Herbicidal Activities of Some Allelochemicals and Their Synergistic Behaviors toward Amaranthus tricolor L.

Abstract

Seven allelochemicals, namely R-(+)-limonene (A), vanillin (B), xanthoxyline (C), vanillic acid (D), linoleic acid (E), methyl linoleate (F), and (±)-odorine (G), were investigated for their herbicidal activities on Chinese amaranth (Amaranthus tricolor L.). At 400 μM, xanthoxyline (C) showed the greatest inhibitory activity on seed germination and seedling growth of the tested plant. Both vanillic acid (D) and (±)-odorine (G) inhibited shoot growth, however, apart from xanthoxyline (C), only vanillic acid (D) could inhibit root growth. Interestingly, R-(+)-limonene (A) lightly promoted root length. Other substances had no allelopathic effect on seed germination and seedling growth of the tested plant. To better understand and optimize the inhibitory effects of these natural herbicides, 21 samples of binary mixtures of these seven compounds were tested at 400 μM using 0.25% (v/v) Tween® 80 as a control treatment. The results showed that binary mixtures of R-(+)-limonene:xanthoxyline (A:C), vanillin:xanthoxyline (B:C), and xanthoxyline:linoleic acid (C:E) exhibited strong allelopathic activities on germination and seedling growth of the tested plant, and the level of inhibition was close to the effect of xanthoxyline (C) at 400 µM and was better than the effect of xanthoxyline (C) at 200 µM. The inhibition was hypothesized to be from a synergistic interaction of each pair of alleochemicals. Mole ratios of each pair of allelochemicals ((A:C), (B:C), and (C:E)) were then evaluated, and the best ratios of the binary mixtures A:C, B:C and C:E were found to be 2:8, 2:8, and 4:6 respectively. These binary mixtures significantly inhibited germination and shoot and root growth of Chinese amaranth at low concentrations. The results reported here highlight a synergistic behavior of some allelochemicals which could be applied in the development of potential herbicides.

Inhibitory Effects of a Variety of Aldehydes on Amaranthus tricolor L. and Echinochloa crus-galli (L.) Beauv.

“…In the preliminary investigation, Chinese amaranth was selected as a representative dicotyledon. According to our previous study [ 45 ] 0.25% ( v / v ) aqueous solution of Tween ® 80 (Sigma-Aldrich, Singapore) was used as a surfactant. A basic structure-activity relationship (SAR) study was performed by using three groups of aldehydes namely; aliphatic, aromatic and heteroaromatic respectively.…”

Recent advances in allelopathy for weed control: from knowledge to applications

“…), exhibited strong allelopathic activity towards germination and seedling growth of the weed Amaranthus tricolor L. through a synergistic interaction with xanthoxyline. A 2:8 m ratio of ( R ‐(+)‐limonene:xanthoxyline) caused the highest inhibition for these allelochemicals . Limonene, which is released through leaching and volatilization from Juniperus ashei , has also been tested in field experiments.…”

“…Researchers have taken account of the poor water solubility of monoterpenes, and studies with surfactants have been carried out. For example, Tween® 80 has been used to retain the inhibitory effect of mixtures with vanillin, limonene or xanthoxyline …”

“…A 2:8 M ratio of (R-(+)-limonene:xanthoxyline) caused the highest inhibition for these allelochemicals. 76 Limonene, which is released through leaching and volatilization from Juniperus ashei, has also been tested in field experiments. An allelopathic interaction of limonene, together with camphor and bornyl acetate, influenced germination and growth of the native grass Bouteloua curtipendula from limestone slopes of central Texas.…”

“…For example, Tween ® 80 has been used to retain the inhibitory effect of mixtures with vanillin, limonene or xanthoxyline. 76 The SAR of monoterpenes has not been comprehensively studied. Most monoterpenes seem to act on the photosynthetic apparatus due to the high production levels of reactive oxygen species; particularly damage to the antenna complex, pigment degradation due to lipid peroxidation, reduction in photosystem II efficiency and reduction of electron transport rate.…”