Growth Promotion of Guava “Pear” (Psidium guajava cv.) by Sinorhizobium mexicanum in Southern Mexican Agricultural Fields

Round 1

Reviewer 1 Report

 

1.    What does PGPB stand for? Please write down when it first appears!

2.    Method must be improved; for example, how many doses of triple 17, diammonium phosphate, and nitrabor were applied?

3.    This statement “The treatment formulated with S. mexicanum ITTG-R7T, Triple 17, Diammonium phosphate, and Nitrabor had the highest positive effect on the plant total height (331.5 cm), foliar cover (532.5 cm), basal diameter (108.33 cm), number of flowers (30), number of fruits (62), and chlorophyll content (3.49 mg mL-1) compared with the rest of the treatments” (line 201-206),  does not match the data and statistical analysis in table 1.  All parameters are not significant to T4 (except for chlorophyll content). So, the positive effect of ITTG-R7 is still in big question.

4.    Your data shows something different, that chemical fertilizer treatment (Triple 17 + Diammonium phosphate + Nitrabor) increased guava growth both with S. mexicanum ITTG-R7 (T1) and without S. mexicanum ITTG-R7 (T4). There is no significant difference in the effect of T1 with T4, so the role of your PGPB is still a big question. Follow this statement: "Means followed by the same letter are non-significant", so AB = B = A

5.    The statement on discussion lines 242-243 “The strongest positive effect in guava was with the inoculation of ITTG-R7T mixed with chemical nutrients” is not agree with the result (Tabel 1) as mentioned in point no. 4 above.  Your data shows something different, that chemical fertilizer treatment (Triple 17 + Diammonium phosphate + Nitrabor)  increased guava growth both with S. mexicanum ITTG-R7 (T1) and without S. mexicanum ITTG-R7 (T4). There is no significant difference in the effect of T1 with T4, so the role of your PGPB is still a big question.  Follow this statement: "Means followed by the same letter are non-significant",  so AB = B = A

6.    This statement “The superior effect obtained by S. mexicanum  ITTG-R7T compared with A. brasilence CD can be attributed to the fact that ITTG-R7T is a native strain, adapted to the environmental conditions of  the area” (lines 255-258)  does not agree with the data and statistic analysis in Table 1. Your data show that the effect of T1 (S. mexicanum ITTG-R7) treatment was not significantly different from the effect of T3 (A. brasilense CD) treatment except for the Basal Diameter.

7.    So, your claim that "Our new findings on an outstanding Sinorhizobium strain and its promotion of guava growth would provide support for new agricultural practices for fruit producers in areas of low income and poorly developed agriculture" (lines 268-271) is not acceptable.

8.    So, based on the comments on points 3-7 above, your conclusion “It stands out that the use of this strain as an agricultural bioinoculant can reduce the use of chemical fertilizers” (lines 322-323) cannot be accepted because it is not supported by data and statistical analysis.

 

1 

Comments for author File: Comments.pdf

Author Response

(Reviewer 1)

Comments and Suggestions for Authors

 

Manuscript Number: Sustainability-1899766

Title: Growth Promotion of Guava “pear” (Psidium guajava cv.) by Sinorhizobium mexicanum in Southern Mexican Agricultural Fields

 

We appreciate the reviewer's observations and comments to our work. We have carefully reviewed the manuscript and made the modifications suggested by the reviewer for a better understanding.

Point 1.    What does PGPB stand for? Please write down when it first appears!

Response 1: PGPB stands for Plant Growth Promoting Bacteria. At the beginning of the document, we have written the meaning of these words.

Point 2.    Method must be improved; for example, how many doses of triple 17, diammonium phosphate, and nitrabor were applied?

Response 2: We agree with the reviewer. In the M&M section, we have added more information on the application of chemical fertilizer. The treatments were applied in ring method 70 cm away from tree trunk. Every 3 months, the plants were inoculated, over an experimental period of 9 months. “In the same way, triple 17 fertilizer, diammonium phosphate and nitrabor were applied to the plants using a fertigation system and according to the phytotechnical procedure used by the farmer”.

Point 3.    This statement “The treatment formulated with S. mexicanum ITTG-R7T, Triple 17, Diammonium phosphate, and Nitrabor had the highest positive effect on the plant total height (331.5 cm), foliar cover (532.5 cm), basal diameter (108.33 cm), number of flowers (30), number of fruits (62), and chlorophyll content (3.49 mg mL-1) compared with the rest of the treatments” (line 201-206),  does not match the data and statistical analysis in table 1.  All parameters are not significant to T4 (except for chlorophyll content). So, the positive effect of ITTG-R7 is still in big question.

Response 3: We agree with the reviewer. In the results section, at the point 3.5. “Effect of bacterial inoculation in Guava development”. Line 201-206, we have correctly written the results indicated in Table 1. We reviewed the statistical data analysis (ANOVA and Tukey's test) and now the results are presented with higher quality for better understanding.

Point 4.    Your data shows something different, that chemical fertilizer treatment (Triple 17 + Diammonium phosphate + Nitrabor) increased guava growth both with S. mexicanum ITTG-R7 (T1) and without S. mexicanum ITTG-R7 (T4). There is no significant difference in the effect of T1 with T4, so the role of your PGPB is still a big question. Follow this statement: "Means followed by the same letter are non-significant", so AB = B = A

Response 4: We agree with the reviewer.We have carefully reviewed the results related to the effect of the inoculation of the bacterial strain S. mexicanumin guava plants. In particular, we reviewed the statistical data analysis and correctly wrote the results shown in Table 1. Based on the Tukey mean comparison analysis, the effect of the treatments is explained following the reviewer's recommendations on the level of significance (p<0.05) between the means of the treatments evaluated for each variable studied. We believe that now the results are explained in a better way

Point 5.    The statement on discussion lines 242-243 “The strongest positive effect in guava was with the inoculation of ITTG-R7T mixed with chemical nutrients” is not agree with the result (Tabel 1) as mentioned in point no. 4 above.  Your data shows something different, that chemical fertilizer treatment (Triple 17 + Diammonium phosphate + Nitrabor)  increased guava growth both with S. mexicanum ITTG-R7 (T1) and without S. mexicanum ITTG-R7 (T4). There is no significant difference in the effect of T1 with T4, so the role of your PGPB is still a big question.  Follow this statement: "Means followed by the same letter are non-significant”, so AB = B = A

Response 5: We agree with the reviewer. We modify the entire result paragraph in this section and rewrite the results with better quality. We reviewed the analysis of the Tukey comparison of means and followed the reviewer's recommendation regarding the correct use of significance levels in the means of the treatments evaluated for each study variable. We hope that this new wording of results responds to the reviewer's observation.

Point 6.    This statement “The superior effect obtained by S. mexicanum  ITTG-R7T compared with A. brasilence CD can be attributed to the fact that ITTG-R7T is a native strain, adapted to the environmental conditions of  the area” (lines 255-258)  does not agree with the data and statistic analysis in Table 1. Your data show that the effect of T1 (S. mexicanum ITTG-R7) treatment was not significantly different from the effect of T3 (A. brasilense CD) treatment except for the Basal Diameter.

Response 6: We agree with the reviewer. We have reviewed this section of the document and provided more information on the results so that there is more relationship with the affirmation of the effect of bacterial strains on guava cultivation.

Point 7.    So, your claim that "Our new findings on an outstanding Sinorhizobium strain and its promotion of guava growth would provide support for new agricultural practices for fruit producers in areas of low income and poorly developed agriculture" (lines 268-271) is not acceptable.

Response 7: We agree with the reviewer. We have deleted the following sentence “Our new findings on an outstanding Sinorhizobium strain and its promotion of guava growth would provide support for new agricultural practices for fruit producers in areas of low income and poorly developed agricultura and now we have added the following paragraph: Considering the PGPB multifunctional qualities observed in the S. mexicanum ITTG-R7^Tstrain (such as N₂fixation, phosphate solubilization, auxin synthesis, among others) and based on the results obtained from the inoculation test, the use of this bacterium can represent an efficient, simple and low-cost agrobiotechnological alternative for fruit producers in areas of low income and poorly developed agriculture.

Point 8.    So, based on the comments on points 3-7 above, your conclusion “It stands out that the use of this strain as an agricultural bioinoculant can reduce the use of chemical fertilizers” (lines 322-323) cannot be accepted because it is not supported by data and statistical analysis.

Response 8: We agree with the reviewer.We have modified this sentence. We wrote the following conclusion: “It is highlighted that the use of this strain as biofertilizer can contribute to the growth of guava plants and the quality and health of the soil. Likewise, the combination of biofertilizers formulated with S, mexicanum and nitrogenous fertilizers showed important effects on plant growth, which is interesting for the formulation of nutrients with greater efficiency for this type of fruit crops”.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments to the Authors

Manuscript Number: Sustainability-1899766

Title: Growth Promotion of Guava “pear” (Psidium guajava cv.) by Sinorhizobium mexicanum in Southern Mexican Agricultural Fields

 Major comments:

1. The completeness of the Abstract is not enough. Generally, the Abstract should include the research background, deficiency, methods, results and conclusion; and, the results should include some data results. Regarding this manuscript, the research deficiency is insufficient and the research results need to be improved.

2. The research background of the Introduction should be improved. The authors did not put forward the innovation of this study on the basis of fully summary of the existing researches. i) Why did the authors select the “Sinorhizobium. mexicanum ITTG-R7^T” as PGPB? Due to some special properties, or others? ii) Why was it important for the growth promotion of Guava "pear" plants in Southern Mexican agricultural fields? Was it an important cash crop in local, or others? iii) How did the residents or researchers improve the growth of Guava "pear" plants previously? By chemical fertilizers, or others? What is the current research progress? iv) Has any existing research investigated the PGPB used for the growth promotion of Guava "pear" plants? Please summarize them.

 Minor comments:

Line 16: “PGPB”, “ACC”, etc. Please mark the abbreviation when it first appears.

Line 16-18: Within the Abstract section, the authors mentioned that “the ITTG-R7^T showed different properties as PGPB”, but the results are too general to understand what was special about this PGPB. Please be specific.

Line 18-19: “and when combined with chemical nutrients, had the highest positive effect on the growth and development of guava plants.” This part should be a single sentence. Moreover, the variations of plant growth index should be provided to demonstrate the plant growth promotion ability of ITTG-R7^T.

Line 33: It should be “the production of phytohormones”

Line 34: Delete “to”.

Line 37, 55, 62, 99, 102, 274: “N”, “2100”. “NDVI”, “IAA”, “ACC”, etc. Please do not begin a sentence with the symbol of chemical element, chemical formula or abbreviation as well as the number. Check and correct it throughout the manuscript.

Line 39-41: “The phyla α-Proteobacteria and β-Proteobacteria harbor different bacterial genera collectively called rhizobia, with the ability to fix nitrogen by forming nodules in legumes.” The definition of “rhizobia” is confusing. The essence of rhizobia is “bacterial genera from phyla α-Proteobacteria and β-Proteobacteria”? Or “bacterial genera with the ability to fix nitrogen by forming nodules in legumes”? Please rewrite this part.

Figure 2: Did the “treatments” in figure 2 include the “five treatments”, “T1-T5”? Or, just the treatment of T1? If there were “five treatments”, the authors should distinguish and mark the different treatment places.

Line 170: It should be “(pH, 6.4±0.13)”.

Line 170: “dSm^-1”. What did the “d” mean in this unit?

Line 171-172: “The amount of total N was 0.16±0.05 %, 0.87±0.13 % for organic C content, and a 5.4±2.18 C:N ratio.” This sentence is not clear for me. The expression is confusing.

Figure 3: It was unacceptable that the figure 3 was too blurry. Please improve the figure resolution. Moreover, the readers cannot get any valuable information from figure 3. Please put three sub-figures together.

Line 194: The photo of “solubilization halos” should be provided.

Line 245: “seemingly in relation to the roots produced in response to auxins” This sentence is not clear for me.

Line 282-284: “Some authors have reported that through technological innovations such as satellite information, the average yield of the farmers may be increased.” This sentence is not clear for me.

Line 287: It should be “the accumulation”.

Line 305-307: “we proposed to complement the physicochemical analyses with assessments of the structure and diversity of the bacterial communities present in agricultural soils.” The results of the structure and diversity of the bacterial communities were absent in this study. Please provide them.

Conclusion: Please highlight the important conclusions, and rewrite conclusion section according to the climactic logical relations.

At last, the manuscript needs to be reviewed by an English native speaker since the language should be improved.

Author Response

(Reviewer 2)

Comments and Suggestions for Authors

Manuscript Number: Sustainability-1899766

Title: Growth Promotion of Guava “pear” (Psidium guajava cv.) by Sinorhizobium mexicanum in Southern Mexican Agricultural Fields

We appreciate the reviewer's observations and comments on our work. We have carefully reviewed the manuscript and made the modifications suggested by the reviewer for a better understanding.

 Major comments:

Point 1. The completeness of the Abstract is not enough. Generally, the Abstract should include the research background, deficiency, methods, results and conclusion; and, the results should include some data results. Regarding this manuscript, the research deficiency is insufficient and the research results need to be improved.

Response 1: We agree with the reviewer. We have restructured the abstract and added more information according to the reviewer's suggestion. A brief introduction, objective, methods, results and a brief conclusion have been included.

Point 2. The research background of the Introduction should be improved. The authors did not put forward the innovation of this study on the basis of fully summary of the existing researches. i) Why did the authors select the “Sinorhizobium. mexicanum ITTG-R7^T” as PGPB? Due to some special properties, or others? ii) Why was it important for the growth promotion of Guava "pear" plants in Southern Mexican agricultural fields? Was it an important cash crop in local, or others? iii) How did the residents or researchers improve the growth of Guava "pear" plants previously? By chemical fertilizers, or others? What is the current research progress? iv) Has any existing research investigated the PGPB used for the growth promotion of Guava "pear" plants? Please summarize them.

Response 2: We agree with the reviewer. In the Introduction section, we have provided more information and details on the use of the bacterial strain S. mexicanumand its qualities as PGPB. Also, we added more data to answer the reviewer's questions. At the end of this section we place some background on investigations of the application of PGPB bacterial inoculants in guava crops. We believe that now the introduction has more quality information, which allows a better understanding of the subject.

 Minor comments:

Point 3, Line 16: “PGPB”, “ACC”, etc. Please mark the abbreviation when it first appears.

Response 3: We agree with the reviewer. We have added the meaning of the words PGPB and ACC.  

Plant Growth Promoting Bacteria (PGPB)

ACC (1-aminocyclopropane-1-carboxylate) deaminase

Point 4, Line 16-18: Within the Abstract section, the authors mentioned that “the ITTG-R7^T showed different properties as PGPB”, but the results are too general to understand what was special about this PGPB. Please be specific.

Response 4: We agree with the reviewer. In the introduction, results and discussion section, we have added more information about the PGPB qualities of the ITTG-R7 strain in order to support the comment made in the abstract.

For example, in the introduction we add the following: “From the studies cited above, Sinorhizobium mexicanum ITTG-R7^Tstands out for being the best strain to promote plant growth and to compete in interstrain nodule competition assays [20]. Also, the complete genome sequencing of the strain S. mexicanum ITTG-R7^Thas allowed the identification of a cluster of genes related to the ability to fix N₂, solubilize phosphate, auxin synthesis, and siderophore production [22]. These genomic qualities detected in the strain ITTG-R7^Tled us to determine biochemically the PGPB potential of this sinorhizobian bacterium.

Point 5, Line 18-19: “and when combined with chemical nutrients, had the highest positive effect on the growth and development of guava plants.” This part should be a single sentence. Moreover, the variations of plant growth index should be provided to demonstrate the plant growth promotion ability of ITTG-R7^T.

Response 5: We agree with the reviewer. We modified the sentence and added the following paragraph: “When the ITT-R7^Tstrain was combined with chemical nutrients had the highest positive effect on the growth and development of guava plants. Guava biofertilization with ITTG R7^Thad a significant influence (p<0.05) mainly on the total plant height (368.83 cm), number of flowers (36.0) and the amount of chlorophyll (2.81 mg ml^-1) in comparison with the other treatments evaluated”.

 

Point 6, Line 33: It should be “the production of phytohormones”

Response 6: We appreciate the reviewer's comment. We have changed phytohormones for “the production of phytohormones”.

Point 7, Line 34: Delete “to”.

Response 7: We agree with the reviewer. We have eliminated the word "to"

Point 8, Line 37, 55, 62, 99, 102, 274: “N”, “2100”. “NDVI”, “IAA”, “ACC”, etc. Please do not begin a sentence with the symbol of chemical element, chemical formula or abbreviation as well as the number. Check and correct it throughout the manuscript.

Response 8: Sorry for the inconvenience. We have corrected this grammatical error in lines 37, 55, 62, 99, 102, 274.

Point 9, Line 39-41: “The phyla α-Proteobacteria and β-Proteobacteria harbor different bacterial genera collectively called rhizobia, with the ability to fix nitrogen by forming nodules in legumes.” The definition of “rhizobia” is confusing. The essence of rhizobia is “bacterial genera from phyla α-Proteobacteria and β-Proteobacteria”? Or “bacterial genera with the ability to fix nitrogen by forming nodules in legumes”? Please rewrite this part.

Response 9: We appreciate the reviewer's comment. We have rewritten this paragraph as follows: “The phyla α-Proteobacteria and β-Proteobacteria harbor different bacterial genera, including the Sinorhizobiumgenus. Sinorhizobiumhave the ability to fix nitrogen in symbiosis with leguminous plants”.

Point 10, Figure 2: Did the “treatments” in figure 2 include the “five treatments”, “T1-T5”? Or, just the treatment of T1? If there were “five treatments”, the authors should distinguish and mark the different treatment places.

Response 10: We appreciate the reviewer's observation. In images A and B of figure 2, we show the satellite image of the experimental plot from guava crop where the five treatments were applied. The treatments were applied following a completely randomized design as explained in point 2.6 Experimental Design for Field Inoculationof the M&M section.

Point 11, Line 170: It should be “(pH, 6.4±0.13)”.

Response 11: We agree with the reviewer. We have added the standard deviation in each one of the mean values of the physicochemical parameters evaluated in this work. “The pH was near-neutral [6.4 ±(0.012)] and electrical conductivity (EC) was 0.91±(0.015) dSm-1. The cation exchange capacity (CEC) value was 21.51 ±(0.018) Cmol kg-1. In relation to the fertility parameters N, C and P, it was found that, the amount of total N was 0.16%±(0.020), 0.87%±(0.015) for organic C content. The C:N ratio is considered an important parameter related to soil fertility. In our study, the soil of the guava crop had a low value of C:N ratio (5.4±0.15) according to the Official Mexican Standard NOM-021-SEMARNAT-2000, indicating a rapid mineralization and release of N, which is available for plant uptake”.

Point 12, Line 170: “dSm^-1”. What did the “d” mean in this unit?

Response 12: We appreciate the observation.  dSm^-1= International system of units for the measurement of Electrical Conductivity (EC). The "d" means "decisiemens"

The SI derived unit for electric conductance is the siemens. 1 siemens is equal to 10 decisiemens.

Point 13, Line 171-172: “The amount of total N was 0.16±0.05 %, 0.87±0.13 % for organic C content, and a 5.4±2.18 C:N ratio.” This sentence is not clear for me. The expression is confusing.

Response 13: We agree with the reviewer. We have added more information about the carbon (C)/nitrogen (N) ratio determined in the physicochemical analysis. “The C:N ratio is considered an important parameter related to soil fertility. In this study, the soil of the guava crop had a low value of C:N ratio (5.4±0.15) according to the Official Mexican Standard NOM-021-SEMARNAT-2000, indicating a rapid mineralization and release of N, which is available for plant uptake”.

Point 14, Figure 3: It was unacceptable that the figure 3 was too blurry. Please improve the figure resolution. Moreover, the readers cannot get any valuable information from figure 3. Please put three sub-figures together.

Response 14: We appreciate the reviewer's recommendation. We have increased the quality and resolution of the images in figure 3.

Point 15, Line 194: The photo of “solubilization halos” should be provided.

Response 15: We appreciate the reviewer's recommendation. We have added Figure S1: Phosphate solubilization by Sinorhizobium mexicanumITTG-R7^Tin the supplementary material section.

Point 16, Line 245: “seemingly in relation to the roots produced in response to auxins” This sentence is not clear for me.

Response 16: We agree with the reviewer. We have modified this sentence and added the following text: “Similar effects have been found in guava plants inoculated with Azospirillum brasilense. The auxins produced by the bacteria stimulate the increase in root mass and this improves the efficient use of chemical fertilizers [44]”.

Point 17, Line 282-284: “Some authors have reported that through technological innovations such as satellite information, the average yield of the farmers may be increased.” This sentence is not clear for me.

Response 17: We agree with the reviewer. We changed “Some authors have reported that through technological innovations such as satellite information, the average yield of the farmers may be increased” to “Some authors have reported that through technological innovations such as satellite information, data can be generated in real time, which would allow farmers to make the best decisions for sustainable management of their crops“[53,54].

Point 18, Line 287: It should be “the accumulation”.

Response 18: We agree with the reviewer. we changed “accumulation” to “the accumulation”.

Point 19, Line 305-307: “we proposed to complement the physicochemical analyses with assessments of the structure and diversity of the bacterial communities present in agricultural soils.” The results of the structure and diversity of the bacterial communities were absent in this study. Please provide them.

Response 19: We appreciate the observation of the reviewer. It is a proposal for future research, which will allow us to learn more about the relationship between soil, plant and bacteria and how some physicochemical parameters can define the structure, diversity and abundance of the bacterial community in a fruit crop.

Point 20, Conclusion: Please highlight the important conclusions, and rewrite conclusion section according to the climactic logical relations.

Response 20: We agree with the reviewer. We carefully review the conclusion. We rewrite the conclusion including quality information and with a decisive logical approach

Point 21, At last, the manuscript needs to be reviewed by an English native speaker since the language should be improved.

Response 21: The manuscript has been sent to English language editing by MDPI. We obtained a certificate indicating that the text has been checked for correct use of grammar and common technical terms, and edited to a level suitable for reporting research.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I agree with the corrections and improvements that have been made by the authors.

Reviewer 2 Report

The authors have addressed my earlier concerns, and the paper is now acceptable for publication after a careful proofreading.