Allelopathy and influence of leaves of Palicourea rigida (Rubiaceae) on seed germination and seedling formation in lettuce

Abstract

Palicourea rigida is a shrub found in South America. So far, no studies have been forthcoming with regard to the species' allelopathic potential. Therefore, the current work seeks to verify the phytochemistry and potential allelopathic effect of different leaf extract concentrations of P. rigida on the germination of lettuce seeds and seedling growth. P. rigida leaf samples were collected from the Campo Grande region in Mato Grosso do Sul state, Brazil. From these samples, extracts were prepared in 20% ethanol and aqueous and submitted to phytochemical analysis. Bioassays were carried out in laboratory with aqueous and ethanolic extracts in concentrations of 0% (control), 1, 2.5, 5, 10 and 20%, with completely randomized experimental design, analyzing the percentage and germination time, besides seedling growth. Chemical prospecting identified the presence of phenolic compounds, tannins, flavonoids, cathechins, coumarins, steroids, triterpenes, alkaloids and saponins, with the foaming rate (Afrosymmetric) of 1250, considered high. The rate of germination from lettuce seeds was little affected by the different concentrations of extracts. However, the speed of germination was adversely affected in almost all concentrations. The development of primary roots and aerial part was notably impeded in 5, 10 and 20% (aqueous extracts) and 10 and 20% (ethanolic extracts).