Identification of QTL conferring resistance to stripe rust (Puccinia striiformis f. sp. hordei) and leaf rust (Puccinia hordei) in barley using nested association mapping (NAM).

Thomas Vatter,Klaus Pillen,Frank Ordon,Dragan Perovic,Doris Kopahnke,Andreas Maurer,Chengdao Li

doi:10.1371/journal.pone.0191666

Thomas Vatter, Klaus Pillen + Show 5 more

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https://doi.org/10.1371/journal.pone.0191666

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Abstract

The biotrophic rust fungi Puccinia hordei and Puccinia striiformis are important barley pathogens with the potential to cause high yield losses through an epidemic spread. The identification of QTL conferring resistance to these pathogens is the basis for targeted breeding approaches aiming to improve stripe rust and leaf rust resistance of modern cultivars. Exploiting the allelic richness of wild barley accessions proved to be a valuable tool to broaden the genetic base of resistance of barley cultivars. In this study, SNP-based nested association mapping (NAM) was performed to map stripe rust and leaf rust resistance QTL in the barley NAM population HEB-25, comprising 1,420 lines derived from BC1S3 generation. By scoring the percentage of infected leaf area, followed by calculation of the area under the disease progress curve and the average ordinate during a two-year field trial, a large variability of resistance across and within HEB-25 families was observed. NAM based on 5,715 informative SNPs resulted in the identification of twelve and eleven robust QTL for resistance against stripe rust and leaf rust, respectively. Out of these, eight QTL for stripe rust and two QTL for leaf rust are considered novel showing no overlap with previously reported resistance QTL. Overall, resistance to both pathogens in HEB-25 is most likely due to the accumulation of numerous small effect loci. In addition, the NAM results indicate that the 25 wild donor QTL alleles present in HEB-25 strongly differ in regard to their individual effect on rust resistance. In future, the NAM concept will allow to select and combine individual wild barley alleles from different HEB parents to increase rust resistance in barley. The HEB-25 results will support to unravel the genetic basis of rust resistance in barley, and to improve resistance against stripe rust and leaf rust of modern barley cultivars.

Highlights

Artificial infection resulted in a moderate disease pressure in both years, despite dry weather conditions impeding the initial infection process in the beginning of field trials
HEB families 1, 3, and 25 showed the highest resistance to both pathogens based on the Average ordinate (AO) median
For Puccinia hordei (Ph), cultivar Barke showed an intermediate degree of resistance compared to the wild donor parents, whereas in case of Psh the common parent Barke showed a very high degree of resistance

Summary

Methods

This study is based on the HEB-25 NAM population [69]. HEB-25 comprises 1,420 BC1S3 lines in 25 families, originating from crossing 25 highly divergent wild barley accessions Spontaneum and H. agriocrithon) with the modern spring barley cultivar Barke Due to a loss of genotypes during field trials, the analysis is based on 1,401 genotypes of the HEB-25 population. Field trials were conducted at the Julius Kuehn-Institute, Federal Research Centre for Cultivated Plants, in Quedlinburg, Germany, during the seasons 2014 and 2015 using a randomized incomplete block design with two replications. Screening for resistance to Ph and Psh was performed in separate field trials. Spreader strips were spray inoculated with an oil-spore mixture using a hand-held spinning disc sprayer (ULVA+, Micron Sprayers, Bromyard, Herefordshire, U.K.) to ensure homogeneous disease pressure. For stripe rust (Psh) trials, the very aggressive race R-24 was used, which is wildly spread in Europe and the Americas [4, 7, 53]

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Conclusion