J. R. Fonseca

Microsatellite diversity and genetic structure among common bean (Phaseolus vulgaris L.) landraces in Brazil, a secondary center of diversity

Brazil is the largest producer and consumer of common bean (Phaseolus vulgaris L.), which is the most important source of human dietary protein in that country. This study assessed the genetic diversity and the structure of a sample of 279 geo-referenced common bean landraces from Brazil, using molecular markers. Sixty-seven microsatellite markers spread over the 11 linkage groups of the common bean genome, as well as Phaseolin, PvTFL1y, APA and four SCAR markers were used. As expected, the sample showed lower genetic diversity compared to the diversity in the primary center of diversification. Andean and Mesoamerican gene pools were both present but the latter gene pool was four times more frequent than the former. The two gene pools could be clearly distinguished; limited admixture was observed between these groups. The Mesoamerican group consisted of two sub-populations, with a high level of admixture between them leading to a large proportion of stabilized hybrids not observed in the centers of domestication. Thus, Brazil can be considered a secondary center of diversification of common bean. A high degree of genome-wide multilocus associations even among unlinked loci was observed, confirming the high level of structure in the sample and suggesting that association mapping should be conducted in separate Andean and Mesoamerican Brazilian samples.

Identificação de duplicidades de acessos de feijão por meio de técnicas multivariadas

Fifty bean (Phaseolus vulgaris L.) samples from the Active Germplasm Bank of Embrapa - Centro Nacional de Pesquisa de Arroz e Feijao (CNPAF), Goiânia, GO, Brazil, were studied using multivariable techniques to screen descriptors for characterization, to measure genetic diversity and to group samples, looking for repetitive access identification. Germplasm evaluation was carried out in June 1993, using the randomized block design with two replications. Ten quantitative and phenologic descriptors were used for characterization and analysed by canonic variables and Mahalanobis distance techniques. There were no redundant characters and all descriptors were important for sample description. The grouping technique using the diversity genetic measures through the Mahalanobis generalized distance showed to be efficient and viable for identification of repetitive samples, being an appropriate procedure to be used in genebanks.

Genetic variability of Brazilian rice landraces determined by SSR markers

The objective of this study was to evaluate the genetic variability of rice (Oryza sativa) landraces collected in Brazilian small farms. Twelve simple sequence repeat (SSR) markers characterized 417 landraces collected in 1986, 1987 and 2003, in the state of Goias, Brazil. The number of landraces with long and thin grain type increased in the evaluated period, probably due to market demand. Based on the molecular data, the genetic variability increased during this period and, as per to the factorial correspondence analysis, most of the accessions were grouped according to the year of collection. The incorporation of modern rice cultivars in landrace cultivation areas and the selection carried out by small farmers are the most probable factors responsible for increasing landrace genetic variability, during the evaluated period. Genotype exchange between farmers, selection practice and local environmental adaptation are able to generate novel adapted allele combinations, which can be used by breeding programs, to reinitiate the process.