The Biological and Genetic Mechanisms of Fruit Drop in Apple Tree (Malus × domestica Borkh.)
, Vidmantas Stanys 1 and Birutė Frercks 1,*
Round 1
Reviewer 1 Report (New Reviewer)
Comments and Suggestions for AuthorsThis manuscript cites many references and summarizes physiological fruit drop in an easy-to-understand and easy-to-read manner. I have three concerns. Please consider them.
1. The title states the mechanism of "yield self-regulation," but this manuscript explains the mechanism of "physiological fruit drop." If the term "yield self-regulation" is used, it should describe how the crop load after physiological fruit drop affects the yield in the current year and the following year. There are varieties that can produce stable yields every year without hand-thinning and biennial varieties that bear fruit every other year unless they are thinned. Isn't it necessary to explain the difference in alternate bearing between the varieties in relation to physiological fruit drop?
2. In the introduction, "yield self-regulation" (line 38) and "stability of apple fruit yield" (line 50) are mentioned separately, but the difference between their meanings is unclear. Please explain in more detail what characteristics or phenomena each refers to.
3. The mechanism of physiological fruit drop is explained in terms of plant hormone dynamics and gene expression. However, there is no explanation for when fruitlets are destined to drop. For example, could you explain that when differences in hormone levels exceed a certain threshold, the fruit with lower amounts of hormone are destined to drop? There is a period of about 2-3 weeks between the first fruit drop, which occurs due to incomplete pollination, and the second fruit drop, called June drop. Although the growth of each fruitlet varies greatly within the tree, the June drop occurs a relatively short period of time. What determines this timing?
Author Response
- : The title states the mechanism of "yield self-regulation," but this manuscript explains the mechanism of "physiological fruit drop." If the term "yield self-regulation" is used, it should describe how the crop load after physiological fruit drop affects the yield in the current year and the following year. There are varieties that can produce stable yields every year without hand-thinning and biennial varieties that bear fruit every other year unless they are thinned. Isn't it necessary to explain the difference in alternate bearing between the varieties in relation to physiological fruit drop?
A: Thank you for your remark. I agree that the title of the article is too broad. The title has been changed to “The biological and genetic mechanisms of fruit drop in apple trees (Malus x domestica Borkh.)”
- R: In the introduction, "yield self-regulation" (line 38) and "stability of apple fruit yield" (line 50) are mentioned separately, but the difference between their meanings is unclear. Please explain in more detail what characteristics or phenomena each refers to.
A: Thank for your comment in this part of manuscript we are talking about the same phenomena. In the text, the expressions were unified.
- R: The mechanism of physiological fruit drop is explained in terms of plant hormone dynamics and gene expression. However, there is no explanation for when fruitlets are destined to drop. For example, could you explain that when differences in hormone levels exceed a certain threshold, the fruit with lower amounts of hormone are destined to drop? There is a period of about 2-3 weeks between the first fruit drop, which occurs due to incomplete pollination, and the second fruit drop, called June drop. Although the growth of each fruitlet varies greatly within the tree, the June drop occurs a relatively short period of time. What determines this timing?
A: Thank you for your comment. I hope that in line 230-232 explanation for decrease of auxin leads to increase ethylene and that which results in fruit drop is about it. But exact amount of hormones differs very depending on variety of apple. This I stated my self during my PhD studies, when I analyzed phytohormone concentrations during fruit drop, which were erratic and varied according to a number of factors, so that it is not possible to give a specific value for the onset of fruit drop. There were only general trends and the concentrations varied considerably between varieties, at different stages of fruit drop and under different environmental conditions.
The mentioned period (2-3 weeks after blooming) by some authors is distinguished as part of the first drop. The reason of this drop is poor fertilization of the blossom. The fruit at this stage has few or no developing seeds. Without seeds, the biosynthesis of phytohormones does not take place and the fruit competition for nutrients with normally developing fruit. As this is part of the first drop of fruitlets, I don’t think it is necessary to distinguish it.
Author Response File: 
Author Response.pdf
Reviewer 2 Report (New Reviewer)
Comments and Suggestions for AuthorsThe work "The biological and genetic mechanisms of yield self-regulation in apple tree (Malus × domestica Borkh.)" by Aurelijus Starkus et al. (Horticulturae-3197488) is a very interesting manuscript that aims to review the internal influencing factors of apple fruit drop, it has theoretical guiding significance for apple production. However, there are several issues that prevent me from recommending the publication of the manuscript in its present form.
First of all, the title of the manuscript needs to be revised, would ‘The biological and genetic mechanisms of fruit drop in apple tree (Malus × domestica Borkh.)’ is a more appropriate title ?
Secondly, please increase the research progress of auxin related genes in 3.3, increase the outlook and put forward the future research focus or the production guidance significance of the review.
Finally, there are many minor errors in the manuscript, especially the gene names need to be italicized.
Some minor problems are as follows:
-line 182: ‘4,25’ should be ‘4.25’？
-line 183: ‘6,25’ should be ‘6.25’？
-line 184: ‘MADS-box’ should be revised to ‘MADS-box’.
-line 250: the name of genes should be italics.
-line 253: ‘SA’ appears for the first time, the full name should be added.
-line 253: ‘IAA/Z’ ?
-line 272-273: the name of genes should be italics. ‘PK7’ appears for the first time, the full name should be added.
-line 312: ‘starch Apple trees’ ?
-line 340: ‘Subsequent The reactions’ ?
-line 343-393: the name of genes should be italics. Some genes names appears for the first time, the full name should be added.
-line 395: ‘mane’ or ‘name’ ?
-line 409: the name of genes should be italics.
-line 414, 417: the name of genes should be italics.
-line 422- 452: the name of genes should be italics.
-line 473: ‘GD’ appears for the first time, the full name should be added.
Comments for author File: Comments.pdf
Author Response
R: First of all, the title of the manuscript needs to be revised, would ‘The biological and genetic mechanisms of fruit drop in apple tree (Malus × domestica Borkh.)’ is a more appropriate title ?
A: Thank you for your remark. Title of manuscript was changed according to your suggestion.
R: Secondly, please increase the research progress of auxin related genes in 3.3, increase the outlook and put forward the future research focus or the production guidance significance of the review.
A: Thank you for your comment. Research of auxin related genes in part 3.3 was increased. Lines 420 - 425
R:Finally, there are many minor errors in the manuscript, especially the gene names need to be italicized.
Some minor problems are as follows:
-line 182: ‘4,25’ should be ‘4.25’？
-line 183: ‘6,25’ should be ‘6.25’？
-line 184: ‘MADS-box’ should be revised to ‘MADS-box’.
-line 250: the name of genes should be italics.
-line 253: ‘SA’ appears for the first time, the full name should be added.
-line 253: ‘IAA/Z’ ?
-line 272-273: the name of genes should be italics. ‘PK7’ appears for the first time, the full name should be added.
-line 312: ‘starch Apple trees’ ?
-line 340: ‘Subsequent The reactions’ ?
-line 343-393: the name of genes should be italics. Some genes names appears for the first time, the full name should be added.
-line 395: ‘mane’ or ‘name’ ?
-line 409: the name of genes should be italics.
-line 414, 417: the name of genes should be italics.
-line 422- 452: the name of genes should be italics.
-line 473: ‘GD’ appears for the first time, the full name should be added.
A: Thank you for your efforts improving the manuscript. Changes has been made according to your remarks.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report (New Reviewer)
Comments and Suggestions for AuthorsThis manuscript has been appropriately revised in response to my comments.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe contribution provides valuable information on fruit development processes in apples and the causes of fruit drop.
However, the writing frequently establishes generalities based on a single reference, which indicates a lack of depth in the information search.
It is essential review carefully the writing and punctuation of the paper.
Methodology for search and selection information is not specified (databases consulted, keywords used, selection of cited documents, etc.).
The document is limited to present information without generating a discussion that determines the needs for basic or applied research on each of the topics addressed.
In some references, the conditions and environments where the research is carried out are omitted, so conclusions are written that seem to be applied to the entire species, without being so.
The conclusions should be the summary.
Comments for author File: Comments.pdf
Author Response
R: The contribution provides valuable information on fruit development processes in apples and the causes of fruit drop.
R: However, the writing frequently establishes generalities based on a single reference, which indicates a lack of depth in the information search.
A: Thanks for suggestion, the single references for generalized statements are review articles, but we added some references (19) in the manuscript.
R: It is essential review carefully the writing and punctuation of the paper.
A: The writing was checked with Grammarly program and manually again.
R: Methodology for search and selection information is not specified (databases consulted, keywords used, selection of cited documents, etc.).
A: Thanks for suggestion. Despite there are some review articles with statistics of data base and keywords search, we don’t used it in our article, as the search was done mostly with keywords, provided in “Keywords” section of manuscript.
R: The document is limited to present information without generating a discussion that determines the needs for basic or applied research on each of the topics addressed. In some references, the conditions and environments where the research is carried out are omitted, so conclusions are written that seem to be applied to the entire species, without being so.
A: Thank you for your remark. In some references, the conditions were described.
R: The conclusions should be the summary.
A: Thank you for your remark the conclusions have been summarized.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe review aims to describe the influence of biological and genetical factors on the yield self-regulation mechanism in apple. Physiological processes involved in the source-sink relationships within the canopy are considered to better highlight the competitions that can affect the entity and timing of flowers/fruit abscission.
In my humble opinion, despite an efficient organization of the section of the paper it results quite hard to read due to the not really fluent writing. Short sentences, and too many grammar fails affect the overall quality of the paper.
I believe that a decise revision could really help to improve the manuscript since the content is valuable and the reference consistent.
Figure 1 is relevant and very well done, but most of the caption content can be shortened and referred to the text
Comments for author File: Comments.pdf
Author Response
R: In my humble opinion, despite an efficient organization of the section of the paper it results quite hard to read due to the not really fluent writing. Short sentences, and too many grammar fails affect the overall quality of the paper. I believe that a decise revision could really help to improve the manuscript since the content is valuable and the reference consistent.
A: The writing was checked with Grammarly program and manually again.
R: Figure 1 is relevant and very well done, but most of the caption content can be shortened and referred to the text
A: Thank you for your comment. Text of the figure1 caption content was shortened.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
Submitted paper entitled "Genetic mechanisms of yield self-regulation in apple tree (Malus × domestica Borkh.)" is very interesting in terms of summarizing the state of art of the knowledge about fruit setting and drop phenomenas and underlying physiological mechanisms. Unfortunately, the revision showed that preparing this article for successful publication still needs some efforts and calrifications.
The first part of your work (Introduction and 2. Physiological processes during fruit drop) seems to be organized not well. It looks like you really do not have an idea how to introduce the reader to the subject. You should be more streamlined - especailly in the Introduction part.
Starting from 3. Genetic regulation of fruit drop your work starts to be more thoroughly planned and carefully thought through. On the other hand there are many mistypes and other editiorial flaps here that makes me wonder how many times your manuscript have been revised and if all scholars contributing to this paper made the proofreading before submission. Below you have few examples:
Line 190 - missing t for Goldschmidt
Line 206 - missing dot (.)
Line 207 - Arabidopsis without italics while below you use it
Line 224 missing dot again
Line 244 - treshold)
Line 278 - pola should not starts with capital letter
Line 319 and 322 - missing spaces
There are much more such little deficiences especially in the second part of your study and I found it little irritating while it shows that you did not prepare the manuscript carefully.
Below you will find some remarks, which I believe would be helpful in increasing the quality of presented study, and also some specific questions I would be very grateful to you for answering them.
Title
In my opinion The Title should give some broader light on the subject of your paper. Genetic mechanisms are only a part of presented work. You should mentioned also about physiological background that you broadly described, or as you stated in Line 21 "The biological factors and genetic mechanism.."
Line 16 - you mentioned "several technologies" here, while these are simply methods or thinning techniques
Line 30/31 - does really high quality of fruits depend on maturity, shipping conditions andstorage technology? In my opinion these are important but still only minor factors.
Line 34-38 - I did not get the meaning of this sentence. Please rearrange it.
Line 52-55 - what are harmful side-effects of using urea or ammonium thiosulphate (ATS) in early thinning? The same question can be stated for IAA and BA. To be honest this is my biggest doubt about the introducing the significance of your review. While your statement (Line 52-55) is so straightforward please support it with some more references.
Line 105 - use only AZ while you already presented/defined this abbreviation in the text
Line 137 - it would be better: Role of seeds in regulation of abscission
Line 170 - see above
Line 194 - ... and their role in fruit drop process - sounds better
Line 254 - list those experts giving appropriate citations
Line 310-313 - give appropriate referrences
I hope you will find it helpful.
Best regards,
Author Response
R: The first part of your work (Introduction and 2. Physiological processes during fruit drop) seems to be organized not well. It looks like you really do not have an idea how to introduce the reader to the subject. You should be more streamlined - especailly in the Introduction part.
A: Thank you for the comment. Introduction part was completely rearranged. Now information is presented more clearly, and objectives of this review is highlighted.
R: Starting from 3. Genetic regulation of fruit drop your work starts to be more thoroughly planned and carefully thought through. On the other hand there are many mistypes and other editiorial flaps here that makes me wonder how many times your manuscript have been revised and if all scholars contributing to this paper made the proofreading before submission. Below you have few examples:
Line 190 - missing t for Goldschmidt
Line 206 - missing dot (.)
Line 207 - Arabidopsis without italics while below you use it
Line 224 missing dot again
Line 244 - treshold)
Line 278 - pola should not starts with capital letter
Line 319 and 322 - missing spaces
There are much more such little deficiences especially in the second part of your study and I found it little irritating while it shows that you did not prepare the manuscript carefully.
Below you will find some remarks, which I believe would be helpful in increasing the quality of presented study, and also some specific questions I would be very grateful to you for answering them.
A: Thank you for the comment, the writing now was checked with Grammarly program and manually again, and we hope there are no such mistakes anymore.
R: Title. In my opinion The Title should give some broader light on the subject of your paper. Genetic mechanisms are only a part of presented work. You should mentioned also about physiological background that you broadly described, or as you stated in Line 21 "The biological factors and genetic mechanism.."
A: Thank you for suggestion, we extended the title name according to your suggestion.
R: Line 16 - you mentioned "several technologies" here, while these are simply methods or thinning techniques
A: Thank you for suggestion. The phrase "several technologies" had been changed by your suggestion
R: Line 30/31 - does really high quality of fruits depend on maturity, shipping conditions and storage technology? In my opinion these are important but still only minor factors.
A: Thank you for comment. New reference and more important factors influencing fruit quality were added.
R: Line 34-38 - I did not get the meaning of this sentence. Please rearrange it.
A: Thank you for remark. Sentence was rearranged.
R: Line 52-55 - what are harmful side-effects of using urea or ammonium thiosulphate (ATS) in early thinning? The same question can be stated for IAA and BA. To be honest this is my biggest doubt about the introducing the significance of your review. While your statement (Line 52-55) is so straightforward please support it with some more references.
A: Thank you for comment. This part was written based on old references. In today horticulture harmful chemical thinners are banned. I agree that here are non-harmful chemical thinners . nowadays, but also there are thinners that could cause some health issues. In this part of manuscript we made some changes in order to ensure that chemical thinning doesn`t seems so negative The aim of this article is to show that there are natural mechanisms of yield self-regulation. By studying these mechanisms and gaining new knowledge, new varieties could be developed with stabile fruiting features, that does not require thinning.
R: Line 105 - use only AZ while you already presented/defined this abbreviation in the text
A: Thank you for remark. Changes had been made based on your suggestion.
R: Line 137 - it would be better: Role of seeds in regulation of abscission
A: Thank you for remark. Changes had been made based on your suggestion.
R: Line 170 - see above
A: Thank you for remark. Changes had been made based on your suggestion.
R: Line 194 - ... and their role in fruit drop process - sounds better
A: Thank you for remark. Changes had been made based on your suggestion.
R: Line 254 - list those experts giving appropriate citations
A: Thank you for comment. Citation were given.
R: Line 310-313 - give appropriate references
A: Thank you for comment. References were added
R: I hope you will find it helpful.
A: Yes, thank you very much, as we believe, after your review our article becomes more valuable
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsDear authors, I have checked different sections of your manuscript and I am afraid that the current submission is not acceptable for publishing in Horticulturae. This review try to deep our knowledge about fruitlet abscission and flower/fruit thinning in apple, but the understanding of this very extended phenomenon that you show is not enough. I recommend you an extensive reading of the mechanisms and final causes leading to the absccision of young fruitlets. Alternatively, you may focus on genetic control of the selection process and the role of hormones, but in the first pages, the redaction is very often confusing and misleading for the readers. I list below some examples, but I attach also the edited pdf with many other corrections and suggestion for your consideration.
Abstract L17: Please, rewrite. Do you mean mechanical thinning? Not usual? And never bud elimination, flower and fruit thinning are both possible, but the elimination of flower buds..(not the same)
Introduction
L31 This is something farmers cannot controlled and cannot be put together with preharvest factors
L41 There are many reasons while heavy yields are negative, and lack of vegetative growth is the least.
L52 It is not about high productivity. It is that mechanical thinning methods very often cause the fall of larger fruitlets, potentially, larger at harvest, and also damage reamaining fruitlet by bruising.
Please, if you want to compare different methods of thinning you have to develop a little more the pros and cons of them.
L58. I am sorry, but I think you don't fully understand the ultimate reasons behind fruitlet competition and abscission. And, please, do not mix leaves (sources) with fruit (sinks), being flowers drops before anthesis unusual (happening only in some crops like Citrus) and mostly after bloom due to lack of fertilization. This mix is confusing.
L58-60 Please, thousand of plants, and dozens of crops, exhibit "June drop" and you have plenty of information in the Literature about the characteristics and causes behind June drop. Citing Betel-nut Palm??? No the best example.
L74 water stress only accentuates fruitlet abscission and selection of the fittest, but June drop based on seed number of other factors will happen even under the best grwowing conditions. Again you are misleading readers.
L82-85. Preharvest drop has nothing to do with the subject you have to develop. I am afraid you are mixing postbloom drops with preharvest drop in almost ripen fruit. They have little in common.
L92. Buds rarely fall. When they do, it is because lack of chilling requirements, and this has nothing to do with the subject you are developing.
I added some other suggestions and corrections, deleting some sentences, trying to improve the manuscript. Please, consider them when submitting ths manuscript to other Journals
Comments for author File: Comments.pdf
Although English is not my mother tongue, I made many corrections and added some suggestions, because I found the ms hard to follow.
Author Response
R:I have checked different sections of your manuscript and I am afraid that the current submission is not acceptable for publishing in Horticulturae. This review try to deep our knowledge about fruitlet abscission and flower/fruit thinning in apple, but the understanding of this very extended phenomenon that you show is not enough. I recommend you an extensive reading of the mechanisms and final causes leading to the absccision of young fruitlets. Alternatively, you may focus on genetic control of the selection process and the role of hormones, but in the first pages, the redaction is very often confusing and misleading for the readers. I list below some examples, but I attach also the edited pdf with many other corrections and suggestion for your consideration.
A: Thank you for your efforts to improve the manuscript. Corrections or answers were given in response to your comments
R: Abstract L17: Please, rewrite. Do you mean mechanical thinning? Not usual? And never bud elimination, flower and fruit thinning are both possible, but the elimination of flower buds..(not the same)
A:Thank you for comment. We made a mistake when writing. I agree that it is not possible to thin flower buds, only flowers or fruitlets. But it is possible to inhibit flower bud differentiation.
Introduction
R: L31 This is something farmers cannot controlled and cannot be put together with preharvest factors
A: Thank you for comment. New reference and more important factors influencing fruit quality and preharvest fruit drop were added.
R:L41 There are many reasons while heavy yields are negative, and lack of vegetative growth is the least.
A:Thank you for comment. Part of the vegetative growth was deleted.
R:L52 It is not about high productivity. It is that mechanical thinning methods very often cause the fall of larger fruitlets, potentially, larger at harvest, and also damage reamaining fruitlet by bruising.
A: Thank you for your remark. That’s exactly what we want to say. Incorrect word was used. We changed word productivity with quality. I think it should be clearer.
R: Please, if you want to compare different methods of thinning you have to develop a little more the pros and cons of them.
A: Thank you for your comment. Thinning and their methods is not a topic of this review. The aim of this part is to inform the reader that the following thinning methods exist and growers use them. The aim of this article is to show that there are natural mechanisms of yield self-regulation. By studying these mechanisms and gaining new knowledge, new varieties could be developed with stabile fruiting features, that does not require additional thinning.
R:L58. I am sorry, but I think you don't fully understand the ultimate reasons behind fruitlet competition and abscission. And, please, do not mix leaves (sources) with fruit (sinks), being flowers drops before anthesis unusual (happening only in some crops like Citrus) and mostly after bloom due to lack of fertilization. This mix is confusing.
A:Thank you for comment. Changes has been made. Hope it will be more clear.
R: L58-60 Please, thousand of plants, and dozens of crops, exhibit "June drop" and you have plenty of information in the Literature about the characteristics and causes behind June drop. Citing Betel-nut Palm??? No the best example.
A: Thank you for comment. We had I investigated changes of phytohormones levels during different fruit-drop periods in apple-tree. Same tendencies were identified in Betel – nut palm. It’s a distal plant from apple-tree, but probably physiological processes and mechanisms during fruit drop are similar. Anyway, in this part example of Betel-nut palm was deleted.
R:L74 water stress only accentuates fruitlet abscission and selection of the fittest, but June drop based on seed number of other factors will happen even under the best grwowing conditions. Again you are misleading readers.
A: Thank you for comment. In this section, we want to explain that different varieties differ in the nature of their yield self-regulation. The line you mention does not refer to all varieties in general, but only to those with fewer seeds. They are more susceptible to environmental stress like drought than varieties with more seeds. This suggests that there are different mechanisms of yield self-regulation.
R:L82-85. Preharvest drop has nothing to do with the subject you have to develop. I am afraid you are mixing postbloom drops with preharvest drop in almost ripen fruit. They have little in common.
A: Thank you for comment. This is general information about fruit drop and different periods. Our aim is not to elucidate the factors that cause fruit drop, but to elucidate the processes and mechanisms during them, whether it is June drop or pre-harvest. In each case, the same physiological process takes place.
R:L92. Buds rarely fall. When they do, it is because lack of chilling requirements, and this has nothing to do with the subject you are developing.
A: Thank you for comment. Word buds was deleted.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
I am very glad that my suggestions were useful during improving of your manuscript. In my opinion corrections you did are sufficient and in terms of substantative content the article is ready to proceed in next steps of publishing process.
Regards,
Author Response
Dear Reviewer,
thank you for your time and your comments, we are waiting for further steps from journal.
