Allelopathic Effects of sunflower (Helianthus annuus) on Germination and Growth of Seedling Cow Soapwort (Vaccaria hispanica) & Russian knapweed (Acroptilon repens)

Sunflower [Helianthus annuus (L.) Koch.] contains watersoluble allelochemicals that inhibit the germination and growth of other species. This characteristic could be used in weed management programmers''. Greenhouse and laboratory experiments were conducted to determine the effects on Vaccaria hispanica and Acroptilon repens. Its effect on two weedy species V. hispanica and A. repens was studied with a view to explore its herbicidal potential. Germination of both the weeds was reduced with increasing concentration of sunflower and a dose-response relationship was observed. This provided information on LC50 and Inhibition threshold concentrations of sunflower that could be useful for future studies. Further, sunflower also inhibited the growth of both the weeds in terms of root and shoot length and seedling dry weight. Inhibition of root growth was greater than that of shoot growth. Similar observations were made when the test weeds were grown in soil amended with different concentrations of sunflower. In addition to growth, there was a reduction of chlorophyll content in the growing seedlings. It also caused water loss in the weedy species. The study, therefore, reveals that sunflower exerts an inhibitory effect on the growth and development of both weeds and can be further explored as an herbicide for future weed management strategies.