*Article Persicaria lapathifolia* **Essential Oil: Chemical Constituents, Antioxidant Activity, and Allelopathic Effect on the Weed** *Echinochloa colona*

**Ahmed M. Abd-ElGawad 1,2,\*, Giuliano Bonanomi 3,4, Sarah A. Al-Rashed <sup>5</sup> and Abdelsamed I. Elshamy <sup>6</sup>**


**Abstract:** The exploration of new green, ecofriendly bioactive compounds has attracted the attention of researchers and scientists worldwide to avoid the harmful effects of chemically synthesized compounds. *Persicaria lapathifolia* has been reported to have various bioactive compounds, while its essential oil (EO) has not been determined yet. The current work dealt with the first description of the chemical composition of the EO from the aerial parts of *P. lapathifolia*, along with studying its free radical scavenging activity and herbicidal effect on the weed *Echinochloa colona*. Twenty-one volatile compounds were identified via GC–MS analysis. Nonterpenoids were the main components, with a relative concentration of 58.69%, in addition to terpenoids (37.86%) and carotenoid-derived compounds (1.75%). *n*-dodecanal (22.61%), α-humulene (11.29%), 2,4-dimethylicosane (8.97%), 2*E*hexenoic acid (8.04%), γ-nonalactone (3.51%), and limonene (3.09%) were characterized as main compounds. The extracted EO exhibited substantial allelopathic activity against the germination, seedling root, and shoot growth of the weed *E. colona* in a dose-dependent manner, showing IC50 values of 77.27, 60.84, and 33.80 mg L−1, respectively. In addition, the *P. lapathifolia* EO showed substantial antioxidant activity compared to ascorbic acid as a standard antioxidant. The EO attained IC50 values of 159.69 and 230.43 mg L−1, for DPPH and ABTS, respectively, while ascorbic acid exhibited IC50 values 47.49 and 56.68 mg L−1, respectively. The present results showed that the emergent leafy stems of aquatic plants such as *P. lapathifolia* have considerably low content of the EO, which exhibited substantial activities such as antioxidant and allelopathic activities. Further study is recommended to evaluate the effects of various environmental and climatic conditions on the production and composition of the EOs of *P. lapathifolia*.

**Keywords:** pale smartweed; essential oil; phytotoxicity; green chemistry; herbicides
