Genetic admixture in species of Conyza reveladas por marcadores microsatelites

The distinction among Conyza canadensis, C. bonariensis, and C. sumatrensis is a challenge for weed science. In the current study, primers for microsatellite (SSR) loci were used to investigate the molecular divergence among the three species, the genetic structure of the populations at the molecular level and the level of genetic admixture among Conyza plants from southern Brazil. Twelve primers amplified well-defined DNA segments for all 88 samples of the three Conyza species. The estimated proportion of SSR polymorphic loci, number of alleles, and mean expected heterozygosity were higher in samples of C. bonariensis than in samples of C. sumatrensis or C. canadensis. Conyza canadensis was the species with the lowest molecular diversity. High genetic divergence was observed among the three species. The well-defined ancestral groups for each species led to the identification of samples of Conyza with ancestral genomes from the three species. Hybridization events between pairs of these species may have occurred in crop fields from southern Brazil. The high molecular diversity in resistant biotypes of C. sumatrensis indicated that these biotypes have a high potential to colonize new areas, which increases its potential as a weed. Keywords: horseweed, molecular divergence, SSR loci. A identificacao das especies Conyza canadensis, C. bonariensis e C. sumatrensis tem sido desafiadora para a ciencia das plantas daninhas. No presente estudo, primers para locos microssatelites (SSR) foram utilizados para investigar a divergencia molecular entre as tres especies; mostrar como as populacoes estao geneticamente estruturadas em nivel molecular e avaliar o nivel de mistura genetica entre as plantas de Conyza no Sul do Brazil. Doze primers amplificaram segmentos de DNA bem definidos em todas as 88 amostras das tres especies. A proporcao estimada de locos SSR polimorficos, o numero de alelos, e a heterozigosidade media esperada foram mais altos nas amostras de C. banariensis do que nas demais. C. canadensis foi a especie com menor diversidade molecular. Divergencia genetica alta foi observada entre as tres especies. A formacao de grupos ancestrais bem definidos para cada especie levou a identificacao de amostras de Conyza com genoma ancestral das tres especies. A ocorrencia de hibridizacao entre as tres especies pode ter ocorrido nas lavouras do Sul do Brasil. A diversidade molecular alta em biotipos resistentes de C. sumatrensis indicou que estes biotipos tem um alto p