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.

La phaeoramulariose des agrumes (Pseudocercospora angolensis) attaque les agrumes en Afrique tropicale et constitue une menace pour les autres pays producteurs situés en zone tropicale. La lutte chimique est le seul moyen de lutte efficace contre cette maladie. Cependant, elle est couteuse et néfaste pour l'environnement. La mise en place de stratégies de lutte permettant de minimiser l'emploi de fongicides contre est donc nécessaire. La connaissance des facteurs de risque de la phaeoramulariose est une étape préliminaire à cette démarche. Le travail entrepris avait pour but de préciser, à l'aide d'une enquête et des expérimentations, les effets de certains facteurs sur le développement de la maladie. L'enquête a été effectuée dans 39 sites de production des agrumes au Cameroun. Elle a permis de recenser les facteurs pédoclimatiques et biologiques dans l'environnement des arbres et de retenir les plus importants dans l'épidémiologie. Les expérimentations sur 8 sites ont permis de confirmer et évaluer les paramètres retenus après l'enquête. L'altitude, le type de sol, l'espèce d'agrumes et le type de végétation ont été retenus comme principaux facteurs de développement de la maladie. Les relations entre ces facteurs et l'incidence de la maladie sont illustrées dans les arbres de segmentation. Les expérimentations ont confirmé la grande sensibilité des pomélos et orangers vis-à-vis P. angolensis. En revanche, les mandariniers et la lime Tahiti se sont avérés moins sensibles. L'incidence de la maladie augmente avec une élévation en altitude, une diminution de la température et de la pluviométrie. La texture du sol s'est avérée plus déterminante du niveau de la maladie que sa composition. Le rôle de l'ombrage s'est avéré déterminant sur l'incidence de la maladie. L'analyse de la structure spatiale de la maladie a permis de mettre en évidence une structure agrégée. La structure spatiale des sous populations de familles d'arbres d'une parcelle agroforestière était aussi agrégée. La dispersion de la phaeoramulariose au sein d'une telle parcelle entre les différents agrégats d'agrumes serait limitée. L'analyse de régression a permis de déceler des différences entre les paramètres contribuant au développement de la maladie sur pomélos, satsuma et orangers. La possibilité d'une conception des systèmes agroforestiers raisonnés pour diminuer la pression des bioagresseurs est envisagée. / Phaeoramularia leaf and fruit spot disease of citrus (PLFSD) caused by Pseudocercospora angolensis attacks citrus in tropical Africa. It also constitutes a threat for the other producer countries located in tropical zone. Chemical treatment is the only method used for effective control of this disease. However, in addition to causing ecological problems, this method lies beyond the reach local smallholders. The development of ecologically friendly strategies to ensure effective protection of citrus is thus necessary. To this end, knowledge of PLFSD risk factors is pre-required. The purpose of this study was to specify, by means of a survey and experiments carried, the effects of certain biotic and abiotic factors on the development of the disease. The survey carried out in 39 production sites of Cameroon, targetted a collection of environmental and biological tree characteristics. Experiments on 8 sites enabled a confirmation and evaluation of suspected factors. A stepwise logistic regression analysis of survey data made it possible to target altitude, soil type, citrus species and vegetation type as main factors influencing disease development. Relations between these factors and disease incidence are illustrated in segmentation trees. Experiments confirmed the great sensitivity of grape fruit and orange trees, while tangerine and Tahiti lime trees were less sensitive. Disease incidence increased with a rise in altitude and a reduction in temperature and rainfall. Soil texture proved to be more determinant in disease development than its chemical composition. Experimentation showed that trees planted under shade are less affected than those located in sunshine. A spatial structure analysis of the disease made it possible to highlight an aggregate structure indicating small scale disease dispersion. An analysis of the spatial structure of an agro forestry farm showed an aggregate structure of the sub populations of constituent tree families. This structure suggested that the dispersion of PLFSD within such a farm would be limited between the various citrus aggregates. PLS regression analysis suggested that several of these parameters play a determinant role in contributing to the development of disease on grape fruit, orange and Satsuma mandarin trees. The development of integrated agro forest systems which enable a decrease of the pressure of pest and diseases is envisaged.