The neotropical bracken fern Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae) is described as an aggressive pioneer plant species. It invades abandoned or newly burned areas and represents a management challenge at these invaded sites. Native to the Atlantic Forest and Cerrado (Tropical Savanna) Brazilian biomes, P. arachnoideum has nevertheless become very problematic in these conservation hotspots. Despite some reports suggesting a possible role of allelopathy in this plant’s dominance, until now there has been little evidence of isolated and individually identified compounds with phytotoxic activities present in its tissues or in the surrounding environment. Thus, the aim of this study was to investigate the allelopathic potential of P. arachnoideum by isolating and identifying any secondary metabolites with phytotoxic activity in its tissues, litter, and soil. Bioguided phytochemical investigation led to the isolation and identification of the proanthocyanidin selligueain A as the major secondary compound in the green fronds and litter of this fern. It is produced by P. arachnoideum in its green fronds, remains unaltered during the senescence process, and is the major secondary compound present in litter. Selligueain A showed phytotoxic activity against the selected target species sesame (Sesamum indicum) early development. In particular, the compound inhibited root and stem growth, and root metaxylem cell size but did not affect chlorophyll content. This compound can be considered as an allelochemical because it is present in the soil under P. arachnoideum patches as one of the major compounds in the soil solution. This is the first report of the presence of selligueain A in any member of the Dennstaedtiaceae family and the first time an isolated and identified allelochemical produced by members of the Pteridium species complex has been described. This evidence of selligueain A as a putative allelochemical of P. arachnoideum reinforces the role of allelopathy in the dominance processes of this plant in the areas where it occurs.

ABSTRACT:The aim of this study was to evaluate the phytotoxic activity of aqueous extracts from mature leaves, stem bark and roots of Drimys brasiliensis Miers on germination and initial seedling development of two target species, Triticum aestivum L. (wheat) and Raphanus sativus L. (radish). The aqueous extract was prepared in a proportion of 10 g of plant powder, dissolved in 100 mL of distilled water, resulting in a 10% extract concentrate. Dilutions were made with distilled water to 7.5; 5.0; 2.5% and 0% (control). Germination and seedling growth bioassays were carried out under controlled laboratory conditions. The different plant parts exerted inhibitory effects on germination and early growth of wheat and radish, however, the extract obtained from the leaves was more effective in inhibiting the germination of radish. All plant parts of D. brasiliensis may constitute a promising source in the search for compounds capable of acting as natural phytotoxins.

Drimys brasiliensis Miers (Winteraceae), commonly called casca d'anta, is found in the Atlantic Forest and in Cerrado domain. It is considered an important source of natural compounds with pharmacological properties, however little is known about their phytotoxic potential on other plants. This study aims to evaluate the phytotoxic effects of D. brasiliensis leaf extracts collected in two seasons (dry and rainy) on the germination and seedling growth of Sesamum indicum L., as well as evaluating the effect of the most active extract on metaxylem cell size in the roots of the target species. The aqueous extract was prepared with 10 g of dried, ground leaves dissolved in 100 mL of distilled water, resulting in a 10% extract concentrate. Dilutions were made with distilled water to 7.5; 5.0; 2.5% and 0% (control). The leaf extracts showed phytotoxicity on germination and early growth of sesame, with more pronounced activity in leaves collected in the dry season. The inhibitory effects were observed at the cellular level in sesame roots, with a significant reduction in the size of the metaxylem cells in the presence of all concentrations of leaf extract. The extract from leaves of D. brasiliensis may constitute a promising source in the search for natural phytotoxins for use in sustainable agriculture practices.Key words: inhibition, seasonality, germinability, metaxylem, sesame. RESUMEN Drimys brasiliensis

ABSTRACT. This study aims to evaluate the phytotoxicity potential of leaf and root extracts of Drimys brasiliensis on the germination and seedling growth of Panicum maximum and Euphorbia heterophylla and its influence on metaxylem cell size in the seedling roots of the latter specie. The leaf and root extracts were fractionated by partition chromatography, and the hexane and ethyl acetate fractions obtained from each organ were evaluated at different concentrations for phytotoxic activity in several bioassays. In seedling growth tests, we compared the effects of these fractions with the herbicide oxyfluorfen. The hexane fraction of the root extracts showed a higher inhibitory potential on the germination and growth of weeds and reduced the average size of the metaxylem cells of E. heterophylla roots by more than 50%. The inhibitory effects of the root hexane fraction on seedling growth was similar to the herbicide, indicating that D. brasiliensis is a possible alternative form of control for the weed species examined.Keywords: allelopathy, inhibition, germination, early growth. Potencial fitotóxico de Drimys brasiliensis Miers para o controle de plantas daninhas RESUMO. O objetivo do estudo foi avaliar o potencial fitotóxico de frações do extrato de folhas e raízes deDrimys brasiliensis sobre a germinação e o crescimento de plântulas de Panicum maximum e Euphorbia heterophylla, e sua influência sobre as células do metaxilema da última espécie. Os extratos de folhas e raízes foram fracionados por cromatografia de partição e as frações hexânica e acetato de etila obtidas de cada órgão foram avaliadas nos bioensaios, em diferentes concentrações. No teste de crescimento, comparou-se o efeito das soluções das frações com o herbicida oxyfluorfen. A fração hexânica das raízes apresentou maior potencial para inibir a germinação e crescimento das espécies infestantes e ocasionou redução em mais de 50% no tamanho das células do metaxilema de E. heterophylla. As inibições no crescimento inicial, decorrentes da aplicação da fração hexânica das raízes, foram similares ao efeito produzido pelo herbicida comercial, indicando a eficiência de D. brasiliensis para o controle das espécies infestantes estudadas.Palavras-chave: alelopatia, inibição, germinação, crescimento inicial.

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