Status of Begomoviruses in Ghana: The Case of Vegetables and Root and Tuber Crops

Abstract

In developing countries, including Ghana, a greater proportion of the population depends on small-scale farming for their income and livelihood. Crops are frequently affected by a wide array of virus diseases showing varying degrees and kinds of symptoms including leaf curling and distortion, green or yellow foliar mosaic, stunting of plants, and reduced yields. An emerging and economically important group of plant viruses belonging to the genus Begomovirus, family Geminiviridae, are known to cause extreme yield reduction in a number of economically important crops in Ghana. These begomoviruses have a very wide host range, infecting dicotyledonous plants, and are transmitted by the whitefly vector, Bemisia tabaci (Genn.). Vegetable crops such as tomato, okra, and pepper and root and tuber crops such as cassava and sweet potato are greatly affected by begomoviruses resulting in substantial yield losses. Begomoviruses associated with tomato yellow leaf curl disease in Ghana include tomato leaf curl Kumasi virus (ToLCKuV), tomato leaf curl Ghana virus (ToLCGHV), tomato leaf curl Mali virus (ToLCMLV), and tomato leaf curl virus (TYLCuV). Pepper leaf curl diseases have been observed in pepper fields in several parts of Ghana, but begomoviruses associated with these diseases have not been characterized even though pepper veinal mottle virus (PVMV) and tomato yellow leaf curl virus (TYLCV) are the most widespread in the Western Africa subregion. The coat protein gene of cotton leaf curl Gezira virus (CLCuGV) and the DNA-β of satellite DNA have been amplified from diseased okra leaf samples collected from the Central Region of Ghana with characteristic leaf curl disease symptoms. Viruses are the second most important constraint to the production of sweet potato (Ipomoea batatas) after weevils, resulting yield losses by up to 90%. Sweet potato leaf curl virus has been detected in Ghana using both PCR and disease symptoms. Cassava mosaic disease (CMD), caused by cassava mosaic geminiviruses mainly African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV), is the most important constraint to the production of cassava in Ghana. In view of the increasing economic importance of begomoviruses in Ghana and worldwide, there is an urgent need for their effective management in order to improve yields and quality of crop plants. This requires accurate detection and identification procedures, stimulating intensive research efforts focused on virus biology, diversity, and epidemiology to develop successful control strategies. Inadequate plant virologists with requisite skills and knowledge in plant virology together with inadequate logistical and financial supports coupled with low institutional and governmental supports hinder the efforts in developing effective management strategies against the numerous viral diseases confronting the country.