We have identified AFLP markers tightly linked to the locus conferring resistance to the leaf rust Melampsora larici-populina in Populus. The study was carried out using a hybrid progeny derived from an inter-specific, controlled cross between a resistant Populus deltoides female and a susceptible P. nigra male. The segregation ratio of resistant to susceptible plants suggested that a single, dominant locus defined this resistance. This locus, which we have designated Melampsora resistance (Mer), confers resistance against E1, E2, and E3, three different races of Melampsora larici-populina. In order to identify molecular markers linked to the Mer locus we decided to combine two different techniques: (1) the high-density marker technology, AFLP, which allows the analysis of thousands of markers in a relatively short time, and (2) the Bulked Segregant Analysis (BSA), a method which facilitates the identification of markers that are tightly linked to the locus of interest. We analyzed approximately 11,500 selectively amplified DNA fragments using 144 primer combinations and identified three markers tightly linked to the Mer locus. The markers can be useful in current breeding programs and are the basis for future cloning of the resistance gene.

The phylogenetic relationships between naturally occurring Atlantic Crassostrea oyster species were inferred through analyses of mitochondrial (cytochrome oxidase subunit I and 16S) and nuclear (second internal transcribed spacer) sequences. We also scored 15 allozyme loci on 422 oysters to study population structuring of C. rhizophorae and C. brasiliana along 9000 km of the Western Atlantic coastline. Despite morphological similarities, C. virginica was genetically more closely related to C. rhizophorae than to C. brasiliana. In contrast, C. paraibanensis was genetically indistinguishable from C. brasiliana, which is probably a junior synonym of the African C. gasar. Significant genetic differentiation between populations of C. rhizophorae and C. gasar were found along the Western Atlantic coast, supporting an isolation-by-distance pattern.

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Penaeid shrimps are important resources for worldwide fisheries and aquaculture. In the Southwest Atlantic, Farfantepenaeus brasiliensis, F. paulensis, F. subtilis, Farfantepenaeus sp. and Litopenaeus schmitti are among the most important commercially exploited species. Despite their high commercial value, there is little information available on the different aspects of their biology or genetics and almost no data on their stock structure. We used allozymes to estimate variability levels and population genetic structure of F. brasiliensis, F. paulensis, L. schmitti and the recently detected species Farfantepenaeus sp. along as much as 4,000 km of Brazilian coastline. No population heterogeneity was detected in F. brasiliensis or L. schmitti along the studied area. In contrast, F ST values found for Farfantepenaeus sp. and F. paulensis indicate that the populations of those two species are genetically structured, comprising different fishery stocks. The largest genetic differences in F. paulensis were found between Lagoa dos Patos (South) and the two populations from Southeast Brazil. In Farfantepenaeus sp., significant differences were detected between the population from Recife and those from Fortaleza and Ilhéus.