A Novel QTL for Powdery Mildew Resistance in Nordic Spring Barley (Hordeum vulgare L. ssp. vulgare) Revealed by Genome-Wide Association Study.

Therése Bengtsson,Ahmed Jahoor,Outi Manninen,Therese Christerson,Lene Krusell,Inger Åhman,Lars Reitan,Jens Due Jensen,Jihad Orabi

doi:10.3389/fpls.2017.01954

Abstract

The powdery mildew fungus, Blumeria graminis f. sp. hordei is a worldwide threat to barley (Hordeum vulgare L. ssp. vulgare) production. One way to control the disease is by the development and deployment of resistant cultivars. A genome-wide association study was performed in a Nordic spring barley panel consisting of 169 genotypes, to identify marker-trait associations significant for powdery mildew. Powdery mildew was scored during three years (2012–2014) in four different locations within the Nordic region. There were strong correlations between data from all locations and years. In total four QTLs were identified, one located on chromosome 4H in the same region as the previously identified mlo locus and three on chromosome 6H. Out of these three QTLs identified on chromosome 6H, two are in the same region as previously reported QTLs for powdery mildew resistance, whereas one QTL appears to be novel. The top NCBI BLASTn hit of the SNP markers within the novel QTL predicted the responsible gene to be the 26S proteasome regulatory subunit, RPN1, which is required for innate immunity and powdery mildew-induced cell death in Arabidopsis. The results from this study have revealed SNP marker candidates that can be exploited for use in marker-assisted selection and stacking of genes for powdery mildew resistance in barley.

Highlights

Powdery mildew is one of the major diseases of barley (Hordeum vulgare L.) caused by the powdery mildew fungus, Blumeria graminis f. sp. hordei, an obligate biotrophic pathogen (Glawe, 2008)
The distribution of the phenotypic values for powdery mildew resistance was skewed toward resistant reactions and the residuals did not follow a normal distribution (Figure 1)
The present study revealed that the proportion of lines with mlo alleles was 88% in K1 and 26% in K2, whereas no mlo alleles were found in the admixed group consisting of cultivars and breeding lines from the northern part of the Nordic region

Summary

Introduction

Powdery mildew is one of the major diseases of barley (Hordeum vulgare L.) caused by the powdery mildew fungus, Blumeria graminis f. sp. hordei, an obligate biotrophic pathogen (Glawe, 2008). Control of powdery mildew may be achieved by fungicide applications, by deployment of resistant cultivars or a combination of the two. A Novel QTL for Powdery Mildew pathogen overcomes the resistance. One way to avoid the ‘boom and bust cycles’ is to grow cultivars with broad-spectrum resistance, effective against several or all pathotypes. A successful example of this in barley is the use of the loss-of-function (mlo) alleles of the Mlo gene on chromosome 4H which has led to nearly complete resistance to powdery mildew, durable for more than 50 years (Jørgensen, 1992; Büschges et al, 1997). The locations of several major genes and quantitative trait loci (QTLs) associated with powdery mildew resistance have been identified in barley (Friedt and Ordon, 2007). Major resistance genes have been mapped to chromosome 1H (Mla, Mlat, Mlk, Mlnn, Mlra, MlGa, and Mlp), 2H (MlLa), 4H (Mlg), 5H (Mlj), 6H (Mlh), and 7H (mlt and Mlf ) (Jensen and Jørgensen, 1975; Doll and Jensen, 1986; Hilbers et al, 1992; Görg et al, 1993; Jørgensen and Wolfe, 1994; Schönfeld et al, 1996; Wei et al, 1999)

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Results

Conclusion