Polyploidy, or whole genome duplication, has played a major role in the evolution of many eukaryotic lineages. Although the prevalence of polyploidy in plants is well documented, the molecular and cytological consequences are understood largely from newly formed polyploids (neopolyploids) that have been grown experimentally. Classical cytological and molecular cytogenetic studies both have shown that experimental neoallopolyploids often have meiotic irregularities, producing chromosomally variable gametes and progeny; however, little is known about the extent or duration of chromosomal variation in natural neoallopolyploid populations. We report the results of a molecular cytogenetic study on natural populations of a neoallopolyploid, Tragopogon miscellus, which formed multiple times in the past 80 y. Using genomic and fluorescence in situ hybridization, we uncovered massive and repeated patterns of chromosomal variation in all populations. No population was fixed for a particular karyotype; 76% of the individuals showed intergenomic translocations, and 69% were aneuploid for one or more chromosomes.

Genetic diversity of accessions of the mangaba germplasm bank in Sergipe, BrazilAbstract -The objective of this work was to estimate the genetic variability of mangaba accessions of natural populations, from 11 locations, using RAPD markers. The accessions belong to Banco Ativo de Mangaba of Embrapa Tabuleiros Costeiros, in Itaporanga d'Ajuda, SE, Brazil. A total of 13 primers were used, which generated 82 fragments, of which 78 (95%) were polymorphic. Genetic analysis among regions showed low genetic diversity; however, genetic similarity ranged from 0.02 to 0.91, for the 55 accessions. Divergent groups were identified by UPGMA and ACoP clustering. The least similar accessions were derived from Ipiranguinha (Conde, PB, Brazil) and Preguiça (Indiaroba, SE, Brazil), and the most similar from Jandaíra (Costa Azul, BA, Brazil). From the total, 49 accessions were genetically distinct and six were similar. By using RAPD markers, it was possible to obtain a unique molecular profile, besides estimating the variability among the accessions evaluated. The Banco Ativo de Germoplasma de Mangaba of Embrapa Tabuleiros Costeiros shows low genetic diversity among locations.

Brazilian orchids are currently threatened with extinction due to habitat loss and, because of their high ornamental value, intense collecting pressure. Genetic diversity can play a key role in the survival of endangered orchid species. Here we provide the first data on genetic diversity and structure of wild populations in the genus Cattleya, in particular C. labiata, using random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) markers. We studied 130 individuals, 117 belonging to Cattleya labiata and 13 from 10 other species in the same genus. Data generated from 12 ISSR and 12 RAPD primers were used to determine genetic variability via a model-based Bayesian procedure (Structure) and molecular variance analysis. In addition, Shannon index, genetic diversity and Jaccard coefficients were also estimated. The marker data indicated that C. labiata has a high level of polymorphism, and five reconstructed populations were identified by Structure. The unweighted pair group method with arithmetic mean dendrogram did not group the samples by origin, which was also confirmed by Bayesian analysis, demonstrating the complex genetic structure of C. labiata. Other Cattleya species showed no relationship with any C. labiata sample. This genetic characterization of Cattleya from northeast Brazil contributes to knowledge of the genetic structure of the species and can be used to define strategies for conservation and breeding programmes.