Allelopathic potential and phytochemical screening of ethanolic extracts from five species of Amaranthus spp. in the plant model Lactuca sativa

The genus Amaranthus (Amaranthaceae) comprises plants considered to be weeds, but also consumed as food and in popular medicine. These plants are rich in biologically active compounds that can be exploited to produce bioherbicides. In this sense, the present work aimed to evaluate the allelopathic effect of the ethanolic leaf extract from five Amaranthus species (A. spinosum, A. viridis, A. deflexus, A. hybridus and A. retroflexus) by phytochemical screening, as well as its effects on germination, initial development and cell cycle of seedlings or meristematic cells of Lactuca sativa L. (lettuce). All five studied species presented organic acids, carotenoids and steroids in the obtained ethanolic extracts. Polysaccharides, proteins and amino acids, azulenes, depsides, coumarins and saponins were observed in extracts of at least one of the evaluated species. The tested extract concentrations (0.25-4.0 g/L) inhibited the germination and the germination speed index of the exposed L. sativa seeds in a dose-dependent manner. The highest tested concentration (4.0 g/L) caused more than 95% inhibition in all evaluated extracts. Consequently, a significant reduction in the development of treated seedlings was observed. In the microscopic analysis, mitodepressive effect was verified with extracts of A. spinosum and A. viridis, whereas those from A. deflexus, A. hybridus and A. retroflexus induced a significant increase in the frequency of mitotic cells with chromosomal alterations, most frequently c-metaphases and sticky chromosomes. Condensed nuclei were also observed as a consequence of cell exposure to the extracts, with a significant increase in the treatments with extracts from A. spinosum, A. deflexus and A. retroflexus.