Estrutura genética de populações do begomovírus Tomato severe rugose virus (ToSRV)

• Autor(a) principal: Sande, Osvaldo Francisco Lino
• Data de Publicação: 2014
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4438
• topic: Tomate - Doenças e pragas; Begomovírus - Genética; Begomovírus - Variabilidade; Filogenia; Tomato - Diseases and pests; Begomovirus - Genetics; Begomovirus - variability; Phylogeny; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

The incidence of begomoviruses in Brazil has increased since 1990 with the introduction of the invasive Bemisia tabaci Middle East Asia Minor 1 (MEAM1, previously known as biotype B). The objective of this work was to evaluate the spatio- temporal dynamics of populations of Tomato severe rugose virus infecting tomato crops. Foliar samples with begomovirus-like symptoms such as dwarfing, yellow mosaic and leaf curl were collected in tomato fields located in rural areas of the municipalities of Coimbra in 2013 and 2014 and Florestal in 2014. Total DNA was extracted and used as a template for the amplification of viral genomes using the phi29 DNA polymerase. Viral genomes were cloned in plasmid vectors and fully sequenced. A total of 76 full-length DNA-A clones were obtained. The isolates obtained from tomato samples indicate an almost absolute predominance of Tomato severe rugose virus (ToSRV) in Florestal and Coimbra (replacing Tomato common mosaic virus, ToCmMV, as the dominant begomovirus in Coimbra). Phylogenetic analysis, including additional ToSRV sequences from a number of cultivated and non-cultivated hosts available in GenBank, divided ToSRV isolates into four major clades: (i) Florestal/2008, (ii) São Paulo, Goiás and the Federal District, (iii) Florestal/2014 and (iv) Viçosa, Coimbra, Carandaí and Jaíba. Isolates from Florestal/2008 represent the most divergent group, with a time of divergence from the most recent common ancestor of 15-20 years. However, isolates obtained from Florestal in 2008 and 2014 form distinct clades, suggesting a time-based structuring. The inferred phylogenetic network showed evidence of intraspecific recombination, with the previously described isolates BR:Ube1:2000 and BR:Vic20:10 identified as potential recombinants. The genetic variability of the ToSRV population is not equally distributed among subpopulations, with subpopulations from Viçosa and Florestal/2008 providing a greater contribution to the variability. Neutrality tests were applied to assess evidence of selection on coding regions. The results indicate the occurrence of purifying selection on the CP gene of the subpopulations from Viçosa, Carandaí and Florestal/2014 and on the Rep gene from the subpopulations from Viçosa and Carandaí. Coalescence analysis mapped the mutations occurring along the viral genome. All mutations observed in peppers and in non-cultivated hosts are common to tomatoes and show the same relative age, suggesting that ToSRV is well adapted to tomatoes, with occasional transfer to other hosts by the insect vector.