Low-concentration repeated exposure and high-concentration single exposure of cyanamide suppressed the growth of redroot pigweed in the alfalfa field.

The inclination toward natural products has led to the onset of the discovery of new bioactive metabolites that could be targeted for specific therapeutic or agronomic applications. Despite increasing knowledge coming to light of plant-derived materials as leads for new herbicides, relatively little is known about the mode of action on herbicide-resistant weeds. Cyanamide (CA) is a naturally occurring herbicide synthesized by hairy vetch (Vicia villosa Roth.). However, it has not been experimentally verified whether CA suppresses target plants via sustained discharge at low concentrations, as is often the case with most plant-derived materials. This study aimed to detect the toxicity and the mode of action of CA to alfalfa (Medicago sativa L.) and redroot pigweed (Amaranthus retroflexus L.). The toxicity of CA toward the alfalfa and redroot pigweed by three different exposure patterns was compared: low-concentration repeated exposure with 0.3 g/L CA (LRE), high-concentration single exposure with 1.2 g/L CA (HSE), and distilled water spray as control. The results showed that CA had a stronger inhibitory effect on redroot pigweed growth compared to alfalfa under both LRE and HSE exposure modes, with leaves gradually turning yellow and finally wilting. Beyond that, field trials were conducted to corroborate the toxicity of CA to alfalfa and redroot pigweed. The results have also shown that CA could inhibit the growth of redroot pigweed without significant adverse effects on alfalfa. The outcomes concerning electrolyte permeability, root activity, and malondialdehyde (MDA) content indicated that CA suppressed the growth of redroot pigweed by interfering with the structure of the cell membrane and impacting cellular osmotic potential. CA could destroy the cell membrane structure to inhibit the growth of the redroot pigweed by both LRE and HSE exposure modes, which provides a theoretical basis for preventing and controlling redroot pigweed in alfalfa fields.

Allelopathic Toxicity of Cyanamide Could Control Amaranth (Amaranthus retroflexus L.) in Alfalfa (Medicago sativa L.) Field.

The inclination toward natural products has led to the onset of the discovery of new bioactive metabolites that could be targeted for specific therapeutic or agronomic applications. Despite increasing knowledge coming to light of allelochemicals as leads for new herbicides, relatively little is known about the mode of action of allelochemical-based herbicides on herbicide-resistant weeds. Cyanamide is an allelochemical produced by hairy vetch (Vicia villosa Roth.). This study aimed to detect the toxicity of cyanamide to alfalfa and amaranth. Seed germination experiments were carried out by the filter paper culture, and the seedling growth inhibition experiment was carried out by spraying alfalfa (Medicago sativa L.) and amaranth (Amaranthus retroflexus L.) seedlings with cyanamide. The results showed that when the concentration of cyanamide was 0.1 g·L-1, the germination of amaranth seeds could be completely inhibited without affecting the germination of alfalfa seeds. At the concentration of 0.5 g·L-1, cyanamide could significantly inhibit the growth of the root and stem of amaranth seedlings but did not affect the growth of alfalfa. This effect was associated with the induction of oxidative stress. The ascorbate peroxidase (APX) and catalase (CAT) activity of amaranth decreased by 6.828 U/g FW and 290.784 U/g FW, respectively. The malondialdehyde (MDA) content, peroxidase (POD), and superoxide dismutase (SOD) activity of amaranth firstly increased and then decreased with the increasing concentration of CA. These enzyme activities of amaranth changed more than that of alfalfa. Activities of the antioxidant enzymes APX, CAT, POD, and SOD and the content of MDA varied dramatically, thereby demonstrating the great influence of reactive oxygen species upon identified allelochemical exposure. In addition, cyanamide can also inhibit the production of chlorophyll, thereby affecting the growth of plants. From the above experiments, we know that cyanamide can inhibit the growth of amaranth in alfalfa fields. Thus, the changes caused by cyanamide described herein can contribute to a better understanding of the actions of allelochemical and the potential use of cyanamide in the production of bioherbicides.