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Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions
Thesis (PhD)--University of Pretoria, 2010.
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University of Pretoria
2013
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| _version_ | 1867613662435344384 |
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| access_status_str | Open Access |
| author2 | Korsten, Lise |
| author_browse | Korsten, Lise |
| author_facet | Korsten, Lise |
| collection | Thesis |
| dc_rights_str_mv | © 2010 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD)--University of Pretoria, 2010. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/28968 |
| institution | University of Pretoria (South Africa) |
| last_indexed | 2026-06-10T12:39:42.666Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2013 |
| publishDateRange | 2013 |
| publishDateSort | 2013 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/28968 Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions Korsten, Lise Venter, Marieka truterm@arc.agric.za Truter, Mariëtte Citrus black spot disease Phytosanitary trade restrictions G. citricarpa Citrus leaf litter UCTD Thesis (PhD)--University of Pretoria, 2010. Citrus black spot (CBS), caused by Guignardia citricarpa Kiely, occurs in various citrus producing regions of the world. Due to the potential phytosanitary risk associated with the export of fruit from CBS positive production areas to CBS-free countries, restrictive trade barriers have been introduced. This study aimed to further elucidate some epidemiological aspects of CBS that can be used to address critical questions identified in the pest risk assessment submitted by South Africa to the World Trade Organisation to address phytosanitary trade restrictions. Results indicated that Eureka lemon leaf litter exposed to viable pycnidiospores under controlled conditions or in the field in different production regions of South Africa, were not infected and colonised by G. citricarpa. Symptomatic CBS fruit or peel lying on the ground underneath citrus trees therefore can not lead to infection and colonisation of freshly detached leaves or leaf litter, or represent a source of inoculum in citrus orchards. Symptomatic fruit therefore pose no danger for the establishment of the pathogen in CBS-free orchards and are not considered to be a pathway for the pathogen. The period of leaf susceptibility to G. citricarpa was indicated to be maximum eight and ten months from development, for Valencia orange and Eureka lemon, respectively, in a greenhouse study. The susceptibility period of citrus leaves to infection by the black spot pathogen could be longer than previously perceived. Ascospores were captured, using the newly developed Kotzé Inoculum Monitor (KIM), from natural Valencia orange and Eureka lemon leaf litter during October to March with peak ascospore availability between December to February. The KIM is the first sampler designed to capture fungal spores directly from plant material in the laboratory without environmental influences and was effectively used to confirm that ascospores production is seasonal. The KIM in combination with environmental data can be used to improve control through more targeted fungicide applications. Techniques such as isolations and DNA amplification with species-specific primers to detect the pathogen directly from symptomless green leaves have a low success rate due to the restricted growth of the pathogen in latently infected tissue. Artificial leaf wilting enhanced the detection of G. citricarpa from symptomless leaves. Leaf wilting is a reliable, fast and effective method to detect the CBS pathogen and can be applied to monitor citrus nurseries and orchards throughout the year. It can also be applied to monitor pest-free orchards to maintain its CBS pest-free status. This study confirmed that sanitation practices, such as leaf litter removal and mulching of leaf litter with wheat straw can decrease the primary inoculum, ascospores, of CBS and contribute to better management of the disease in a commercial orchard. Regardless of the prevailing climatic conditions each year, control achieved through leaf litter management resulted in >95% clean fruit and are equal to the control achieved with industry standard fungicides. This approach provided improved integrated disease control and an alternative to chemical control. Microbiology and Plant Pathology unrestricted 2013-09-07T14:34:10Z 2010-10-24 2013-09-07T14:34:10Z 2010-09-02 2010-10-24 2010-10-23 Thesis Truter, M 2010, Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://hdl.handle.net/2263/28968 > D10/708/ag http://hdl.handle.net/2263/28968 http://upetd.up.ac.za/thesis/available/etd-10232010-164940/ © 2010 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf application/pdf application/pdf application/pdf application/pdf application/pdf application/pdf University of Pretoria |
| spellingShingle | Citrus black spot disease Phytosanitary trade restrictions G. citricarpa Citrus leaf litter UCTD Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions |
| title | Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions |
| title_full | Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions |
| title_fullStr | Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions |
| title_full_unstemmed | Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions |
| title_short | Epidemiology of citrus black spot disease in South Africa and its impact on phytosanitary trade restrictions |
| title_sort | epidemiology of citrus black spot disease in south africa and its impact on phytosanitary trade restrictions |
| topic | Citrus black spot disease Phytosanitary trade restrictions G. citricarpa Citrus leaf litter UCTD |
| url | http://hdl.handle.net/2263/28968 http://upetd.up.ac.za/thesis/available/etd-10232010-164940/ |