No abstract

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.

Phylogeographic analysis of the Coffea subgenus Coffea was performed using data on plastid DNA sequences and interpreted in relation to biogeographic data on African rain forest flora. Parsimony and Bayesian analyses of trnL-F, trnT-L and atpB-rbcL intergenic spacers from 24 African species revealed two main clades in the Coffea subgenus Coffea whose distribution overlaps in west equatorial Africa. Comparison of trnL-F sequences obtained from GenBank for 45 Coffea species from Cameroon, Madagascar, Grande Comore and the Mascarenes revealed low divergence between African and Madagascan species, suggesting a rapid and radial mode of speciation. A chronological history of the dispersal of the Coffea subgenus Coffea from its centre of origin in Lower Guinea is proposed. No relation was found between phylogenetic topology and the age of emergence of the volcanic islands that Coffea species have colonised in the Indian Ocean, suggesting dispersal from mainland Africa after the emergence of the youngest island, Grande Comore, 500,000 years ago. Additional sequences were obtained from GenBank for 24 species of other Rubiaceae genera, including the Rubia genus whose origin has been dated from the Upper Miocene. Estimates of substitution rates suggested that diversification in Coffea subgenus Coffea occurred about 460,000 years ago or as recently as the last 100,000 years, depending on the cpDNA region considered and calibration. The phylogenetic relationships based on plastid sequences confirmed biogeographic differentiation of coffee species, but they were not congruent with morphological and biochemical classifications, or with the capacity to grow in specific environments. Examples of convergent evolution in the main clades are given using characters of leaf size, caffeine content and reproductive mode.

Knowledge of the genetic variability among genotypes is important for the transfer of useful genes and to maximize the use of available germplasm resources. This study was carried out to assess the genetic variability of 14 elite Coffea arabica cultivars using random amplified polymorphic DNA (RAPD) associated with a prior digestion of genomic DNA with restriction endonucleases. The accessions were obtained from the Coffea collection maintained at the Instituto Agronômico do Paraná (IAPAR), located in Londrina, Paraná, Brazil. Twenty-four informative RAPD primers, used in association with restriction enzymes, yielded 330 reproducible and scorable DNA bands, of which 224 (68%) were polymorphic. The amplified products were used to estimate the genetic variability using Dice's similarity coefficient. The data matrix was converted to a dendrogram and a three-dimensional plot using principal coordinate analysis. The accessions studied were separated into clusters in a manner that was consistent with the known pedigree. The associations obtained in the dendrogram and in the principal coordinate analysis plot suggest the probable origin of the Kattimor cultivar. The RAPD technique associated with restriction digestion was proved to be a useful tool for genetic characterization of C. arabica genotypes making an important contribution to the application of molecular markers to coffee breeding.

The genetic complexity in the genus Musa has been subject of study in many breeding programs worldwide. Parthenocarpy, female sterility, polyploidy in different cultivars and limited amount of genetic and genomic information make the production of new banana cultivars difficult and time consuming. In addition, it is known that part of the cultivars and related wild species in the genus contain numerous chromosomal rearrangements. In order to produce new cultivars more effectively breeders must better understand the genetic differences of the potential crossing parents for introgression hybridization, but extensive genetic information is lacking.As an alternative to achieve information on genetic collinearity we make use of modern chromosome map technology known as high-resolution fluorescent in situ hybridization (FISH). This article presents the technical aspects and applications of such a technology in Musa species. The technique deals with BAC clone positioning on pachytene chromosomes of Calcutta 4 (Musa acuminata ssp. burmanicoides, A genome group, section Eumusa) and M. velutina (section Rodochlamys). Pollen mother cells digestion with pectolytic enzymes and maceration with acetic acid were optimized for making cell spread preparations appropriate for FISH. As an example of this Euphytica (2009) 166:431-443 DOI 10.1007 approach we chose BAC clones that contain markers to known resistance genes and hybridize them for establishing their relative positions on the two species. Technical challenges for adapting existing protocols to the banana cells are presented. We also discuss how this technique can be instrumental for validating collinearity between potential crossing parents and how the method can be helpful in future mapping initiatives, and how this method allows identification of chromosomal rearrangements between related Musa species and cultivars.