Allelopathic potential of Inula viscosa against crops and weeds

Aqueous (10, 20, 30 & 40 g L^-1) and organic (hexane, chloroform & methanol, at 3 & 6 mg mL^-1) extracts of Inula viscosa L. (roots, stems, leaves & flowers) were evaluated for their allelopathic activities on radish, lettuce, peganum and thistle. In addition leaf and flower powder was incorporated in soil at 1.25 and 2.5 g kg^-1. PEG (Polyethylene glycol) solutions, with similar osmotic potentials of aqueous extracts, at the highest concentration, were without effect on target species, this eliminates the extracts osmotic effect. Germination index was not affected by root and stem extracts and significantly decreased by the two other ones. For growth, leaves and flowers extracts had the most significant toxicity, inducing up to total inhibition. Leaves leachates strongly inhibited seedling growth of lettuce (93.5%) and it was more toxic than leached-leaves extract (43%); however, toxicity of unleached-leaves extracts was slightly lower (90.5%). For organic extracts, the three fractions of leaves and flowers were more toxic; thistle was more sensitive especially to chloroform and methanol fractions of various organs. The two organs residues incorporation caused (at 2.5g kg^-1) an average reduction between 34 and 100% for root and shoot length of target species. Irrigating soil with leaves and flowers aqueous extracts decreased seedlings length by 100% for peganum and 82% for thistle shoot. Results show that I. viscosa allelopathic potential seems to be attributed mainly to leaf leachate, which indicates the facility of providing this product and its use in irrigation for sustainable weed management.