A origem de populações emergentes do patógeno da queima-da-folha (Rhizoctonia solani AG-1 IA) da Urochloa spp. na Amazônia e seu potencial de adaptação a outros agroecossistemas brasileiros

• Autor(a) principal: Chavarro Mesa, Edisson [UNESP]
• Data de Publicação: 2015
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/126553; http://www.athena.biblioteca.unesp.br/exlibris/bd/cathedra/11-08-2015/000843674.pdf
• topic: Pastagens; Fungos fitopatogenicos; Adaptação (Biologia); Enzimas; Genetica de populações; Enzymes

The fungus Rhizoctonia solani AG-1 IA emerged in the early 1990s as an important pathogen causing leaf blight and collar rot on pastures of the genus Urochloa (signalgrass) in South America. This pathogen first emerged in Colombia in areas where rice, a host highly susceptible to the fungus, was replaced with Urochloa in response to increased demand for extensive livestock farming. Urochloa is an extremely important forage grass crop for livestock farming in tropical Latin America. Described in the first part of our study, a broad survey was conducted in the Amazon in Pará, Rondônia, Roraima states and in Mato Grosso Cerrado areas, and paddy plains in the Paraíba Valley, in São Paulo, between 2012 and 2013. Our findings revealed that R. solani AG-1 IA was the predominant pathogen associated with the leaf blight on Urochloa in the Brazilian Amazon biome, especially in Rondônia. In the second part of our study, describing the population genetic structure of different host and regional populations of R. solani AG-1 IA infecting Urochloa, rice and soybean, we tested the hypothesis that the emergence of this pathogen occurred due to host shift or jump as a result of geographical overlapping of the host species. To study the genetic structure of populations, a total of 335 R. solani AG-1 IA isolates were sampled from fields of U. brizantha, Urochloa hybrid Mulato, rice and soybeans in Colombia and Brazil. These isolates were genotyped using nine microsatellite loci. The historical patterns of migration of populations from different hosts indicated that the populations currently infecting Urochloa in Colombia most likely originated from a population that originally infected rice. In contrast, in Brazil a similar clear asymmetric pattern of historical migration was not established because the migration rates among Brazilian R. solani AG-1 IA populations from Urochloa, soybean and rice were all symmetric in magnitude (average 20 migrants ...