Calcium and Potassium Imbalance Favours Leaf Blight and Defoliation Caused by Calonectria pteridis in Eucalyptus Plants

Round  1

Reviewer 1 Report

Dear authors

the MS is in my view very well written and results well presented. 

If I understood correctly, you are looking for the best fertilization scheme on Eucalyptus in order to limit the impact of Calonectria pteridis infections and help the plant coping with the disease along its life. If this is the case, I think it is more appropriate to speak about "tolerance" instead of "resistance" (but I acknowledge that it is an issue still under debate). 

My main concern is on the methodology: the absence of control, the very limited number of replicates and the high number of combinations make hard the comparison of obtained results. I would be interested in seeing error bars, for example. More details are provided below on the specific sections. 

INTRODUCTION

some problems in the numbering of references in the text

the relevance of this pathogen to the eucalyptus plantations is very lightly described (I found a good example by Alfenas et al Stud Mycol. 2015 Mar; 80: 89–130)

"balanced mineral fertilization is an alternative strategy in the integrated management of eucalyptus diseases": it is not very precise, as in reality a good nutrient balance is a widely acknowledged strategy to limit the favorable condition for pathogens attack and symptoms expression, in all plant species.

M&M

Not clear why you do not have any control replicates with on-infected plants. In this way it is impossible to distinguish between nutrient imbalance and pathogen symptoms affecting plant growth, chlorophyll content and leaf nutrient content.

Fig 1: please add in the lines legend that the five concentrations are Ca. Error bars are missing.

REFERENCES

I would suggest reducing as much as possible references in languages other than English as this will make their use very limited for most of your readers.

Author Response

Dear reviewer,

Thank you for the suggestions of great value. Below your questions answered.

- the relevance of this pathogen to the eucalyptus plantations is very lightly described (I found a good example by Alfenas et al Stud Mycol, 2015 Mar; 80: 89-130): answered in the text

- "balanced mineral fertilization is an alternative strategy in the integrated management of eucalyptus diseases": it is not very precise, as in reality to good nutrient balance is a widely acknowledged strategy to limit the favorable condition for pathogens attack and symptoms expression, in all plant species: answered in the text

- Not clear why you do not have any control replicates with on-infected plants. In this way it is impossible to distinguish between nutrient imbalance and pathogen symptoms affecting plant growth, chlorophyll content and leaf nutrient content:

Our control is represented by the treatment 6 mmol L-1 K × 4 mmol L-1 Ca, suggested by Clark for eucalyptus fertilization. For this type of work, authors use the standard dosage of each culture. The main purpose of the study was verifying the effect of the symptoms of the nutritional imbalance in the disease. For this reason we fix the control treatment at the level of comparison, since the fertilizations of eucalyptus to the field are based on these doses for these nutrients. All the acquired results were based on the consequence not only of the presence of the pathogen, but also of the effect of the nutritional imbalances, that is, of these factors together.

Fig 1: please add in the lines that the five levels are Ca. Error bars are missing: Done

I would suggest reducing as many references as possible in English other than English as this will make them very limited for most of your readers: Done

Reviewer 2 Report

The study of Soares et al. entitled "Calcium and potassium imbalance favors leaf blight and defoliation caused by Calonectria pteridis in Eucalyptus plants" investigates the effect of the dose and nutritional balance between calcium (Ca) and potassium (K) on the severity of leaf spot and defoliation caused by the fungus Calonectria pteridis. Despite the subject is of moderate interest, I do not think the analysis is adequately done/shown.

-          The introduction should be better focused: there is no clear description on the chosen methods and their relevance to the topic;

-          Materials and methods are well described; however, each method and result respect different sampling times (p.e.: The incidence and severity were observed in the leaves at 24, 48, 72, 96 and 120 h after inoculation (hai)/ The nutritional status of the seedlings was determined before implementing the treatments, and leaf samples were taken before and after the end of the experiment). This decision makes the results hard to follow and discuss.

-          Results on the statistical analysis as described in the section (Statistical analyses were carried out using the statistical software R) are not available, and most of the results lack a significant result.

-          The adequacy of the way the authors chose to show the results can be arguable. The reader is unaware of the actual results. I think these data are essential (average ± standard error or deviation).

-          The previous flaws impair the quality of the discussion and conclusion.

Author Response

Dear reviewer,

Thank you for the suggestions of great value. Below your questions answered.

-  The introduction should be better focused: there is no clear description on the chosen methods and their relevance to the topic: Some modifications have been made.

-  Materials and methods are well described; however, each method and result respect different sampling times (p.e.: The incidence and severity were observed in the leaves at 24, 48, 72, 96 and 120 h after inoculation (hai)/ The nutritional status of the seedlings was determined before implementing the treatments, and leaf samples were taken before and after the end of the experiment). This decision makes the results hard to follow and discuss:

The way it was written was equivocal about a methodology for checking the nutritional status of plants. It has been corrected. However, these times were chosen to verify the initial and final state of the seedlings and to compare them. For this variable it would be impracticable to make the collections at the same time that the severity and incidence of the disease were evaluated. This is because the collection of leaves to make the analysis of the nutritional content of the leaves must be a considerable volume. If we did the collections in times 24, 48, 72 and 120 ha, there would be no leaves left to analysis the other variables. Corrections were made in the text.

-  Results on the statistical analysis as described in the section (Statistical analyses were carried out using the statistical software R) are not available, and most of the results lack a significant result.

All results shown in graphs were significant. All significant results were presented in the text. In the graphs presented, all analyzes of variances were significant, as described in the text. Non-significant variables were described only in the text.  Corrections were made in the text. A table was added to clarify the results.

- The adequacy of the way the authors chose to show the results can be arguable. The reader is unaware of the actual results. I think these data are essential (average ± standard error or deviation).

Standard error bars have been added to all graphics.

Author Response File: Author Response.docx

Round  2

Reviewer 1 Report

I received the authors' clarifications and reviewed thoroughly the updated MS. I agree with the proposed amendments as in my view they improved the clarity of the text and described methodology. I remain convinced about the importance of having healthy plants as controls, but at this point you can take it as a suggestion for future trials, when you want to ensure that all the different factors are equally quantifiable and that each specific effect is not masked by others.

With my kindest regards

Reviewer 2 Report

The study of Soares TPF and colleagues entitled "Calcium and potassium imbalance favors leaf blight and defoliation caused by Calonectria pteridis in Eucalyptus plants" investigates the effect of the dose and nutritional balance between calcium (Ca) and potassium (K) on the severity of leaf spot and defoliation caused by the fungus Calonectria pteridis. The authors took into consideration the raised concerns/suggestions and performed a thorough revision that significantly increased the quality of the manuscript.