S.14. Geminivirus disease complexes: emerging problems and possible solutions

Begomoviruses (family Geminiviridae) are responsible for many economically important crop diseases worldwide. The majority of these diseases are caused by bipartite begomoviruses, although a rapidly growing number of diseases of the Old World are associated with monopartite begomovirus infections. With the exception of several diseases of tomato, most of these are caused by a monopartite begomovirus in association with a recently discovered essential satellite component (DNA-â). These begomovirus/satellite disease complexes are widespread, diverse, and collectively infect a wide variety of crops, weeds and ornamental plants. Non-essential sub-viral components (DNA-1) originating from nanoviruses are frequently associated with these disease complexes and there are tantalising hints that further novel satellites may also be associated with some begomovirus diseases. DNA-â components can be maintained in permissive plants by more than one distinct begomovirus, reflecting less stringent requirements for trans-replication that will undoubtedly encourage diversification and adaptation as a consequence of component exchange and recombination. In view of their impact on agriculture, there is a pressing need to develop a comprehensive picture of the diversity and distribution of the disease complexes, and to understand how they interact with the plant host to produce disease symptoms. Several distinct approaches are being investigated to achieve resistance to these viruses in crops. The ultimate success of these will depend upon their ability to work against a broad range of viruses, if a durable resistance is to be achieved.