Stacking Resistance Genes in Multiparental Interspecific Potato Hybrids to Anticipate Late Blight Outbreaks

Round 1

Reviewer 1 Report

Overview comments:

This is a very large body of work to characterize late blight in a large number of different potato hybrids/lines. I thank the authors for pulling these multi-year datasets together and providing a good resource to the potato breeding community. While the concept of stacking disease resistance genes to provide a more durable tolerance is a tried and true concept, this work does a nice job in characterizing many diverse stacks and will certainly be of value to the community. Overall, the paper seems well put together. Some of the tables get confusing to follow the columns and rows across pages, but I assume the copy editing will work on the formatting to fit the journal style and page formats. Below are a small number of detailed points to address.

Detailed comments:

Intro, Paragraph 5: the phrase “successfully raked” is awkward.

Materials and Methods, Paragraph 2: Please define SCAR markers that first time it is used.

Table 2: It is a bit unclear to me on the source of the LB resistance scores for the field. Is this an average over multi-year experiments? How many years of data went into the scores for a given hybrid? Also, at the field sites, was there any evidence of LB pathovar drift over the years (as in one subspecies of LB becoming less common, while another subspecies becoming more common)? These are all things that can influence field ratings, and while field work always has to work around these uncertainties, it would be nice to describe this in more detail.

Section 2.2: Unsure what decades of the month are, please define.

Conclusion, Paragraph 2: Is it possible that the resistance seen is not due to additional Rpi genes, but other defense pathways (or non-specific tolerance)?

Conclusion: One thing that I would like to see addressed is the potential for yield drag as you stack more of these together. I understand that these experiments were not set up to address yield and focus on LB disease pressure instead. However, this is an important factor in commercial production, so it would be nice to address if only as a future direction.

Author Response

We gladly thank the Reviewer 1 for benevolent and constructive suggestions and have tried to meet them.

• Page 2, line 70; raked with deleted, searched using
• Page 3, the first paragraph is edited, and the authors are now indicated after the Latin names of Solanum
• Page 3, line 118, abbreviation defined: Sequence Characterized Amplified Region (SCAR).
• Table 2 and the corresponding text:
• Field trials were run for seven years, except several hybrids, which were assessed only for three years. The evaluation of such data for variation with the Student’s criterion is rather difficult.
• To elucidate this fragment, we added a short description of evaluating LB resistance in field trials:

Page 7; Pathogen population at two sites was represented by numerous diverse and highly aggressive complex races of P. infestans comprising seven to eleven virulence genes [35]. 

The field assessment of the partial LB resistance of potato plants was carried out each 10-12 days, and these data were used to calculate the area under the disease progress curve (AUDPC) in the course of the growth season and the corresponding yield losses caused by the early destruction of leaves (%). To evaluate the LB resistance level, the calculated yield losses were converted into 1-9-point scores, where 9 points correspond to the highest resistance level [35].

Concerning the probable pathovar drift, the isolates of P. infestans were acquired from lesions on potato leaves at the St. Petersburg  and Moscow sites (2013-2015 and 2018-2019, correspondingly) from the hybrids described in our MS and further maintained as clones. When assessed with the Mastenbroek-Black differential set, we always registered at both experimental sites numerous diverse and highly aggressive complex races of Phytophthora infestans comprising seven to eleven virulence genes. The presence of both A1 and A2 mating types (Sokolova, E.A. et al., 2017. Schepers, H.T.A.M., Ed., Wageningen, DLO Foundation. no. 18, 259-268) provided for rapid diversification of pathogen population. These isolates (in some cases single-cell lines were obtained) were used for the SSR analysis by the standard 12-loci protocol and the assessment of ten Avr genes (Li, Y. et al. 2013. J. Microbiol. Meth. 92, 316–322; Sokolova, E.A. et al., 2017. Schepers, H.T.A.M., Ed., Wageningen, DLO Foundation. no. 18, 259-268; Chizhik, V.K. et al. 2019. PAGV-Special Report. Schepers, H.T.A.M. Ed. Wageningen, DLO Foundation, no. 19. p. 231-240). As a whole, we conclude that the Russian pathovars considerably differed from those in the West Europe.

• Page 7, line 144; in the first decade of is deleted, early in is inserted.
• Page 22, lines 63-64; We gratefully accept the suggestion by Reviewer 1 and add: Another possibility would link such resistance to other defense pathways. including non-specific tolerance. The corresponding change was made in the ABSTRACT (page 1, line 21).

Page 22, lines 97-99: In CONCLUSION, the following lines are added:

By their productivity (0.89-1.25 kg of tubers per plant), most tested hybrids were comparable to cv. Sarpo Mira, the international standard of LB resistance, and considerably overtook the susceptible standard cv. Bintje. However, within the selection of highly resistant genotypes with 4+ markers of Rpi genes per plant (Table 5), it is difficult to relate tuber yield immediately to plant resistance and the number of resistance genes.

Reviewer 2 Report

Manuscript can be published in Agronomy- MDPI.

But, I suggest better harmonizing this paper. Please be careful to use the abbreviations only once where they appear. Please read and carefully remove some English language errors.

Table 3 can be supplementary.

There should be a separate section for discussions.

Line: 87-89: unclear information.

Use clear labelling for figures and tables, especially figures are difficult to predict.

Author Response

We appreciate the broad-range recommendations to improve our MS and have made numerous changes, small and considerable, concerning the content, style and spelling.

However, we would rather keep Table 3 within the main body of the paper, as it contains an important information on the prototype Rpi genes under study.

Concerning the suggestion to separate the sections RESULTS and DISCUSSION, such separation would lead to unnecessary repeats.

Lines numbered 87-89 are found on the pages 2 and 23. In the second case, lines 86-89 were rewritten to:

There are two ways to combine a sufficient number of Rpi genes of broad specificity towards diverse pathogen races and in this way to develop the basis of long-lasting and durable LB resistance: to stack several efficient genes in a single potato genotype or to produce a mosaic of Rpi genes in a potato stand combining several cultivars

Labelling for figures and tables was checked and in some cases modified.