Maria Tereza Grombone-Guaratini

Seed bank and seed rain in a seasonal semi-deciduous forest in south-eastern Brazil

To examine the influence of seasonality on the abundance and com- position of species in the community, we studied the seed rain and the seed bank in a seasonal, semi-deciduous forest in south-eastern Brazil. Soil samples (depth 3 cm, 0.25 m 2 ) were collected within a 1-ha plot in the dry seasons of 1996 and 1997 and the rainy season of 1997 (84 samples per collection). Thirty-five seed traps (0.25 m 2 each) were placed randomly in the forest from March 1997 to February 1998. The greatest density of seeds in the soil occurred in samples collected during the rainy season, the period which coincides with the main fruiting period in this forest. The Sorensen similarity index values for the seed bank composition among the three periods were high (> 0.50). The fallout of propagules was strongly sea- sonal, with more than half of the annual total number of seeds being caught in the two months around the end of the dry season and beginning of the rainy season. The mean density of seeds in the soil bank was nearly 86% lower than the seed rain density. There was no clear evidence of seasonal effects on species den- sity and richness in this forest.

Reproductive biology in species of Bidens L. (Asteraceae)

Estudos de biologia reprodutiva de especies invasoras podem ter implicacoes sobre o estabelecimento de praticas de controle que minimizem o efeito das populacoes destas especies em areas agricolas. A biologia da polinizacao de Bidens alba (L.) DC., B. pilosa L. e Bidens subalternans DC. foi estudada em diferentes locais e estacoes climaticas. Bidens pilosa e B. subalternans sao especies amplamente distribuidas em areas agricolas, em habitats perturbados e em margens de estradas. Bidens alba ocorre somente em regioes litorâneas. As tres especies sao auto-compativeis e nao sao agamospermicas. A composicao da comunidade de polinizadores apresenta diferencas durante o ano e entre locais. Himenopteros e lepidopteros sao os visitantes mais frequentes nas especies de Bidens. Embora as especies sejam auto compativeis, a presenca de polinizadores pode afetar os niveis de endocruzamento. A atracao de insetos por especies de Bidens pode beneficiar as culturas agricolas e apresentar importantes implicacoes para a biologia da conservacao.

The seed bank of a gallery forest in Southeastern Brazil

The soil seed bank was studied in a gallery forest in Southeastern Brazil. Samples were collected from edge to edge along transects perpendicular to the river during the wet (December, 1990) and dry (August, 1991) seasons. The number of seeds found in the seed bank samples was greater in the dry season than in the wet season indicating that there was important variation in the seed stocks in these two periods. The similarity values between the seed bank and the community composition were low. The high density of weed species might be reflecting forest fragmentation and indicating a degree of perturbation.

Resistance and differential susceptibility of Bidens pilosa and B. subalternans biotypes to ALS-inhibiting herbicides

The frequent application of herbicides in agricultural areas may select resistant biotypes in weed populations, whose biological characteristics influence the speed and patterns of resistance. This research aims to charactere, simultaneously, resistance patterns and differential susceptibility of Bidens pilosa and B. subalternans biotypes to ALS-inhibiting herbicides of the imidazolinone and sulfonylurea chemical groups. Six hairy beggarticks biotypes, four suspected resistant and two known susceptible, were treated with eight rates of chlorimuron-ethyl or imazethapyr, in greenhouse conditions. Percent control and percent fresh weight of the plants were evaluated at 28 days after the application. B. subalternans is less susceptible to ALS-inhibiting herbicides than B. pilosa; B. subalternans biotypes were more resistant than B. pilosa biotypes; there are B. pilosa and B. subalternans biotypes with cross resistance to the ALS-inhibiting herbicides of the sulfonylurea and imidazolinone groups; there are different patterns of cross resistance to the diverse groups of ALS-inhibiting herbicides.

Low Allozymic Variation in the Bidens pilosa L. Complex (Asteraceae)

Bidens alba, B. subalternans, and B. pilosa form a complex group based on their morphological similarities. Bidens pilosa L. and B. subalternans DC. are herbs with a wide distribution in agricultural and disturbed areas. Bidens alba (L.) DC. varies in size from herb to subshrub and has a coastal distribution. Enzyme electrophoresis was used to evaluate genetic diversity in 12 populations of Bidens. All but three loci (Lap-1, Est, and Got) were monomorphic. Est-1 and Got were polymorphic only in B. alba. Lap-1 was polymorphic only in B. pilosa and B. subalternans. The estimates of genetic variability were low for all three taxa and all of the populations studied. Genetic diversity varied from 0.01 to 0.03. Mean genetic identities were high among populations of each species (0.99 for B. alba and 1.00 for B. pilosa and B. subalternans) and among the three species (1.00). Bidens pilosa and B. subalternans could be considered a single species if the taxonomy of the group were based solely on isozyme data.

Development of microsatellite markers for Aulonemia aristulata (Poaceae) and cross-amplification in other bamboo species

PREMISE OF THE STUDY Microsatellite primers were developed for Aulonemia aristulata, an endangered species of economic interest, to further describe its genetic variability and population structure. We also tested cross-amplification in 18 other bamboo species. METHODS AND RESULTS Using an enrichment genomic library, 13 microsatellite loci were isolated and characterized in A. aristulata. Seven of these loci were polymorphic. Twelve markers were cross-amplified in at least ten of the tested bamboo species. CONCLUSIONS These markers will be useful for studies on the genetic diversity and structure of A. aristulata, which are important for future conservation, management and breeding programs of this species.

Genetic Diversity and Age Class Structure of Seedlings and Saplings after a Mast Flowering of Bamboo in the Brazilian Atlantic Forest

Premise of research. Aulonemia aristulata (Döll) McClure—an endemic Brazilian species—flowers, sets seed, and subsequently dies after many years of vegetative growth. After it has died, plants regenerate by seed germination on the forest floor. Because of the sporadic and unusual records of the flowering cycle and the difficulty of identifying individuals, few studies of the genetic structure of bamboo populations have been published. In this study, we investigated how the flowering event affects the genetic diversity among different populations and evaluated the genetic variability between two ontogenic stages. Methodology. We collected seedlings in July 2009 and saplings in February 2010 in two study areas. We investigated the genetic diversity using markers with different modes of inheritance: nuclear simple sequence repeats (SSRs) and chloroplast SSRs. Pivotal results. The nuclear genetic diversity of the study populations was higher than in other bamboo species. All populations had high and significant inbreeding values, indicating a deficiency of heterozygotes. In general, saplings exhibited less inbreeding than seedlings. Moreover, chloroplast genetic diversity was low, which may indicate that individuals share maternal ancestors. Conclusions. This study demonstrates that sexual reproduction, demographic history, and colonization patterns may contribute to population diversity. The decrease in plant density between ontogenetic stages (i.e., from seedling to sapling) was associated with a higher frequency of homozygotes in seedlings compared with saplings and could indicate intraspecific competition coupled with inbreeding depression as the main factor reducing plant density in bamboos.