young, potted apple trees (Malus domestica Borkh. cv. ‘Golden Delicious’) in the Western Cape
(Stellenbosch : Stellenbosch University, 2019-02) Cameron, Anouska; Lotze, Elmi; Hoffman, L. (Lynn) (Horticulturalist); Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Two-year-old ‘Golden Delicious’/M7 apple trees were chosen as the experimental material for this study. Potted trees were fertigated with a low calcium (Ca), balanced nutrient solution over two consecutive seasons (2015/16 and 2016/17). In the first season, trees were either left to drop their leaves naturally (NLD) during autumn and winter or were completely defoliated by hand earlier in autumn (AD), during April 2016. At the beginning of the second root flush, in winter (May 2016), calcium nitrate (Ca(NO3)2) was applied to the soil at three different rates: no additional Ca (control), moderate Ca (1X) and high Ca (2X). At the end of winter (August 2016), all trees were destructively sampled for macro mineral analysis of the different plant organs. Although an increase in soil Ca supply did not have a significant impact on white root numbers during winter (determined by minirhizotrons), early leaf loss via AD caused a drastic decline in white root numbers during winter. Despite this, Ca uptake and reserve accumulation in the roots and stems of the 2X(AD) treatment was not compromised, indicating possible active uptake by older, brown roots. Sap flow rates in leafless trees (determined by dendrometers) also remained above zero during winter, suggesting that leaf transpiration-driven sap flow is not essential for root Ca uptake and translocation in the xylem. In the NLD trees, an increase in autumn soil Ca supply resulted in a significant increase in leaf Ca concentration following the extended leaf drop period. At the same time, scanning electron microscopy and wavelengthdispersive x-ray spectroscopy (SEM-WDS) results indicated rapid uptake of soil-applied Ca by apple white root tips during winter. As 50 % leaf drop was reached late in winter (July), a substantial fraction of total Ca uptake in the 2X(NLD) treatment was lost via leaf abscission at the expense of Ca allocation to the reserve tissues during winter. The preferential allocation of Ca to the leaves was possibly the result of relative high rates of leaf transpiration-driven sap flow prior to 50 % leaf drop. Calcium partitioning in relation to periods of active white root growth, after harvest in the second season, were also investigated. Treatments comprising Ca(NO3)2 soil applications included a summer-only (2X) treatment, an autumn-only (2X) treatment and a summer (1X)/autumn (1X) treatment. Although fruit Ca concentrations were satisfactory at harvest, no significant differences were found between treatments. Whilst confirming primary xylem transport to the more dominant leaf and shoot sinks, the lack of response to summer applications (current season, 2016/17) indicates the predominant role of Ca reserve accumulation in the trees in supporting new growth the following season. In contrast to the summer/autumn treatment, a significantly higher % of total Ca content was found in the fruit of the autumn-only treatment. These results suggest that under local conditions of insufficient winter chilling, relatively high rates of soil-applied Ca(NO3)2, both in summer and autumn during active white root growth, may benefit the next season’s crop through remobilization of stored Ca in the roots and reserve tissues of the stems.
Carbohydrates and leaf blackening of Protea cut flowers
(Stellenbosch : Stellenbosch University, 2003-12) Meyer, Celeste; Jacobs, G.; Holcroft, D. M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Sciences.
ENGLISH ABSTRACT: Protea cut flowers are exported worldwide but the vase life of some species and cultivars is considerably shortened by post-harvest leaf blackening. Research has established carbohydrate depletion to be positively correlated with this disorder. Consequently, a study had been made of the carbohydrate status of various species and cultivars, as well as the effect of supplemental glucose (pre and post-storage) on leaf blackening. Glucose, fructose, sucrose and starch concentrations of various Protea species and cultivars held in water were measured at harvest, and again at leaf blackening initiation. All measured carbohydrates declined significantly in 'Carnival', 'Pink Ice' and 'Sheila'. In 'Cardinal' all carbohydrate concentrations decreased significantly, except the sucrose concentration in the inflorescence. 'Susara' and 'Ivy' had very high initial carbohydrate concentrations in the leaves which decreased significantly. The very high initial carbohydrate concentrations in the inflorescence of 'Ivy' declined significantly. 'Brenda' differed from the other cultivars and species in that glucose concentrations increased over time. Carbohydrate concentrations of most of the tested proteas declined significantly from harvest to the initiation of leaf blackening. This highlighted the dependence of the leaves and inflorescence on the carbohydrate reserves, further substantiating the carbohydrate depletion theory. The inflorescences were characterized by high fructose and glucose concentrations and low sucrose concentrations when compared to the leaves. It was hypothesized that glucose pulsing and cold storage at 1°C for three weeks would significantly reduce leaf blackening. 'Brenda', 'Cardinal', 'Carnival', 'Pink Ice', 'Susara ' and 'Sylvia' had significantly less leaf blackening with glucose treatments of 4 and 10%. Leaf blackening of 'Sheila', P. cynaroides and P. grandiceps was not significantly reduced by glucose pulsing. P. magnifica showed a small, but significant, reduction in leaf blackening in response to the 3, 6 and 9% treatments after 10 days only, but despite this, leaf blackening was unacceptably high. 'Pink Ice' harvested at the soft tip stage had less leaf blackening than those harvested open or closed. Toxicity symptoms on the leaves, and in some instances flowers, were observed at higher glucose concentrations (8 and 10%) onP. grandiceps, P. cynaroides, 'Cardinal' and 'Sheila'. All glucose treatments resulted in toxicity symptoms on P. magnifica. A decrease in nonstructural carbohydrates post-harvest apparently occurs in all proteas but it appears that only members of the Ligulatae respond to glucose. Glucose pulsing followed by cold storage at 1°C for three weeks in combination with post-storage glucose vase solutions, significantly reduced leaf blackening of some Protea cultivars. Glucose (1 and 2%), with hypochlorite, significantly delayed leaf blackening in 'Cardinal' and 'Sylvia' after seven days. Leaf blackening of 'Brenda', 'Carnival', 'Pink Ice' and 'Susara' was not significantly reduced by the glucose vase solutions. Other disinfectants, in combination with the sugar treatments, need to be evaluated since the hypochlorite treatment had a dehydrating effect on all the cultivars and resulted in increased leaf blackening. Carbohydrate supplementation of protea flowers with glucose, pre and post-storage, will help meet the post-harvest carbohydrate requirements of certain Protea cultivars and species to an extent. Glucose treatments must be seen in conjunction with maintaining the cold chain and when combined with cold chain maintenance, can extend the storage and vase life.
Chemical thinning of European pear cultivars (Pyrus communis L.)
(Stellenbosch : Stellenbosch University, 2008-12) Chabikwa, Tinashe Gabriel; Theron, K. I.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
Chemical thinning of fruit trees has become a central management practice for ensuring high fruit quality at harvest and return bloom the following season. Three trials were conducted in the 2004/5, 2006/7 and 2007/8 seasons to investigate the efficacy and mode of action of chemical thinning agents on European pear cultivars (Pyrus communis L) in the Western Cape, South Africa. The first trial was conducted in the 2004/5 and 2006/7 seasons to evaluate the efficacy of 50, 100 and 150 mg.l-1 6-benzyladenine (BA), and 30 and 40 mg.l-1 naphthylacetamide (NAD) on ‘Early Bon Chrétien’ pear. BA was more effective than NAD in reducing crop load and improving fruit size. Crop load decreased and fruit size increased with increasing rate of BA. BA significantly improved, whilst NAD failed to improve return bloom. In the second trial, three experiments were conducted in the 2006/7 and 2007/8 seasons to evaluate the efficacy of 100 to 200 mg.l-1 BA on ‘Forelle’ pear. The first experiment was conducted in the 2006/7 season where BA rates of 100, 125 and 150 mg.l-1 generally failed to reduce crop load or to improve fruit size and fruit size distribution and return bloom. The second experiment was conducted in the 2007/8 season where two BA rates, 150 and 200 mg.l-1 and a split-application of 3 x 50 mg.l-1 improved fruit size. The 200 mg.l-1 rate was the most effective treatment. BA did not improve fruit size distribution and return bloom. The third experiment was conducted in the 2007/8 season where the effect of rate and timing of BA applications was evaluated. Two rates, 150 and 200 mg.l-1 were applied 8, 11 and 17 days after full bloom (d.a.f.b.). There was no significant interaction between BA rate and application time. The 200 mg.l-1 rate and the 11 d.a.f.b. (i.e. 8 to 10 mm average fruit size) applications were more effective in reducing crop load, and improving fruit size. BA at 150 and 200 mg.l-1 and at all application times significantly improved return bloom relative to the control. From these trials we concluded that BA is a reliable thinner for ‘Early Bon Chrétien’ at rates of 100 or 150 mg.l-1. On ‘Forelle’, BA is not a reliable thinner and we recommended further trials with BA in combination with other thinning agents. In the third trial, three experiments were conducted in the 2007/8 season to investigate the mode of action and effect of BA application time on European pear cultivars. The effect of site of application, bourse shoot growth and fruit size at time of application on the efficacy of BA was evaluated. Results from the experiments on the effect of site of application and bourse shoot growth were inconclusive. In terms of fruit abscission, there was a significant interaction between BA application time and fruitlet size. Early BA applications (8 d.a.f.b.) were significantly more effective in promoting fruit abscission, than later (11 and 17 d.a.f.b.) applications. Smaller fruit (6 to 8 mm) were found to be more susceptible to BA-induced fruit abscission than bigger fruit (8 to 12 mm).
Cold storage of Leucospermum cutflowers and Leucadendron greens
(Stellenbosch : Stellenbosch University, 2005-12) Graham, Shelly; Jacobs, G.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Quality of certain Leucospermum and Leucadendron cultivars after approximately 21 days shipping has been reported to be substandard due to ‘drying out’ of leaves and, in the case of Leucadendrons, involucral leaves. The nature of the symptoms of this ‘drying out’ and the conditions under which they form, viz. long exposures to low temperatures, has led us to hypothesize that these are symptoms of chilling injury (CI). Chilling injury, as far as we are aware, has not been documented on Leucospermums or Leucadendrons. Typical CI symptomology is discussed and shown for Leucospermum ‘Gold Dust’, ‘High Gold’ and ‘Succession’ and for Leucadendron ‘Chameleon’, ‘Laurel Yellow’ and ‘Safari Sunset’. The nature of CI symptoms for Leucospermums and Leucadendrons was generally membranous breakdown that manifested in some cases as a ‘water soaked’ appearance which, at a more advanced stage, was generally visible as ‘dried out’ patches on the leaves. In the case of the Leucadendrons CI was also visible on the immature involucral leaves which are more sensitive to chilling conditions than mature leaves. Dark discoloration of especially immature involucral leaves is also a symptom of CI. As water uptake of shoots with chilling injury is hindered the styles of the Leucospermums wilt. As can be expected, the lower the temperature below the threshold temperature and the longer the exposure the more severe the symptoms. CI was recorded on cut flower shoots of Leucospermum ‘Gold Dust’, ‘High Gold’, ‘Rigoletto’, ‘Succession’ and ‘Vlam’ after 21 and 24 days storage at 1ºC. After 24 days storage the chilling injury was more severe than after 21 days storage in most cases. Each cultivar was pulsed with 5 ml per stem of a 2% (w/v) sugar solution of either lactulose, sucrose, glucose, fructose or mannose before storage. After storage, CI was recorded on day 0, 3, 7 and 10 of the vase phase. Of the cultivars tested ‘Vlam’ and especially ‘Rigoletto’ were more prone to chilling injury development. ‘High Gold’ and ‘Vlam’ shoots were pulsed with 0 (control), 1.5, 3 or 4% (w/v) solutions of either mannose or fructose. The best control of CI for both cultivars was achieved with 1.5% (w/v) solution. Lower concentrations of mannose and fructose were tested on ‘High Gold’ shoots, with a 1% (w/v) solution giving the best control for both. At high concentrations signs of toxicity became evident directly after pulsing. ‘High Gold’ shoots were pulsed with 1% (w/v) solutions of mannose and fructose and sugar analyses were performed on shoots at different stages of storage and after 10 days in the vase. A slight increase in mannose and fructose was detectable in the stems of the shoots directly after pulsing but not in the leaves or the inflorescences. This is due to the low concentrations being used. The levels of all the carbohydrates decreased during the 21 days storage and more so during the vase phase of the flowering shoots. The fact that such low concentrations were effective in controlling chilling injury suggests that the sugars may have an effect other than on the osmotic potential. Cut ‘flower’ shoots of Leucadendron ‘Chameleon’, ‘Laurel Yellow’ and ‘Safari Sunset’ were stored for 14, 21 and 28 days, at 1º, 3º and 5ºC and CI development recorded during the subsequent 10 day vase phase. ‘Laurel Yellow’ and ‘Safari Sunset’ showed signs of chilling injury on the leaves after 28 days storage at 3ºC or lower and ‘Safari Sunset’ stored for 21 days developed chilling injury during the vase phase. Immature involucral leaves were more sensitive to chilling injury than leaves. CI increased with longer exposure times and lower storage temperatures for all three cultivars evaluated. ‘Chameleon’ was the most chilling tolerant of the cultivars up to 21 days. At 5ºC chilling injury was low irrespective of cold storage duration but longer exposures to 1º and 3ºC resulted in increased chilling injury development during the vase phase. All three cultivars were pulsed with 5 ml per stem of a 1% (w/v) solution of lactulose, sucrose, glucose, fructose or mannose and stored for 14, 21 and 28 days at 1ºC. The sugars reduced chilling injury on the leaves for ‘Safari Sunset’ when stored for 28 days and, to a lesser extent, in ‘Chameleon’. The sugars failed to reduce chilling injury of the involucral leaves of ‘Chameleon’ and ‘Laurel Yellow’ whereas there was some control especially after 28 days for ‘Safari Sunset’. In some cases the sugar pulse exacerbated chilling injury. Chilling injury generally increased rapidly after storage during the first three days in the vase and then at a lower rate for the next seven days. Leucadendron ‘Chameleon’, ‘Laurel Yellow’ and ‘Safari Sunset’ ‘cut flower’ shoots were pulsed with a 1% (w/v) glucose solution. Expressed on a dry weight basis, an increase in glucose concentration was not detected. The reduction in chilling injury of leaves by a sugar pulse is speculated, as for the Leucospermums, to be as a result of their presence in the apoplast and not the symplast and that their presence there protects the membranes against chilling conditions in some way.
Colour improvement of bi-coloured pears
(Stellenbosch : Stellenbosch University, 2001-03) Reynolds, Johan Schalk; Theron, K. I.; Jacobs, G.; Huysamer, M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Poor colour development in bi-coloured pears is a big concern for the South African deciduous fruit industry, resulting in low Class 1 packouts with huge financial implications. The objective of this study was, therefore, to evaluate manipulation practices to improve colour development. The effect of summer pruning on the colour development of 'Rosemarie' pear fruit was studied over two seasons. Pruning consisted of removing the upright shoots of the current season's growth on the lateral branches. The effect of the time of summer pruning on Class 1 packout percentage and average fruit mass were determined. The percentage blushed fruit (colour grading 1-10) of the trees pruned in November or pruned repeatedly from November to just before harvest were significantly higher than for unpruned control trees or trees pruned at other times. Fruit mass was not affected by summer pruning. A second study was conducted on 'Rosemarie' and 'Forelle' pears and the treatments consisted of non-pinched and pinched, where the bourse shoots were cut back at petal drop. There were no significant differences in fruit colour, fruit size, flesh firmness and total soluble solids after pinching compared to the control. In a third study on 'Rosemarie' and 'Forelle' trees, bourse shoots were removed in combination with defoliation. Spur leaves were removed at different times throughout the season from petal drop towards harvest. Both bourse shoots (Rosemarie), or one bourse shoot (Forelle) per cluster was removed as control, one treatment where no bourse shoots were removed served as a secondary control. Spur leaf removal on 'Rosemarie' and 'Forelle' did not have any significant effect on fruit set, fruit size or total soluble solids. In 'Rosemarie', there was also no significant effect on fruit colour. In 'Forelle', colour improved significantly between unmanipulated branches (control 1) and branches were one bourse shoot was removed (control 2). However, all treatments compared to control 1, improved red colour, indicated by a significant decrease in the hue angle values and an increase in Class 1 packout. A fourth study was conducted on 'Flamingo', 'Forelle' and 'Rosemarie' pears. A number of urea applications were made onto the fruit. Fruit nitrogen content increased with urea sprays. Urea sprays did not affect red colour of 'Flamingo', 'Forelle' and 'Rosemarie' pears. Urea sprays had no effect on the anthocyanin concentration (ug.g") of 'Rosemarie' and 'Flamingo'. However, there was a quadratic relationship between number of urea sprays and anthocyanin concentration of 'Forelle'. There were not significant differences in the chlorophyll a and b concentrations of 'Flamingo' and 'Forelle'. Urea applications significantly increased the chlorophyll a concentration of 'Rosemarie'. In contrast there was no significant difference in the chlorophyll b concentration of 'Rosemarie'. The carotenoid concentration of 'Flamingo' and 'Forelle' was not affected by urea applications. In contrast the carotenoid concentration of 'Rosemarie' increased significantly after the urea applications. Overhead cooling was applied with a micro-irrigation system to 'Rosemarie' pears. The water was applied with pulsed irrigation for a three-week period (24 December 1998 to 14 January 1999) before harvest. The system was activated when internal fruit temperature reached 24°C (day) and 19°C (night), and irrigation continued until internal fruit temperature reached 21°C (day) and 16°C (night). No significant differences were found in colour, soluble solids; fruit size, fimmess or yields. A study was conducted on 'Bon Rouge', 'Red d' Anjou' and 'Forelle' pears to assess the effect of storage period for 6 and 8 weeks at -O.SoC and ripening at 21°C for 1 week on anthocyanins, carotenoids, chlorophyll a and chlorophyll b content. There were no significant differences in the anthocyanin concentration in 'Bon Rouge' after cold storage compared to fruit at harvest, whilst for 'Red d' Anjou' anthocyanin concentration increased significantly after cold storage. Results with 'Forelle' were inconsistent. During ripening anthocyanin of 'Red d' Anjou' did not change, whereas the results for 'Bon Rouge' and 'Forelle' were inconsistent. However, cold storage had no effect on the anthocyanin concentrations of 'Bon Rouge' and 'Forelle'. Cold storage significantly decreased the carotenoid concentrations of 'Bon Rouge', but not in 'Red d' Anjou' and 'Forelle'. The carotenoids of 'Bon Rouge', 'Red d' Anjou' and 'Forelle' decreased significantly more during ripening at 21°C. The chlorophyll concentrations of 'Bon Rouge' decreased significantly during storage at -O.SoC, compared to fruit at harvest, but not in 'Red d' Anjou' and 'Forelle'. During ripening at 21°C chlorophyll a and chlorophyll b decreased significantly in 'Bon Rouge', 'Red d' Anjou' and 'Forelle'. In conclusion it is clear from this study, that although light is important for initial colour development, high December and January temperatures remain the biggest problem in maintaining good red colour at harvest. Other factors, e.g. fertilisation are secondary.
Comparative analysis of four early white, seedless table grape cultivars in the Orange River area
(Stellenbosch : Stellenbosch University, 2002-12) Burger, Henning (Henning Jacobus),1978-; Vivier, Melane A.; Orth, C.; Sadie, A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: The table grape industry is a major contributor to the South African economy, directly through foreign earnings from this predominantly export-based industry, as well as indirectly through the employment of thousands of people. It is a growing industry and consists of several production areas. The fastest growing table grape production area in South Africa is the Lower Orange River area, which produces some of the earliest grapes in the Southern Hemisphere. The biggest river in South Africa irrigates this area and it has an extreme climate characteristic of semi-desert areas. This area is considered to be optimal for the production of high quality, early, white seedless grapes. Previously, this area was predominantly planted to Sultanina vines for the purpose of raisin production. When seedless table grapes became a consumer preference, the producers very successfully converted their production practices to yield export quality seedless grapes from the established Sultanina vineyards. Extensive new plantings as well as re-plantings occurred in this area, also including newer cultivars from local and overseas breeding programmes. Being a viticultural and economical hot-spot, the Lower Orange River area is attracting much attention as a table grape production area and it also formed the backdrop to this study. The cultivar profile is changing in the area and it is projected that Sultana-, Regal-, Prime Seedless and Sugraone will be the four major early, white seedless cultivars in 2005. Based on this knowledge and prompted by a lack of information regarding production costs and general profitability of the new cultivars, this study was initiated in the form of a comparative analysis between the four mentioned cultivars spanning the early, middle and late regions of the Lower Orange River area. The approach used extracted information regarding cultural input costs (specifically labour as man-hours and the consequent costs) per manipulation performed in the vineyards. This approach is different from the more general method of obtaining input costs for a specific area based on combined mean values, often not distinguishing between cultivars. The specific aims of the study included a comparative analysis of input costs for production cultural practices per main manipulation action, as well as a comparative analysis taking into account productivity, value and extraordinary costs related to each of the four cultivars. To this end, 22 experimental plots were identified for use in the study. Collaboration of the production managers of each of the experimental plots were procured and information regarding production costs per manipulation and productivity of each cultivar and experimental plot were extracted from their own record keeping systems or from documents provided to the production managers. The value (price achieved) of the various cultivars for the 2001/2002 table grape season were put into perspective by using data from a survey which included information regarding payments for the various cultivars during the season in the Lower Orange River area. Information regarding fruit and vine royalties was obtained from the various plant breeders' rights holders of the various cultivars, where applicable. Primary descriptions of each experimental plot concerning general cultivation practices and information regarding the specific season were used to qualify results obtained from the various blocks. Several complicating factors impacted on the study and specifically the subsequent analyses of the results. Some of the factors were already identified as complicating factors in the planning stage of the study and were mostly linked to the recent introduction of two of the cultivars to the Orange River area. From the data gathered and the analyses performed it became clear that it would be difficult to discern significant differences (where significant is defined as PS0.10), but clear trends were observed and indications obtained. Based on the input cost analyses of this study it is proposed that mature Prime Seedless will have the highest labour input and cultural production cost of the four cultivars, followed by Sugraone. The labour input and the cost for the production cultural practices studied for young Prime Seedless vines were very high in comparison to the mature Sultana Seedless and Sugraone vines, especially for the canopy management and bunch manipulation actions. Prime Seedless was especially prone to the set of small and uneven berries, which lead to very high labour input requirements and subsequent cost for bunch manipulations. Sugraone is also known for the set of small and uneven berries in the Lower Orange River area, especially in difficult climatic seasons, also requiring high labour input for bunch manipulations. The initial indication is that mature Sultana- and Regal Seedless will require similar labour inputs for cultural production practices. The fact that Regal Seedless does not require expensive gibberellic acid (GA) applications, or girdling for thinning and berry enlargement purposes, is a tremendous advantage from a production cost point of view. Accordingly, initial indications are that Regal Seedless will have the lowest cultural production cost of the four cultivars. Regal Seedless was prone to the set of uneven berries during the year of study and accordingly it is suspected that this factor will ultimately determine the labour requirements and cultural production input cost, especially in difficult climatic seasons. The labour input and ultimately the cultural production cost for Sultana Seedless will be determined by the correct timing and concentration of the GA applications for thinning and berry sizing. Sultana Seedless and Sugraone produced high yields during the 2001/2002 table grape season in the Lower Orange River area. Yield information from the various experimental plots confirmed that there is little to choose between the two cultivars in terms of yield when cultivation conditions and practices are optimal. Large variation was observed in the yield results from the Regal- and Prime Seedless experimental plots. This is largely due to the recent introduction of the cultivars to the area and the consequent scarcity of blocks of these cultivars that are in full production. It was impossible to identify clear trends in terms of the future productivity of mature Regal- and Prime Seedless, but some indications of labour inputs could be extracted and qualified. Early maturing Prime Seedless and Sugraone performed very well in terms of price, especially in the harvest period prior to week 50. This advantage of high prices early in the season is, however, not always applicable to early cultivars in the later maturing regions of the Lower Orange River area. Later during the season, after week 50, when the supply of table grapes to the overseas markets has increased sharply, Sultana Seedless is usually the best performer in terms of price of the four cultivars. The ultimate price obtained by a cultivar is to a large extent determined by supply and demand, quality and acceptance of the specific cultivar. This study and its outcomes have a strong regional (Lower Orange River) and local (South Africa) impact and the specific results will undoubtedly be valuable to the producers, exporters and other role-players with vested interest in the cultivars studied or in table grape production per se. The methodology adopted in this study, however, is of broader interest and dearly shows the advantage of having detailed and qualified information regarding cultivation practices and bringing it in relation to the labour and consequent costs required per action. This should lead to more business intelligence and realistic planning on the producer side when decisions regarding the choice of a cultivar for a specific production area with a particular marketing scope have to be made. This study has also paved the way for similar studies, specifically with regard to the detailed description of the methodology that was established. Knowledge of the problems experienced in this study provides a useful reference for the planning and execution of similar studies.
Comparative financial efficiency of training systems and rootstocks for 'Alpine' nectarines (Prunus persica var. nectarine)
(Stellenbosch : University of Stellenbosch, 2007-03) Maree, Waldo J.; Stassen, P. J. C.; Lombard, J. P.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticulture.
Most nectarine orchards in South Africa are currently planted at a distance of 4 x 1.5 m (2 500 trees/ha). These trees are mainly sylleptically trained to a central leader, although many producers also use the proleptic route. The former produces relatively high yields early in the lifetime of the orchard. A problem with nectarine production in South Africa is the lack of efficient rootstocks in terms of aspects such as size-control and the use of nematode-resistant rootstocks. The aim of this study is to evaluate different training systems for nectarine production and to investigate the role of three rootstocks that play a dominant role in the peach industry in South Africa. ‘Alpine’ nectarines were planted in the winter of 2002 at Lushof near Ceres, Western Cape, South Africa (33º18’S, 19º20’E). The trees were trained according to four different training systems: a four-leader system (5 x 3 m; 667 trees/ha), a two-leader system (5 x 1.5 m; 1 333 trees/ha), a proleptically trained central leader (5 x 1 m; 2 000 trees/ha), and a sylleptically trained central leader (5 x 1 m; 2 000 trees/ha). The trees were planted on three different rootstocks: GF 667; SAPO 778; Kakamas seedling. The time spent per tree on pruning, thinning and picking was recorded. During harvest, the number of fruit and fruit mass per tree were recorded. Light measurements were recorded annually after summer pruning. The measurements were taken at different heights and at different depths in the canopy. To compare the training systems on an economic basis, the data from the trial together with projected data gathered from farmers and advisors were used to calculate the net present value (NPV) and internal rate of return (IRR) for each training system. The results showed that rootstock only played a significant role when it came to fruit mass (fruit size). Fruit from trees on SAPO 778 were heavier, indicating bigger fruit, than fruit from trees on Kakamas seedling rootstocks and this can play a role in packout percentage and income. In terms of the training system, the four-leader system took the most time to manage per tree. However, this system took the least time to manage per hectare during the initial years. No differences were found between the two central leaders. They both took the longest time to manage per hectare. The four-leader system produced significantly less fruit than any of the other systems during the first two years of production. In the third year of production, there was no significant difference found between the systems. Light penetration seemed to be the poorest at the middle and bottom of the canopy for trees trained to a central leader. Because of the open centre of the four-leader system, light penetration into the middle of these trees was good, but poor light penetration occurred in the upper and outer parts of the canopy underneath the scaffold branches. Poor light penetration occurred in the parts lower than 1.5 m from the ground for all the systems. This was the area that was measured in this study. The result of an economic comparison showed that according to the IRR rating, the fourleader system should be preferred. The final decision should however be made according to the NPV rating. Results obtained from NPV calculations did not lead to the same conclusions as could be made from the IRR calculations. According to the rating of the NPV at five percent discounting rate, the two-leader should be the preferred system, while the proleptically trained central leader system should be preferred at a ten percent discounting rate. This implies that when the opportunity cost is low, the two-leader system should be preferred, and when the opportunity cost is high, the proleptically trained central leader system should be preferred.
Consumer reference (of red-fleshed apples) an quantification of quality related traits, particularly skin and flesh colour, in apple breeding families
(Stellenbosch : University of Stellenbosch, 2009-12) Thovhogi, Fhatuwani; Steyn, Willem J.; Labuschagne, I.; Muller, M.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: In order to develop a novel pink- or red-fleshed apple for the fresh consumer market,the red-fleshed genotype, ‘KAZ 91’ (Malus niedzwetzkyana Dieck.), was crossed with ‘Meran’ (M. domestica Borkh) at the Agricultural Research Council (ARC) apple breeding programme in South Africa. The objective of this study was to evaluate and quantify colour variability in the flesh and peel of this progeny (Family 1), to assess quality traits (i.e., acidity and total soluble solids) and phenolic levels in fruit peel and flesh, and to investigate consumer preference for the taste and appearance of redfleshed apples. All data, except for consumer preference, were also collected on two white-fleshed M. domestica Borkh families, i.e., ‘Reinette Burchardt’ x ‘Treco Red Gala’ (Family 2) and ‘Meran’ x ‘Treco Red Gala’ (Family 3). Fruit of Family 1 seedlings were on average darker red with greater blush coverage and higher anthocyanin and phenolic levels compared to fruits of Family 2 and 3. The proportion of bearing trees with red-fleshed fruits in Family 1 increased from 25% in 2007 to 35% in 2008. The intensity and distribution of red pigmentation in the flesh varied considerably between seedlings and even between individual apples from the same tree. A high intraclass correlation coefficient was found for red-flesh coverage within Family 1, indicating a high level of genetic determination that can be used in breeding. When only red-fleshed seedlings were considered, an intermediate repeatability coefficient (0.54) for red-flesh coverage indicates that the extent of red flesh coverage varies to some extent between seasons. The effect of environmental factors on red flesh colour needs to be assessed and breeders need to take care to select for genotypes with stable flesh colour intensity and coverage. Small intraclass correlations were found between families for other traits. No correlation was found for anthocyanin and total phenolics in both peel and flesh or between anthocyanin levels in the peel and flesh of Family 1 fruit. This suggests that red-fleshed fruit will not necessarily be high in antioxidants – since phenolics is by far the greatest contributor to fruit antioxidant capacity. The lack of a correlation between peel and flesh anthocyanin levels also suggest that fruit with dark red flesh will not necessarily have a dark red skin colour. Family 1 fruit were more prone to flesh browning and were more acidic compared to fruit of Families 2 and 3. With regard to consumer preference for flesh colour, 74% of South African consumers preferred white flesh while 64% preferred an attractive “floral” pattern created by the combination of a red cortex and white core. Consumers indicated a much lower liking for other distribution patterns and lower intensities of red flesh colour. Consumers preferred the taste of apples that were crisp, crunchy and high in apple flavour irrespective of flesh colour. Red-fleshed fruit were generally acidic or had poor texture, and some were also astringent. However, despite a general dislike in acidic fruit, consumers showed a preference for acidic fruit if that fruit also had high red-flesh coverage.

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