Thesis (M. Sc. (Botany)) -- University of the North, 1999 / Refer to the document

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Chilling injury in banana fruit is caused by prolonged exposure to temperatures less than 13°C. This can occur during bunch development in the field or postharvest handling and storage. Mild symptoms of chilling injury are localised to peel tissue and reduce visual quality of fruit. Light microscopy was used in the present study to analyse symptoms of mild chilling injury in Cavendish cv. Williams banana. Following storage at 5°C for 24hours, symptoms of chilling injury in the form of brown discolouration was observed within laticifers in sub-epidermal peel tissue. Browning was not observed in other vascular tissues as previous research has suggested. Causal mechanisms associated with browning of latex within laticifers were investigated. Polyphenol oxidase (PPO) activity in fractions of banana peel latex was measured and found to be highest in the lutoid fraction. PPO activity also provided indirect evidence that phenolics were present in peel latex. Literature suggests possible compartmentalisation of PPO and phenolics in banana lutoids. In this study it is suggested that PPO and phenolics associated with lutoids in banana peel latex may be involved in browning due to chilling stress. The lipid content of lutoids from banana latex was also investigated using FTIR spectroscopy, but showed no further involvement of lutoids in the browning reaction caused by chilling. Control of field chilling using modified bunch covers was investigated. Bunch covers used in modern banana production are usually polyethylene bags, placed over bunches during development in the field. Experiments in a northern Queensland plantation investigated effects of modified bunch covers on fruit yield and quality characteristics of Cavendish cv. Williams bananas, including the development of mild chilling injury symptoms. A further field trial was conducted using different coloured bunch covers with varied interception of photosynthetically-active radiation (PAR), to determine any negative effects of bunch cover shading on fruit yield and quality. Different coloured and layered polyethylene films (blue, double green, silver yellow and silver black) modified PAR transmission of bunch covers (PAR transmission [%] = 56, 38, 7, 0). During summer 2003, varying PAR transmission of bunch covers significantly affected fruit size. Fruit from blue polyethylene covers, which transmitted most light, were larger than fruit from covers with less light transmission. Between cover treatments of lower light transmission, fruit size remained similar. It is suggested, during summer when cloud cover in northern Queensland limits solar radiation, bunch covers with high PAR transmission facilitate greater bunch photosynthesis, which improves fruit size. Fruit quality was generally unaffected by varying PAR transmission of bunch covers, but cover treatments were found to influence peel colour. Peel colour of fruit from 'silver black' covers was significantly paler. This may have impacted upon green life due to increased de-greening. Results from this experiment suggest that bunch photosynthesis significantly influences fruit size and peel colour during summer growing periods. Modified bunch covers constructed from existing bunch cover films and polyethylene bubble wrap ('blue + silver bubble' and sealed and non-sealed 'silver blue + silver bubble') were used to test control of field chilling during winter 2003 and 2004. Compared to standard blue polyethylene bunch covers, modified covers significantly reduced exposure of bunches to chilling conditions in the field and the development of visible chilling injury symptoms on the peel surface and in underpeel tissue. Greatest control of field chilling was shown using the non-sealed 'silver blue + silver bubble' cover design. Relative to the standard blue cover, in winter 2003 the non-sealed 'silver blue + silver bubble' cover design reduced chilling exposure by 95% at the top and 45% at the bottom of bunches. This totally controlled chilling injury symptoms in the top and middle bunch regions. In winter 2004 chilling conditions were more severe and chilling exposure was reduced by 85% using the non-sealed 'silver blue + silver bubble' cover. This reduced the severity of peel surface chilling symptoms by 67% in the top bunch region relative to fruit from blue covers. Yield characteristics were positively influenced by 'blue + silver bubble' and sealed and non-sealed 'silver blue + silver bubble' covers. Improved fruit size and weight was probably due to enhanced temperature conditions inside the bunch environment, relative to 'control' covers. Fruit quality was generally unaffected by 'blue + silver bubble' and sealed and non-sealed 'silver blue + silver bubble' covers. However peel colour was significantly influenced by these cover treatments, compared to the 'control' covers. Reduced light transmission of covers produced paler fruit. This may have influenced other quality characteristics, such as green life and SSC levels, as it confounded assessment of ripening stage. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1241852 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture and Wine, 2006

Made available in DSpace on 2014-06-11T19:33:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-05-11Bitstream added on 2014-06-13T19:44:33Z : No. of bitstreams: 1 miguel_aca_dr_jabo.pdf: 5169762 bytes, checksum: 9976d67d3d00b8169b60eeb898705743 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Determinou-se os binômios temperatura x tempo de armazenamento, que podem ocasionar injúria pelo frio em mangas ‘Tommy Atkins’ e ‘Palmer’, com avaliação das alterações no seu metabolismo, o que permitiu que se testasse o uso de tratamento térmico e de radiação ultravioleta (UV-C) para minimizar ou eliminar esta injúria. Avaliou-se também a eficiência do uso de quitosana como alternativa à cera, comumente aplicada após o tratamento térmico. No 1º e 2º experimentos, frutos colhidos no estádio “de vez”, foram armazenados a 2 ºC, 5 ºC e 12 ºC por 1, 2, 3 e 4 semanas. Ao final de cada período, foram transferidos para condição ambiente, por até 7 dias. No 3º e 4º experimentos, uma parte dos frutos foi tratada hidrotermicamente a 46,1 ºC por 90 min ou 55 ºC por 5 min e a outra, submetida à ação de radiação (UV-C) nas doses de 1,14 kJ m-2 e 2,28 kJ m-2, antes do armazenamento sob condição promotora de injúria por frio, a 5 ºC por 14 dias (‘Tommy Atkins’) e a 5 ºC por 4 dias (‘Palmer’). No 5º e 6º experimentos, frutos tratados com radiação (UV-C) receberam filme de cera de carnaúba ou quitosana a 1% e 1,5%, antes de serem armazenados sob condição promotora de injúria, a 5 ºC por 14 dias (‘Tommy Atkins’) e a 5 ºC por 4 dias (‘Palmer’), sendo após esse período, transferidos para a condição ambiente, onde foram mantidos por 7 dias para a ‘Tommy Atkins’ e por até 12 dias, para a ‘Palmer’. Em todos os experimentos, os frutos foram avaliados semanalmente durante o armazenamento refrigerado, e a cada 2 dias depois de levados ao ambiente, quanto ao murchamento, coloração, podridões, massa fresca, firmeza, danos pelo frio, atividade respiratória, teores de sólidos solúveis, acidez titulável, açúcares solúveis e... / It was determined the binomials temperature vs. time, which can cause chilling injury in mangoes 'Tommy Atkins' and 'Palmer', with the evaluation of the changes in their metabolism, allowing to test the use of heat treatment and UV-C radiation to minimize or eliminate this injury. It also evaluated the effectiveness of the use of chitosan as an alternative to the carnauba wax, usually applied after the heat treatment. In the 1st and the 2nd experiments, fruits harvested at “medium ripe” were stored at 2 ºC, 5 ºC and 12 ºC for 1, 2, 3 and 4 weeks. At the end of each period, they were transferred to the environmental condition up to 7 days. In the 3rd and the 4th experiments, a part of the fruits was treated hydrothermally at 46.1 ºC for 90 min or 55 ºC for 5 min and another part submitted to the action of UV-C radiation at doses of 1.14 kJ m-2 and 2.28 kJ m-2, before the storage under chilling injury condition, at 5 ºC for 14 days (‘Tommy Atkins’) and at 5 ºC for 4 days (‘Palmer’). In the 5th and 6th experiments, fruits treated with UV-C radiation were coated with carnauba wax or chitosan at 1% and 1.5%, before being stored under chilling injury condition, at 5 ºC for 14 days (‘Tommy Atkins’) and at 5 ºC for 4 days (‘Palmer’), and thereafter transferred to the environmental condition, where they were maintained up to 7 days (‘Tommy Atkins’) and up to 12 days (‘Palmer’). In all experiments, the fruits were evaluated weekly during the cold storage, and every two days after they were taken to the environment, for the wilting, color, rottenness, mass loss, firmness, chilling injury, respiration rate, soluble solids, titratable acidity, soluble and reducing sugars, ascorbic acid and total polyphenols, total antioxidant activity and the enzymes of peroxidase, polyphenoloxidase and phenylalanine ammonia-lyase. The results... (Complete abstract click electronic access below)

Orientador: Jose Fernando Durigan / Banca: Ben-Hur Mattiuz / Banca: Angelo Pedro Jacomino / Banca: Rogério Lopes Vieites / Banca: Gustavo Henrique de Almeida Teixeira / Resumo: Determinou-se os binômios temperatura x tempo de armazenamento, que podem ocasionar injúria pelo frio em mangas 'Tommy Atkins' e 'Palmer', com avaliação das alterações no seu metabolismo, o que permitiu que se testasse o uso de tratamento térmico e de radiação ultravioleta (UV-C) para minimizar ou eliminar esta injúria. Avaliou-se também a eficiência do uso de quitosana como alternativa à cera, comumente aplicada após o tratamento térmico. No 1º e 2º experimentos, frutos colhidos no estádio "de vez", foram armazenados a 2 ºC, 5 ºC e 12 ºC por 1, 2, 3 e 4 semanas. Ao final de cada período, foram transferidos para condição ambiente, por até 7 dias. No 3º e 4º experimentos, uma parte dos frutos foi tratada hidrotermicamente a 46,1 ºC por 90 min ou 55 ºC por 5 min e a outra, submetida à ação de radiação (UV-C) nas doses de 1,14 kJ m-2 e 2,28 kJ m-2, antes do armazenamento sob condição promotora de injúria por frio, a 5 ºC por 14 dias ('Tommy Atkins') e a 5 ºC por 4 dias ('Palmer'). No 5º e 6º experimentos, frutos tratados com radiação (UV-C) receberam filme de cera de carnaúba ou quitosana a 1% e 1,5%, antes de serem armazenados sob condição promotora de injúria, a 5 ºC por 14 dias ('Tommy Atkins') e a 5 ºC por 4 dias ('Palmer'), sendo após esse período, transferidos para a condição ambiente, onde foram mantidos por 7 dias para a 'Tommy Atkins' e por até 12 dias, para a 'Palmer'. Em todos os experimentos, os frutos foram avaliados semanalmente durante o armazenamento refrigerado, e a cada 2 dias depois de levados ao ambiente, quanto ao murchamento, coloração, podridões, massa fresca, firmeza, danos pelo frio, atividade respiratória, teores de sólidos solúveis, acidez titulável, açúcares solúveis e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: It was determined the binomials temperature vs. time, which can cause chilling injury in mangoes 'Tommy Atkins' and 'Palmer', with the evaluation of the changes in their metabolism, allowing to test the use of heat treatment and UV-C radiation to minimize or eliminate this injury. It also evaluated the effectiveness of the use of chitosan as an alternative to the carnauba wax, usually applied after the heat treatment. In the 1st and the 2nd experiments, fruits harvested at "medium ripe" were stored at 2 ºC, 5 ºC and 12 ºC for 1, 2, 3 and 4 weeks. At the end of each period, they were transferred to the environmental condition up to 7 days. In the 3rd and the 4th experiments, a part of the fruits was treated hydrothermally at 46.1 ºC for 90 min or 55 ºC for 5 min and another part submitted to the action of UV-C radiation at doses of 1.14 kJ m-2 and 2.28 kJ m-2, before the storage under chilling injury condition, at 5 ºC for 14 days ('Tommy Atkins') and at 5 ºC for 4 days ('Palmer'). In the 5th and 6th experiments, fruits treated with UV-C radiation were coated with carnauba wax or chitosan at 1% and 1.5%, before being stored under chilling injury condition, at 5 ºC for 14 days ('Tommy Atkins') and at 5 ºC for 4 days ('Palmer'), and thereafter transferred to the environmental condition, where they were maintained up to 7 days ('Tommy Atkins') and up to 12 days ('Palmer'). In all experiments, the fruits were evaluated weekly during the cold storage, and every two days after they were taken to the environment, for the wilting, color, rottenness, mass loss, firmness, chilling injury, respiration rate, soluble solids, titratable acidity, soluble and reducing sugars, ascorbic acid and total polyphenols, total antioxidant activity and the enzymes of peroxidase, polyphenoloxidase and phenylalanine ammonia-lyase. The results... (Complete abstract click electronic access below) / Doutor

>Magister Scientiae - MSc / Fruit storage at cold temperatures is normally used to delay decay while maintaining the fruit’s quality. However, storage at low temperatures for a prolonged period causes some important metabolic functions within the fruit to stop functioning properly. This phenomenon is even more critical and complex in chilling-sensitive fruits. Fruits that originated in the tropical and sub-tropical regions are known to be chilling sensitive; their storage at low but non-freezing temperatures causes them to experience chilling injury (CI). Chilling injury causes irreversible damage to the external and internal attributes of the fruits. Pomegranate, which is investigated in this study, is consumed as fresh arils in many regions of the world. / 2023

Thesis (M. Sc. (Horticulture)) -- University of Limpopo, 2019 / The South African Avocado Industry is continuously expanding with ‘Hass’ cultivar occupying the largest land and therefore, the most exported cultivar. Expansion of the industry implies an increased demand for irrigation water. However, South Africa is a water scarce country characterised by low and erratic rainfall, where fruit production relies heavily on irrigation. The agricultural sector is under an obligation to reduce water use due to the increasing demand for water by other economic sectors. Therefore, it must find efficient water use techniques to save water and ensure water availability for other economic sectors. Partial root-zone drying (PRD) is an irrigation technique which may lead to 50% reduction in water use, half of the root system is kept wet while the other half is left dry to a predetermined level of soil water depletion, the dry and the moist sides are alternated at regular intervals. During storage and transportation of fresh produce, low temperature is a post-harvest tool used to maintain quality, especially when fruit are destined for long distant export markets. This study investigated the effect of PRD and low temperature storage on post-harvest quality parameters of ‘Hass’ avocado fruit. The experiment was laid as a factorial arranged in randomised complete block design (RCBD). The treatment factors for chilling injury, electrolyte leakage and vascular browning were 2 x irrigation regimes (Full Irrigation (FI) vs. PRD) and 2 x storage temperatures (2.0 and 5.5°C). However, treatment factors for fruit weight loss, respiration rate, fruit firmness, ripening percentage and fruit skin colour were 2 x irrigation regimes (Full Irrigation (FI) vs. PRD), 2 x storage temperatures (2.0 and 5.5°C) and 4 ripening days (0, 2, 4 and 6 days). Mature ‘Hass’ avocado fruit were harvested from PRD and fully irrigated trees and thereafter fruit of each treatment were stored at 2.0 and 5.5°C for 28 days. Each treatment consisted of 6 replicates, with an exception of electrolyte leakage, whereby the experiment was replicated 4 times. After 28 days’ storage at 2.0 and 5.5°C, fruit were ripened at 21°C. The effect of PRD and low temperature storage was determined by evaluating the following physico-chemical fruit parameters during ripening: external chilling injury, electrolyte leakage, fruit weight loss, respiration rate, firmness, fruit skin colour and vascular browning. During ripening, ‘Hass’ avocado fruit stored at 2.0°C showed significantly higher incidences of external chilling injury symptoms compared with xiii 5.5°C, irrespective of irrigation treatment. Furthermore, an interaction between irrigation treatment and low storage temperature had a significant (P<0.05) effect on cell membrane electrolyte leakage. All evaluated fruit showed similar weight loss, irrespective of irrigation and storage treatment. Irrigation, storage temperature and ripening days did not have effect on respiration during ripening. Fruit reached the respiratory climacteric peak on the same day (day 2). Furthermore, there was no significant interaction effect (P˃0.05) on fruit firmness. However, PRD treated fruit showed slightly low firmness when compared with control fruit. ‘Hass’ avocado fruit harvested from PRD and fully irrigated trees and stored at 5.5°C ripened quicker compared to fruit stored at 2.0°C. There was no significant interaction effect (P˃0.05) on fruit skin lightness (L), chroma (C), hue angle (h°) and fruit eye colour due to irrigation and cold storage treatment. In general, fruit showed skin colour change from emerald green to approximately 75% coloured. Furthermore, irrigation and storage temperature did not have effect on vascular browning, however, there incidence was high on fruit stored at 2.0°C when compared with 5.5°C. The results of this study indicated that ‘Hass’ avocado fruit stored at 2.0°C was negatively affected by low temperature storage and this cold storage temperature is not recommended. PRD reduced water use during irrigation, however, its effect on post-harvest quality of ‘Hass’ avocado fruit subjected to 5.5°C must be further investigated before recommended for export markets. / Agricultural Research Council-Tropical and Subtropical Crops (ARC-TSC) and Agricultural Sector Education Training Authority (AgriSeta)

Thesis (M.Sc.(Agricultural Management )) -- University of Limpopo, 2020 / Avocado fruit ‘Hass’ harvested during early-season and exposed to temperature at 5.5°C for 28 d are susceptible to chilling injury (CI); and therefore, develop poor skin colour during ripening. In ‘Hass’ avocado fruit, skin colour change during ripening is used by European market to indicate fruit ripeness and softness. Therefore, the aim of this study was to evaluate the use of hot water (HW) and methyl jasmonate (MJ) as postharvest treatment dips to mitigate CI; and thereby, enhance ‘Hass’ avocado fruit peel colour during ripening. Fruit were harvested randomly from 5 selected trees treated alike during early season (April 2018); and thereafter, transported to the laboratory. At the laboratory, experiments of this study were divided into 2: experiment (1) fruit were dipped into HW (38, 42 and 46°C for 30, 25 and 20 min, respectively); and experiment (2) fruit were dipped into MJ (10 and 100 µmol/L for 2 min) treatments. In both experiments after these treatments, fruit were allowed to dry for 60 minutes at ambient (±25°C) temperature and untreated fruit were used as control. Thereafter, fruit were stored at commercial shipping temperature (5.5°C) for up to 28 d. After removal from cold storage, fruit were ripened at ambient temperature (±25°C) and evaluated every after 2 d for weight loss, firmness loss, objective colour parameters (lightness-L*, chroma-C* and hue angle-h*), subjective colour (eye colour) and ripening percentage. However, chilling injury (CI) and electrolyte leakage (EL) were evaluated immediately after removal from cold storage. The results showed that HW significantly (P< 0.05) increased weight and firmness loss during ripening. Furthermore, HW reduced EL and external chilling injury (ECI) of ‘Hass’ avocado fruit during cold storage. In addition, the results showed that HW had significant effect (P< 0.05) on colour parameter L* and eye colour rating, but did not affect (P> 0.05) C* and h*. Avocado ‘Hass’ fruit subjected to HW at 42°C/25 and 46°C/20 min developed purple colour (eye colour rating 4.47 and 4.36, respectively) during ripening when compared with HW at 38°C/30 min and control fruit. Moreover, results showed that dipping fruit in 10 µmol/L had a significant effect (P< 0.05) on reducing weight loss during ripening. Methyl jasmonate (10 and 100 µmol/L) treatment reduced EL and alleviated external chilling injury (ECI) of ‘Hass’ fruit during cold storage. The results showed that MJ (10 and 100 µmol/L) treatments had significant effect (P< 0.05) on colour parameter L*, h* and eye colour rating, but did not affect (P> 0.05) C*. Furthermore, ‘Hass’ fruit treated with 10 and 100 µmol/L MJ reached the purple skin colour (eye rating 5.39 and 5.19, respectively) during ripening. Fruit dipped in MJ (10 µmol/L) had low weight loss when compared with fruit treated with MJ (100 µmol/L). In conclusion, the results of this study indicated that HW (42°C/25 minutes) and MJ (10 µmol/L) effectively alleviated external chilling injury; and therefore, improved ‘Hass’ skin colour development during ripening / Agricultural Research Council-Institute (Agriseta) and University of Limpopo

The primary objective of the research was to study the physiological and biochemical changes in Hass avocado fruit stored in different combination of oxygen and carbon dioxide concentrations at both 0 degrees and 5 degrees Centigrade (C), and to determine whether storage in controlled atmosphere (CA) can decrease the incidence of chilling injury (CI). A secondary objective was to identify possible correlations between CA, the incidence of CI, the activity of some ripening related enzymes and changes in proteins during ripening at 20 degrees C following storage at low temperatures. Fruit suffered no CI and ripened normally following CA storage for 3 weeks at both 0 degrees and 5 degrees C, then transferred to air for 6 days at 20 degrees C. CI symptoms did develop after CA storage for 6 and 9 weeks at 0 degrees C. Changes in proteins during ripening were analysed by 2D-PAGE. Some polypeptides were detected in unripe fruit but decreased with ripening. Polypeptides of 16.5, 25, 36 and 56 kD (kilo Dalton) were present early in ripening and their levels further increased during ripening. The appearance of three ripening related polypeptides with estimated molecular weights 80 kD (pI 3.6), 36 kD (pI 5.8) and 16.5 kD (pI 5.7) was observed in fruit at the climacteric stage. Three polypeptides with estimated molecular weights of 41 kD (pI7.8), 36 kD (pI 5.8) and 33 kD (pI 5.1) were found in air stored fruit but were not detected in fruit stored in CA. This research showed that CA did not ameliorate CI at 0 degrees C, instead storage at 0 degrees C caused a premature increase in ethylene production when the fruit were returned to air at 20 degrees C. In contrast, CA storage at 5 degrees C retarded ethylene production and ripening in fruit after it was returned to air at 20 degrees C. / Doctor of Philosophy (PhD)

Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / The South African Avocado Industry has recently announced plans to expand exports into new markets, such as the United States (US). As a requirement for these markets, fruit of high quality must be stored at ultra-low temperature to mitigate phytosanitary risks. However, ‘Hass’ avocado fruit are susceptible to chilling injury when stored at temperatures below 3°C. Moreover, CI development resulted in uneven ripening and disease infestation due to damaged cell membranes. Therefore, the objective of this study was to evaluate the potential of methyl jasmonate (MeJA) and salicylic acid (SA) on quality maintenance of 'Hass' avocado fruit during ultra-low cold storage. Matured ‘Hass’ avocado fruit were harvested at commercial dry matter (22%). The experiment was conducted using a completely randomized design (CRD) with eight replications per treatment. Treatment concentrations for methyl jasmonate (MeJA) were 0 (control), 10 and 100 μmol•L−1 , while those for salicylic acid (SA) were 0 (control), 1.0, 2.0 and 3.0 mM. After treatments, fruit were stored at 2°C for 31 days and thereafter, ripened at ambient temperature (±25°C) until fully ripe. During ripening, fruit were evaluated for weight loss, exocarp colour, firmness, chilling injury, as well as physiological (vascular browning) and pathological disorders (fruit rot). In this study, dipping fruit in MeJA solution significantly (P < 0.05) reduced ‘Hass’ avocado fruit firmness loss. Moreover, MeJA showed a significant effect (P < 0.05) on hue angle (h°) but did not significantly affect (P > 0.05) visual colour rating, chroma (C*), lightness (L*) and weight loss. The results showed that ‘Hass’ avocado fruit treated with 10 μmol•L−1 MeJA reduced weight loss when compared with 100 μmol•L−1 MeJA from day 2 to day 8 of ripening. Overall results showed a visual change in ‘Hass’ avocado fruit exocarp colour, with eye colour changing from rating 1 (emerald-green) to 3 (olive- green) for control and fruit treated with MeJA throughout the ripening days. Furthermore, MeJA reduced ‘Hass’ avocado fruit external chilling injury, physiological and pathological disorders. With respect to SA treatments, the result showed that dipping fruit at 1.0 and 2.0 mM SA had a significant effect (P < 0.05) on reducing firmness loss during ripening. Salicylic acid (1.0 mM) reduced and alleviated ‘Hass’ avocado fruit external chilling injury during ultra-low cold storage. Furthermore, result showed that 1.0 and 2.0 mM SA treatments had significant affect (P < 0.05) on firmness loss. Moreover, a significant effect was observed on visual colour and C* but did not affect (P > 0.05) L* and h°. Fruit treated with SA showed poor exocarp colour development with extended exposure to ultra-low cold storage, as a result, developed chilling symptoms. The treatment of ‘Hass’ avocado fruit with 1.0 mM SA inhibited the incidence of fruit rot and vascular browning when compared with control and fruit treated with 2.0 and 3.0 mM SA. In conclusion, 10 and 100 μmol•L−1 MeJA and 1.0, 2.0 and 3.0 mM SA effectively preserved ‘Hass’ avocado fruit quality during storage at ultra-low temperature. / Agricultural Sector Education Training Authority (AgriSeta) and National Research Foundation (NRF)

Thesis (M.Sc.( Agriculture (Horticulture)) -- University of Limpopo, 2022 / Avocado fruit ‘Hass’ exocarp changes colour from green to purple and black during ripening. However, uniform purple or black exocarp colour is not achieved during ripening, leading to consumers' rejection of fruit for not meeting quality standards. Avocado ‘Hass’ fruit harvested early remain green or develop a multicoloured appearance, concurrently devaluing their commercial value; and, therefore, unattractive to consumers. Therefore, this study aimed to investigate the role of sucrose and calcium postharvest pulsing on early matured ‘Hass’ avocado exocarp colour change during ripening. In this study, early matured ‘Hass’ avocado fruit were harvested from Halls and Sons, Mataffin farm (25°25’39.13” S, 30°55’52.84” E), Nelspruit, South Africa with 10 cm pedicel at commercial dry matter content (22%). Thereafter, the fruit were transported to the University of Mpumalanga laboratory. In the laboratory, the study was divided into two experiments: Experiment 1 ‘Hass’ fruit were continuously infused through the pedicel with different sucrose concentrations; 0 (control), 0.2 and 0.5 mM L-1. Experiment 2 fruit were infused with different calcium chloride (CaCl2) concentrations; 0 (control), 2 and 3 mM L-1. In both experiments, treated and untreated fruit were stored at 5.5°C for 28 days. After removal from cold storage, fruit were ripened at room temperature (±25°C) and evaluated every other day for firmness, subjective colour (visual colour), objective colour parameters (lightness-L*, chroma-C* and hue angle- h°), external chilling injury and ripening percentage. The results showed that Su (0.2 mM L-1) pulsing extended the ripening period by one day, corresponding with maintained fruit firmness. Furthermore, Su (0.2 mM L-1) treated fruit reduced the ‘Hass’ avocado fruit chilling injury index (CII) during cold storage. With respect to colour change, Su (0.5 mM L-1) treated fruit developed purple colour when compared with Su (0.2 mM L-1), which only developed to olive colour on the final ripening day (day 6). In addition, the results showed that all sucrose concentrations had a significant decreasing effect (P < 0.05) on objective colour parameters (L*, C* and h°) and increasing visual colour rating. With respect to CaCl2 treatments, fruit firmness decline was significantly delayed, which resulted in extended ripening time. Moreover, CaCl2 (2 and 3 mM L-1) significantly decreased (P < 0.05) pericarp objective colour parameters (L*, C* and h°) and increased visual colour rating and developed purple colour on the final ripening day (days 6 and 8, respectively). In addition, pulsing with CaCl2 (2 and 3 mM L-1) concentration reduced chilling injury during storage compared with control fruit. In conclusion, the results of this study indicated that Su and CaCl2 applied as postharvest treatments may contribute to avocado colour development by increasing anthocyanin accumulation. However, future research is required to investigate whether these treatments affect anthocyanin biosynthesis at the gene level.