Antioxidant activity of seven plant extracts collected from Tunisia and their allelopathic potential on Lactuca sativa L. and Phalaris minor L.

The objective of the present work was to quantify the total phenolic, flavonoid and tannin contents, and determine the antioxidant activity and the allelopathic potentiality of the aerial part of seven medicinal plants collected from Tunisia against two target species, including Lactuca sativa (crop) and Phalaris minor (weed). After the calculation of the extraction yield, the phenolic compounds contents of the extracts were determined and the antioxidant and allelopathic activity of the extracts showing the best extraction yield values were evaluated. Total phenolic, flavonoid and condensed tannin contents were quantified spectrophotometrically using Folin-Ciocalteu, aluminum chloride and vanillin 4%, respectively as reagents, while the antioxidant activity was determined according to the DPPH scavenging activity and Ferric reducing antioxidant power assay. The allelopathic activity was evaluated by the calculation of the percentages of the inhibition or stimulation of seeds germination and the length of the hypocotyls and radicles. The results obtained revealed that 80%-aqueous MeOH extracts presented the best extraction yield values. In addition, 80%-aqueous MeOH extract of Cynoglossum creticum showed the highest contents of phenolic and flavonoid, while 80%-aqueous MeOH extract of Ammi majus had the highest content of condensed tannin. The results also showed that Cynoglossum creticum exhibited the best antioxidant activity determined by the DPPH and FRAP assays. Moreover, Cynoglossum creticum, Echium plantagineum and Echium arenarium showed total inhibition of the Phalaris minor seeds germination, radicles and hypocotyls length at a concentration of 6 mg/mL, while Anchuza azurea and Borrago officinale extracts showed the highest stimulation of the radicles and hypocotyls length at 3 mg/mL. Furthermore, Echium arenarium showed the highest inhibition of Lactuca sativa seeds germination, radicles and hypocotyls length at the concentration 9 mg/mL, whereas, Opuntia ficus indica extract presented the highest stimulatory effect of the seed germination and hypocotyl length at 3 mg/mL. These results make Cynoglossum creticum a suitable source of allelochimicals potentially usable to control weeds.