The presented study transpired in 2015–2016 in the Wasit Province, Iraq, to investigate the allelopathic impact of two sunflower (Helianthus annuus L.) cultivars, namely, Asgaro and Flamme, on weed suppression. The study found that sunflower cultivars significantly reduced the number and biomass of companion weeds in sunflower fields, with a varying reduction depending on the cultivar genotype. The cultivar Asgaro exhibited the most pronounced allelopathic effects, resulting in a 68.6% reduction in total weed numbers and a 61.0% reduction in weed biomass compared with the control (no sunflower). However, the genotype Flamme had the minimum allelopathic effects. Specifically, genotype Flamme reduced weed population by 24% and weed biomass by 35.4% compared with the control. More analysis revealed that the root exudates of the Asgaro genotype were more efficient in suppressing weeds than the Flamme genotype. Substance analysis demonstrated that the Asgaro genotype had a significantly higher amount (0.403 mg/g) than the Flamme genotype (0.220 mg/g) of specific compounds and phenols. The study found that aggregate phenolic levels increased after 28 days, then declined by the end of the season, with chromogenic tests revealing several allelochemicals in the root exudates.

Keywords: Sunflower (Helianthus annuus L.), cultivars, allelopathic effect, phenolic compounds, weed flora and biomass

Key findings: Sunflower cultivars with allelopathic potential have significantly reduced the total population and biomass of companion weeds in the sunflower fields. However, the extent of reduction varied, depending on the genotype of the sunflower cultivar. This action refers to having different allelochemical compounds affecting weeds.