Thesis (MSc. (Agricultural Economics)) -- University of Limpopo, 2018 / The avocado industry is a major industry in South Africa and this can be seen by its economic contribution. Limpopo Province is one of the major avocado producing areas in South Africa, and avocado production within the province ranges from smallholder to commercial production. Smallholder avocado producers within the province have a significant role to play, especially if their full potential is unleashed. For smallholder farmers to play such a role they need to be competitive. The concept of competitiveness can be defined as the ability of an industry or firm to compete successfully in order to achieve sustainable growth while earning at least the opportunity cost on resources employed. The main aim of this study was to analyse the determinants of competitiveness of smallholder avocado farmers in the Vhembe District of the Limpopo Province based on the Porter’s Diamond model framework in order to assess the level of competitiveness of farmers and to establish how the farmers can be assisted to reach their full potential. The study was conducted in the Vhembe District Municipality and a sample of 60 farmers was interviewed. SPSS (SPSS 26.0) was used to analyse the data. Three analytical techniques were used in the analysis for this study. Firstly, factor analysis was used to reduce and group the number of variables associated with competitiveness of the farmers. Secondly, profitability analysis through enterprise budgeting was used to categorise the farmers into two groups; competitive and noncompetitive. Thirdly, Logistic regression was used to establish the socio-economic and Porter’s Diamond model determinants that could be linked to the competitiveness of the farmers. From the factor analysis, 5 factors were extracted, namely; “chance”, “government, related and supporting industries”, “factor conditions”, “firm strategy structure and rivalry” and “demand conditions”. From the profitability analysis the farmers were grouped into competitive and non-competitive categories with 22 farmers classified as being competitive and 38 farmers as being non-competitive. From the results of logistic regression, 7 out of 12 hypothesised variables were found to be statistically significant, these were; age of farmer, number of trees planted, related and supporting industries, firm strategy structure and rivalry, chance, demand conditions and factor conditions. Chance was the only variable with a statistically significant v negative influence on the competitiveness of the farmers, this was because factors that were tested for their influence on the competitiveness of the farmers are among others: Crime, HIV/AIDS, fires, frost and floods. Based on the research findings, several policy suggestions were made, these include; mentorship and encouragement of youth participation in farming, provision of agricultural land, capacity building for farmers, government support and stakeholder mobilization, specialized extension service and formation of cooperatives as well as encouraging commercialization.

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.

This work identifies transcription factors (TF) controlling triacylglycerol (TAG) synthesis and accumulation in plant tissues. TAG plays vital role in plants and are used by humans. Most plants accumulate oil in the seed, but some species accumulate oil in other tissues. The Wrinkled1 (WRI1) TF has been shown to regulate oil accumulation in multiple species and tissues. Here, four WRI homologues in avocado were identified, their phylogeny was examined and three of them were cloned into expression vectors for further characterization. However, WRI1 likely does not act alone in regulation of TAG accumulation in plants. Additional candidate TFs were identified by using transcriptome data from a variety of species, and cloned into expression vectors. Future studies will be able to use this information to better understand regulation of TAG accumulation, which will allow increased oil accumulation in plants for various human uses.

Avocado is an economically important crop with ~ 60-70 % oil, by dry weight, in its fruit mesocarp tissue. The steady increase in global demand for avocado (9% per year) has driven interest to identify the biochemical and molecular factors that regulate its triacylglycerol (TAG, oil) biosynthesis. Using 454- and Illumina-based RNA-Seq approaches, we examined the transcriptional basis for TAG biosynthesis in developing mesocarp of avocado. Deep transcriptional profiling data allowed us to identify several transcripts that were differentially represented between the early and late developmental stages of mesocarp. Further analysis of the transcriptome, during oil accumulation, revealed an increased expression of genes mostly associated with fatty acid biosynthesis in plastid but not that of TAG assembly in the endoplasmic reticulum. This pattern of expression was similar to that previously observed in other seed and non-seed tissues. Moreover, WRINKLED1 transcription factor, a regulatory element associated with oil biosynthesis in seed and non-seed tissues of monocot and dicot plants, was identified in avocado as well. Our studies point to distinctive modes of regulation of fatty acid biosynthesis and TAG assembly that are conserved in both seed and non-seed oil-rich plants.

Avocados are one of the major food sources in tropical and subtropical regions and are an important horticultural crop in South Africa. Avocados are exported over long distances and may have storage times of up to 30 or more days at temperatures of about 5.5oC. This procedure increases the risk of poor fruit quality, including physiological disorders, early softening and postharvest disease incidence. A major component of the postharvest diseases is Anthracnose caused by Colletotrichum gloeosporioides. Anthracnose infects unripe fruit and once infected, the fungus remains dormant in the fruit until ripening begins. This leads to a problem for producers and packers, as the presence of the disease cannot be detected on the pack line, and fruit is not removed. Anthracnose control is normally done through pre-harvest treatment with copper-based fungicides. While effective such treatment needs to be repeated frequently, resulting in copper residues on the avocados. The study was conducted to investigate the effects of phosphoric acid and potassium silicate on known antifungal compounds and critical enzymes of the pathways elemental for systemic resistance inducers, so as to evaluate the potential for using them as alternatives to or in conjunction with, copper fungicides in the control of Anthracnose in avocado fruit. The study included storage temperature and time variations, to take account of the logistics in shipping avocado fruit to distant markets. Pre- and postharvest applications of phosphoric acid and potassium silicate were used, and after harvest, fruit were either ripened at room temperature (22oC) without storage or stored for 28 days at temperatures of 5.5oC or 2oC before analysis. Concentrations of phenolics, activity of the enzyme phenylalanine ammonia lyase (PAL) and a known antifungal diene were determined in the fruit exocarp. Pre-harvest treatments of phosphoric acid showed that the highest phenolic concentration was found in fruit harvested 14 days after application for fruit stored at room temperature. For fruit stored at 5.5°C it was seen that as fruit softened, phenolic concentrations increased compared with hard fruit immediately after storage, with the highest increase noted for fruit harvested 7 days after application. When comparing the three storage temperatures, phenolic concentrations were enhanced most when fruit was stored at 2°C. Postharvest treatments showed a significant increase in phenolic concentrations for potassium silicate treated fruit stored at room temperature and 2°C when determined immediately after storage. Fruit stored at 5.5°C showed an increase in phenolic concentrations as it became softer. When considering PAL enzyme activity, it was found that postharvest treatments of both potassium silicate and phosphoric acid influenced enzyme activity, with potassium silicate having greater effects. Similarly, an increase in PAL activity was noted in the pre-harvest phosphoric acid treatment harvested 14 days after application for fruit ripened immediately as well as fruit stored at 5.5°C. Fruit stored at 2°C showed the highest PAL activity for fruit harvested 7 days after application. No results were obtained in the analysis of antifungal compounds for both pre- and postharvest treatments. However, it is suggested that the antifungal diene could follow similar trends to those found for phenolics. It is concluded that applications of both phosphoric acid and potassium silicate do create changes in phenolic concentrations and the activity of the enzyme PAL which is involved in the synthesis of phenolic compounds known to possess antifungal properties. It is therefore possible that phosphoric acid and potassium silicate may be used as part of an integrated programme for Anthracnose control, and should be tested as potential alternatives for high volume copper-based fungicides. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Avocado sunblotch disease is a graft-transmissible disorder known for over 60 years and has now been recorded in at least eight countries around the world. Affected trees develop yellow, depressed streaks on young stems and fruit, marked rectangular cracking of the mature bark and a decumbent style of growth. Often a tree with symptoms produces completely symptomless shoots, termed 'recovery' growth, which are latently infected. There is a reported 95 to 100% transmission of sunblotch through the seed of such branches, and "the resultant seedlings are themselves symptomless. Indexing for sunblotch to ensure that scion and, in view of seed transmission, especially rootstock material is free of the disease is very important . The standard method used for many years has been to graft tissue onto healthy indicator seedlings and observe for symptom development for 18 months to two years. One aim of the study presented in this thesis was to develop more rapid methods for detecting the sunblotch agent. By conducting the standard indexing method in a glasshouse at controlled high temperatures of 30/28º C (day/ night) and by cutting back the indicator plants every three months, the time was reduced from two years to eight months. While this represents a considerable saving in time, the ideal must be to develop a laboratory diagnostic test that requires no more than a few days, at most, to complete. A comparative study was therefore initiated on the phenol metabolism of healthy and sunblotch-infected avocados to determine whether infection causes any major change that may reliably serve as a marker for diagnostic purposes. Significantly increased peroxidase (PO) and phenylalanine ammonia-lyase (PAL) activities, decreased indoleacetic acid (IAA) oxidase activity and higher sinapic acid levels were detected in bark tissue showing sunblotch symptoms, but not in symptomless 'recovery' growth. In contrast, increased polyphenoloxidase (PPO) activity and isoenzymes, total soluble protein levels, water soluble phenols and reduced ferulic acid levels were found in the bark of all infected trees tested, both with symptoms and symptomless. However, these latter changes have been associated with other plant-virus systems and are therefore not necessarily specific for sunblotch. Neither is any sufficiently large to be definitive as a diagnostic test. Two unidentified phenols were detected in infected, mature bark, but not in infected young bark and leaves. introduced the possibility of rapid disease detection by polyacrylamide gel electrophoresis (PAGE) of extracted RNA's as used for known viroids. In this study the presence of previously reported small molecular weight sunblotchassociated RNA's was confirmed using PAGE methods requiring two to four days to complete. This thesis presents as a further development a more rapid method of PAGE detection of RNA's enabling indexing for sunblotch to be completed in under six hours. Whilst the biochemical studies did not reveal diagnostically meaningful differences between healthy and infected avocados, there were tendencies towards differences between healthy and symptomless carrier tissues, further investigation of which may lead to a future understanding of symptom development and the symptomless condition. These include apparent higher PO and lower PAL activities in symptomless carrier tissue, as well as higher PO isoenzyme a[1] and lower IAA oxidase isoenzyme a[1] activities. General studies on sunblotch-infected avocados showed that fruit from symptomless 'recovery' growth branches are significantly larger and have a higher oil content than those from healthy or diseased branches, the latter finding possibly indicating a more advanced state of maturity of 'recovery' growth fruit due to earlier flowering. The avocado sunblotch agent was shown to have an in vivo thermal inactivation point of 55º C, a temperature higher than the avocado tissue can withstand thereby eliminating the possibility of thermotherapy of infected twigs. In a host range study four lauraceous plant species, Persea Schiedeana, Cinnamomum zeylanicum, C. camphora and Ocotea bullata, were successfully infected with sunblotch by grafting from infected avocado. This is the first demonstration of any host other than avocado. A phanerogametic member of the same family, Cassytha filiformis, was shown to be able to transmit the disease from avocado to avocado. No hosts from other families were found. During an electron microscope study of sunblotch-infected avocado leaf tissue, gross alterations of the chloroplasts in the yellow areas were observed. These changes included organelle swelling, loss of grana and stroma lamellae, rearrangement of remaining membranes and presence of vesicles. Also in the yellow areas paramural bodies were encountered in higher numbers and displaying altered structure than in healthy and symptomless infected leaf tissue. This study on avocado sunblotch disease was successful in both of its aims. Firstly with regard to quicker indexing techniques, the standard method using indicator plants was shortened from two years to eight months, while a rapid, six-hour test based on PAGE analysis, was developed. Secondly, more light has been shed on the biochemical and ultrastructural effects of sunblotch on its host, the avocado, as well as providing information regarding the thermal sensitivity and the host range of the agent. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1980.

This study covered both the Hass and Fuerte varieties of avocado pears. The quality of extracted avocado oil produced by different extraction techniques was assessed to determine the effect the extraction method had on the nutritional and storage value of the oil. While microwave extraction produced the highest yield of oil (70.0 %), supercritical fluid extraction produced oil with a wider range of fatty acids. Although the Hass variety produced a higher oil yield, oil extracted from the Fuerte variety was shown to have a higher monounsaturated fatty acid to saturated fatty acid ratio, which makes the latter oil more beneficial to health. Oils of the Fuerte variety also possessed a higher concentration of co-extracted metals, which makes it more susceptible to lipid oxidation. The overall choice for the most efficient extraction method was microwave extraction as it produced the highest yield and quality of oil. The impact of soil quality on elemental uptake into locally grown avocado fruit sampled from six different locations was determined. Of the 14 selected metals investigated, avocado fruit was found not to accumulate Cd, Co, Cr, Pb and Se. Generally, the concentration of elements in both varieties of fruit was in the order of Mg > Ca > Al > Zn > Fe > Mn > Cu > Ni > As. Relative bioaccumulation plots were used to establish the essential and non-essential elements for normal growth of avocado fruit. It was found that the plant has an involuntary uptake mechanism for As due to similarity in ion species to P, which is an essential element. The impact of soil quality parameters pH, cation exchange capacity and soil organic matter were determined and their impact on plant-soil interactions was analysed. Statistical analysis revealed a plethora of metal interactions at the plant-soil interface. However, the plant was still seen to control uptake of specific elements such as Cu, Fe and Ca, due to its physiological requirements. CEC was found to have a greater effect on availability of elements than pH and SOM. Geoaccumulation indices indicated moderate enrichment of Pb in soils; however this result had no bearing on the elemental uptake of the fruit at all sites. Comparisons to recommended dietary allowances (RDAs) for human diet reveal the average contribution of avocado to be 70% and 45% for Cu and Mn, respectively. Low levels of As was found in fruit which warrants continued monitoring of this element in the plant due to its similarity to P. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2011.

Orientador: Aloísio Costa Sampaio / Coorientador: Marco Antonio Tecchio / Banca: Terezinha de Fátima Fumes / Banca: Luis Lessi dos Reis / Banca: Tatiana Eugena Cantuarias Avilés / Banca: Jose Eduardo Creste / Resumo: O desenvolvimento de um modelo fenológico para o abacateiro em clima subtropical, poderá subsidiar consideravelmente um melhor planejamento das práticas culturais, incluindo uma adubação e nutrição equilibradas, com consequências diretas na ativa- ção de mecanismos de defesa da planta. Neste contexto, o presente trabalho teve como objetivo avaliar o desempenho fenológico e a nutrição mineral das cultivares de abacateiros 'Hass' (8 anos), 'Fortuna' (14 anos) e 'Margarida' (24 anos). O trabalho foi realizado na Fazenda 'Campo de Ouro' localizada no município de Piraju - SP, no sudoeste do Estado de São Paulo, situado, nas coordenadas 23º11'37" S, 49º23'02" N com altitude média de 757 metros. Foram realizados dois experimentos, sendo que em um deles, avaliaram-se as etapas fenológicas das três cultivares: início e término do florescimento, florescimento pleno, fixação e abscisão de frutos, crescimento de ramos, raízes e frutos. O delineamento experimental foi inteiramente casualizados, utilizando-se três tratamentos, correspondentes às cultivares 'Fortuna' (plantado em 1998), 'Hass' (plantado em 2008) e 'Margarida' (plantado em 1991), com 10 repetições e 1 planta por parcela. Foram avaliados dois ciclos agrícolas 2014/2015 e 2015/2016 empregada a meio de estatística descritiva. No segundo experimento foram avaliados os teores de macro e micronutrientes das inflorescências, ao longo do ciclo, folhas e frutos. Com coletas mensais de folhas, enquanto outras partes vegetais foram co... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: For avocado trees under subtropical conditions, developing a phenological model can considerably subsidize planning system of good practices, including a balanced crop nutrition and fertilization that activates the plant defense mechanism. Therefore, the current study aimed to assess the phenological performance and mineral nutrition of three avocado cultivars, that is, 'Hass' (8 years old), 'Fortuna' (14 years old) and 'Mar-garida' (24 years old). This study took place at 'Campo de Ouro' Farm that is located in the municipality of Piraju, state of São Paulo. The farm is in the southwest of the state, is determined by the limits of 23º11'37"S and 49º23'02"N, with an altitude of 757m. Furthermore, two experiments were carried out, in which one of them evaluated the phenological phases of the three cultivars: flowering from beginning to end; full-flowering; fruit fixing and abscission; branch, root and fruit growth. A completely ran-domized design was set by using three treatments, corresponding to each cultivar, that is, 'Fortuna' (planted in 1998), 'Hass' (planted in 2008) and 'Margarida' (planted in 1991), with 10 replicates and 1 plant per plot. Moreover, two agricultural cycles 2014/2015 and 2015/2016 were evaluated by using descriptive statistics. In the second experiment, macro-and micronutrient contents of the inflorescences were evaluated, along the cycle, leaves and fruits. Besides leaves were picked on a monthly basis, while other plant parts were collected during flowering and harvest. Average results indicate that flowering period was of 42 days in avocado trees, being 'Fortuna' the earliest and 'Margarida' the latest, but also the most productive. Also, there were four peaks of root growth in each evaluated crop. Regarding to mineral analysis, nitrogen, phosphorus and potassium were the most extracted from fruits. Inflorescence ... / Doutor

Biological pre- and postharvest disease control strategies depend on successful colonisation and survival of the introduced antagonists on the infection court. Effective and economical applications involve targeting the antagonists where they are critically needed i.e. the infection court. Honeybee dispersal is one method of antagonist application to such specific sites. In view of this, an in vitro experiment was conducted to investigate attachment, colonisation and survival of Bacillus subtilis on avocado flowers. Scanning electron microscopy studies showed that the bacterium could attach and colonise avocado flower surfaces. It can also survive on the flowers for longer periods of time. In vivo mode of action of the antagonist against stem-end rot (SER) pathogens was also studied where results showed lysis and degradation of hyphae and conidia. However, no viable colonies were retrieved from bee antagonist dispersal under field conditions. Bee antagonist dissemination was compared with antagonist and fungicide spray applications in terms of SER control and the added effect on other diseases such as Cercospora spot and anthracnose. Spray applications of the antagonist were more effective in reducing the incidence of SER than bee dissemination. Integrated sprays of the antagonist and fungicides significantly reduced the incidence of both pre- and postharvest diseases. The identity of Dothiorella aromatica, one of the most important SER pathogens, was investigated at a molecular level. RAPD techniques using the discriminatory OPC02 primer successfully separated isolates into three groups based on banding profiles. A further study using RFLP identified the pathogen as a Botryosphaeria spp. The most dominant specie was B. parva followed by B. rhodina. Further studies should focus on assessing the distribution of these pathogens within avocado-growing regions of South Africa. / Dissertation (MSc (Plant Pathology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

The avocado mesocarp contains up to 60-70% oil by dry weight where triacylglycerol (TAG) is the major constituent. There is significant human nutritional demand for vegetable oil, but its use in production of renewable biomaterials and fuels has intensified the need to further increase oil production. In plants, the final and committed step in TAG biosynthesis is catalyzed by diacylglycerol acyltransferases (DGAT) and/or a phospholipid: diacylglycerol acyltransferases (PDAT). Both DGAT and PDAT contribute to TAG biosynthesis in an independent or overlapping manner, depending on the species. However, preferred pathway for TAG biosynthesis is not well studied in nonseed tissues such as mesocarp. Based on the transcriptome data of Persea americana it is hypothesized that both DGAT and PDAT are likely to catalyze the conversion of diacylglycerol to TAG. In this study, putative DGAT1 was identified and comprehensive in silico analyses were conducted to determine the respective start codons, full-length coding sequences, transmembrane domains, predicted protein structures and phylogenetic relationships with other known DGAT1s. These data reveal that the putative DGAT1 of a basal angiosperm species retain features that are conserved not only among angiosperms but also other eukaryotes. For further functional analysis, the avocado DGAT1 was expressed in H1246, a TAG-deficient yeast strain and lipotoxicity rescue assays, TLC analysis, Nile Red staining were conducted. The complementation of this yeast strain confirmed enzyme activity and supported the possible role of avocado DGAT1 in TAG biosynthesis. Finally, substrate specificity of DGAT was determined by incubating microsomes with different radiolabeled substances and found that avocado DGAT1 has a preference toward oleic acid (18:1) compared to palmitic acid (16:0) while it is converting diacylglycerol (DAG) to triacylglycerol. In summary, we characterized functional DGAT1 in a basal angiosperm species, which may be metabolically engineered into crop species to produce TAG enriched in oleic acid.