Diversidade e estrutura genética de Begomovírus que infectam plantas daninhas no Nordeste brasileiro

• Autor(a) principal: SILVA, Sarah Jaqueline Cavalcanti da
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFRPE
• Texto Completo: http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/6681
• topic: Begomovírus; Geminiviridae; Planta daninha; Diversidade genética; FITOSSANIDADE::FITOPATOLOGIA

The incidence and severity of diseases caused by begomoviruses has increase rapidly in many areas of the world, including Brazil, where they are limiting factors to tomato and common bean production. Begomoviruses are also associated with a wide range of weed plants which in some cases act as inoculum sources for cultivated plants. It is believed that begomoviruses infecting weed hosts can be horizontally transferred to crop plants and that in the new host they will rapidly evolve by recombination and pseudorecombination, giving rise to novel species. Acting as reservoirs these plants can play a relevant role in viral epidemics in several crops species. The study of plant virus epidemics is greatly facilitated when a population genetics approach is employed. The first step to study viral population is to define their genetic structure, which refers to their degree of variability. Knowledge of the dynamics of genetic variability is essential to understand the potential of the population to evolve, which directly affects the durability of disease management strategies based on the deployment of resistance genes. Studies to understand the genetic structure and dynamics of begomovirus populations in wild reservoirs and the possible effects on epidemics in crop species are scarce. Thus, the aim of this study was to determine the species diversity and population genetic structure of begomoviruses infecting weeds in Northeastern Brazil, as a step towards assessing their role as begomovirus reservoirs. Weed samples belonging to the family Fabaceae and Capparaceae displaying typical symptoms of begomovirus infection were collected in Alagoas (AL), Bahia (BA), Paraíba (PB), Pernambuco (PE) and Sergipe (SE) states from May/2005 to July/2010. A total of 59 leguminous weeds including 42 samples of Macroptilium spp. and 23 samples of Cleome affinis (fam. Caparaceae) were collected. Total DNA was extracted from the samples and full-length begomovirus genomes were amplified and 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 six begomoviruses in leguminous weeds (five in Macroptilium spp.), four of them representing novel species. Sequence features indicate that all four novel species are typical New World, bipartite begomoviruses which clustered with Brazilian begomoviruses in the phylogenetic tree. In contrast, only one begomovirus was found infecting C. affinis, suggesting low species diversity in this host phylogenetic reticulate analysis was used to detected possible recombination events in begomovirus populations in leguminous weeds and C. affinis. Putative recombination events were confirmed by RDP3 package analysis. We detected recombination events in Macroptilium yellow spot virus (MaYSV) and Cleome leaf crumple virus (ClLCrV) populations. Analysis of the genetic structure of these virus populations indicates a high degree of genetic variability in both cases. Mutation and recombination are important processes involved in the high genetic variability found in MaYSV and ClLCrV populations. Together, these results suggest that Macroptilium spp. and Cleome affinis can be important begomovirus reservoirs.