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 PhosphateSolubilizing 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.