Phytotoxic Effects of Zataria multiflora and Rosmarinus officinalis Essential Oils on Growth and Physiological Traits of Amaranthus r

Abstract

This study investigated the effects of essential oils (EOs) from rosemary ( Rosmarinus officinalis L.) and Shirazi thyme ( Zataria multiflora Boiss.) on the early growth and physiological characteristics of three weed species: Amaranthus retroflexus L., Chenopodium album L., and Cirsium arvense (L.) Scop. conducted at Razi University. the experiment utilized a factorial design with varying concentrations of EOs in laboratory (0.5, 1, 2, 5, 10, and 20 µL mL⁻¹) and greenhouse (5, 10, and 20 µL mL⁻¹) settings. Control treatments included distilled water, distilled water + Tween 20 (1%), and trifluralin and glyphosate. GC-MS analysis revealed 15 major compounds in rosemary EO and 23 in Shirazi thyme EO. A significant inhibition of plumule and radicle lengths was reported across all species. In greenhouse trials, Shirazi thyme EO at 10 and 20 µL mL⁻¹ reduced stem length by up to 75.2% and 74.5% in A. retroflexus , surpassing reductions caused by rosemary EO (57.2% at 20 µL mL⁻¹) and glyphosate (65.2%). Root length reductions were most pronounced with Shirazi thyme EO, reaching up to 83.9% inhibition in A. retroflexus at 10 µL mL⁻¹, exceeding effects of rosemary EO and glyphosate. Shirazi thyme EO causing up to 54.4% reduction in stem dry weight of C. arvense and 82.7% reduction in root dry weight of A. retroflexus . Leaf greenness, photosynthetic efficiency, and maximum quantum yield of photosystem II (PSII) also decreased markedly with increasing EO concentrations, particularly under Shirazi thyme EO, which in some cases completely abolished photosynthetic efficiency, outperforming glyphosate.