Caracterização biológica, molecular e análise da variabilidade genética de Cowpea mild mottle virus (CPMMV) em soja no Brasil

• Autor(a) principal: Zanardo, Larissa Goulart
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4783
• topic: CPMMV; Soja; Caracterização; Variabilidade genética; CPMMV; Soybean; Characterization; Genetic variability; CNPQ::CIENCIAS BIOLOGICAS::GENETICA

Since 2000, field soybean plants in the states of Bahia, Goiás, Maranhão, Mato Grosso, Minas Gerais, Paraná and Tocantins have been described with symptoms of soybean stem necrosis disease. The symptoms are varied, some milder other severe. The disease has been associated with Cowpea mild mottle virus (CPMMV, family Betaflexiviridae, genus Carlavirus). This study is aimed at the biological characterization and molecular and genetic analyses of genetic variability of isolates of CPMMV that cause symptoms of stem necrosis in soybean fields of different producing Brazil states. The study was conducted with samples collected in the states of Bahia, Goiás, Maranhão, Mato Grosso, Minas Gerais and Pará. The isolates caused a variety of symptoms in soybean cv. CD206, and mild and severe isolates were observed. The complete genomes of six isolates were sequenced and additionally the partial sequence of another 12 isolates was also determined (ORF2- 3'end). No Brazilian CPMMV isolate, from any host, had been entirely sequenced until now. Biological and molecular characterization showed that the six Brazilian isolates, whose genomes have been completely determined, belong to a new CPMMV strain distinct from that which belongs to the only isolated CPMMV previously sequenced from Ghana in Africa. The ORF1 (RdRp) of these six Brazilian isolates showed values of sequence identity (60-61% to 58-69% for nt and aa), less than that set by the International Committee on Taxonomy of Viruses (ICTV), when they were compared with a Ghanaian CPMMV isolate. ORF5 (CP), however, showed identity values (79% to 95-96% for nt and aa) greater than those established by the ICTV when they were compared with the Ghanaian isolate. Both proteins are used to classify isolates of the genus Carlavirus in the same species. Pairwise comparisons and phylogenetic analysis showed that Brazilian isolates are highly related to each other and distinct from isolates of other species of the genus Carlavirus. The phylogenetic trees constructed with partial sequences of the genomes did not show groupings based on geographic region or collection year, but groupings based on symptoms were observed for trees constructed with partial sequences (ORF2-3'end), ORF2 (TGB1), ORF5 (CP) and ORF6 (NABP). Besides the relationship between isolates CPMMV demonstrated by partial sequencing, there are variations between the Brazilian isolates. Evidence of two possible CPMMV strains were found in Brazil with biological and molecular variations between isolates of both strains. Recombination events were identified in genome of the isolates, and they occurred mainly in the ORF1 region of the polymerase, less frequently in other regions of the genome. With this study it was found that the taxonomic criteria, which define the genus Carlavirus may fail in cases where only a partial sequence is determined: if only the ORF1 had been determined during the study we could propose that our isolates belong to a new species of the genus Carlavirus. In addition, there is clearly the need to determine the occurrence of seed transmission in Brazilian CPMMV isolates, since the transmission by seed and/or whitefly Bemisia tabaci, with high dispersibility may have contributed to the spread of the virus in different soybean producing states. These facts justify the nongrouping of isolates based on geographic region or collection year.