Traditional and novel strategies for geminivirus management in Brazil.

摘要

The presence of geminiviruses has been recognized in Brazil since the 1950s. In the early 1990s, after the introduction of a new biotype of the whitefly (Bemisia tabaci) vector, successive reports of geminivirus infection indicated the establishment of these pathogens in tomato crops. Initial reports suggested that new species were emerging in different parts of the country. Further studies indicated the presence of eight novel species, namely Tomato rugose mosaic virus, Tomato chlorotic mottle virus, Sida micrantha mosaic virus, Tomato mottle leaf curl virus, Tomato crinkle virus, Tomato infectious yellows virus and Tomato yellow vein streak virus. Similarities between tomato- and weed-infecting viruses suggested that indigenous viruses were being transferred to tomatoes by the insect vector. Sequence analysis indicated that recombination and pseudo-recombination were already taking place among these new viruses. Management of tomato geminiviruses has been a major challenge. Successful control depends on an integrated management approach. Although most growers rely solely on heavy pesticide application, cultural practices which help to reduce viral load have displayed much better results. The main component of this approach is a tomato-free period of at least 30 days. In the areas where such measures were adopted, together with the use of virus-free transplants and rational chemical control of the vector, geminivirus incidence was greatly reduced. Meanwhile, novel approaches being developed include genetically-modified tomatoes using RNA silencing, either targeting the viral genome or host genes which are essential for viral replication..