Abstract
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.
Highlights
Pteridium plants are cosmopolitan heliophyte ferns that are among the most abundant plant taxa on the planet, present on all continents except Antarctica [1,2]
The results reported corroborate the hypothesis of allelopathy in bracken fern with the identification of a phytotoxic condensed tannin, a polyphenolic compound produced by the green fronds of P. arachnoideum and present as a major secondary metabolite in frond litter
This study expands on our knowledge of the phytochemical constituents of Pteridium arachnoideum, reporting for the first time that proanthocyanidin selligueain A is present in a member of the Dennstaedtiaceae family
Summary
Pteridium plants are cosmopolitan heliophyte ferns that are among the most abundant plant taxa on the planet, present on all continents except Antarctica [1,2]. Plants of the Pteridium genus exhibit extensive phenotypic plasticity with many morphological intermediates between definable morphotypes and the ability for these to hybridize over long distances. Until 2009, the genus was considered monotypic with two subspecies Eight varieties were recognized within subspecies aquilinum, all found in Europe, and four were recognized within subspecies caudatum, found in South and Central America, Asia, and Oceania [1,2]. Pteridium arachnoideum is a separate species according to this classification [1]. The most recent nomenclature has been adopted, many of the references on the biology, ecology, and phytochemistry of Pteridium species adhere to the previous classification system
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