Thesis (Ph.D. (Plant Production)) -- University of Limpopo, 2022 / In 'Hass' avocado fruit, pre-harvest and postharvest factors affecting exocarp colour change during ripening are vital to maintain the industry’s credibility, competitiveness and profitability. Currently, the South African ‘Hass’ avocado fruit exocarp colour development is affected by pre- and postharvest factors, ultimately, fruit does not develop the required purple colour during ripening. These pre- and postharvest factors must be understood in order to implement strategies that avoid downgrading of South African 'Hass' avocado fruit by lucrative markets due to insufficient purple colour development during ripening. In 'Hass' avocado fruit, exocarp colour development is associated with an increase in anthocyanin synthesis and accumulation during ripening. However, limited information is available regarding factors regulating anthocyanin synthesis and accumulation in 'Hass' avocado fruit during ripening. Therefore, the overall aims of this study were to investigate pre-harvest practices and postharvest treatment that increase exocarp anthocyanin synthesis during ripening. In addition, determine whether exocarp glucose and other antioxidants contribute to 'Hass' avocado fruit exocarp colour development during ripening. In chapter 3, the study looked at how crop load adjustment affects ‘Hass’ avocado fruit exocarp colour development during ripening at three different harvest maturities. The crop load adjustment treatments were applied as: high (100%), moderate (50%) and low (25%) at three harvest times (early, mid- and late). After harvest, fruit were stored at 5.5°C for 28 days, thereafter, ripened at 25°C. The experimental design was carried out as 3 x 3 factorial, arranged in a completely randomized design (CRD) with three replications. The results showed that total anthocyanin and cyanidin 3-O-glucoside concentrations of ‘Hass’ avocados increased following crop load adjustment from normal (100%) to moderate (50%) and low (25%) loads, resulting in improved exocarp colour development during ripening. Furthermore, we discovered that fruit harvested from moderate (50%) and low (25%) crop loads accumulated higher exocarp sugars (D-mannoheptulose and perseitol) at three harvest maturities when compared with high crop load (100%). Moreover, total phenolic concentration of fruit harvested from moderate (50%) and low (25%) crop loads was higher than that obtained from high load fruits, irrespective of harvest maturities. In chapter 4, the study examined the interaction between branch girdling and harvest maturation on the development of 'Hass' avocado fruit exocarp colour during ripening. The experimental design was carried out as 2 x 2 factorial, arranged in a completely randomized design (CRD). The results showed that fruit harvested from girdled trees had poor exocarp colour development as compared to fruit harvested from control trees, regardless of harvest time. Fruit harvested from girdled and ungirdled avocado trees did not show significant differences in visual exocarp colour during early and mid-maturity. Apart from crop load adjustment and girdling as pre-harvest methods to manipulate postharvest exocarp colour, glucose was also infused through the pedicel. Studies on the effect of glucose infusion through the pedicel on the exocarp colour of the ‘Hass’ avocado fruit during ripening were presented in chapter 5. The study included five treatments; control fruit with pedicel and infused with distilled water and glucose concentrations (0.05, 0.13 and 0.28 mM). The distilled water, glucose infused and control fruit were stored at 5.5°C for up to 28 days. After cold storage, fruit were kept at ambient temperature 25°C for ripening. The experiment was conducted as a completely randomized design (CRD) with three replications per treatment. The results showed that glucose infusion through the pedicel markedly increased anthocyanin and cyanidin 3-O-glucoside concentration during ripening. Interestingly, glucose concentrations (0.05 and 0.13 mM) resulted in purple colour development after 8 days at 25°C when compared with control, distilled water and highest concentration (0.28 mM). In chapter 6, the relationship between 'Hass' avocado fruit size, exocarp colour and related pigments with antioxidants capacity and sugar concentration during ripening were investigated. The fruit were categorized by their weight; small (< 200 g) and large (> 201 g). Their diameter and length were also measured using a vernier calliper. Fruit ware stored at 5.5°C for 28 days, then ripened at 25°C. The experimental design was carried out as a completely randomised design (CRD), using 25 fruit replications per category. The results showed that small-sized fruit developed the desirable purple to black exocarp colour when compared with large-sized fruit. Additionally, the results showed that small-sized fruit had higher antioxidant capacity as measured by 2,2 diphenyl 1 picrylhydrazyl (DPPH), ascorbic acid and flavonoid content during ripening when compared with large-sized fruit. Furthermore, it was found that small-sized fruit accumulated higher exocarp and seeds (D-mannoheptulose, perseitol, sucrose and glucose) sugar concentration. We demonstrated and concluded that exocarp colour, pigments, antioxidants and sugar concentration are closely related to size in 'Hass' avocado fruit. Knowledge from this thesis contributes toward the understanding of pre and postharvest factors that may influence colour development of ‘Hass’ avocado fruit during ripening. This study contributes towards bridging the gap in the literature on the biochemical changes associated with colour development of ‘Hass’ avocado fruit during ripening / Agricultural Research Council-Tropical and Subtropical Crops (ARC-TSC) and National Research Foundation (NRF)

The role of agriculture in rural development is widely documented in literature. Many analysts regard agriculture, specifically small-scale agriculture, as the cornerstone for viable and sustainable economic growth. Furthermore, the agricultural sector is seen as an effective instrument for poverty reduction, particularly in rural communities of developing countries where a large amount of poor people are concentrated. Indeed, analysts now agree that developing the agricultural sector is perhaps one of the most effective ways to address high levels of poverty evident in the developing world, and call on the world leaders to commit themselves to direct more investment into this sector. Using the avocado industry in Giheta-Burundi, this dissertation argues that some emerging crops (such as avocados) present enormous opportunities to income generation for small-scale farmers with the potentiality of diversifying cash crop farming in Burundi, an area currently dominated by coffee, tea and cotton. This study further suggests that avocado farming presents the economic, market and health potentiality to contribute to a viable and sustainable rural economy in Giheta Burundi, thereby reducing levels of poverty in this area. The main research question is as follows: “To what extent does the production of avocados benefit the income and wellbeing of small-scale farming households in Giheta?” Accordingly, the main policy concern is that if avocados are playing a crucial role for income generation, wellbeing and diet of the small-scale farmers in Giheta, the avocado sector needs to be substantially supported by both the private and public sectors in order to increase the capacity of avocado production in this area and subsequently enable small-scale farmers to gain greater income from this sector. All of which will contribute significantly to reducing levels of poverty in Giheta. This dissertation is 42 266 words in length excluding references and appendices. / Thesis (M.A.)-University of KwaZulu-Natal, Durban, 2011.

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.