Variation in phytochemical constituents and allelopathic potential of Nigella sativa with developmental stages

Abstract

This study was conducted to evaluate the phytochemical content and allelopathic potential of two Nigella sativa varieties, having a Tunisian and Indian origin. Aqueous extracts of seeds and aerial parts harvested at three developmental stages (vegetative, flowering and fruiting) were evaluated on lettuce germination and seedling growth. The total phenolics, flavonoids, flavonols and flavones, alkaloids and proanthocyanidins contents in the aqueous extracts were highest in the vegetative stage. For allelopathic activity, all aqueous extracts significantly delayed germination, reduced its rate and affected seedling growth, while seeds aqueous extracts affect only seedling growth. In addition, the analysis using the Whole-range assessment method (WESIA software) showed a stronger inhibition index of the Tunisian variety aqueous extracts of aerial parts harvested at flowering stage compared to the two other stages. While, Indian variety was most phytotoxic at the vegetative stage. Seeds of the two varieties showed similar toxicity for lettuce and they are less toxic than aerial parts. Results showed that it would be advisable to identify the development stage of a plant that has the greatest level of allelochemicals to assist harvest time and to maximize efficiency of the allelopathic potential of a given plant.