https://etd.cput.ac.za/handle/20.500.11838/726 Mon, 11 May 2026 08:24:29 GMT 2026-05-11T08:24:29Z https://etd.cput.ac.za/handle/20.500.11838/4247 Title: Application of yeast-based biocontrol agents against fruit spoilage moulds Authors: Gomomo, Zukisani Abstract: Fruits such as apples, oranges, strawberries and grapes are of commercial importance, serving as primary sources of essential growth factors, including vitamins and minerals. However, their production, safety, and economic contributions to the agricultural sector are severely impacted by mould-induced spoilage. Pathogens such as Botrytis cinerea and Penicillium spp. cause substantial losses during pre- and post-harvest stages, with over 50% of fruit losses in developing countries attributed to these fungi. In South Africa, annual fruit losses due to mould spoilage exceed 60%. Synthetic chemical fungicides are widely used to manage fruit spoilage fungi, but their prolonged application raises concerns regarding environmental safety, consumer health, and the development of fungicide-resistant strains. Consequently, non-Saccharomyces yeasts have emerged as promising, eco-friendly biocontrol agents. These yeasts utilise diverse mechanisms such as nutrient competition, parasitism, and the secretion of antimicrobial compounds to inhibit fungal growth. This study aimed to evaluate non-Saccharomyces yeasts for extracellular enzyme production, antifungal activity against key fruit spoilage fungi, and their viability and stability assessments on fruit surfaces under post-harvest conditions. Among 23 yeast isolates screened for extracellular enzyme activity, five were selected for further analysis: Aureobasidium melanogenum (Y6), Suhomyces pyralidae (Y63), Pichia kluyveri (Y64), Meyerozyma guilliermondii (Y88) and Zygoascus hellenicus (Y89). These yeasts were tested in vitro using radial inhibition, dual culture, and double Petri dish assays, as well as in vivo post-harvest trials on apples, strawberries, and oranges. The yeasts were evaluated for antagonistic effects against three B. cinerea strains (B05.10, IWBT-FF1, PPRI 30807) and three Penicillium species (Penicillium expansum PPRI 5654, P. italicum PPRI 10380 and P. digitatum PPRI 30517). Compatibility and potential synergistic effects were assessed through yeast-yeast interaction assays. Extracellular enzyme production varied among the isolates, with Aureobasidium melanogenum demonstrating robust activity for proteases, glucanases, chitinases, cellulases and pectinases. This yeast achieved 55%, 52% and 40% inhibition against B. cinerea strains B05.10, IWBT-FF1 and PPRI 30807, respectively. Pichia kluyveri and M. guilliermondii showed 100% inhibition of B. cinerea spore germination, while S. pyralidae exhibited 100% inhibition for two strains (B. cinerea B05.10 and IWBT-FF1), and 87% for B. cinerea PPRI 30807. Volatile organic compounds (VOCs) such as isobutanol, 2-phenylethanol, and isoamyl acetate, identified using solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME-GC-MS) were found to contribute to mould inhibition. During post-harvest trials, S. pyralidae achieved the highest inhibition of B. cinerea on apples with a mean inhibition of 43%, while M. guilliermondii was most effective against P. digitatum and P. italicum on oranges. Commercial fungicides demonstrated higher efficacy in some instances, though yeast treatments provided viable alternative control. Stability and viability assays revealed varying levels of yeast survival on fruit surfaces, with a decrease in yeast cell concentrations observed after oven drying, while stability was maintained during the storage period. The study concludes that the selected non-Saccharomyces yeasts hold significant potential as biological control agents against fruit spoilage moulds. While post harvest trials demonstrate promising results, further optimisation and field applications are recommended to enhance their efficacy and adoption in agricultural practices. Description: Thesis (Doctor of Agriculture)--Cape Peninsula University of Technology, 2004 Mon, 01 Jan 2024 00:00:00 GMT https://etd.cput.ac.za/handle/20.500.11838/4247 2024-01-01T00:00:00Z https://etd.cput.ac.za/handle/20.500.11838/727 Title: Seed flavonoid concentration in cowpea genotypes and the effect of plant density on growth, N₂ fixation and rhizosphere phosphatases and grain yield of cowpea intercropped with sorghum Authors: Makoi, Joachim HJR Abstract: A 3-factorial experiment involving two cowpea densities (83,000 and 167,000 plants.ha-1), two cropping systems (i.e. monoculture and mixed culture) and five cowpea genotypes (i.e. three farmer-selected cultivars, Bensogla, Sanzie and Omondaw and two improved varieties, ITH98-46 and TVu1509) was conducted in the field for two consecutive years in 2005 and 2006. The aim was to assess the effect of plant density, cropping system and cowpea genotypes on: (i) chlorophyll and gas-exchange, (ii) rhizosphere mineral concentration and tissue uptake of nutrients, (iii) acid and alkaline phosphatase activities in the rhizosphere, (iv) plant growth and symbiotic performance, and (v) concentration of flavonoids and anthocyanins in seed extracts and plant organs and their effect on pest infestation and diseases. The results showed that high plant density (167,000 plants.ha-1) and mixed culture significantly decreased gas-exchange parameters, leaf chlorophyll content, 13C and %C in both cowpea and sorghum plants compared with low plant density (83,000 plants.ha-1) and monoculture. The data also showed significantly higher 13C and lower %C in ITH98-46 and TVu1509 compared with Bensogla, Omondaw and Sanzie genotypes with a significant correlation between 13C and water-use efficiency. At harvest, grain yield of cowpea and sorghum was significantly decreased by high plant density and mixed culture compared with low plant density and monoculture. Sanzie genotype was generally superior in grain yield (2,550 kg.ha-1) followed by cvs. Omondaw and Bensogla (2,250 and 2,150 kg.ha-1, respectively) compared with the improved cultivars. Sorghum plants in mixture with cv. TVu1509 or cv. ITH98-46 performed better (1,570 and 1,550 kg.ha-1, respectively) compared with those in mixture with other cultivars. The results also showed greater land equivalent ratio (LER = 1.42 to 1.52), suggesting that mixed culture produced greater total yields per unit land area compared with monoculture. Description: Thesis (DTech (Faculty of Applied Sciences)--Cape Peninsula University of Technology, 2009 Thu, 01 Jan 2009 00:00:00 GMT https://etd.cput.ac.za/handle/20.500.11838/727 2009-01-01T00:00:00Z