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Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants
Thesis (MSc)--Stellenbosch University, 2025.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614108470214656 |
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| access_status_str | Open Access |
| author | Goodchild, Shannon |
| author2 | Maree, Hans Jacob |
| author_browse | Goodchild, Shannon Maree, Hans Jacob |
| author_facet | Maree, Hans Jacob Goodchild, Shannon |
| author_sort | Goodchild, Shannon |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134622 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:46:47.817Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134622 Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants Goodchild, Shannon Maree, Hans Jacob Bester, Rachelle Stellenbosch University. Faculty of Science. Dept. of Genetics. Citrus -- Diseases and pests -- Biological control Greening disease -- South Africa Citrus fruit industry -- South Africa Candidatus Liberibacter africanus (CLaf) -- Genetic aspects Plant cells and tissues -- Diseases UCTD Thesis (MSc)--Stellenbosch University, 2025. Goodchild, S. 2025. Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/e5f5eca7-5881-4021-a51d-0bd89b1d9d51 ENGLISH ABSTRACT: Huánglóngbìng (HLB) is one of the most significant biological threats to the global citrus industry. It is caused by three closely related, phloem-limited bacteria: ‘Candidatus Liberibacter asiaticus’ (CLas), ‘Ca. L. americanus’ (CLam), and ‘Ca. L. africanus’ (CLaf). The laBer, responsible for the milder form of the disease known as ‘African Greening’, is transmiBed by the insect vector Trioza erytreae (Del Guercio). Despite its long-standing presence in South Africa, many aspects of the CLaf pathosystem remain poorly understood, particularly its long-term impact on tree health and its epidemiological paBerns in commercial orchards. This study aimed to advance understanding of CLaf by evaluating its spatial and temporal distribution in different tissue types and citrus types across multiple timepoints. Greenhouse experiments evaluated bacterial localisation in leaves, bark, and root tissue of Carrizo Citrange, Swingle Citrumelo, and Mexican Lime using quantitative real-time polymerase chain reaction (qPCR). Results indicated that citrus type significantly influenced bacterial concentration in tissue types. Mexican Lime harboured the highest concentrations in bark and leaf samples, whereas Swingle Citrumelo showed the greatest CLaf concentration in roots. In parallel, a commercial orchard was monitored at three-month intervals, from April 2024 to July 2025, where foliar symptoms were visually scored and mapped to track disease progression. Leaf, branch, and trunk tissue was sampled from seven selected trees to determine bacterial concentration and assess spatial paBerns of infection. Foliar symptom surveying in the orchard illustrated strong seasonal fluctuations, with the most symptoms observed during cooler months and a cumulative increase in the observed period, demonstrating progressive disease development. Trunk samples consistently tested positive, confirming systemic infection, while leaf and branch samples displayed patchy and sectoral distribution. Notably, some asymptomatic leaves tested positive and lower branches frequently remained infected even when upper branches did not, underscoring the risk of undetected positive material. Therefore, symptomatic leaves remain a good, non-destructive sampling tissue as they consistently had higher concentrations of CLaf, while trunk samples give insight into overall tree infection status. Overall, this study enhances the characterisation of African Greening by providing insights into the spatial and temporal distribution of CLaf. These findings contribute to improved sampling strategies and disease management strategies, as well as a more comprehensive understanding of CLaf epidemiology, ensuring the long-term sustainability of citrus production in affected regions. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2025-12-19T07:07:05Z 2025-12-19T07:07:05Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134622 en Stellenbosch University x, 77 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Citrus -- Diseases and pests -- Biological control Greening disease -- South Africa Citrus fruit industry -- South Africa Candidatus Liberibacter africanus (CLaf) -- Genetic aspects Plant cells and tissues -- Diseases UCTD Goodchild, Shannon Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants |
| title | Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants |
| title_full | Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants |
| title_fullStr | Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants |
| title_full_unstemmed | Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants |
| title_short | Evaluation of the spatial and temporal distribution of ‘Candidatus Liberibacter africanus’ in citrus host plants |
| title_sort | evaluation of the spatial and temporal distribution of candidatus liberibacter africanus in citrus host plants |
| topic | Citrus -- Diseases and pests -- Biological control Greening disease -- South Africa Citrus fruit industry -- South Africa Candidatus Liberibacter africanus (CLaf) -- Genetic aspects Plant cells and tissues -- Diseases UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/134622 |
| work_keys_str_mv | AT goodchildshannon evaluationofthespatialandtemporaldistributionofcandidatusliberibacterafricanusincitrushostplants |