Viviane de Cassia Pereira

Effect of Serjania lethalis ethanolic extract on weed control

The objective of this study was to evaluate the effect of the ethanolic extract of Serjania lethalis leaves and stems on the diaspore germination and seedling growth of wild poinsettia (Euphorbia heterophylla) and barnyardgrass (Echinochloa crus-galli). The crude ethanolic extract was prepared from 100 g of dry plant material dissolved in 500 ml of ethanol. The extracts were solubilized in a buffer solution containing dimethyl sulfoxide (DMSO) at concentrations of 10.0, 7.5, 5.0 and 2.5 mg mL-1. The effect of these extracts was compared with herbicide oxyfluorfen in bioassays. The ethanolic extracts of S. lethalis leaves and stems inhibited the germination and seedling growth of barnyardgrass and wild poinsettia in a concentration-dependent manner. The reduction in the root length of E. heterophylla seedlings might be attributed to the reduced elongation of metaxylem cells. The phytotoxicity of the extracts ranged according to the receptor species, and for some variables, the inhibitory effect was similar, and even superior, to that of the commercial herbicide. Thus, S. lethalis extracts might be a promising alternative for sustainable weed management.

Phytotoxic potential of young leaves from Blepharocalyx salicifolius (Kunth) O. Berg (Myrtaceae)

The loss of leaves by plant species found in the Cerrado (Brazilian savanna) is an energetically expensive process due to adverse environmental conditions and predation by herbivory. The mature leaves have adaptations which minimize these events. However, the young individuals lack these structures and produce high leaf concentrations of secondary metabolites as a form of protection. These compounds can be used in bioprospection of natural herbicides. Thus, this study aimed to evaluate the phytotoxicity of hexane, ethyl acetate and aqueous extracts of young leaves from Blepharocalyx salicifolius (Kunth) O. Berg on the elongation of wheat coleoptiles (Triticum aestivum L.) and evaluate the potential phytotoxic of ethyl acetate extract on germination, growth and cell size of metaxylem of sesame (Sesamum indicum L.) seedlings. The hexane and ethyl acetate extracts inhibited the elongation of wheat coleoptiles at all concentrations; however, the most promising results were observed in coleoptile fragments treated with the ethyl acetate extract. This treatment changed the mean germination time and the synchrony of sesame seeds, inhibited the growth of shoots and roots, reduced the dry weight of seedlings, led to abnormalities in the seedlings and reduced the length of the metaxylem cells in the sesame seedlings. These results demonstrated the phytotoxic potential of young leaf extracts of B. salicifolius and the high phytotoxicity of the ethyl acetate extract in the initial development of S. indicum.

In vitro herbicide activity of crude and fractionated leaf extracts of Blepharocalyx salicifolius (Myrtaceae)

The excessive use of synthetic herbicides is harmful to natural and managed ecosystems. In order to solve this issue, the search for natural compounds with lower toxicity to the environment has been intensified. This study aimed (a) to evaluate the phytotoxic activity of leaf extracts of Blepharocalyx salicifolius by taking into account the elongation of wheat coleoptile as well as of the crude ethyl acetate extract on the germination and growth of two weeds; (b) to fractionate the ethyl acetate extract; and (c) to test the phytotoxicity of fractions on etiolated wheat coleoptile. Hexane, ethyl acetate, and aqueous crude extracts were obtained through extraction with organic solvents. We used the column chromatography to fractionate the ethyl acetate extract, which resulted in 11 ethylic acetate fractions (Fr1–Fr11). The bioassays of wheat coleoptile elongation, germination, and seedling growth of guinea grass as well as the morning glory showed that the ethyl acetate extract possessed pronounced phytotoxic potential to inhibit the elongation of wheat coleoptile at all tested concentrations. In addition to this, the extract changed the mean germination time of guinea grass seeds and inhibited the growth of shoots and roots of both weeds, the fact that caused anomalies, such as necrosis and severe atrophy. Furthermore, we identified that Fr5 and Fr6 are the most promising ethyl acetate fractions. Thus, this study presents that the ethyl acetate extract of mature leaves of B. salicifolius has potential to produce natural herbicides and that the main phytotoxins are present in the Fr5 and Fr6 fractions, thereby offering scope for further studies.