Assessing Fruit Maturity and Quality of ‘Buckeye Gala’ Grown on a Diverse Panel of Apple (Malus domestica Borkh.) Rootstocks in Western Maryland
Round 1
Reviewer 1 Report
Dear Authors,
Considering rootstocks are a key component of apple production systems and can significantly influence scion cultivar physiology and there is limited information about rootstock effects on maturity and quality of apples grown in Western Maryland, this study is very important. On the other hand, although there are several reports on the effects of rootstocks on apple maturity and quality characteristics, the results are inconsistent from site to site and/or for different scion cultivars. In the present study indicated that a general trend for delayed fruit maturity, lower fruit weight and higher yield with increasingly vigorous rootstocks. Consequently, authors noted that rootstock impact must be considered when making preharvest and postharvest management decisions in ‘Buckeye Gala’ fruit grown under Western Maryland conditions.
Manuscript overall is pretty well written but the abstract needs some improvement. In addition, I suggest that the conclusions section be presented as more scientific outputs rather than the results given in the findings. Because what is written in this section has already been read in the results, therefore the conclusions section no needs to be rewritten. After these revisions, I think the manuscript can be published.
English Language mistakes are very few.
Author Response
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
Manuscript overall is pretty well written but the abstract needs some improvement. In addition, I suggest that the conclusions section be presented as more scientific outputs rather than the results given in the findings. Because what is written in this section has already been read in the results, therefore the conclusions section no needs to be rewritten. After these revisions, I think the manuscript can be published.
We thank the reviewer for the comment. We have rewritten both, the abstract and the conclusion as suggested.
Reviewer 2 Report
The manuscript was reviewed. It describes the influence of 10 rootstock varieties on the horticultural performance and fruit quality of 'Buckeye Gala' apple in western Maryland.
In general, the manuscript is well written. I have some major concerns:
1) Size of the experiment is small and all of them have been already studied.
2) How those varieties were obtained? classical breeding or mutations?
3) Statistical analysis not apropriate for the nature of data
a) Adjunt a GLMM to include random variable "Season" (year) and blocking factor
b) Delete LDA and improve writing of PCA results. Both yielded equivalent results (two fancy ways to show the same). However, PCA is more appropiate for small data set, like yours.
4) Discussion section is too large for the size of your results. Highlight only the most relevant results, those that, in your thinkning, contribute to fill some possible gaps in the knowledge.
More detailed suggestions are given in the attached file.
Comments for author File: 
Comments.pdf
Author Response
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below, as well as in the attachment (pdf file with responses to each one of your valuable comments). Additionally, all the corresponding revisions/corrections highlighted/in track changes can be found in the re-submitted files.
In general, the manuscript is well written. I have some major concerns:
- Size of the experiment is small and all of them have been already studied.
We thank the reviewer for the comment. We respectfully disagree with the reviewer as this type of study has not been conducted under Western Maryland conditions before, and particularly using ‘Buckeye Gala’ as a scion cultivar. Additionally, this study is including rootstock genotypes that have not yet been reported in the literature (NZ.1, NZ.2) before. This number of replications and number of trees per replication are very usual in this type of studies (e.g. Lordan, J., Fazio, G., Francescatto, P., & Robinson, T. L. (2019). II. Horticultural performance of ‘Honeycrisp’grown on a genetically diverse set of rootstocks under Western New York climatic conditions. Scientia Horticulturae, 257, 108686).
- How those varieties were obtained? classical breeding or mutations?
We thank the reviewer for the question. These rootstock genotypes were obtained mainly by classical breeding, and the M.9 is mainly sport mutations.
- Statistical analysis not apropriate for the nature of data
- a) Adjunt a GLMM to include random variable "Season" (year) and blocking factor
We thank the reviewer for the comment and this analysis was included as suggested.
- b) Delete LDA and improve writing of PCA results. Both yielded equivalent results (two fancy ways to show the same). However, PCA is more appropiate for small data set, like yours.
We thank the reviewer for the comments. We decided to conduct and keep both PCA and LDA, as first, they support the consistency of our results (we think it is positive and important to show that both analyses are consistent using the same dataset), and secondly because conducting an LDA allows us to better distinguish and define the statistically significant number of clusters into which the 10 assayed rootstocks were classified, as compared to PCA, and this is an important target for our research. LDA is a supervised dimensionality reduction technique that simultaneously achieves classification of the data, while PCA is an unsupervised dimensionality technique that ignores the class label. There are several papers that have used both approaches with consistent results between them and with small and large datasets (e.g., Ren, Y., Ramaswamy, H. S., Li, Y., Yuan, C., & Ren, X. (2018). Classification of impact injury of apples using electronic nose coupled with multivariate statistical analyses. Journal of Food Process Engineering, 41(5), e12698; Wu, X., Wu, B., Sun, J., Li, M., & Du, H. (2016). Discrimination of apples using near infrared spectroscopy and sorting discriminant analysis. International Journal of Food Properties, 19(5), 1016-1028).
4) Discussion section is too large for the size of your results. Highlight only the most relevant results, those that, in your thinkning, contribute to fill some possible gaps in the knowledge.
We thank the reviewer for the comments. We tried to reduce the size of the discussion section as best as we could, trying to also incorporate the comments from other reviewers.
More detailed suggestions are given in the attached file.
We thank the reviewer for the comments, and all the suggestions were answered and incorporated in the attached file (please see attached file).
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors investigate the effects of root stock genotype on fruit quality. This is an important gap in our understanding of factors that influence fruit quality. The experimental design is good, but the number of fruit used to estimate various fruit quality parameters is a bit small. I also have some concerns about the apparent confounding issue of finding differences in fruit maturity, when all fruit were monitored in order to pick them at optimal commercial maturity. It seems that this could be a sampling bias.
The quality of writing is good, and the figures appropriate and clear, yet the results indicate contrasts of maturity, and unless the authors carefully accounted for this, the differences may have been introduced.
This is not an easy project to do, but claims about the rootstock effect on maturity could be accounted for by multiple harvests, or standardized pick dates DAFB (or by other estimates of commercial harvest. Certainly, picking the fruit form different treatments at different times is not appropriate (the passage in the materials methods is ambiguous).
If this was not done, was a check treatment used as a standard? That is, was just one variety monitored for advancing maturity, and then all treatments were picked at the time of commercial maturity for the check?
The differences here seem to be related exclusively to differences in maturity. It would help the reader to see the trees, namely because (as the authors indicate ay line 386) the canopy density/structure can influence fruit maturity.
The authors carefully qualify that the results are relevant to conditions in Maryland, which is appropriate. However, the authors could improve the manuscript to discuss the growing conditions, and even speculate a bit about how this information could be transferred to the major production regions for Gala (i.e. the PNW) which have a very different climate.
In the very least, the authors could suggest specific experiments that could help make these results more transferrable, rather than the generic "... needs to be further investigated."
At line 464, the authors state that at harvest fruit flesh firmness impacts fruit softening ability.
Then, further on, they state these differences may be noticed by consumers... a large proportion of Gala apple fruit are stored for months, and fruit texture changes during that time. Furthermore, fruit firmness can decline at different rates during the postharvest period depending on numerous variables. Addressing this, either by acknowledging that at-harvest fruit quality and postharvest fruit quality likely differ, or finding some supporting literature will help contextualize the results.
Besides some needed clarification, the manuscript is well written.
Author Response
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
This is not an easy project to do, but claims about the rootstock effect on maturity could be accounted for by multiple harvests, or standardized pick dates DAFB (or by other estimates of commercial harvest. Certainly, picking the fruit form different treatments at different times is not appropriate (the passage in the materials methods is ambiguous). If this was not done, was a check treatment used as a standard? That is, was just one variety monitored for advancing maturity, and then all treatments were picked at the time of commercial maturity for the check?
We thank the reviewer for the comment. We used rootstock M9.T337 as reference rootstock for defining harvest time for all assayed genotypes (they were all harvested at the same time). We clarified this in the manuscript: “We used ‘Buckeye Gala’ fruit grafted on M9.T337 as reference rootstock for defining harvest time for all assayed genotypes.”
The differences here seem to be related exclusively to differences in maturity. It would help the reader to see the trees, namely because (as the authors indicate ay line 386) the canopy density/structure can influence fruit maturity.
We thank the reviewer for the suggestion. Unfortunately, we do not have any pictures of each of the rootstocks with fruit on them. We recognize this is a mistake and we will make sure to document with pictures any future studies of this type (we didn’t consider it as we have not seen these types of studies including pictures of the trees). All trees are trained in the same way, as indicated in the manuscript.
The authors carefully qualify that the results are relevant to conditions in Maryland, which is appropriate. However, the authors could improve the manuscript to discuss the growing conditions, and even speculate a bit about how this information could be transferred to the major production regions for Gala (i.e. the PNW) which have a very different climate.
In the very least, the authors could suggest specific experiments that could help make these results more transferrable, rather than the generic "... needs to be further investigated."
We thank the reviewer for the comment and we have modified the text as suggested: “However, the resulting clustering of ‘Buckeye Gala’ fruit may be only applicable for fruit grown under Western Maryland hot and humid conditions. Thus, this study needs to be replicated in major production regions of ‘Gala’ with different environmental conditions, such as the Pacific Northwest (hot and dry climate), to assess the transferability of these results between regions”.
At line 464, the authors state that at harvest fruit flesh firmness impacts fruit softening ability.
Then, further on, they state these differences may be noticed by consumers... a large proportion of Gala apple fruit are stored for months, and fruit texture changes during that time. Furthermore, fruit firmness can decline at different rates during the postharvest period depending on numerous variables. Addressing this, either by acknowledging that at-harvest fruit quality and postharvest fruit quality likely differ, or finding some supporting literature will help contextualize the results.
We thank the reviewer for the comment and we have modified the text as suggested: “The differences in flesh firmness detected in this study may be noticeable by consumers at- harvest, as it has been reported that consumers can detect differences in firmness that are greater than 6N [73]. However, these differences might not be maintained in fruit after postharvest storage, as has been shown in previous studies [14]. Fruit texture, and overall quality, is affected by numerous variables during storage [74] that have not been accounted for in this study, but are currently under investigation”.
Reviewer 4 Report
The importance of grafting studies on vegetables and fruits has increased in recent years. Rootstocks are mostly used for yield and quality increase and biotic and abiotic stress tolerance. Grafting and rootstock use are also common in apple, one of the most important horticultural crops in the world. In this study, rootstock performance of 10 different rootstock cultivars and cultivar candidates were determined. For this purpose a kind of pen was used. It is important that the study includes two years of data. In addition, the study methodology is scientific. As a result of the study, important results have emerged in terms of agriculture. However, I have made the following observations regarding this article:
1-A cultivar of scion was used in the study. In fact, the use of more than one type of scion in such studies, even the use of ungrafted scion plant data will reveal more scientific data. Some cultivar of scion was used in this manuscript. Information about why this cultivar of scion (Buckeye Gala) is preferred should be added.
2- It was stated that the study was performed in 5 replications and measurements were made on 5 plants in each replication. However, the information given in the table explanations is different from this. If 5 samples are measured, this number will not give reliable statistical results. n=5/25 ? issue should be clarified.
3- I suggest checking statistics. It has been stated that the Tukey test is used in statistics. However, no information was given about whether the data were normally distributed or not. Tukey test is not suitable if the data is not normally distributed.
4-I suggest checking the results of the correlation analysis. Correlation was detected in all the parameters except one, and even the correlation values were high in almost all of them. These data are inconsistent with the literature. If there are studies that match, they should be cited. The p values obtained as a result of the correlation analysis should be checked again. If necessary, these data should be presented in tabular form.
5-There are errors in some references. Reference number 10 of the references in line 34 does not match the content of the sentence. There is no information about grafting in this article. The reference spelling on line 34 to the wool is incorrect. It can be written as [4–16]. Reference spelling on line 379 should be corrected, the order is incorrect.
6-A dot should be added to the name of the author given in the title and abstract. "Borkh." should be in the form.
7-On line 149. sentence is the result sentence. This should be written in the results section, not the method section. Also, the p value information in this sentence should be corrected. p>0.05 should be.
8-Some corrections should be made in the reference list. Species names on lines 600, 610 and 691 should be written in italics.
9-Apart from these, there are some minor typos. Spelling error “M.9T337and” on line 88. Line 313, the letter P should be written in lowercase.
In conclusion: it is clear that this study has very important results in terms of fruit growing. I recommend that this article be accepted after corrections and validation of correlation analyzes.
Author Response
Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.
1-A cultivar of scion was used in the study. In fact, the use of more than one type of scion in such studies, even the use of ungrafted scion plant data will reveal more scientific data. Some cultivar of scion was used in this manuscript. Information about why this cultivar of scion (Buckeye Gala) is preferred should be added.
We thank the reviewer for the comment. As indicated, we added the reason why this scion cultivar was selected: “In terms of apple scions, ‘Gala’ is one of the most planted cultivars worldwide. In areas such as Western Maryland, where climatic conditions are not ideal for suitable red color development at harvest, the use of strains such as ‘Buckeye Gala’ has been widely adopted due to their enhanced red skin coloration [47]”.
2- It was stated that the study was performed in 5 replications and measurements were made on 5 plants in each replication. However, the information given in the table explanations is different from this. If 5 samples are measured, this number will not give reliable statistical results. n=5/25 ? issue should be clarified.
We thank the reviewer for the comment. We assessed 5 replications of 3 trees each, totaling 15 trees evaluated. Our ‘n’ corresponds to the number of replications that we have, which is n=5. We clarified this in the “Plant Material” section of the manuscript: “….. with a total of five three-tree replicates per each rootstock genotype (therefore a total of 15 trees per rootstock)”. This number of replications and number of trees per replication are very usual in this type of studies (e.g. Lordan, J., Fazio, G., Francescatto, P., & Robinson, T. L. (2019). II. Horticultural performance of ‘Honeycrisp’grown on a genetically diverse set of rootstocks under Western New York climatic conditions. Scientia Horticulturae, 257, 108686).
3- I suggest checking statistics. It has been stated that the Tukey test is used in statistics. However, no information was given about whether the data were normally distributed or not. Tukey test is not suitable if the data is not normally distributed.
We thank the reviewer for the comment. We did check for normality and thus clarified in the manuscript that the data was effectively normally distributed by adding the sentence: “The data met normality assumptions”.
4-I suggest checking the results of the correlation analysis. Correlation was detected in all the parameters except one, and even the correlation values were high in almost all of them. These data are inconsistent with the literature. If there are studies that match, they should be cited. The p values obtained as a result of the correlation analysis should be checked again. If necessary, these data should be presented in tabular form.
We thank the reviewer for the comment. As suggested by the reviewer we checked the results of the correlation analysis and these did not change, thus validating the results. All correlations are significant (*, p£0.05) as stated in the Table, except for SSC.
The lack of correlation between SSC and starch is addressed in the discussion and we also added a sentence explaining the lack of correlation of SSC with most of the assessed variables: “The lack of significant correlations of SSC with other variables in this study could be due to the particular environmental conditions of Western Maryland.”
We think that it cannot be expected that all correlations obtained are consistent with literature as we are testing different rootstocks and under unique environmental conditions.
Furthermore, we added a citation supporting the negative correlation between fruit weight and TCA/yield: “This is also supported by supports the negative correlation obtained between fruit weight and both TCA and yield, in this work and agrees with previous studies [32].”
Furthermore, many of the correlations obtained in our study are consistent with literature and this is mentioned throughout the discussion with citations, as for example:
“…..the positive correlations of IEC with fruit weight, skin blush and SPI, as well as the negative associations of IEC with flesh firmness, TA, skin and flesh hue angle and index of absorbance difference (IAD), are in agreement with other studies [24,55] and are indicative of IEC promoting an increase in fruit maturity”.
“Studies reporting that scion cultivars grafted in dwarfing rootstocks have an advanced fruit maturity as compared to vigorous rootstocks [30,54,64] are consistent with our findings, and support the negative correlation obtained between IEC and both TCA and yield”.
“These results support the significantly negative correlations between IAD and IEC obtained for fruit in all trees on all assessed rootstocks in this work, and is consistent with other studies in apples [55] and peaches [24,51]”.
“Consistent with the positive correlation obtained between TCA and yield with flesh firmness in this study, higher flesh firmness in ‘Gala’ fruit from grafted in the more vigorous rootstocks such as M.26 as compared to the dwarfing G.41, has been reported [14]. These results can be partially explained by the higher IEC displayed by fruit from dwarfing rootstocks, as a negative correlation between IEC and flesh firmness has been widely shown in different fruit [19,21,24,69,70]. Furthermore, the negative correlation between flesh firmness and fruit weight obtained in this study agrees with previous authors assessing effects of different apple rootstocks on various apple scion cultivars, including ‘Gala’ [26,32,33,40,55]. Additionally, the higher flesh firmness displayed by fruit grafted in the more vigorous and higher yielding rootstocks in this work can also be supported by their higher IAD values, as a positive correlation between these parameters is consistent with studies in apples [55] and peaches [24,71,72]”.
5-There are errors in some references. Reference number 10 of the references in line 34 does not match the content of the sentence. There is no information about grafting in this article. The reference spelling on line 34 to the wool is incorrect. It can be written as [4–16]. Reference spelling on line 379 should be corrected, the order is incorrect.
We thank the reviewer for the comment, and this was modified as suggested.
6-A dot should be added to the name of the author given in the title and abstract. "Borkh." should be in the form.
We thank the reviewer for the comment, and this was added as suggested.
7-On line 149. sentence is the result sentence. This should be written in the results section, not the method section. Also, the p value information in this sentence should be corrected. p>0.05 should be.
We thank the reviewer for the comment, and this was modified as suggested.
8-Some corrections should be made in the reference list. Species names on lines 600, 610 and 691 should be written in italics.
We thank the reviewer for the comment, and this was modified as suggested.
9-Apart from these, there are some minor typos. Spelling error “M.9T337and” on line 88. Line 313, the letter P should be written in lowercase.
We thank the reviewer for the comment, and this was modified as suggested.
