Palavras chave: Guilandina bonduc, Fitotoxicidade, exsudados radiculares, Caesaldekarin C 15 ABSTRACTPlants emit a variety of secondary metabolites, that can influence negative or positively on the growth and development of neighbor species. Such phenomenon is called allelopathy. One of the mechanismes for emission of allelochemicals is through root exudate. It has been noticed that there are halos of bare soil around Guilandina bonduc ( Fabaceae) and its roots reach a population of Cyperus atlanticus, a endemic specie of the Trindade Island, that are suffering with G. bonduc expansion. Therefore, this work aimed to investigate phytotoxic activity of compounds in the root tissue and in the exudate of G. bonduc root and to identify compounds in this interaction. Root exudate of G. bonduc were obtained in hydroponic mean, and roots collected in the field (Trindade Island) provided aqueous and methanol extracts. Biological activity of the extracts were tested considering the initial growth of Lactuca sativa and Raphanus sativus grown in petri dishes in the concentrations of 125, 250, 500, 1000 and 2000ppm of extracts. Activity of root exudate randomly collected was also tested against the same species as above. It was also estimated the concentration of exudates in the field. Activity of aqueous extract, at the same concentrations mentioned previously, was also investigated using soil collected in the field, at Trindade Insland, with and without microorganisms. It was isolated one product from methanolic extract, identified using NMR, and its activity was tested at the concentrations of 10, 30, 100, 300 and 1000µM. There was a negative correlation between root exudates production in the laboratory and plant total weight. Estimated concentration of exudate in the field was similar to the ones used in the laboratory bioassays. Root exudate and aqueous extract stimulated growth of tested species. On the other hand, methanolic extract inhibited initial growth of the same species, especially in the roots. Aqueous and methanolic extracts together with root exudate revealed different chromatographic profiles; showing that each was quantitatively and qualitatively different. Results of bioassay of aqueous extract in the soil were different to the one in petri dishes -there was no significant difference in the growth of tested species. The isolated product from methanolic extract is a cassane furanoditerpene, known as Caesaldekarin C. It showed phytotoxic activity similar to total extract, however lower, suggesting a synergistic effect.Key-words: Guilandina bonduc, phitotoxicity, root exudates, Caesaldekarin C 16 1. Introdução Metabolismo secundárioO conjunto de reações químicas que ocorrem nos organismos vivos é conhecido como metabolismo, que trabalha prioritariamente em processos que sintetizem substâncias orgânicas, essenciais à sua sobrevivência e reprodução, como carboidratos, proteínas, gorduras e ácidos nucleicos, sendo estes pertencentes ao metabolismo primário. Esses metabólitos têm reconhecidas funções nos proces...