Citrus is among the most important fruit crops worlstwide, and therefore the preservation and improvement of citrus germplasm is of the essence. Citrus breeders are often faced with the difficulty of distinguishing between new and existing cultivars because of the ambiguous nature of morphological traits due to environmental influences and error in human judgement. The protection of new varieties is very important to the breeder. New varieties cannot be patented in South Africa, but it can be protected by Plant Breeders' Rights, only if it is genetically distinguishable and significantly different economically from existing varieties. Cultivars in four genera (c. sinensis, C. paradisi, C. grandis and C. reticulata) included in the Citrus Improvement Programme (CIP) or cultivars awaiting recognition of Plant Breeders' Rights by the International Union for the Protection of New Plant Varieties (UPOV) were analyzed with Isoenzymes, Restriction Fragment Length Polymorphism (RFLP) and Random Amplified Polymorphic DNA (RAPD). Five enzyme systems (PGM, PGI, MDH, GOT and IDH) were analyzed and founded to be suitable for grouping together cultivars belonging to the same genera. It was not suited for routine discrimination of cultivars in a particular genus. RFLP studies were conducted on five grapefruit cultivars, using cDNA clones from a genomic library of Rough Lemon. RFLP studies were valuable for the discrimination of closely related cultivars which probably originated from a common ancestor by bud mutations. This technique was, however, abandoned due to its biohazardous nature and replaced by the PeR-based Random Amplified Polymorphic DNA. RAPDs are easy to perform and gave promisin& results which were exploited to reveal polymorphisms between cultivars within the various groups. Although the interpretation of data produced by this method is often suspicious, it is the best method currently available for cultivar identification. It can playa complementary role in the protection of new varieties when classical morphological interpretation of differences is not capable of determining sufficient distinctness for the awarding of Plant Breeders' Rights.

Ph.D. (Agriculture)) -- University of Limpopo, 2021 / The rind physiological disorders incidence such as rind pitting is a challenge to the citrus industry as it affects appearance; and ultimately, acceptability and purchase in both local and international markets. Although the internal quality is not directly affected by rind pitting, fruit damaged by this disorder are rejected in the fresh fruit market. The susceptibility to this disorder varies among citrus fruit cultivars. Other factors impacting rind physiological disorders include; pre-harvest environmental conditions and postharvest storage conditions. However, the main cause of this disorder is still unknown. In South Africa, ‘Benny’ valencias are the most prone orange cultivars to rind pitting disorder within the sweet-orange-type. Therefore, the aim of this study was to investigate production site and postharvest treatments’ effect on physico-chemical, biochemical properties, antioxidants, rind soluble sugars and gene expression in relation to rind pitting development of ‘Benny’ valencia citrus fruit. During 2016 and 2017 seasons, the study was conducted, whereby, ‘Benny’ valencia citrus fruit were harvested from Tzaneen, Groblersdal and Musina in South Africa. After harvesting, the fruits were transported to the Agricultural Research Council- Tropical and Subtropical Crops (ARC-TSC) postharvest laboratory in Nelspruit for sorting, grading treatment, cold storage and post-storage quality evaluation. After sorting and grading, fruits were subjected to the following treatments: T1 = no wax plus dehydration, T2 = wax plus dehydration and T3 = wax plus no dehydration. Dehydrated treatments were applied for 3 days at relative humidity of ±45%, thereafter, fruit were stored at -0.6 and 4.5°C for 28 days plus 7 days shelf-life. After removal from cold storage plus 7 days shelf-life, fruit were analysed for rind pitting incidence (RPI), weight loss percentage (WL), firmness, total electrolyte leakage (TEL), total soluble solids (TSS), titratable acidity (TA) and TSS: TA ratio. xxvi Afterwards, fruit were peeled to remove flavedo, thereafter; the flavedo peels were freeze-dried, milled and stored at -21°C for further physiological analysis. Freeze dried flavedo peel was analysed for total flavonoids, total phenolics, vitamin C, soluble sugars (glucose, fructose and sucrose), antioxidant assays (FRAP, DPPH, ABST and ORAC) and genes. The results showed that rind pitting incidence was high on fruit subjected to wax plus no dehydration across all storage temperatures and production sites. Furthermore, results showed that fruit harvested from Musina exposed to T1 had higher incidence of rind pitting than those from Groblersdal and Tzaneen, irrespective of storage temperature. Meanwhile, fruit harvested from Musina had the highest TEL when compared with Groblersdal and Tzaneen irrespective of treatments and storage temperatures. A significantly higher (P<0.05) WL was observed in Musina fruit harvested from Tzaneen exposed to T3 at both storage temperatures. Moreover, increased TSS was observed after storage across all production site and postharvest treatments. The study showed that production site and postharvest treatments had a significant influence on rind pitting and total electrolyte leakage. Additionally, fruit treated with no wax + dehydration was found to be more susceptible to rind pitting. However, fruit sourced from Tzaneen had significantly (P<0.0001) high TPC and TFC, irrespective of postharvest treatments therefore, low rind pitting incidence. While rind vitamin C was higher in fruit from Groblersdal when compared with Tzaneen and Musina. However, low RPI was also observed in fruit sourced from Groblersdal. Fruit from Musina subjected to wax plus dehydration had higher RSA and low RPI at both temperatures when compared with fruit sourced from Groblersdal and Tzaneen. Therefore, wax plus dehydration resulted in low rind pitting with an increased accumulation of rind biochemical concentrations, xxvii irrespective of cold storage temperatures. These results suggested that there is a link between rind pitting and rind biochemical concentrations in the ‘Benny’ valencia citrus fruit. Moreover, fruit from Musina subjected to wax plus dehydration had higher antioxidant measured by DPPH and low RPI at both low storage temperatures when compared with fruit harvested from Groblersdal and Tzaneen. Furthermore, fruit harvested from Musina and treated with no wax plus dehydration, thereafter, stored at -0.6°C had low RPI with high antioxidant activity measured by FRAP than Tzaneen and Groblersdal regions in both seasons. With respect to sugars, fructose was not significantly (P<0.05) affected by production sites, postharvest treatments and cold storage temperature, hence, the low pitting incidence. The highest glucose was observed in fruit harvested from Groblersdal, irrespective of treatments and cold storage temperatures when compared with those from Tzaneen and Musina, low RPI was also observed in fruit harvested from Groblersdal. However, fruit harvested from Groblersdal treated with wax plus dehydration and stored at 4.5°C had higher sucrose and low RPI when compared with Tzaneen and Musina. Moreover, this study suggested that soluble sugars in ‘Benny’ valencia flavedo during cold storage is involved in rind pitting tolerance mediated by wax plus dehydration treatment. Three homologic genes: CsCP gene; CsNAC-domain protein gene; CsCP-F gene; were chosen to examine the relationship between their expression and citrus rind pitting through quantitative RT-PCR analysis in pitting and no-pitting fruits. Results showed that the expression of CsCP, CsNAC and CsCP-F genes were all higher in the pitting rind fruit harvested from Tzaneen and low in fruit with low pitting. Groblersdal and Musina fruit had low expression of genes and low rind pitting was observed. Therefore, findings suggested that CsCP, CsNAC and CsCP-F genes may xxviii be linked to non-chilling rind pitting and could serve as targets for future investigation. Generally, the overall results obtained in this study provided an understanding into the previous unknown complexities of citrus non-chilling rind pitting. Moreover, the study revealed that the studied factors had an influence on non-chilling rind pitting and physico-chemical properties of ‘Benny’ valencia citrus fruit. In addition, postharvest treatments resulted in low non-chilling rind pitting with an increased accumulation of rind biochemical concentrations. The fruit with high antioxidant capacity were found to be tolerant to rind pitting, whereas, fruit with low antioxidant capacity were found to be susceptible to rind pitting. Furthermore, soluble sugars are believed to be involved in the defence mechanisms against non-chilling rind pitting in the fruit. Gene expression changes also provided clues about the possible mechanisms involved in non-chilling rind pitting development. / National Research Fund, Agricultural Research Council Tropical and Subtropical Fruit Crops and Citrus Academy

MSc (Applied Mathematics) / Department of Applied Mathematcs / See the attached abstract below

The main objective of this study was to analyse South African (SA) citrus farmers’ perceptions of the benefits and costs of complying with quality assurance (QA) certification schemes for citrus exports to the European Union (EU). The study used an e-mail and postal survey questionnaire mailed to a stratified random sample of 260 SA commercial citrus growers during July 2007. The survey yielded 108 usable responses - a response rate of 10.8% from the target population of 1001 commercial SA citrus growers. The main factors motivating respondents to adopt QA certification were to keep and maintain access to existing markets; to improve customer confidence in their products; to access new markets; and to meet food safety and retailer requirements. Principal Component Analysis (PCA) identified six underlying dimensions of motivators, which suggest a drive by sampled respondents to gain certification to meet market requirements, achieve intra-farm benefits such as cost-reduction, and to remain competitive in existing and new foreign markets. The sampled respondents identified the main internal benefits from QA certification as the ability to retain existing markets; improved worker health and safety; better access to foreign markets; better farm organisation; and improved fruit safety and orchard management. The PCA identified six broad dimensions of these internal benefits. Comparing the motivator and perceived benefit dimensions, most of the motivators seem to have been in part realised by the respondents. Respondents rated shared goals and values about the product; more joint decision making on fruit safety; more working together on quality assurance; a better business working relationship; improved coordination; and improved trust as the six major supply chain benefits from QA certification. The two dimensions identified from these external benefits by PCA were: (1) Improved working relationship and product quality benefits, and (2) Improved cooperation and contractual benefits. The major costs of implementing EUREPGAP certification related to initial investment costs and the recurrent annual costs of compliance. The respondents, on average, spent an estimated R70655 on initial compliance costs, mainly for infrastructure, additional buildings and employees training. Some 60% of respondents spent less than 1% of annual farm turnover on initial compliance costs, while most of the respondents (84%) spent less than 1% of annual farm turnover on recurrent costs of compliance. Growers that owned a pack-house had statistically significantly higher initial and annual costs of compliance. Most (63%) of the respondents had a relatively high level of overall satisfaction with QA certification. The second objective of this study was to analyse the determinants of SA citrus farmers’ overall level of satisfaction with QA certification. Ordinary Least Squares (OLS) regression estimated that perceived dimensions of internal benefits, namely (1) Foreign market access benefits; (2) Intra-farm benefits; (3) Improved fruit safety and orchard management; (4) Quality and worker welfare benefits; and (5) Ability to retain existing markets, all had a statistically significant positive influence on the sampled growers’ overall level of satisfaction with QA certification. Supply chain benefits also had a positive effect on overall level of satisfaction, although the effects were not statistically significant. Similarly, no statistically significant relationship could be established between farm size or the respondents’ level of satisfaction with their certifying agents and their overall level of satisfaction with QA certification. Record keeping is required by nearly all EUREPGAP control chapters and for farm audits. Crop protection is also perceived as a complex requirement of the EUREPGAP protocol. Policymakers thus need to be aware of the extra costs that protocols create for management. The Citrus Growers’ Association of Southern Africa (CGA) could consider providing more extension advice to farmers on the technical requirements of certification (particularly best practices for implementing the control chapters). Comparing the motivator and perceived benefit dimensions, most of the motivators for QA certification seem to have been in part realised by the respondents. For instance, the drivers to improve business image/market competitiveness/market access requirements/farm profitability were realised via perceived reputation/input cost savings/foreign market and profit improvement benefits. The study results, therefore, provide some evidence that QA certification is a necessary strategy for maintaining competitiveness in EU citrus markets. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.