Diversidade e estrutura genética de begomovírus em duas regiões produtoras de tomate do Sudeste do Brasil

• Autor(a) principal: Urquiza, Gloria Patricia Castillo
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1021
• topic: Begomovírus; Tomate; Genética de populações; Vírus de plantas; Begomovirus; Tomato; Population genetics; Plant virus; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

The incidence of begomoviruses has sharply increased in Brazil since the mid 1990 s, after the introduction of the B biotype of the whitefly Bemisia tabaci. It is believed that the insect vector transferred indigenous viruses infecting wild and weed hosts to tomato. After a rapid evolutionary process, novel species adapted to the new host became prevalent in the field. To date, five begomovirus species infecting tomatoes have been characterized, and six tentative species have been partially characterized. The objectives of this work were to determine the diversity and the genetic structure of begomovirus populations infecting tomatoes and associated weeds in two major tomato growing regions of Southeastern Brazil, the cities of Paty do Alferes (Rio de Janeiro state) and Coimbra (Minas Gerais state). The genetic structure of populations refers to the degree of genetic variability and its distribution within and between subpopulations, reflecting the evolutionary history and the potential of the population to evolve. A total of 119 tomato samples were collected in Paty do Alferes in May 2005. In Coimbra, 17 tomato samples and 43 weed samples were collected in July 2007. Total DNA was extracted from the samples and full-length begomovirus genomes were cloned by rolling circle amplification. Clones were completely sequenced and the sequences were used for comparisons with previously described begomoviruses, for phylogenetic analysis and for the determination of the genetic structure of viral populations. Sequence comparisons indicated the presence of two novel begomovirus species in tomato plants collected in Paty do Alferes, three novel species in weed samples collected in Coimbra, and one novel species in tomato samples collected at both locations. Sequence features indicate that all six species are typical New World, bipartite begomoviruses. Four of the novel species (represented by 42 DNA-A clones) clustered with Brazilian viruses in the phylogenetic tree. Interestingly, the two other new species (represented by 27 DNA-A clones) clustered with begomoviruses from Mexico and Central America. These two species could represent a distinct lineage of New World begomoviruses, found in Brazil for the first time. Analysis of the genetic structure of ToYVSV and ToCmMV populations indicates a higher degree of genetic variability for ToCmMV. Furthermore, comparison between the ToCmMV subpopulations from Coimbra and Paty do Alferes indicates greater variability in Coimbra. Considering that the presence of begomoviruses in tomatoes has been verified in Coimbra since 2001, but was verified for the first time in Paty do Alferes only in 2005, these results are consistent with a recent introduction of viral populations in Paty do Alferes, followed by a rapid populational expansion. In Coimbra, the virus and its host may have been coevolving for a longer time. Further analyses will investigate the existence of recombination events among the detected viruses, as well as their phylogeographic relationships.