Masters Degrees (Horticulture)

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Effect of fruit canopy position, harvest maturity and storage duration on post-harvest mealiness development of ‘Forelle’ pears (Pyrus communis L.)
(Stellenbosch : Stellenbosch University, 2019-12) Cronje, Rudolph John; Crouch, E. M.; Steyn, Wiehann J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Preliminary studies indicated a link between fruit canopy position and higher total soluble solids (TSS), respectively, and mealiness development during ripening of ‘Forelle’ pear. In this study this link is further explored to establish whether different parts of the canopy result in differences in maturity and ripening rates which affect mealiness incidence after ripening post-harvest. This study also investigates whether mealiness incidence is related to the micro-climactic differences within the canopy. Mealy textured pears were in general bigger sized fruit associated with higher TSS, lower titratable acid (TA), a redder blush colour, yellower background colour, and lower firmness after a period of ripening. Mealy fruit were also associated with a lower juice area and juice mass that were measured using a confined compression method. Mealiness incidence was the highest for red blushed outer canopy ‘Forelle’ pears associated with the highest exposure to sunlight, coupled with the highest fruit surface temperatures and vapour pressure deficit. The shading of outer canopy pears reduced mealiness incidence significantly, compared to that of sun-exposed outer canopy pears, which could be an indication that direct exposure to full sunlight coupled with high fruit temperatures for most part of the day could be one of the determining factors in ‘Forelle’ mealiness development. However, not all outer canopy fruit developed a mealy texture and therefore another unidentified tree factor might also play a role. The ripening rate developed earlier for outer canopy pears (earlier loss of firmness and an earlier transition to a more yellow ground colour) compared to intermediate and shaded inner canopy pears for both seasons, irrespective of harvest maturity. This is an indication that outer canopy fruit are in a more advanced stage of maturity than the other fruit positions. Fruit harvested at post-commercial maturity seems to be more susceptible to mealiness development. Highest mealiness incidence was observed after 8 weeks of cold storage at - 0.5 °C with 4, 7 and 11 days of ripening at 20 °C (8w RA + 4, 7 and 11d SL), while mealiness decreased with prolonged cold storage. Mealiness does however, not seem to be directly linked to ethylene production rate.
Effect of fruit maturation and ripening potential for optimum eating quality of 'Forelle' pears
(Stellenbosch : University of Stellenbosch, 2011-03) Carmichael, Patricia Cassie; Lotze, Elmi; Theron, K. I.; Crouch, E. M.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Climatic differences between production areas or seasons directly affect the rate of fruit maturation and the eating quality following storage and ripening. South African ‘Forelle’ pears are harvested at an optimum firmness of 6.4 kg and have mandatory cold storage duration of 12 weeks at -0.5°C to ensure even ripening. The firmness variable alone, however, is not a good indicator of ripening potential. Hence, various maturity variables (ethylene production, ground colour, firmness, total soluble solids (TSS) titratable acidity (TA), and starch breakdown) and their rates of change were evaluated to identify consistent maturity indices that can be reliably used in a prediction model to determine optimum harvest maturity (Chapter 2). This was then related to the ripening potential (Chapter 3) and eating quality (Chapter 4), defined by optimum ‘edible firmness’ (3.5 kg), presence or absence of astringency or mealiness. Fruit were harvested from three main producing areas: Warm Bokkeveld (WBV), Elgin and Koue Bokkeveld (KBV). Harvesting was done biweekly on five harvest dates over three successive seasons (2007-2009). At harvest, 20 of 240 fruit per block were used to determine maturity using all the mentioned parameters in order to understand their changes and behaviour pre-harvest. The remaining 220 fruit were stored at -0.5°C for three storage durations followed by ripening at 15°C. At harvest, the 2007 season’s fruit were more advanced in ground colour and were significantly softer (6.7 kg) than the 2008 (7.0 kg) and 2009 (7.1 kg) seasons. Firmness, ground colour, TSS and TA, all displayed a linear relationship with days after full bloom. For the firmness and ground colour, more than 90% and 73%, respectively, was explained by the variation in the linear model, while for the TSS and TA less than 70% could be accounted for by the model. Fruit harvested before commercial harvest (pre-optimum) in 2007 and 2009 failed to ripen to an ‘edible firmness’ when stored for eight weeks at -0.5oC plus 11 days at 15oC. In 2008, eight weeks storage was sufficient to induce ripening changes in pre-optimum harvested fruit. The development of ripening potential in the 2008 earlier harvested fruit, corresponded with a higher rate of change (3.15 µL.kg-1.h-1.day-1) in ethylene production at 15oC compared to the 2007 (1.98 µL.kg-1.h-1.day-1) and 2009 (1.87 µL.kg-1.h-1.day-1) seasons. The 2007 season fruit experienced maximum incidence of astringency (36.7%) on the first harvested fruit. In all three seasons, fruit harvested at commercial harvest time and later (optimum and post-optimum), required an eight week storage period to induce ripening. However, the eight weeks storage period developed highest mealiness. More than 40% of the last harvested fruit were mealy after eight weeks at -0.5°C plus seven days at 15°C. Mealiness significantly reduced with prolonged storage at -0.5°C. Fruit from the WBV and Elgin, warmer areas than the KBV, were more prone to mealiness. In conclusion, firmness was the most consistent variable at harvest and could be used in conjunction with ground colour to determine ‘Forelle’ harvest maturity. Furthermore, the study does not support shortening the current mandatory 12 weeks period at -0.5°C due to the higher incidence of astringency and mealiness.
Harvest maturity, storage conditions and tree age influencing internal browning and fruit quality of Rosy Glow apple (Malus domestica Borkh)
(Stellenbosch : Stellenbosch University, 2020-04) Doe, James Wonder; Crouch, E. M.; Thirupathi Karuppana P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
ENGLISH ABSTRACT: ‘Rosy Glow’ being a limb/bud sport variety of ‘Cripps’ Pink’ apple, is also regarded prone to internal flesh browning (IFB) similar to its parent cultivar. IFB in ‘Cripps’ Pink’ apples has been reported to be influenced by both pre-harvest and post-harvest factors, such as harvest maturity, tree age, mineral nutrition, storage temperature, and duration. The application of chemicals, such as 1-methylcyclopropene (1-MCP) and diphenylamine (DPA), also influences the development of IFB. This study investigated the effect of tree age, harvest maturity, storage temperature, 1-MCP treatment, and storage duration in controlled atmosphere (CA) on IFB development in ‘Rosy Glow’ apples over two seasons (2014/2015 and 2015/2016). Fruit were harvested at <40% and >50% starch breakdown (SB) for the harvest maturity trial (Trial 1) and <40% SB for the storage duration, temperature, 1-MCP (Trial 2), and tree age trial (Trial 3). Trial 1 and Trial 3 fruit were stored for 7 months in CA (1% CO2 and 1.5% O2) plus 6 weeks in regular atmosphere (RA) at -0.5 °C and 7 days at 20 °C and evaluated after each period. Trial 2 fruit, treated with or without 1-MCP, were stored at -0.5 °C or 2 °C and evaluated after 3, 5, and 7 months in CA plus 6 weeks in RA and a 7-day shelf-life period. Fruit were evaluated for IFB, SB, firmness, background colour, total soluble solids (TSS), titratable acidity (TA), greasiness, and blush colour at the end of each storage period. The results showed that diffuse browning (DB), radial browning (RB), combination browning (CB), and CO2 browning (CO2B) were the types of IFB observed in all three trials. Optimum harvested fruit exhibited a lower susceptibility to IFB in general in both seasons (2015 and 2016), comparative to fruit harvested post-optimum. 1-MCP treated fruit had a lower IFB incidence and no tree age effect was observed in this trail. DB and RB was first observed after 5 months in CA plus 6 weeks RA at -0.5 °C. DB was the main type of browning present. Harvest maturity (>50% SB) played a significant role in ‘Rosy Glow’ IFB development. Fruit quality was better retained at -0.5 °C than at 2 °C, while 1-MCP treated fruit quality was better maintained than control fruit over time. An orchard influence was observed on ‘Rosy Glow’ IFB and requires further investigation.
Long-term storage of late season avocado cultivars Hass and Gem™
(Stellenbosch : Stellenbosch University, 2021-12) Van Rensburg, Megan; Crouch, E. M.; Theron, K. I.; Thirupathi Karuppana P.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Avocados experience a physiological disorder known as mesocarp discolouration, also known as grey pulp, which is associated, but not limited, with storage and advanced maturity and leads to large amounts of waste. Avocados have heterogeneous maturities on the same tree, which make storage and marketing complicated. Ripening is essential in making fruit acceptable to consumers but finding the balance between extended storage periods and safe transit is key. The time it takes for the fruit to ripen after storage indicates what transport is possible and what the risk is for physiological disorders and rots to develop. Pathogenic rots are a quality concern that accompany the storage of fresh produce and are the cause of a large percentage of postharvest losses in the avocado industry. Therefore, the objective of this study was to determine the viability of long-term storage of ‘Hass’ and Gem™ to extend the supply of avocados to the local South African market. This was done by evaluating the effect of controlled atmosphere (CA) storage and temperature on grey pulp severity incidence, days to “cutting firmness” of fruit from arrival measured by densimeter, and pathogenic fungal growth. Fruit were stored at 1 and 3 °C in three different atmospheres including regular atmosphere (RA; air), CA (2% O2 and 6% CO2), and dynamic controlled atmosphere-chlorophyll fluorescence (DCA-CF; ≈0.4% O2 and 6% CO2) for various time intervals (4, 6, 7, and 8 weeks) to determine which storage conditions minimise the potential development of the grey pulp disorder, days to “cutting firmness” and pathogenic fungal occurrence. For grey pulp severity, it was possible to store fruit for extended periods (6-8 weeks) at 1 °C in both CA and DCA-CF with a reduced incidence of the disorder. For shorter storage periods, viz. 4 weeks, storing fruit at 1 °C (after step-down cooling) could negate the need for CA. Mesocarp discolouration / grey pulp severity incidence was worse when fruit were stored at higher storage temperatures (3 °C), for longer storage periods, and stored in RA. This study showed that fruit stored in both CA and DCA-CF took longer to soften to a “cutting firmness” and ripened more evenly than fruit stored in RA. It was also shown that where the temperature regime was statistically significant, fruit stored at lower temperatures (1 °C) softened slower to a “cutting firmness” than fruit stored at higher temperatures (3 °C). In the 2016-2017 season, DCA-CF treatment showed a lower incidence of stem-end and body rots compared to the CA and RA treatment. However, in the 2017-2018 season, both CA and DCA-CF treatment often controlled the incidence of stem-end rots and body rots better. Low temperature (1 °C) and both CA and DCA-CF treatment therefore reduced the incidence of stem-end and body rots, as well as the complex rot disorder development in the avocado fruit. This study showed that grey pulp severity or mesocarp discolouration, and decay are better controlled by low temperature and low oxygen environments in storage. These storage methods, combined with the right harvest maturity and transport, will allow longer storage and slower softening, thereby ensuring supply of good quality, late-season avocados to the local market.
Quantifying the role of vapour pressure deficit in the development of lenticel breakdown in ‘Braeburn’ apple
(Stellenbosch : Stellenbosch University, 2021-12) Mzize, Nolubabalo; Lotze, Elmi; Crouch, E. M.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Lenticel breakdown (LB) is a physiological disorder that can develop in different apple cultivars including Braeburn during cold storage and shipping. Several researchers mentioned various pre and post-harvest factors influencing LB, however, the effect of vapour pressure deficit (VPD) has not been discussed. In trial 1, the anatomical and morphological development of lenticels on ‘Braeburn’ fruit was studied from 40 to 166 DAFB, and fruit harvested post-optimum to increase risk of LB incidence. Fruit from the East side had smaller epidermal and hypodermal cell sizes, a higher number of lenticels per fruit, open lenticel and developed more LB. Lenticel developmental stage was not influenced by canopy side and transitioning of stomata into lenticel was only observed from 82DAFB onwards, a bit later compared to other apple cultivars. In trial 2, LB incidence was related to: delayed cooling (24 h, 0 h) and the use of wet blankets in the orchard (+/- Blanket), in ‘Braeburn’ after harvest. The study showed that 24 h– Blanket increased cumulative VPD significantly and the 0 h (immediate cooling) and wet blanket reduced cumulative VPD significantly over time. Delayed cooling and wet blanket (24 h + Blanket) contributed to LB incidence, with the 24 h+Blanket treatment developing 7%, 0 h-Blanket 5% and other treatments, 3% (2019/2020). No significant effects were found in 2018/2019. Delayed cooling advances maturity whereas use of wet blanket and immediate cooling-maintained fruit quality. In trial 3, LB incidence was related to: two precooling types (Forced air (FAC) and passive cooling (PC)) and different times and temperatures (-1 °C and 3 °C) with reference to cooling speed before storage. Passive cooling is a non-mechanical cooling system that cools fruit inside the cool room, while forced air cooling is a technique that exposes fruit to forced cooled air at a higher pressure, either in situ, though a tunnel or in the cool room. The study revealed no significant effect between treatments in cooling speed, time and temperature (2018/2019), yet, the -1 °C temperature had a faster cooling speed and shorter cooling time (2019/2020). The PC -1 °C showed increase in cumulative VPD, whilst FAC -1 °C lowered cumulative VPD significantly. LB incidence, fruit weight loss and firmness were not significantly affected by the treatments. In trial 4, LB incidence was related to: the use of different fan speeds, liners and packaging on re-cooling rate during 6 weeks of simulated shipping. Fan speeds 2 and 3 had a rapid re- cooling rate, shorter re-cooling time and higher cumulative VPD compared to Fan speed 1. Fan speed 3 showed significantly increased fruit weight loss compared to Fan speeds 1 and 2. The study did not show any significant effect in LB incidence, although treatments had a significant effect on fruit quality. Punched and Micro-perforated liners showed a slower re-cooling rate, extended re-cooling time, lower cumulative VPD and reduced fruit weight loss. Both liners significantly and conversely developed more LB, whereas No liner maintained fruit quality at optimum levels. The application of a wet blanket shortly after harvest, immediate cooling (0 h), no application of wet blanket, 24 h delay cooling (24 h) thereafter and packing fruit without liners showed a reduction in LB incidence, but additional studies are required to obtain conclusive results. Thus, whilst fruit quality is maintained, none of the postharvest treatments consistently resulted in LB increases/decreases and therefore we postulated that LB incidence is initiated pre-harvest, as result of a self-defence mechanism of fruit exposed to stress conditions, and not primarily by storage regimes.
Red colour improvement in apple fruit (Malus domestica Borkh.)
(Stellenbosch : Stellenbosch University, 2020-12) Steyn, Natalie; Theron, K. I.; Steyn, Willem J.; Crouch, E. M.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
ENGLISH ABSTRACT: Fruit red colour coverage and intensity determine the market value of bi-colour apples. Anthocyanin synthesis and therefore red colour development is highly light- and temperature dependent, the latter being especially challenging in warmer Mediterranean-type climates such as the Western Cape, South Africa. Colour development also occurs simultaneously with fruit ripening, a process that is highly ethylene sensitive. ‘Cripps’ Pink’ and older strains of ‘Fuji’ apples are notorious for poor and erratic colour development thus limiting producer profits. Bi-colour apples are therefore harvested over multiple picking dates mostly based on the extent of fruit red colour development. Preharvest aminoethoxyvinylglycine (AVG) (125 mg٠L-1), 1-aminocyclopropane-1- carboxylic acid (ACC) (200 μL٠L-1) and a combination of the two were evaluated together with postharvest 1-methylcyclopropene (1-MCP), to determine the effect on red colour development, fruit quality and maturity of ‘Cripps’ Pink’ apples. ACC successfully increased percentage blush coverage of fruit and percentage Pink Lady™ pack-out; however, fruit maturity was advanced. AVG on its own resulted in a delay in red colour development, as well as fruit ripening. The combination of ACC and AVG resulted in fruit colour similar to that of untreated control fruit. The effect of ACC (100 μL٠L-1 – 400 μL٠L-1) applied two weeks before harvest on red colour development of ‘Fuji Kiku’ (Brak) and ‘Cripps’ Pink’ apples was evaluated over one and two seasons, respectively. The internal ethylene concentration (IEC) of ‘Cripps’ Pink’ apples was determined. A rapid increase in IEC of fruit after ACC application in both seasons indicated that ACC was taken up by the fruit and converted to ethylene. This resulted in an earlier shift in harvest distribution for both cultivars, indicating stimulation of red colour development by ACC. Loss in fruit firmness, greater starch breakdown and yellower ground colour of fruit treated with higher rates of ACC (300 μL٠L-1 and 400 μL٠L-1) indicate that the advance in red colour development was due to advanced maturity. ACC applied at 200 μL٠L- 1 followed by postharvest 1-MCP treatment showed potential for aiding colour development of bi-colour apples without negatively affecting fruit maturity. Two commercially available reflective mulches, viz. Lumilys® and ColorIt, were installed four to five weeks before harvest and evaluated on ‘Rosy Glow’ and ‘Fuji’ apples to improve red colour development without advancing fruit maturity. Trials were conducted in open orchards as well as under shade netting. Both reflective fabrics performed similarly in reflecting photosynthetically active radiation and increasing red blush colour of both cultivars, especially of the lower canopy fruit, compared to fruit from trees next to grassed alleys. Fruit maturity was largely unaffected by mulch installation, but varying results in parameters such as fruit firmness of ‘Rosy Glow’ apples indicate that this needs to be further investigated. The high initial input cost of reflective mulches might be justified by its improvement of Class one pack-out of fruit as well as its reusability within a season and over various seasons. Overall, the application of reflective mulching seems to be the better way to improve colour in ‘Cripps’ Pink’ and ‘Fuji rather than ACC application.

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Browsing Masters Degrees (Horticulture) by browse.metadata.advisor "Crouch, E. M."

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