Parthenium hysterophorus is a strong allelopathic plant which belongs to the family Asteraceae of flowering plants. It is a rapidly spreading invasive plant species in the state of Himachal Pradesh up to 2000 m altitude. The allelochemicals produced by P. hysterophorus showed powerful toxic effects on the growth of other plant species. These allelochemicals are either phytotoxic phenolics or flavonoids. The study indicates that residues of P. hysterophorus species when mixed in soil adversely affect the germination and the subsequent seedling growth of native plants (Acacia catechu, Achyranthes aspera and Cassia tora). These allelochemicals in the soil are released by leaching or decomposition and they directly or indirectly affect plant growth by altering the physico-chemical properties of soil. A gradual decrease was observed in the germination, root and shoot length and in dry weight of seedlings of native plants with the increase in the concentration of amended soil residues (1, 2 and 4%). The maximum decrease in seedling dry weight was recorded in A. aspera (54.75%) followed by A. catechu (42.74%) and C. tora 40.25%) respectively at 4% concentration of plant residues.
Key words: Allelochemicals, Parthenium hyterophorus, phenolics.
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