Tropentag, October 5 - 7, 2004 in Berlin "Rural Poverty Reduction through Research for Development and Transformation"

Investigations on Citrus Virus and Virus-like Diseases and their Spread in Citrus Orchards in Semi Arid and Savannah Zones of Sudan

¹Humboldt-Universität zu Berlin, Institute for Horticultural Sciences, Department of Phytomedicine, Germany
²University of Khartoum, Sudan

Abstract

The Sudan is situated within the citrus belt and hence this country offers great potentialities for citrus production. The following citrus species have been introduced to the Sudan and are now mainly grown: baladi (Local) lime (Citrus aurantifolia), grapefruit (Citrus paradisi Macf.), sweet oranges (Citrus sinensis, Osbeck), lemon (Citrus limon) and mandarins (Citrus reticulata Blanco). Fruits are consumed domestically, the surplus is exported to Saudi Arabia, the Gulf States and Europe. Different citrus diseases have been observed in the citrus growing areas of the Sudan by visual inspection, indicating that the commercial citrus varieties are heavily infected with virus and virus-like diseases. These pathogens cause varying degrees of damage affecting quality and quantity of the product as well as the vigour and longevity of the trees. Additionally a new citrus disease, which has not been reported in any other citrus growing areas in the world, was found to occur in the Sudan. It was referred to "Kassala disease" or bark gumming of grapefruit and was first described by Bove (1986) on Foster grapefruit trees in Kassala area.
Up to now, there was no serious work in the diagnosis of citrus diseases occurring in Sudan by other methods than visual inspection. Therefore surveys on citrus virus and virus-like diseases were conducted in 2003 throughout twenty locations in seven regions covering the main citrus growing areas of the Sudan. All together over eight hundred trees were examined. Based characteristic symptoms with diagnostic value different citrus species (sour orange, grapefruit, mandarin, and baladi lime) seem to be infected with Citrus tristeza virus, Citrus variegation virus, Citrus psorosis virus, different viroids (Cachexia, Gummy bark), Phytoplasmas (Witches` broom, Stubborn) and Kassala disease (unknown aetiology) respectively. Leaf material was collected and prepared to be analysed by using different methods. Biological indexing was carried out using a set of indicator plants. In addition serological (ELISA) and molecularbiological (RT-PCR) methods are applied. The occurrence and distribution of selected diseases in the Sudan is described and discussed.

Keywords: Citrus diseases, Sudan

Contact Address: Mohamed Abubaker, Humboldt-Universität zu Berlin, Institute for Horticultural Sciences, Department of Phytomedicine, Lentzeallee 55/57, D-14195 Berlin, Germany, e-mail: mohamed.abubakerstaff.hu-berlin.de