Occurrence and Management of PSII-Inhibitor-Resistant Chenopodium album L. in Atlantic Canadian Potato Production

Round 1

Reviewer 1 Report

This paper presents comprehensive investigations on PSII inhibitor resistance in Chenopodium album in Atlantic provinces of Canada. Results are presented clearly and have significance for the management of these resistant weed populations.

L28: moderate level of resistance to metribuzin – I am not sure why the level of resistance has been downplayed in the abstract. This is inconsistent with the results of the dose response experiments where it is stated: … no tested lamb’s quarter population would be controlled in producer fields (L241).

L60: perhaps sub-groups would be better; PSII inhibiting are herbicide group

L84: serine264-glycine mutation in psbA was the only mechanism investigated in this project. So you only investigated one mechanism not mechanisms. It would be better to state; (2) investigate presence of Ser263-gly mutation in the psbA gene.

L103: ‘minimal seed collection occurred’ – this is vague. Better to state seeds of how many populations were collected each year.

L152: pre-emergence herbicide options – need to state in full – not emerge

Table 2: Tables need to be standalone – I found the table format quite odd. I would suggest presenting cross-resistance pattern as a separate table.

Table 3: The units for LD50 need to be presented – assume kg ha^-1. LD50 for S of 0.003 kg ha^-1 seems very low. Provide some indication of the goodness of fit of the log-logistic function.

L266: C. album should be in italics

Table 4: Clearly you have pooled the results of two field experiments. You need to provide the rationale for this decision to pool the data. Was it due to the absence of any site x treatment interaction? I don’t think any extra value has been derived from presenting the data for 4 WAA and 8 WAA. I would suggest just using the data for 8 WAA. There is a column for ‘other weeds’ at 8 WAA. If this information is vital then you need to mention what these weed species were. I would suggest deleting this data and just maintain focus on C. album.

Table 5 orthogonal contrasts: I don’t think the treatment contrasts are adding much to the interpretation of the data. It is fine to present treatment contrasts when there are small number of treatments. In this case there are 13 contrasts and most of them are non-significant. I also found odd that the contrast between Weed-free and Weedy control was non-significant. This raises the question: how were the weeds controlled in the weed-free plots and was it effective? I would suggest using a multiple comparison test for comparing these weed control treatments.

Table 5: I don’t believe presenting data on all classes of tubers is improving the value of information presented. I would suggest deleting Small yield, Cull yield and Specific gravity.

L366: mechanisms of resistance not mechanism of results

L370: what additional integrated weed management strategies would you suggest?

Author Response

L28: moderate level of resistance to metribuzin – I am not sure why the level of resistance has been downplayed in the abstract. This is inconsistent with the results of the dose response experiments where it is stated: … no tested lamb’s quarter population would be controlled in producer fields (L241). Thank you for the suggestion. We have emphasized resistance in the abstract and mentioned it would not be controlled in producers fields.

L60: perhaps sub-groups would be better; PSII inhibiting are herbicide group Changed

L84: serine264-glycine mutation in psbA was the only mechanism investigated in this project. So you only investigated one mechanism not mechanisms. It would be better to state; (2) investigate presence of Ser263-gly mutation in the psbA gene. Thank you for the suggestion, this has been changed.

L103: ‘minimal seed collection occurred’ – this is vague. Better to state seeds of how many populations were collected each year. Removed and added number of populations each year

L152: pre-emergence herbicide options – need to state in full – not emerge Corrected

Table 2: Tables need to be standalone – I found the table format quite odd. I would suggest presenting cross-resistance pattern as a separate table. Cross-resistance is stand-alone table now.

Table 3: The units for LD50 need to be presented – assume kg ha^-1. LD50 for S of 0.003 kg ha^-1seems very low. Provide some indication of the goodness of fit of the log-logistic function. Added units and comment on how goodness of fit was evaluated.

L266: C. album should be in italics Corrected.

Table 4: Clearly you have pooled the results of two field experiments. You need to provide the rationale for this decision to pool the data. Was it due to the absence of any site x treatment interaction? I don’t think any extra value has been derived from presenting the data for 4 WAA and 8 WAA. I would suggest just using the data for 8 WAA. There is a column for ‘other weeds’ at 8 WAA. If this information is vital then you need to mention what these weed species were. I would suggest deleting this data and just maintain focus on C. album. Added note to M&M that results were pooled as no significant effect of year or location or their interaction was found. Removed data on other weeds. We have chosen to keep 4WAA data for common lambsquarters to show how response changed through time.

Table 5 orthogonal contrasts: I don’t think the treatment contrasts are adding much to the interpretation of the data. It is fine to present treatment contrasts when there are small number of treatments. In this case there are 13 contrasts and most of them are non-significant. I also found odd that the contrast between Weed-free and Weedy control was non-significant. This raises the question: how were the weeds controlled in the weed-free plots and was it effective? I would suggest using a multiple comparison test for comparing these weed control treatments. Weeds were controlled in weed-free plots through hand-weeding and according to in-season biomass it was effective. We cannot explain non-significance in yield between weed-free and weedy controls. We chose not to use multiple means comparisons for yield data as we were more interested in seeing how treatments compared to weedy control.

Table 5: I don’t believe presenting data on all classes of tubers is improving the value of information presented. I would suggest deleting Small yield, Cull yield and Specific gravity. Removed

L366: mechanisms of resistance not mechanism of results Corrected.

L370: what additional integrated weed management strategies would you suggest? Added comment.

Reviewer 2 Report

Overall an extensive screen of Common lambsquarters resistant populations in Canadian potato production. Please see comments on attached pdf for further clarification needed on screening and statistics. 

Comments for author File: Comments.pdf

Author Response

one word – Corrected throughout document

So these populations had already experienced herbicide selection that year? I think this is important to note, that you are just screening individuals that survived herbicide application. - As fields were surveyed at random, field history was unknown. This has been added.

Outlined in the discussion, there are many other psbA mutations that can confer resistance that were not screened here. This map either needs to reflect the discriminating dose data or the term susceptible needs to be replaced with something like does not contain the screened psbA mutation. - Only populations screened for psbA are shown in Figure 1. The figure legend has been updated for clarity.

Did you perform a model fit procedure to ensure the 3 parameter log logistic function was the best fitting model? A statement addressing model fit needs to be added here. - Added comment on assessment of model fit (mean square error).

one word please change throughout – Corrected

NB5 above is listed as resistant to linuron, was this not tested here? - Unfortunately, it was not. Future studies investigating mechanisms of resistance in these populations will evaluate NB5’s response to linuron.

LD90 values need to be included in table 3. Also p-values for pairwise comparisons of LD50 and LD90 values need to be included. – Added estimated LD90 values to table.

Reviewer 3 Report

The manuscript addresses a topic already known in the world of herbicide resistance. However, I believe that the presentation of a new case and new ideas about it can be accepted.

Some comments are indexed in the same pdf as notes.

I think that the authors have to rewrite some aspects in the manuscript.

Comments for author File: Comments.pdf

Author Response

Mechanisms? I only saw one!! The title is incorrect and gives false information. – Removed mechanisms from the title.

which are? – The authors do not feel this is necessary. Adding a list of herbicides to the abstract would significantly increase its length which is already at 207 words.

Formate – Unclear what this refers to.

Subscript – Corrected throughout manuscript.

Cursive – Corrected.