Floral Biology and Pollination Efficiency in Yam (Dioscorea spp.)

Round 1

Reviewer 1 Report

The Review article "Floral biology and pollination efficiency in yam (Dioscorea spp.)” written by Jean M. Mondo et al. is an approach to point out the different tested and untested methods, as well as the challenges and also gaps regarding sexual reproduction and breeding systems of yam. The authors focus on the improving of pollination efficiency for developing a protocol that allows for breeding success and may be adapted to certain factors, sites and infrastructure.

The review article is written in a clear manner and the introduction gives a detailed overview of the objectives of the article by highlighting the importance of yam as an important food and income source, especially in West Africa. While yam usually is reproduced throughout a vegetative mode, sexual reproduction via pollination is crucial for cross-breeding and enhance diversity of cultivars. This is important for allow the selection of valuable traits in terms of resistance to pests and diseases and adaptation to changing environmental and climatic conditions, as well as enhancing yields. The second chapter gives an overview of the floral biology and pollination in yam. The different flowering activities of male and female flowers, as well as possible sex-switches that may occur in plants make it difficult to synchronize the timeframe for viable pollen and receptacle stigmata to ensure pollination success of different cultivars. Another difficulty is the presence of sterile hybrids, especially in triploid species. The next chapter is about pollen viability, storage and longevity and collection. I would recommend reorganizing this chapter and start with point 3.7 as point 3.1 “Pollen collection”, after collecting the pollen it can be tested for viability and so on. I give details in the specific comments following this paragraph. The methods are described adequate and gaps are identified, where additional research is needed and where method testing has to be conducted for yam species. This chapter is followed by the comparison of storage possibilities of pollen, with regard to enhance longevity of pollen samples. In the following chapter pollination practices are described and illustrated nicely with pictures from the experimental field work of the authors. This is followed by a theoretical chapter on how to manipulate the flowering time of tuber plants. Since the cited methods are from studies of other tuber crops/plants, this is merely an outlook, which methods may work in synchronizing or extend the flowering time of yams. The last methodological chapter deals with the rearing a dissemination of native insect pollinators to increase reproductive success. The following conclusions highlight the crucial points for improving the management of yam pollination to obtain good breeding results.

The strength of this review lies clearly in the detailed description of possible methods and the advantages and disadvantages that come along with some techniques, which reads like a user guide to follow in breeding experiments. The article gives a nice overview about the current status of pollination experiments for yams and elaborates an outlook on future research that has to be undertaken to improve breeding outcomes of yams.

Specific comments:

Line 139: I think this is meant to be Figure 4d?

Restructuring of chapter 3:

Line 197: 3.1, please start here with 3.7 “Pollen collection”, I would then suggest to create point 3.2 “Methods for assessing pollen viability and quality “ an start with 3.2.1 “In vitro germination”; 3.2.2 “Staining methods”; 3.2.3 “In vivo germination”; 3.2.4 “Impedance and optical flow cytometry” and 3.2.5 “Imagery and pollen quality assessment”, followed by point 3.3 “Pollen storage and longevity” (former 3.6); 3.3.1 “Storage methods”; 3.3.2 “Factors affecting stored pollen longevity” and 3.3.3 “Post-storage practices, pollen retrieval and usage”.

Line 280: Table 2: I think this table may be deleted, because there is no additional information, that is not described in the text already.

Figures

• Please check the letters for different pictures in one figure, they have to be aligned and the white box should be removed

Figure 6, c & d, please remove the arrows

Author Response

Question: I think this is meant to be Figure 4d?

Response: We thank the reviewer for this observation. The cited Figure number has been corrected. It reads now Figure 4d instead of Figure 3d.

Question: Line 197: 3.1, please start here with 3.7 “Pollen collection”, I would then suggest to create point 3.2 “Methods for assessing pollen viability and quality “ an start with 3.2.1 “In vitro germination”; 3.2.2 “Staining methods”; 3.2.3 “In vivo germination”; 3.2.4 “Impedance and optical flow cytometry” and 3.2.5 “Imagery and pollen quality assessment”, followed by point 3.3 “Pollen storage and longevity” (former 3.6); 3.3.1 “Storage methods”; 3.3.2 “Factors affecting stored pollen longevity” and 3.3.3 “Post-storage practices, pollen retrieval and usage”.

Response: We appreciate the reviewer comment and suggestion to make this review paper more interesting. Chapter 3 has been restructured. Pollen viability assessment and Pollen storage sections were merged mistakenly on the MDPI site. We have separated them as in the original submission to reflect the review suggestion. Pollen collection section could not be moved as it is related to Pollen storage and not the viability assessment methods.

Question: I think this table may be deleted, because there is no additional information, that is not described in the text already.

Response:  Thanks for this suggestion we have deleted Table 2 from the document.

Question:  Please check the letters for different pictures in one figure, they have to be aligned and the white box should be removed

Response: We do appreciate this observation from the reviewer, and we have removed the white boxes from figures.

Question: Figure 6, c & d, please remove the arrows

Response: Thanks for your observation on Figure 6, arrows were removed.

Reviewer 2 Report

This review paper summarizes the knowledge and common practices in yam crossing, either by hand pollination or by insect pollination. I am not an expert in the yam breeding field, so I am not qualified to comment on the details of the practices in yam breeding, like pollen storage, etc. Nevertheless, in general, I think this paper is very comprehensive and well constructed. I feel it will provide very useful information for the researchers and practitioners in the field. I only have a minor suggestion:

The cultivated yam species seem to have inconspicuous flowers, which may not be attractive to many pollinators. The hand pollination practice also seems labor-intensive. I wonder whether there is any study that looked at the pollination of wild yam species? Is the problematic pollination of cultivated yam a result of inbreeding depression? It might be useful to know what is going on with the wild species. Are they attractive to insect pollinators? Is the pollinator also thrip? How efficient are they? For example, if the cultivated yam lacks a volatile that’s attractive to pollinators in the wild yam, maybe applying the volatile to the flower could be helpful to improve the attractiveness of the cultivated yam. Or is it possible to cross between the cultivated yam and wild yam to improve some qualities of the cultivated varieties?

Author Response

Question: The cultivated yam species seem to have inconspicuous flowers, which may not be attractive to many pollinators. The hand pollination practice also seems labor-intensive. I wonder whether there is any study that looked at the pollination of wild yam species? Is the problematic pollination of cultivated yam a result of inbreeding depression? It might be useful to know what is going on with the wild species.

Response: Many thanks for reviewing our paper. Although there is no study dealing exclusively with wild species for this topic, reports show that wild pollination success is higher than cultivated ones. We showed in the introduction and section 1 that flowering and pollination abnormalities may be a result of alterations on sexual reproductive ability due to long domestication process. In fact, wild yam is sexually propagated but with domestication, it was exclusively planted using tubers.

Question: Are they attractive to insect pollinators? Is the pollinator also thrip? How efficient are they? For example, if the cultivated yam lacks a volatile that’s attractive to pollinators in the wild yam, maybe applying the volatile to the flower could be helpful to improve the attractiveness of the cultivated yam. Or is it possible to cross between the cultivated yam and wild yam to improve some qualities of the cultivated varieties?

Response: We do appreciate the review comments and questions. We showed in section 7 that some wild and cultivated yam species attract insects (thrips and ants), and consequently, their natural pollination is high (<90%). However, this is not the case for popular species such as D. alata and D. rotundata. We suggested in the same section the use of attractants as palliative solution or selecting parents with attractive flowers. These align with the reviewer suggestion.  In the line 573, we have added “plant volatiles” to accommodate the vocabulary used by the reviewer.

Reviewer 3 Report

In this paper the authors present a comprehensive review on floral biology and pollination in yam.

The paper is well planned and all aspects related to this subject are covered. The authors, based on the studied works, start from the hypothesis that the efficiency of yam pollination can be improved through an integrated management strategy and propose measures for this.

Author Response

We thank the reviewer for the interest in our paper. No suggestion was proposed.