Studies related to the allelopathic properties of plants have aroused great interest, since species that have compounds with allelopathic activity can be used as bioherbicides in the control of weeds. In this way, the aim of this study was to evaluate the allelopathic action of Dahlstedtia araripensis on the germination and growth of Calotropis procera and Zea mays. The bioassays were prepared using two 50 g portions of leaves, stem bark and D. araripensis roots, and each part of the plant received a hot treatment (1 L of distilled water at 100 °C) and one part cold (1 L of distilled water at 25 °C). The experimental design consisted of six treatments and the control group. The variables analyzed were: Index of Emergency Speed (IES), germinability, length and occurrence of necrotic radicles. The results indicated that the extracts interfered negatively on the germinability of the seeds, mainly on those of C. procera, since all extracts significantly inhibited its germination. In the seeds of C. procera and Z. mays there was delay in IES. The results indicated that the cold and hot extracts of the distinct parts of D. araripensis affected the development of the seedlings, besides promoting root necrosis. The observed effects may be due to the presence of secondary metabolites detected in the different extracts of D. araripensis. However, further research is required to prove the performance of such compounds, as well as their isolation, for future use asnatural herbicides.

Chemical compounds from the secondary metabolism of a plant, termed as allelochemicals, may interfere with the germination and/or development of other plant species, a phenomenon known as allelopathy. The aim of this study was to analyze the allelopathic potential of the Senna cearensis Afr. Fern. aqueous extract at various concentrations, collected from an area in the Chapada do Araripe during two different seasons (dry and rainy), on Lactuca sativa L. and Cenchrus echinatus L. seeds and seedlings, in addition to analysing the extract’s phytochemical prospection. The bioassays were conducted in a germination chamber at 25 °C with a 12h photoperiod and consisted of four treatments (extract at 12.5%, 25%, 50% and 100%) and a control group (distilled water). The variables analyzed were: seed germination, germination speed index, radicle length and caulicle seedling length. The means from each variable were submitted to an analysis of variance and compared using Tukey’s test (p<0.05), through the ASSISTAT. Quantitative prospection of the extract was performed using HPLC-DAD. The extracts reduced L. sativa seed germination, however it did not affect C. echinatus seeds. The extracts caused a reduction in germination rate and presented inhibitory effects on seedling development for both receptor species. Quercitrin was the major compound in both extracts. The allelopathic activity of the S. cearensis aqueous leaf extract collected during dry or rainy periods may be a viable alternative for weed control. Further studies addressing fractionation for separation and the possible isolation of substances responsible for the observed allelopathic activity are necessary.

The allelopathic activity and chemical composition of the essential oil of Croton limae A. P. S. Gomes, M. F. Sales & P. E. Berry (marmeleiro-prateado) have been evaluated in this study. The essential oil was extracted by hydro-distillation. A completely randomized design was used to test the influence of the essential oil from fresh leaves of C. limae in concentrations of 0.10%, 0.25%, 0.50%, 0.75%, 1%, 1.25%, 2.50%, 3.75%, and 5% on the germination and growth of Lycopersicum esculentum Mill. (tomato) seeds by indirect contact, with a control using water and dimethyl sulfoxide (DMSO). Each treatment consisted of five replicates using twenty seeds in each one. The chemical analysis of the essential oil was carried out using gas chromatography coupled with mass spectrometry. The analysis showed the occurrence of 14 chemical compounds, the majority of which were cedrol (28.4%), eucalyptol (17.4%) and α-pinene (13.8). The C. limae essential oil inhibited germination of the tomato seeds at concentrations of 2.50% and upwards and it affected the caulicles and radicles of tomatoes at all concentrations tested. The tests proved that C. limae presents phytotoxic activities.

The aim of this work is to study the effects of the brute aqueous extract (BAE) of seven species of the genus Miconia occurring in the Chapada do Araripe-CE on Lactuca sativa, in addition to identifying the classes of secondary metabolites present in the extracts. The treatments consisted of four concentrations of leaf extract (25, 50, 75 and 100%), in addition to a control (0%) of distilled water, with five replicates each in a totally randomized experiment design layout for seven days. The following were assessed: number of germinated seeds, germination speed index (GSI), caulicle and radicle root length of the seedlings, occurrence of radical root necrosis, changes in the mitotic index and occurrence of chromosomal aberrations. The classes of secondary metabolites present in the extracts were identified through color changes and/or formation of precipitation. The brute aqueous extract of the leaves of M. albicans, M. alborufescens and M. stenostachya inhibited the germination of lettuce. All the BAEs of Miconia spp. had an adverse effect on the growth of the caulicle and radicle root of L. sativa. The extracts of M. albicans, M. ibaguensis, M. lingustroides and M. stenostachya were cytotoxic for the lettuce seedlings. Chromosomal aberrations were observed in all tested extracts. The metabolites found were hydrolysable and condensed tannins, flavonoids, flavones, flavanonols, chalcones, aurones and alkaloids. The tested species of Miconia showed inhibitory allelopathic activity within the parameters tested. The classes of secondary metabolites found could be responsible for the allelopathic and cytotoxic effects observed.

Nesta pesquisa foi abordada as atividades alelopáticas, dos extratos das folhas de Ficus gomelleira Kunth (Gameleira) bem como as observações fenológicas e a prospecção fotoquímica das mesmas. Os tratamentos relativos foram relacionados as diluições dos extratos. Os resultados obtidos indicaram que os extratos de Ficus gomelleira, influenciaram de forma negativa o percentual de germinação. O índice de velocidade de germinação (IVG) das sementes de alface também foi alterado de forma negativa; assim como o desenvolvimento dos caulículos e radículas de alface, que também apresentaram uma redução no comprimento. Em relação à fenologia, o brotamento foliar em Ficus gomelleira ocorreu de forma asincrônica por períodos relativamente curtos nos dois anos de observações, independente do padrão de precipitação de chuva. A espécie demostra possuir potenciais alelopáticos relevantes.