| 1 ALLELOPATHIC AND MITODEPPRESSIVE EFFECTS OF PARTHENIUM HYSTEROPHORUS L. LEACHATES ON ORNAMENTAL SUNFLOWER, Hridya Mohanan & K. Rajendiran Parthenium hysterophorus L. the noxious exotic weed has achieved the status of the countries “Worst Weed” owing to its allelopathic effects on other plants and harmful effects on people and animals. Its accelerated growth is mainly due to its ability to germinate fast and to suppress the growth of plant species in the surroundings. The allelochemics present in this weed have contributed towards its acquisition of dominant status even among crop plants in various areas. Due to its extraordinary spread, dominance and its naturalisation in India quickly, this weed was taken to assess the allelopathic effects and cytotoxity of aqueous extracts of its root, stem, leaf and inflorescence on the seven day old seedlings of an ornamental variety of sunflower, Helianthus annuus L. var. Tall. The LD50 concentration for the leaf and inflorescence extracts was recorded as 27%, while 28% concentrations of both root and stem extracts proved to be LD50. All the extracts decreased the mitotic index of the crop with increasing concentrations (5, 10, 15, 20, 25 and 30%). However the chromosomal aberrations were increased rapidly, the highest being with leaf extract (14.33%), followed by inflorescence (10%), root (9%), and stem (8.66%) at 25% concentration. Chromosomal abnormalities like fragments, stickiness, ring chromosomes, micronuclei, laggards and bridges were observed in all extract applications. The leaves and inflorescence of Parthenium hysterophorus were more potent clastogenic and spindle poisoning agents which played a vital role in maintaining the dominance of the weed by suppressing the cell divisions of the plants. Hence prevention of this weed leachate from further intrusion into parks, gardens and horticultural fields becomes necessary, as the allelochemics will erode the genotype of the ornamental plants. |