Allelopathic effect of Portulaca oleracea and Raphanus raphanistrum leaves extracts on seed germination of Lactuca sativa L.

Abstract

Allelopathy is an important process in plant ecosystems and its studies are of great interest to agriculture. Allelochemicals can replace synthetic herbicides, with the advantage of having no residual or toxic effects. The objective was to evaluate the allelopathic activity and its correlation with the content of phenolic compounds and antioxidant potential of Portulaca oleracea and Raphanus raphanistrum the radish from different extractive preparations and concentrations in the germination of Lactuca sativa. Three extractive methods were used: reflux in water; dynamic maceration in water and dynamic maceration with solvents of increasing polarity. The extracts concentrated in rotary evaporator were diluted in water, obtaining concentrations (0, 2, 4, 6, 8 and 10 g.L^-1). The germination parameters evaluated were germination percentage and velocity index and lenghts of hypocotyl and radicle of L. sativa. The allelopathic effect was correlated with the content of phenolic compounds (total of phenols, flavonoids and dihydroflavonoids) and with the antioxidant potential [Chelating Power (PQ) and Total Antioxidant Capacity (CAT)]. The aqueous extracts of P. oleracea It is R. raphanistrum expressed greater potential in suppressing germination, index of germination speed and root and hypocotyl lenghts of L. sativa, in the highest concentrations. The extracts watery showed lower levels of phenolic compounds and CAT, but indicated greater chelating potential. In conclusion, the allelopathic effects of the extracts were dependent on the concentration and the extraction method. However, the aqueous extracts of P. oleracea and R. raphanistrum have allelopathic activity against L. sativa, especially at a concentration of 10 g.L^-1.