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Oniha, M. I. and Covenant University, Theses (2021) CHARACTERISATION AND MANAGEMENT OF FUNGAL DISEASES OF Carica papaya (L.) IN A RESEARCH FARM. ["eprint_fieldopt_thesis_type_phd" not defined] thesis, Covenant University Ota.

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Fungi are the most important group of microorganisms that attack Carica papaya leading to economic losses. Previous research on papaya disease management tend to focus on post-harvest diseases compared to field diseases which may be directly linked to the post-harvest diseases. Chemical fungicides are the major management mechanism employed to control preharvest fungal diseases with consequent toxicological risks to biota. This study was conducted to evaluate fungal diseases of C. papaya obtained from the pawpaw research demonstration farm in Covenant University. The study also evaluated the antifungal activity of some plant extracts as potential biocontrol agents. The fungal disease symptoms observed during the study, were evaluated and analyzed using disease incidence and severity as measurement tools. Fruit, leaf and stem samples were collected from infected papaya to isolate fungal pathogens during the early and late preharvest seasons. The isolates were first phenotypically characterised and then genotypically identified based on the Internal Transcribed Spacer genes. To assess the pathogenicity of the isolated fungi, the isolates were screened in vitro for cellulolytic and pectinolytic enzyme production using plate screening assay. Then n-Hexane, ethyl acetate, ethanol, methanol and aqueous leaf extracts of Moringa oleifera Lam, Chrysophyllum albidum G. Don, Celosia argentea L, Telfaira occidentalis Hook F. and Bauhinia monandra BmoLLwere evaluated for antifungal activity in vitro. Three aqueous extracts with best activity were further evaluated in vivo on papaya fruits. Results of the study showed that disease severity was significantly higher in the late than the early preharvest season. Phenotypically characterised fungal isolates were confirmed genotypically as Aspergillus niger Van.Tiegham, Aspergillus aculeatus Lizuka, Aspergillus flavus Link, Aspergillus fumigatus Fresineus, Trichoderma reesei QM6a, Trichoderma longibrachiatum Rifai, Rhizopus oryzae Went and Geerlings and Rhizopus delemar Boidin. Aspergillus niger was the most frequently isolated fungus from fruit (29.41%) and stem (27.94%) samples while Geotrichum spp Link was the most frequently isolated from leaves (20.90%). Phylogenetic analysis of the amino acid sequence data showed the evolutionary relatedness of the characterised fungal species with their nearest neighbours. Secretion of cell wall degrading enzymes varied significantly among the fungal isolates indicating significant variation in pathogenicity (p<0.05). In vitro antifungal, minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) assessments showed that the aqueous extracts had significant effects (p=0.000) against all assessed fungal isolates than other extract types except for the ethanolic and methanolic extracts of C. argentea and C. albidum respectively. The highest zones of inhibition of the various aqueous extracts ranged from 23.33-39.00 mm and compared positively against Ketoconazole (11-15 mm; control antifungal agent). The aqueous extract of B. monandra had the highest in vivo activity with 150 mg/ml and 75 mg/ml inhibiting fungal growth for up to 5 and 3 days respectively. This study has generated fresh fungal sequence data which have been deposited into the genebank database. The study also identified that members of Aspergillus and Rhizopus genera are the major fungi responsible for papaya diseases. It also further validated the potentials of some medicinal plants as antifungal agents for the sustainable management of papaya diseases.

Item Type: Thesis (["eprint_fieldopt_thesis_type_phd" not defined])
Uncontrolled Keywords: Carica papaya, Fungi, Antifungal plants, Papaya disease management, Pawpaw farm
Subjects: Q Science > QH Natural history
Q Science > QH Natural history > QH301 Biology
Depositing User: nwokealisi
Date Deposited: 19 Oct 2022 11:58
Last Modified: 19 Oct 2022 11:58

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