Secondary metabolites that could contribute to the monodominance of Erythrina fusca in the Brazilian Pantanal.

Erythrina fusca is a dominant species in the Brazilian Pantanal. We hypothesized that E. fusca possess allelopathic potential and we evaluated effects of extracts on germination and development of Lactuca sativa, a bioindicator species. We tested the effect of leaves, bark, roots, and seeds extracts of E. fusca on germination and speed index, using high, moderate and low concentration (0.2, 1 and 5 mg mL^-1). To evaluate effects on development, we subjected seedlings of L. sativa to the same treatments and measured root and aerial part length. High concentration of extracts reduced L. sativa germination; leaves extract caused the maximum reduction on germination of L. sativa, similar to 2,4-Dichlorophenoxyacetic acid (2,4-D); this extract has flavonoids and saponins as main compounds, classes that also occur in the bark and roots extracts in lower concentrations; bark and roots (5 mg mL^-1), leaves and roots (1 mg mL^-1) decreased these traits as well, but in lower magnitude. A significant reduction in root length was induced by highest concentration of all extracts (5 mg mL^-1); the results suggest that erythrinic alkaloids should interfere in the root length once the seeds accumulate almost exclusively this class of compounds. Our results showed that all parts of E. fusca had adverse effects on germination or development of L. sativa, showing that different class of compounds secondary metabolites is involved in this activity. Possibly, this phytotoxicity influences monodominance of E. fusca in Pantanal, but studies are essential to evaluate effects of it on other native species.