Allelopathic potential of Inula graveolens on crops and weeds

In Lab. bioassay, the effects of aqueous extracts (10, 20, 30 and 40 g/L) and organic extracts (hexane, chloroform and methanol at 3 and 6 mg/mL) of roots, shoots (stems + leaves) and flowers of Inula graveolens L. were tested on the seed germination and seedling growth of Lactuca sativa L., Raphanus sativus L., Peganum harmala L. and Silybum marianum L. While in pot culture, powder of shoots and flowers at 1.25 and 2.5 g/100g was incorporated in soil to evaluate its allelopathic effect on test spp. PEG 4000 solutions with similar osmotic potentials to aqueous extracts at 40 g/L, neither affected the germination index nor growth of target species. Root extracts did not influence the germination index but shoot and flower extracts delayed and reduced the germination in all target seeds. Root extract at 10 g/L stimulated the seedlings growth of lettuce, radish and peganum, but was harmful to thistle. The organic extracts of shoot and flower at 6 mg/mL significantly inhibited the seedling growth especially in chloroform fractions. Soil incorporation of residues significantly decreased the root and shoot length of target species. Application of shoot and flower aqueous extracts in soil decreased the seedlings length, however, flower extract was more inhibitory than shoot.