Viral pathogens of banana: outstanding questions and options for control

The viruses naturally infecting banana include Banana bunchy top virus (BBTV), Cucumber mosaic virus (CMV), Banana bract mosaic virus (BBrMV), Banana mild mosaic virus (BanMMV), Banana virus X (BVX) and the banana streak viruses (BSVs). BBTV is still regarded as the most damaging of the viruses and continues to expand in geographic distribution. The epidemiology of BBTV is very simple, and in Australia it has been effectively controlled and even eradicated from some regions through a combination of roguing, clean planting material schemes and domestic quarantine. BSVs impact on production directly by reducing yield, but also indirectly because of the problems they cause to Musa breeding programmes. Estimates of yield loss from BSVs vary widely but the factors contributing to this variation are largely unknown. All progenitors of the domesticated banana have integrated badnavirus DNA. However, only integrants associated with the B genome in hybrid genetic backgrounds are known to initiate infection. An outstanding question is why the rate of activation of BSV integrants in some hybrids, such as 'Goldfinger' (syn. 'FHIA-01', AAAB genome), is low whilst it is high in other cultivars. Two recently discovered viruses, BVX and BanMMV, were discovered in the course of other virus research. There is indirect evidence that BanMMV is transmitted between plants in the field but, as yet, attempts to find a vector have been unsuccessful. Genetic engineering for virus resistance remains a promising technology, although probably more than a decade away from implementation because of regulatory problems and issues of public acceptance