Filogeografia molecular de Phakopsora pachyrhizi com base em dados de sequenciamento de regiões gênicas do DNA nuclear

• Ano de defesa: 2011
• Autor(a) principal: Freire, Maíra Cristina Menezes
• Orientador(a): Oliveira, Luiz Orlando de
• Banca de defesa: Santos, Jorge Abdala Dergam dos , Guimarães, Valéria Monteze , Zambolim, Eunize Maciel , Paula Júnior, Trazilbo José de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Genética e Melhoramento
• Departamento: Genética animal; Genética molecular e de microrganismos; Genética quantitativa; Genética vegetal; Me
• País: BR
• Palavras-chave em Português: Ferrugem-da-soja; Sequenciamento de nucleotídeo; Soja - Doenças e Pragas; Variação (Genética); Evolução (Biologia)
• Palavras-chave em Inglês: Of soybean rust; Nucleotide sequencing; Soybean - Diseases and Pests; Variation (Genetics); Evolution (Biology)
• Área do conhecimento CNPq: CNPQ::CIENCIAS BIOLOGICAS::GENETICA::GENETICA MOLECULAR E DE MICROORGANISMOS
• Link de acesso: http://locus.ufv.br/handle/123456789/1404

Asian soybean rust caused by Phakopsora pachyrhizi is an important disease in all soybean producing areas, including the two largest producing countries Brazil and the United States. Resistance genes (Rpp) to P. pachyrhizi have been constantly studied in soybean and related species, and some genes have been identified. However, due to the genetic plasticity of P. pachyrhizi these resistance genes are quickly overcome. In order to assess the level of genetic variability of P. pachyrhizi in major soybean producing areas of the world and understand how this variability is distributed a broad sampling of P. pachyrhizi from different countries and continents was made. Most sampling was carried out in Brazil and the United States, the two largest producers. Following sampling genetic variability was estimated from molecular data. Three nuclear gene regions (ADP ribosylation factor, histone H4, and ITS) were amplified, cloned and sequenced from samples of P. pachyrhizi from different locations. A database was created with all the gene sequences for each region. The sequences were compared, and polymorphisms were identified allowing differentiation of the clones. Among the nuclear regions, the ITS (internal transcribed spacer) is the best marker based on the sequencing of DNA used in genetic diversity studies of fungi. The secondary structures formed by the ITS1 and ITS2 regions of P. pachyrhizi were used to examine the pattern of ITS polymorphisms, identify structural characteristics of the ITS regions, investigate the presence of pseudogenes or PCR artefacts and to evaluate the usefulness of ITS in studies of genetic diversity of P. pachyrhizi. The data indicated that the analysis of secondary structures permits us to assess the reliability of mutations in ITS in P.pachyrhizi, allowing the use of this region for studies of genetic diversity. The sequencing of the three genetic regions allowed the differentiation of clones in haplotypes. A network of haplotypes was estimated for each of the databases to understand the genealogical relationship between the haplotypes. The haplotypes were plotted on maps in the respective sampling sites, to better understand the distribution of genetic variability of P. pachyrhizi. Diversity index and gene flow were estimated to assess the genetic structure of populations of P. pachyrhizi. The results showed that P.pachyrhizi has a high level of genetic variability, and that much of this variability is concentrated within populations. These characteristics can be explained by the high mutation rate of the fungus, and the high dispersal ability of spores, causing populations of different countries and continents share the same haplotype. The comparison of the genetic variability of P. pachyrhizi over two years revealed that the Brazilian agricultural field fallowing was not an effective genetic bottleneck of populations of this fungus. Still, the identification of these haplotypes observed in soybean, infecting the bean kudzu, reveals the importance of this alternate host during periods of absence of soybeans in the field. The geographical distribution of haplotypes and analysis of gene flow allowed us to infer the possible routes of dispersal and colonization of P. pachyrhizi. Populations of P.pachyrhizi identified in Brazil showed strong genealogical relationship with the African populations, strengthening the hypothesis that this continent was a source of origin of Brazilian populations. The United States had populations of P. pachyrhizi distantly related to those identified in other countries, complicating the inference of the origin of these populations.