Selection of reference genes is an essential consideration to increase the precision and quality of relative expression analysis by the quantitative RT-PCR method. The stability of eight expressed sequence tags was evaluated to define potential reference genes to study the differential expression of common bean target genes under biotic (incompatible interaction between common bean and fungus Colletotrichum lindemuthianum) and abiotic (drought; salinity; cold temperature) stresses. The efficiency of amplification curves and quantification cycle (C (q)) were determined using LinRegPCR software. The stability of the candidate reference genes was obtained using geNorm and NormFinder software, whereas the normalization of differential expression of target genes [beta-1,3-glucanase 1 (BG1) gene for biotic stress and dehydration responsive element binding (DREB) gene for abiotic stress] was defined by REST software. High stability was obtained for insulin degrading enzyme (IDE), actin-11 (Act11), unknown 1 (Ukn1) and unknown 2 (Ukn2) genes during biotic stress, and for SKP1/ASK-interacting protein 16 (Skip16), Act11, Tubulin beta-8 (β-Tub8) and Unk1 genes under abiotic stresses. However, IDE and Act11 were indicated as the best combination of reference genes for biotic stress analysis, whereas the Skip16 and Act11 genes were the best combination to study abiotic stress. These genes should be useful in the normalization of gene expression by RT-PCR analysis in common bean, the most important edible legume.

Based on nine microsatellite loci, the aim of this study was to appraise the genetic diversity of 42 cassava (Manihot esculenta) landraces from selected regions in Brazil, and examine how this variety is distributed according to origin in several municipalities in the states of Minas Gerais, São Paulo, Mato Grosso do Sul, Amazonas and Mato Grosso. High diversity values were found among the five above-mentioned regions, with 3.3 alleles per locus on an average, a high percentage of polymorphic loci varying from 88.8% to 100%, an average of 0.265 for observed heterozygosity and 0.570 for gene diversity. Most genetic diversity was concentrated within the regions themselves (HS = 0.52). Cluster analysis and principal component based scatter plotting showed greater similarity among landraces from São Paulo, Mato Grosso do Sul and Amazonas, whereas those from Minas Gerais were clustered into a sub-group within this group. The plants from Mato Grosso, mostly collected in the municipality of General Carneiro, provided the highest differentiation. The migration of human populations is one among the possible reasons for this closer resemblance or greater disparity among plants from the various regions.

The phenotypic diversity of sweet potato (Ipomoea batatas) landraces was assessed using morphological traits, verifying how this diversity is distributed among the households and settlements of the Vale do Ribeira, Brazil. A total of 74 accessions, involving 53 landraces, collected from 30 households distributed among 18 settlements that practice traditional agriculture in the municipalities of Iguape, Ilha Comprida, and Cananeia, as well as four commercial varieties acquired in markets of Iguape and Piracicaba, were evaluated under an ex situ experimental condition in Piracicaba, SP, Brazil. Nine phenological and floral descriptors, nine morphological vegetative aerial descriptors and five storage root traits were recorded. The 14 aerial vegetative and root descriptors were evaluated as binary data, totaling 74 attributes. Cluster analyses were made using the Jaccard similarity index and the UPGMA (unweighted pair group method with arithmetic mean) agglomerative method. Binary data was also submitted to a variance analysis (AMOVA). No defined groups were observed, indicating that the diversity of the landraces is not structured in space, but considerable morphological variation was found in this area (Jaccard similarity index varying from 0.12 to 1.0). Most of the variability occurred within households (64.4%), followed by the distribution among households within settlements (27.1%) and among settlements (8.4%). Thus, the traditional agriculturists of Vale do Ribeira maintain a high morphological diversity for sweet potato within their households, which can be assumed to be produced by the outcrossing mating system of this species and somatic mutation events, as well as the exchange system at local and regional levels.

We used simple sequence repeat (SSR) markers to investigate the genetic diversity of 78 sweet potato (Ipomoea batatas) accessions (58 landraces and 20 putative clones) from traditional agricultural households from 19 local communities in the Vale do Ribeira, São Paulo, Brazil. Eight SSR loci were assessed using 6% (w/v) polyacrylamide gels stained with silver nitrate and the accessions genotyped considering the presence or absence of bands. The results were subjected to analysis of molecular variance (AMOVA), and cluster and principal coordinate analyses. Spatial structure was assessed using Mantel's test to compare genetic and geographic distances. Each primer pair generated between three and ten clearly scorable polymorphic fragments. Cluster analyses showed a Jaccard's index from 0.3 to 1.0, indicating high genetic and intravarietal diversity. Accessions from all 19 communities were not spatially structured (r = 0.15, p < 0.054), with AMOVA indicating that most of the variability (58.2%) was distributed within households and only 18.1% of the variability was distributed between households within communities. The outcrossing mating system of sweet potato, and anthropic factors such as selection of different varieties and their maintenance within household small plots and home gardens, as well as an extensive exchange system between agriculturists, may all be contributing to these results.

Microsatellite markers have proved to be useful in genetic diversity assessments of sweetpotato (Ipomoea batatas) but practical DNA extraction methods to ensure good quality and quantity DNA for these studies are yet to be established. This study compares the efficiency of three modified methodologies for DNA extraction of six sweetpotato landraces using the CTAB extraction buffer in regard to quantity and purity of DNA quantification and microsatellite band patterns. All methodologies yielded satisfactory results, but the method based in leaf tissue macerated in liquid nitrogen was deemed more adequate because of its simplicity and lower cost. However, the method based in dry leaf tissue was considered more advantageous, first because elicits practicability in the plant acquisition and drying process, especially when the collection is performed in situ, and also because its simplicity makes possible the cold storage of the dry, ground samples for future DNA extractions. Key words: Ipomoea batatas, SSR, DNA isolation, landraces, protocol MÉTODOS CTAB DE EXTRAÇÃO DE DNA PARA A ANÁLISE DE MICROSSATÉLITES EM BATATA-DOCERESUMO: Os marcadores microssatélites são úteis para a análise da diversidade genética de variedades tradicionais de batata-doce (Ipomoea batatas). Para estes estudos, métodos práticos de extração de DNA precisam ser estabelecidos para assegurar uma boa qualidade e quantidade de DNA extraído. Assim, foi comparada a eficiência de três metodologias para extração de DNA usando o tampão de extração CTAB, todas com modificações. Para verificar a quantidade e pureza na quantificação de DNA, bem como o padrão de bandas de microssatélites para as três metodologias utilizaram-se seis etnovariedades de batata-doce. Os testes mostraram que as três metodologias apresentaram resultados satisfatórios. Uma das metodologias baseada em tecido foliar macerado em nitrogênio líquido mostrouse a mais adequada devido à simplicidade e menor custo. Entretanto, o método baseado em tecido foliar seco foi o mais vantajoso devido à praticidade na aquisição da planta e no processo de secagem, principalmente quando a coleção encontra-se em condições in situ, e pela possibilidade do armazenamento refrigerado das amostras secas e maceradas para futuras extrações de DNA.