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

Round 1

Reviewer 1 Report

The review concerns a research manuscript that presents interesting results, but in my opinion requires some corrections and additions.

1. The title of the manuscript refers to research on M.longifolia, but the authors also used taxa outside the Mentha genus (Nepeta, Agastache) and individual compounds contained in essential oils. The title should reflect the entire content of the article.
2. Line 31 contains data from 2012, which needs clarification from the authors as to why such old data was used.
3. The authors do not explain why they are comparing different taxa with species of the genus Mentha. The components of essential oil in Nepeta cataria and Agastache rugosa differ, and comparing them with Mentha species can be misleading. Admittedly, it is the same botanical family, but authors not specified what taxon selection criteria were adopted by them.
4. In the methodology section, the authors refer to the GC-MS analysis of essential oils that they have previously performed, but I did not find the results of such an analysis in their cited publication. The composition of essential oil is very complex, and its biological activity may result from the synergy of many compounds present in it. Therefore, the authors should include the results of the GC-MS analysis of species or modify the manuscript to account for the heterogeneity of the composition of essential oils.
5. In lines 209 and 230, the authors use the term "isolated compounds," which may be misleading because they did not isolate these compounds themselves, but purchased them from outside. They could replace this term with a more precise one.
6. The authors did not justify why they did not use all individual components of volatile oils in some studies or report results not for all examined taxa (subsections 3.1-3.4). These research decisions require justification so that readers can understand why the authors took such steps.
7. The manuscrip's novelty and whether statistical analysis was performed should be emphasized more. The authors should explain what distinguishes their research from others. Furthermore, they should explain whether statistical analysis of the results was performed and which statistical methods were used.
8. Authors should also modify the manuscript according to the instructions for authors.

Although the paper has potential applications and presents interesting results, it requires corrections and additions in several areas to become more understandable and scientifically valuable.

Author Response

The review concerns a research manuscript that presents interesting results, but in my opinion requires some corrections and additions.

Response: we thank the reviewer for the positive judgement and have addressed all points as outlined below.

1. The title of the manuscript refers to research on M. longifolia, but the authors also used taxa outside the Mentha genus (Nepeta, Agastache) and individual compounds contained in essential oils. The title should reflect the entire content of the article.

Response: the focus was on M. longifolia, which was also used for the proof-of-concept as bioherbicide. The other species were used during the initial phases and rather serve as controls. We have adjusted the title to “Signal, not poison – Screening Mint essential oils for weed control leads to Horsemint”.

1. Line 31 contains data from 2012, which needs clarification from the authors as to why such old data was used.

Response: this was just exemplarily to show the extent of herbicide use, we have now inserted a more recent example.

 

1. The authors do not explain why they are comparing different taxa with species of the genus Mentha. The components of essential oil in Nepeta cataria and Agastache rugosa differ and comparing them with Mentha species can be misleading. Admittedly, it is the same botanical family, but authors not specified what taxon selection criteria were adopted by them.

Response: the taxonomy of the Mints is unclear, definitely Mentha is not monophyletic, the motivation of this work is not to set up taxonomy, but to search for allelopathic activities. We knew already from our previous work that both, Nepeta cataria and Agastache rugosa harbour activity in this respect. Both of them are designated as Mints. We have now inserted a specifying paragraph into the introduction to avoid confusion.

1. In the methodology section, the authors refer to the GC-MS analysis of essential oils that they have previously performed, but I did not find the results of such an analysis in their cited publication. The composition of essential oil is very complex, and its biological activity may result from the synergy of many compounds present in it. Therefore, the authors should include the results of the GC-MS analysis of species or modify the manuscript to account for the heterogeneity of the composition of essential oils.

Response: we have now added the GC-MS data into the supplement.

1. In lines 209 and 230, the authors use the term "isolated compounds," which may be misleading because they did not isolate these compounds themselves but purchased them from outside. They could replace this term with a more precise one.

Response: “isolated” was meant in the sense of “not composed”, not in the sense of chemical isolation. We have now replaced by the term “individual compound”.

1. The authors did not justify why they did not use all individual components of volatile oils in some studies or report results not for all examined taxa (subsections 3.1-3.4). These research decisions require justification so that readers can understand why the authors took such steps.

Response: The study was designed in an iterative way, starting with a screening of oils and compounds, and then funneling down to the mode of action of M. longifolia (the A. rugosa data are already published in Sarheed et al. 2020) and then the proof of concept for bioherbicide application. This prioritisation was necessary, it would not advance our knowledge, but cost a lot of time and resources to do all the ramifications for all plants and compounds. Moreover, it would be a boring paper to read, because these ramifications that were not followed up, were not followed for a good reason, because they were relatively poor in effect. However, we see from the reviewer comment that we should explicitly explain the design of the study in the scope section, what we have done now.

1. The manuscrip's novelty and whether statistical analysis was performed should be emphasized more. The authors should explain what distinguishes their research from others. Furthermore, they should explain whether statistical analysis of the results was performed and which statistical methods were used.

Response: We have added information on the statistical testing, and we have added a paragraph to the conclusion, where we outline the novelty of the study more explicitly.

1. Authors should also modify the manuscript according to the instructions for authors.

Although the paper has potential applications and presents interesting results, it requires corrections and additions in several areas to become more understandable and scientifically valuable.

Response: it is not entirely clear to us, what the reviewer means, possibly the names of the authors after the numbers in the text. Those were for our own orientation and have now been cut out.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, the author had conceptualized allelopathy by essential oils from different Mints as inhibitory signaling to the target plant rather than as a general phytotoxicity. I have only several minor comments.

 

Line 31: Maybe the data in 2012 were outdated. Updating it.

Line 33: Better providing the data for European countries.

Line 135: Drawing a schematic diagram for the experimental design.

line 183: Adding a section of Data Analyses.

Line 351: Confusing in the results; Why does % of control could be more than 100?

Author Response

Reviewer 2

In this paper, the author had conceptualized allelopathy by essential oils from different Mints as inhibitory signaling to the target plant rather than as a general phytotoxicity. I have only several minor comments.

Response: We thank the reviewer for this positive judgement and respond to the minor points below.

In Line 31: Maybe the data in 2012 were outdated. Updating it.

Response: this point was also raised by reviewer 1. this was just exemplarily to show the extent of herbicide use, we have now inserted a more recent example.

Line 33: Better providing the data for European countries.

Response: agreed, we have now added an example from Europe.

Line 135: Drawing a schematic diagram for the experimental design.

Response: we have integrated now a sketch of the design into figure 2.

line 183: Adding a section of Data Analyses.

Response: we have added such a section, also in response to point 7 of reviewer 1.

Line 351: Confusing in the results; Why does % of control could be more than 100?

Response: this value means that there has been a stimulation over the control in case of Agastache rugosa. Allelopathic interaction can sometimes also be positive. We have seen this also in other cases. We can currently only speculate about the mechanism and do not want to expand this in the paper, but for the reviewer: we know that there is an antagonism between microtubules and actin filaments during auxin transport. Thus, the essential oil of A. rugosa that disrupts microtubules might have a positive effect on actin filaments and thus promote the development of Bindweed. While we do not want to overcharge the manuscript with a long excursion on A. rugosa which is not in the focus of the current study, we have now made more explicit that there is a stimulation (leading to a value higher than 100% of the control value) to avoid confusion, and we insert a short explanatory sentence into the discussion.

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

After carefully reviewing the new version of manuscript, I believe that the revisions made by the authors have significantly enhanced its scientific value, making it well-suited for publication in Agriculture. The authors have clearly put in a lot of effort to improve the clarity and coherence of their ideas, which has resulted in a more compelling and robust study. The manuscript  is now presented in a clear and concise manner, which will undoubtedly benefit readers and fellow researchers in the field. Overall, I am confident that the manuscript is now of high quality and will make a valuable scientific contribution.