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Plant virology in sub-Saharan Africa and that about half of the plantations had already been destroyed (Soomro et al. 1992; Khalid etal. 1993).

The virus belongs to the genus Nanavirus and virions are icosahedral, 18-20 nm in diameter (Wu and Su 1990, Dietzgen and Thomas 1991). The virus possesses a mul-ticomponent genome, consisting of at least six circular ssDNA components (Burns et al. 1995; Xie and Hu 1995; Karan et al. 1997). Additional components, which may be satellites, occur with some isolates (Horser et al. 2001).

BBTV is transmitted in a persistent, nonpropagative manner by an aphid vector (Pentalonia nigronervosa), and in vegetative planting materiał, but not by mechanical inoculation (Magee 1927).

Successful methods of control, viz. early identification, and eradication of infected plants and the use of virus-free planting materiał, are successfully applied in Australia (Dale 1987). However, these are unlikely to alleviate the problem in developing coun-tries, where farmers lack the structured organizations required to apply eradication programs throughout affected districts, and funds are lacking to enforce eradication programs. Additionally, no incentives or altemate food sources exist, so that a farmer will not sacrifice the smali source of sustenance his family may have, in order to save a larger area. Furthermore, virus-free planting materiał may also not be readily available.

Banana streak virus (BSV)

BSV, believed to be distributed worldwide on Musa sp. (Lockhart and Olszewski 1993), was not considered a serious problem of bananas until recently. The disease was first noted in Cóte d’Ivoire in 1966 (Lassoudiere 1974), but the causal virus was not isolated until 1986 (Lockhart 1986).

Since then, the disease has been, and continues to be reported from many new coun-tries (Jones and Lockhart 1993; Diekmann and Putter 1996; Tushmereirwe et al. 1996, Pasberg-Gauhl et al. 1996; Reichel etal. 1996; Vuylsteke etal. 1996; Lockhart and Jones 2000). The virus causes a wide rangę of symptoms and damage ranges from mild to severe. It is transmitted mostly through planting materials, but also in a semipersistent manner by some mealybug species (Planococcus citri and Pseudococcus sp.; Lockhart and Jones 2000). Field spread appears to occur in some countries, but not in others (Lockhart pers. comm. 1998). In Uganda, a serious outbreak of the virus was reported in 1996, with some plantations containing 100% infected plants (Tushmereirwe et al. 1996). Damage appeared most severe when the virus was associated with a filamentous virus particie (probably BanMMV).

BS V is a member of the genus Badnavirus. The virions are nonenveloped, bacilliform average 130-150 nm x 30 nm in size, and contain a circular dsDNA genome (Lockhart and Olszewski 1993). A high degree of heterogeneity exists among isolates of BSV,