Allelopathic Potential of Sunflower

Abstract

Allelopathic effects of a sunflower (Helianthus annus L.) variety, Hysun 38, were studied on two wheat varieties Margalla 99 and Chakwall 97. For this, three experiments were conducted. The first experiment was conducted by growing sunflower in pots to evaluate its effect) on beneficial soil microorganisms (Rhizobium, Azosprillum, and Phosphate- Solubilizing Bacteria) and 2) on soil physicochemical properties. The quantification of allelochemicals ( alkaloids, favonoids, and phenols) in leaves, stems and roots of sunflower were made ; more allelochemicals were found in leaves, followed by roots, and the least amount of allelochemicals were found in stem. The Rhizobium, Azosprillum, and phosphate-solubilizing bacterial colonies declined in the soil cultivated with sunflower. Its effects were shown on the carbon nitrogen utilization pattern of the microbes as revealed by the Quick testing system (QTS) while no effect was shown on the gram staining test. The effect of sunflower was also shown on moisture contents of soil, phosphate, etc., the Ca and Mg contents of soil were increase. The second experiment was conducted in petri dishes. The aim was to check allelopathic potential of sunflower on germination rate, fresh weight, dry weight, root length, shoot length, hormonal contents (Indole acetic acid, Gibberellin and Abscisic acid), and chlorophyll, protein, proline, sugar, and DNA contents of wheat seedlings. It was noted that the allelopathic effect was more as the concentrations of extract of sunflower increased as compared with control. The allelochemical effect decreased the values of fresh weight, dry weight, root length, shoot length, GA, IAA, Chlorophyll, protein, proline, sugar, and DNA while increasing the values of ABA. It was also noted that the allelopathic effect of sunflower leaves was greater than the roots, and the least amount of effect was noted in stem. The third experiment was conducted in pots in order to check the effects of sunflower extracts on the comparative growth of wheat and weed. The fresh and dry weight of wheat and weed density at 40 days after sowing (DAS) and at 70 DAS were determined In addition the phytohormone contents, chlorophyll, protein, proline, sugar, DNA contents and yield of wheat were determined. From the pots experiments, it was concluded that sunflower leaves extract had decreased weed fresh weight and dry weight as well as the Gibberrellin and Indole acetic acid contents but increased Abscisic acid contents of wheat seedling.