<span>Chemical composition and herbicidal activity of flower extract from spiked spiralflag ginger (C<i>ostus spicatus</i>)</span>

This study aimed to detemine the chemical composition and evaluate the herbicidal potential of flower extracts from Costus spicatus. The ethanol extract exhibited markedly higher total phenolic and flavonoid contents (0.754 mg GAE/g FW and 0.470 mg QE/g FW) than the aqueous extract (0.182 mg GAE/g FW and 0.038 mg QE/g FW). Notably, the phenolic and flavonoid contents of the ethanol extract (0.754 mg GAE/g FW and 0.470 mg QE/g FW) was four and twelve times greater than that of the aqueous extract (0.182 mg GAE/g FW and 0.038 mg QE/g FW). Bioassays showed that the ethanol extract strongly inhibited seed germination, root elongation, and shoot growth of mustard greens, with the greatest effect on shoot length (IC₅₀=1.431 mg/mL). The herbicidal property increased proportionally to its concentrations. Besides, the ethanol extract, at a concentration of 1.5 mg/mL, markedly lowered chlorophyll a, total chlorophyll, and carotenoid levels in mustard seedlings relative to the control. Regarding pigment biosynthesis, treatment with ethanol extract at 1.5 mg/mL significantly reduced chlorophyll a, total chlorophyll, and carotenoid contents in mustard green seedlings compared to the control. These results indicate that Costus spicatus flowers possess potent allelopathic properties, reducing germination, growth, and photosynthetic pigment levels. These findings indicate that Costus spicatus flowers possess strong inhibitory potency on seed germination, growth, and reduce the photosynthetic capacity of plants. Further studies are needed to isolate and identify active compounds for sustainable weed management.