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Peer-Review Record

Supplementary Light Source Affects Growth and Development of Carnation ‘Dreambyul’ Cuttings

Agronomy 2020, 10(8), 1217; https://doi.org/10.3390/agronomy10081217
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Agronomy 2020, 10(8), 1217; https://doi.org/10.3390/agronomy10081217
Received: 22 July 2020 / Revised: 14 August 2020 / Accepted: 17 August 2020 / Published: 18 August 2020
(This article belongs to the Section Horticultural and Floricultural Crops)

Round 1

Reviewer 1 Report

This manuscript describes an experiment to test several very practical potential improvements for the asexual propagation of a commercially important horticultural crop. The hypothesis that supplemental light could improve the rate and quality of rooted cuttings is very reasonable, considering what is known about the value of light for plants as an energy source and a source of developmental signals. 

The authors have been very thorough in comparing the health of the cuttings in many different ways. 

My main concern is that it is not possible, using this study, to differentiate between the value of increasing the quality or quantity of light vs. increasing the temperature of the cuttings. My guess would be that both modes of action are at work. It is particularly striking that MH appears to increase stomatal conductance, which would normally result in canopy cooling, yet also increases canopy (and soil) temperature. 

As MH lights might be a cost efficient method for warming seedlings, the results are valid from the perspective of growers. However, from a scientific standpoint, it should be pointed out that additional experiments are needed in which plant temperature is controlled and only the light levels are manipulated. 

The authors discuss the role of temperature in the discussion and attempt to show that LED lighting slightly outperforms HPS despite having lower seedling temperatures. This observation is made to show that plant temperature and performance are not always correlated. However, while it may prove to be true that the warming effect of supplemental light is a minor contributor to improved rooting success, this line of argument is weak, given the current data. It is not at all clear that plant temperatures of HPS and LED are statistically different from each other. 

Because the experiment was designed with a classic treatment structure but without (it turns out), adequate controls, a better approach to this problem would be to include plant temperature, plant interception of various wavelengths of light (or ratios of wavelengths) as possible explanatory variables in a "data mining" type of analysis where treatments are ignored and a "decision tree" (or "forest") approach is used to partition the variance between candidate variables. However, it is possible that the number of independent observations of plant temperature, blue-light absorbance, etc. are too few for this kind of approach.

At the minimum, it seems necessary to me to state in the conclusion (and in the abstract) that supplemental lighting are effective but that it can not be determined if other forms of supplemental energy input (e.g. heaters) would also have been equally effective. 

Overall, this is a useful study and I look forward to seeing follow-up studies that clarify the role of heat vs. light. 

 

Minor points: 

  1. Line 104. Please clarify if the supplemental lighting was on during these temperature measurements. The statement "at the end of the experimental period" makes it uncertain if the experimental lighting was being used at that time. 
  2. Line 108. Please define TTC. This abbreviation is defined, but not until much later in the manuscript.
  3. Line 291. The word "discrete" should be replaced with the words "differentiate between" or "discriminate between"

Author Response

Point 1: Line 104. Please clarify if the supplemental lighting was on during these temperature measurements. The statement "at the end of the experimental period" makes it uncertain if the experimental lighting was being used at that time.

Response 1: The supplementary light was on during these temperature measurements. I have rewritten this part to make the description clearer.

Point 2: Line 108. Please define TTC. This abbreviation is defined, but not until much later in the manuscript.

Response 2: The full name of TTC has been added.

Point 3: Line 291. The word "discrete" should be replaced with the words "differentiate between" or "discriminate between"

Response 3: The word ‘discrete’ has been replaced with the words ‘determine’.

 

Reviewer 2 Report

The English grammar could be improved. I give an example by rewriting the Abstract.

In Methods it is hard to tell how the experiment was set up. Was there more than one replicate of each light treatment. If there was only one replicate, then this experiment needs to be redone again. How do the authors prevent light from one treatment from interacting with another?

Abstract: Carnation (Dianthus caryophyllus L.) is a major floricultural crop, cultivated widely for cut flowers. This study was conducted to determine the optimal supplementary light source for propagation of carnation ‘Dreambyul’ cuttings. Terminal cuttings were propagated in a glasshouse with an average of 260 μmol·m-2·s-1 photosynthetic photon flux density (PPFD) coming from the sun (the control), supplemented with one of three artificial light sources: mixed (red: blue: white 6: 1: 1) light-emitting diodes (LED-mix), metal halide (MH) lamps, or high-pressure sodium (HPS) lamps. The supplementary light was provided from 7:00 to 17:00 hr at 100 μmol·m-2·s-1 PPFD during propagation. The cuttings were kept on a fogged bench in a glasshouse for 25 days with 24/15 ℃ day/night temperatures and 88% relative humidity. Compared with the control, better root formation was observed from cuttings grown under supplementary lights after 10 days. After 25 days of propagation, MH significantly increased root length, root number, root fresh and dry weights, and shoot biomass, shoot length, and shoot fresh and dry weights. The best root ball formation and the highest root activities were also found in cuttings propagated with supplementary MH light. Supplementary light increased plant temperature, quantum yield, stomatal conductance, and the contents of chlorophyll, soluble proteins, and carbohydrates. Overall, the root formation and development of carnation ‘Dreambyul’ cuttings were significantly promoted by the three supplementary light sources. Of the three, MH was identified as the optimal supplementary light source.

Line 34 35 change to ‘The economic value of ornamental plants has increased significantly worldwide, by 8–10% annually [1].

Line 39 40 change to ‘Vegetative propagation is common and rapid for several ornamental plant species. It retains the genetic traits of stock plants by creating clones with the same characteristics [5].’

Line 48 49 change to ‘carnation cuttings during propagation.’

Line 54 55 change to ‘Supplementary light is the only way to’

Line 57 What is meant by ‘can reduce the adverse possessions of layered materials and frames’?

Line 67 change to ‘commonly applied in greenhouse horticulture’

Line 79 Why do you say ‘for three months’ when the experiment was for 25 days?

Line 108 What is TTC?

Line 147 change to ‘The cuttings were placed in liquid N2 in a -80 ºC refrigerator for further analysis.

Figure 2 and Table 2 are placed on top of each other on page 5 of the manuscript.

Table 2. Use ‘Number of roots’ rather than ‘No.’

Line 200 201 change to ‘The plant temperature was increased significantly by the supplementary light, and differences were observed among different supplementary light sources.’

Line 259 260 change to ‘lamps strongly enhanced the rooting of carnation ‘Dreambyul’. All of the cuttings grown with supplementary MH lighting rooted, and cuttings exposed to LED-mix and HPS rooted at a lower’

Line 284 change to ‘Rooting of Tsuru-rindo’

Line 288 use ‘observations’ not ‘explorations’

Line 291 ‘used extensively to determine living and lifeless roots, and vitality in plant’

Line 305 insert ‘system’ after ‘PSII’

Line 306 308 change to ‘conditions. When the Fv/Fm value of plants is below this range, the plant is exposed to environmental stresses [51].’

Line 313 change to ‘a healthy range’

Line 314 316 change to ‘The average daily light intensity of control (sunlight) and supplementary light, 260 and 360 μmol·m-2·s-1 PPFD, respectively, were lower than that in the growing season.

Line 341 342 change to ‘The trends in soluble proteins and carbohydrates in the cuttings were similar to those of root biomass and root activities’

Line 355 357 change to ‘The MH supplementary light was found to be the best to increase shoot and root biomass, as well as accelerating root formation.’

Check for typos in the References.

Author Response

Point 1: Line 104. Please clarify if the supplemental lighting was on during these temperature measurements. The statement "at the end of the experimental period" makes it uncertain if the experimental lighting was being used at that time.

Response 1: The supplementary light was on during these temperature measurements. I have rewritten this part to make the description clearer.

Point 2: Line 108. Please define TTC. This abbreviation is defined, but not until much later in the manuscript.

Response 2: The full name of TTC has been added.

Point 3: Line 291. The word "discrete" should be replaced with the words "differentiate between" or "discriminate between"

Response 3: The word ‘discrete’ has been replaced with the words ‘determine’.

 

Round 2

Reviewer 2 Report

The authors responded to all of my comments on their paper. It is ready for publication after responding to one or two other comments.

Line 55 delete ‘Thereby’

Line 87 change to ‘as supplementary light sources,’

Line 136 137 do not put in parentheses ‘The chlorophyll content was expressed as mg of chlorophyll per g of fresh leaf weight. V is the volume of the extract solution.’

Line 146 change to ‘had formed a well-developed root ball that was easily pulled out of the plug tray.’

Author Response

Point 1: Line 55 delete ‘Thereby’

Response 1: It has been deleted according to the suggestion.

Point 2: Line 87 change to ‘as supplementary light sources,’

Response 2: It has been changed according to the suggestion.

Point 3: Line 136 137 do not put in parentheses ‘The chlorophyll content was expressed as mg of chlorophyll per g of fresh leaf weight. The V is the volume of the extract solution.’

Response 3: It has been modified according to the suggestion.

Point 4: Line 146 change to ‘had formed a well-developed root ball that was easily pulled out of the plug tray.’

Response 4: It has been changed according to the suggestion.

Thank you very much for your kind reading and review of the manuscript.

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