Genome-wide association mapping of Pyrenophora teres f. maculata and Pyrenophora teres f. teres resistance loci utilizing natural Turkish wild and landrace barley populations

Wild barley (Hordeum spontaneum) and landraces (Hordeum vulgare) from Turkey contain an abundance of novel Rhynchosporium commune resistance loci

Rhynchosporium commune is a globally devastating pathogen of barley. Wild and landrace barley are underutilized, however, contain an abundance of loci that can be used as potential sources of resistance. Rhynchosporium commune, the causal agent of the disease scald or leaf blotch of barley, is a hemibiotrophic fungal pathogen of global importance, responsible for yield losses ranging from 30 to 40% on susceptible varieties. To date, over 150 resistance loci have been characterized in barley. However, due to the suspected location of the R. commune host jump in Europe, European germplasm has been the primary source used to screen for R. commune resistance leaving wild (Hordeum spontaneum) and landrace (H. vulgare) barley populations from the center of origin largely underutilized. A diverse population consisting of 94 wild and 188 barley landraces from Turkey were genotyped using PCR-GBS amplicon sequencing and screened with six Turkish R. commune isolates. The isolates were collected from distinct geographic regions of Turkey with two from the Aegean region, two from central Turkey and two from the Fertile Crescent region. The data set was utilized for association mapping analysis with a total of 21 loci identified, of which 12 were novel, indicating that these diverse primary barley gene pools contain an abundance of novel R. commune resistances that could be utilized for resistance breeding.

Screening of stable resistant accessions and identification of resistance loci to Barley yellow mosaic virus disease

Background

The disease caused by Barley yellow mosaic virus (BaYMV) infection is a serious threat to autumn-sown barley (Hordeum vulgare L.) production in Europe, East Asia and Iran. Due to the rapid diversification of BaYMV strains, it is urgent to discover novel germplasm and genes to assist breeding new varieties with resistance to different BaYMV strains, thus minimizing the effect of BaYMV disease on barley cropping.

Methods

A natural population consisting of 181 barley accessions with different levels of resistance to BaYMV disease was selected for field resistance identification in two separate locations (Yangzhou and Yancheng, Jiangsu Province, China). Additive main effects and multiplicative interaction (AMMI) analysis was used to identify accessions with stable resistance. Genome-wide association study (GWAS) of BaYMV disease resistance was broadly performed by combining both single nucleotide polymorphisms (SNPs) and specific molecular markers associated with the reported BaYMV disease resistance genes. Furthermore, the viral protein genome linked (VPg) sequences of the virus were amplified and analyzed to assess the differences between the BaYMV strains sourced from the different experimental sites.

Results

Seven barley accessions with lower standardized Area Under the Disease Progress Steps (sAUDPS) index in every environment were identified and shown to have stable resistance to BaYMV disease in each assessed location. Apart from the reported BaYMV disease resistance genes rym4 and rym5, one novel resistance locus explaining 24.21% of the phenotypic variation was identified at the Yangzhou testing site, while two other novel resistance loci that contributed 19.23% and 19.79% of the phenotypic variation were identified at the Yancheng testing site, respectively. Further analysis regarding the difference in the VPg sequence of the predominant strain of BaYMV collected from these two testing sites may explain the difference of resistance loci differentially identified under geographically distinct regions. Our research provides novel genetic resources and resistance loci for breeding barley varieties for BaMYV disease resistance.