ABSTRACT Forest-to-agriculture conversion and soil management practices for soybean cropping are frequently performed in the Cerrado (Brazilian tropical savanna). However, the effects of these practices on the soil microbial communities are still unknown. We evaluated and compared the fungal community structure in soil from soybean cropland with soil under native Cerrado vegetation at different times of the year in the Tocantins State. Soil samples were collected in two periods after planting (December) and in two periods during the soybean reproductive growth stage (February). Concomitantly, soil samples were collected from an area under native Cerrado vegetation surrounding the agricultural area. The soil DNA was analyzed using a fingerprinting method termed Automated Ribosomal Intergenic Space Analysis (ARISA) to assess the fungal community structure in the soil. Differences in the fungal community structure in the soil were found when comparing soybean cropland with the native vegetation (R = 0.932 for sampling 1 and R = 0.641 for sampling 2). Changes in the fungal community structure after management practices for soybean planting in Cerrado areas were related to changes in soil properties, mainly in copper, calcium, and iron contents, cation exchange capacity, base saturation, and calcium to magnesium ratio. These results show the changes in the fungal community structure in the soil as an effect of agricultural soil management in Cerrado vegetation in the state of Tocantins.

Com objetivo de avaliar a variabilidade fenotípica e a divergência genética entre 50 clones de batata doce, foi realizado um ensaio na Estação Experimental da Universidade Federal do Tocantins - Campus de Palmas, no ano agrícola 2009/2010. A divergência genética foi avaliada pelo método de agrupamento de otimização de Tocher. As características estudadas foram produtividade, produção de matéria seca, teor de amido e rendimento de etanol. O método de otimização por Tocher separou os clones em oito grupos geneticamente distintos. As características produtividade (70,15%) e rendimento em etanol (15,06%) foram as que mais contribuíram na divergência genética entre os clones. A presença de variabilidade genética permitiu a identificação de cultivares dissimilares e com média elevada indicando a possibilidade de seleção de genótipos superiores para as características estudadas. Os cruzamentos Duda x 22.19, Marcela x 22.19, Barbara x 22.19, Duda x Barbara, Amanda x 22.19, Amanda x Marcela são promissores para obtenção de híbridos divergentes.

In order to evaluate the phenotypic variability and genetic divergence between 50 clones of the sweet potato, a test was conducted at the Experimental Station of the Federal Universidade of Tocantins, Palmas Campus, in the agricultural year of 2009/2010. The genetic diversity was assessed using the Tocher grouping optimization method. The characteristics studied were productivity, dry matter production, starch content and ethanol yield. The Tocher optimization method separated the clones into eight genetically distinct groups. The characteristics of productivity (70.15%) and ethanol yield (15.06%) were those that most affected genetic divergence among the clones. The presence of genetic variability permitted the identification of dissimilar cultivars with a high average, indicating the possibility of selecting superior genotypes for the traits studied. The Duda x 22.19, Marcela x 22.19, Barbara x 22:19, Duda x Barbara, Amanda x 22:19, Amanda x Marcela crossbreeds are those which are promising for obtaining divergent hybrids.