Signal, Not Poison—Screening Mint Essential Oils for Weed Control Leads to Horsemint

Abstract

Weed control tries to suppress competitors for a crop and often relies on differential intoxication, making use of differences in uptake, development, or metabolism. We explored the possibility of using natural signals to shift competition in favour of the crop. Using the competitive horsemint (Mentha longifolia) as a paradigm, we showed that essential oils from certain mint species suppress the seedling development of different target species in a specific and efficient manner. The specificity concerned both the donor and the receptor. We demonstrated further that the effect of horsemint oil was specific for actin filaments, and not for microtubules. Since the elimination of actin will impair auxin transport, which is essential for root regeneration in vegetatively propagating weeds, we tested the efficacy of horsemint essential oil in combination with a slow-release carrier against field bindweed (Convolvulus arvensis), a pertinent weed in organic cereal production. We observed that the development of this weed can be specifically blocked, especially if the carrier is worked into the soil. We propose that allelopathic interactions, often relying on manipulative chemical signalling, harbour significant potential for organic weed control.

Spearmint targets microtubules by (−)-carvone

“…In the current study, we demonstrate that (−)-carvone is a potent bioactive compound that causes time- and tissue-dependent degradation of microtubules in the root meristem, followed by programmed cell death that prevents root growth and, thus, unfolds allelopathic activity preventing germination of Cress and Poppy, but also of other plants, as shown in a previous study by Sarheed et al. [ 20 ]. The effect depends on the target species, and on the target tissue, is produced at low effective concentration, and strongly dependent on molecular peculiarities.…”

“…Since our previous work [ 20 , 26 ] has shown specific allelopathic activities for essential oils from different Mint species, we assessed a potential bioactivity of (−)-carvone, the main component of Spearmint, and (+)-menthofuran, the main component of Watermint, in a standard Cress germination assay ( Fig. 2 ).…”

“…Instead, it can generate the novel (−)-menthol, which might be linked with the lower (+)-menthofuran content, since (+)-menthofuran inhibits the expression of pulegone reductase, the key enzyme initiating the pathway towards (−)-menthol [ 43 ]. These species-specific chemical profiles are reflected by patterns of allelopathic activity that differ between the essential oils generated from Spearmint, Watermint, and Peppermint [ 20 , 26 ], indicating a potential role for the ecological performance of these species.…”

“…For instance, essential oil of M. spicata , which is rich in (−)-carvone, could almost eliminate the germination of the pertinent weed Amaranthus retroflexus , while half of the seeds of the ornamental plant Alcea pallida were still germinating, demonstrating that suppression depends on the recipient species [ 18 ] and is unlikely to be caused by an overall phytotoxicity. This specificity is in sharp contrast with the generic effect of synthetic herbicides and has also been found for other essential oils, such as that of Eucalyptus [ 19 ] or Horsemint [ 20 ].…”

Mentha suaveolens as Allelopathic Biomass for Weed Control: Phenolics, Organic Acids, and Volatile Organic Compounds Profiles

“…Pardo-Muras et al [85] found that the synergistic interactions among VOCs and water-soluble compounds explained the herbicidal potential of Cytisus scoparius (L.) Link residues when applied as a soil amendment. Sarheed et al [86] proved that the com-plete essential oils of M. spicata, M. spicata crispa, and M. longifolia had more powerful phytotoxic effects than any of their isolated monoterpenes (menthone, linalool, limonene, α-pinene, and β-pinene). Moreover, a chemical analysis of volatile and phenolic compounds from different parts (leaves, stems, and whole plant) of M. suaveolens not only indicated a higher content of the same compound in the whole plant compared to its parts but also the presence of different compounds or in different amounts among the parts [21].…”