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Overview of Musa viruses in sub-Saharan Africa

Introduction

The banana (including plantain, Musa spp.) is one of the worki’ s most important subsis-tence crops. It is widely grown in the tropics and subtropics in all types of agricultural Systems, from smali, mixed, subsistence gardens, to large multinational commercial monocultures. The crop serves in many developing countries as a staple food or the cornerstone of the country’s economy. The largest producers are Latin America and Asia, however, much of the South American production in particular is as an export crop to the developed world.

There has been an increase in the international movement of banana germplasm in recent years, much of it to developing countries, and especially in the form of tissue culture propagated plants. The presence of any virus poses a risk as new viruses or strains may be distributed in large quantities to new sites.

Bananas are affected by four known, relatively well-characterized viruses (Diek-mann and Putter 1996): these are Banana bunchy top virus (BBTV) genus Nanavirus, Banana streak virus (BSV) genus Badnavirus\ Cucumber mosaic virus (CMV) genus Cucumovirus\ and Banana bract mosaic virus (BBrMV) genus Potyvirus. Recently, a filamentous virus, Banana mild mosaic virus (BanMMV, Thomas et al. 2000; Gambley and Thomas 2001) has been shown to be widespread in banana and plantain germplasm materiał and also been noted in bananas from Africa, the Americas, southeast Asia, and Australia (Lockhart 1995; Thomas et al. 2000). Another new virus, Banana die-back virus, has also just been described from Nigeria (Hughes et al. 1998), Abaca mosaic virus (AbaMV) genus Potyvirus infects Abaca (Musa textilis) in the Philippines, and is known to infect banana experimentally. However, there is no information on its possible natural occurrence in banana.

Banana bunchy top virus (BBTV)

Of the known virus diseases of bananas, Banana bunchy top disease (BBTD, caused by BBTV) is the most serious. BBTD is a major constraint to banana production in many areas of southeast Asia and the Pacific (Thomas et al. 1994). The disease has been identified in numerous developing countries in Oceania, Africa, and Asia (Thomas et al. 1994; Diekmann and Putter 1996; Kenyon et al. 1997; Thomas and Iskra-Caruana 2000); Kagy et al. 2001). BBTV is still absent from the countries of Central and South America. Strains of BBTV causing mild or latent symptoms have recently been detected (Su et al. 1993), and the virus may occur at higher incidences than previously believed.

BBTV has caused some devastating epidemics, the latest being in Pakistan, with the disease being observed in 1988 for the first time. By 1992, it showed that the disease was widespread in a number of districts in Pakistan with disease incidences up to 100%,

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