Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Fruit and Leaf Spot Disease (FLSD) of citrus, caused by Phaeoramularia angolensis, is
found only in 18 countries in Africa, the Comores Islands in the Indian Ocean and Yemen in
the Arabian peninsula. The major citrus export countries in Africa are Morocco, South Africa,
Swaziland, and Zimbabwe. Zimbabwe is the only country affected by FLSD. FLSD is a
disease of major phytosanitary and economic importance and its devastating effect on citrus is
highlighted by the fact that the damage is cosmetic, which renders the fruit unmarketable.
Total crop losses are not uncommon in Kenya. The aims of the present study, therefore, was
was to determine the occurrence of P. angolensis in Zimbabwe and neighbouring
Mozambique, to compare these isolates with the Cercospora Fresen. isolates from Swaziland
and South Africa, to determine the epidemiology of the pathogen and to implement an
effective control strategy to prevent the spread of FLSD.
Leaf samples with citrus canker-like lesions collected in the early 1990’s in Zimbabwe
were found to be infected by the fungus, Phaeoramularia angolensis. Surveys were
undertaken to determine the spread and intensity of FLSD in Zimbabwe and Mozambique. In
Zimbabwe, P. angolensis was limited to an area above the 19° south latitude, predominantly
the moist areas and not the low-lying drier parts of the country. In Mozambique, no P.
angolensis symptoms were found. Observations during the survey indicated that no proper
management systems were implemented by Zimbabwean growers.
A cercosporoid fungus causing a new Fruit and Leaf Spot Disease on Citrus in South
Africa was identified. From morphological and rDNA sequence data (ITS 1, 5.8S and ITS 2),
it was concluded that the new disease was caused by Cercospora penzigii, belonging to the
Cercospora apii species complex. The genera Pseudophaeoramularia and Phaeoramularia
are regarded as synonyms of Pseudocercospora, and subsequently a new combination was
proposed in Pseudocercospora as P. angolensis. Cercospora gigantea was shown to not
represent a species of Cercospora, while Mycosphaerella citri was found to be
morphologically variable, suggesting that it could represent more than one taxon.
A control strategy for the control of FLSD was evaluated in the study. The data showed
that P. angolensis in Zimbabwe can be managed successfully by the removal of all old and neglected orchards, and on timely fungicide applications. Trifloxystrobin + mancozeb +
mineral spray oil (20 g + 200 g + 500 ml/100 l water) applied in November, January and
March was the most effective treatment. Three applications of benomyl + mancozeb +
mineral spray oil (25 g + 200 g + 500 ml/100 l water) applied during the same period, was
the second most effective treatment, and two applications (November and January) of
trifloxystrobin + mineral spray oil (20g + 500 ml/100 l water) and difenoconazole (40 g) per
100 l/water applied twice in November and January, the third most effective treatment.
The spore trap and weather data showed that P. angolensis needs high moisture and
temperatures in excess of 25°C for disease development. It is concluded that P. angolensis in
Zimbabwe can be managed successfully by implementing a holistic approach, which should
be supported by the authorities, organised agriculture and all technical personnel involved in
citrus production. / AFRIKAANSE OPSOMMING: Blaar- en vrugvleksiekte (BVVS) op sitrus, veroorsaak deur Phaeoramularia
angolensis, kom in 18 lande in Afrika voor asook die Comores Eilande in die Indiese Oseaan
en Yemen op die Arabiese skiereiland. Marokko, Suid Afrika, Swaziland en Zimbabwe is
die belangrikste uitvoerders van sitrus in Afrika. Van dié lande het slegs Zimbabwe blaar en
vrugvleksiekte op sitrus. Hierdie siekte is van fitosanitêre en ekonomiese waarde en die
nadelige effek van die siekte, wat slegs kosmetiese van aard is, is venietigend aangesien
vrugte onbemarkbaar is. Totale opbrengsverliese is nie ongewoon in lande soos Kenya nie.
Die doelwitte van die studie was dus om die voorkoms van P. angolensis in Zimbabwe te
bepaal, om die Cercospora Fresen. isolate vanaf Swaziland en Suid-Afrika met mekaar te
vergelyk, om die epidemiologie van die siekte vas te stel en om ‘n effektiewe beheermaatreël
teen die siekte te ondersoek.
Blaarmonsters met kankeragtige letsels wat in die vroeë 1990’s in Zimbabwe gevind
is, het getoon dat die blare geinfekteer is met die swam, Phaeoramularia angolensis.
Ondersoeke is geloots om die verspreiding en intensiteit van BVVS in Zimbabwe en
Mosambiek te bepaal. In Zimbabwe was gevind dat P. angolensis beperk was tot gebiede bo
die 19° Suid breedtegraad, wat die hoër vogtiger gebiede insluit eerder as die droeër,
laagliggende gebiede. Geen P. angolensis simptome kon in Mosambiek gevind word nie.
Tydens die opnames was dit duidelik dat geen geskikte beheerstrategieë toegepas word deur
Zimbabwe se produsente nie.
‘n Nuwe cercosporoid swam, wat blaar en vrugvleksiekte op sitrus is in Suid Afrika
veroorsaak is geidentifiseer. Morfologiese en rDNA volgorde (ITS 1, 5.8S en ITS 2) data het
getoon dat die siekte veroorsaak word deur Cercospora penzigii wat tot die Cercospora apii
spesie kompleks behoort. Die genus Pseudophaeoramularia kan as sinoniem van
Pseudocercospora beskou word en ‘n nuwe kombinasie word voorgestel in
Pseudocercospora as P. angolensis. Cercospora gigantea het getoon dat dit nie ‘n spesie van Cercospora kon verteenwoordig nie terwyl Mycosphaerella citri varieërend voorkom en
meer as een takson kan verteenwoordig.
‘n Beheerstrategie vir die beheer van BVVS is ondersoek. Die data wys dat P. angolensis
in Zimbabwe doeltreffend beheer kan word deur die uitroeiing van ou en verwaarloosde
bome, en deur goed beplande fungisied bespuiting. Trifloxystrobin + mancozeb + minerale
spuitolie (20 g + 200 g + 500 ml/100 l water), wat in November, Januarie en Maart toegedien
is, was die mees effektiefste behandeling. Drie bespuitings van benomyl + mancozeb +
minerale spuitolie (25 g + 200 g + 500 ml/100 l water) wat oor dieselfde tydperk toegedien
is, was die naas beste behandeling. Trifloxystrobin (20 g) + minerale spuitolie (500 ml) per
100 l/water en difenoconazole (40 g) per 100 l/water, beide as twee bespuitings toegedien in
November en Januarie, het die derde beste resultaat opgelewer.
Die spoorlokval en klimatologiese data het getoon dat P. angolensis vogtige toestande en
temperature hoër as 25°C benodig vir siekteontwikkeling. Die afleiding uit die studie is dat
P. angolensis suksesvol beheer kan word indien ‘n holistiese benadering gevolg word en alle
rolspelers naamlik die owerheid, georganiseerde landbou en tegniese personeel die proses
ondersteun.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20938 |
| Date | 12 1900 |
| Creators | Pretorius, Mathys Cornelius |
| Contributors | Holz, G., Crous, P.W., Stellenbosch University. Faculty of Agrisciences. Dept. of Plant Pathology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 62 leaves : ill. |
| Rights | Stellenbosch University |
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