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The genetic basis of resistance to Rhynchosporium commune was investigated in a winter barley mapping population derived from a cross between cultivars Saffron (moderately susceptible) and Retriever (moderately resistant). Resistance was assessed in field trials through total infection (measured using qPCR), and visible disease symptoms. Phenotypic correlations between both methods of assessing disease severity were high. QTL mapping from three years of field trials identified five significant QTL effects. One QTL effect on chromosome 2H confirms a previously reported resistance from a population derived from the spring cultivar Cocktail and a winter parent derived from the cultivars Pearl and Cocktail. Another QTL effect on 3H corresponds to the reported position of major resistance gene Rrs1. An effect was detected at the mapped position of the semi-dwarfing gene sdw- 1 despite the fact that neither parent has the semi-dwarf phenotype. Of the remaining two QTL effects, one on 6H may represent a previously reported rhynchosporium resistance (QTLRrs6H), whilst the final QTL, represents a novel resistance. In addition, interactions during early infection stages in the parental lines were studied by confocal microscopy of detached leaves inoculated with a GFP-expressing R. commune isolate. This approach identified a number of major differences in fungal growth morphology between the resistant and susceptible parent. [ABSTRACT FROM AUTHOR]

A partial genetic linkage map was constructed on 71 doubled-haploid lines derived from a cross between the barley lines Tadmor and WI2291 with 181 molecular markers. The segregating population was used to detect markers linked to the geneMlg conferring resistance to powdery mildew (Erysiphe graminis f. sp. hordei) and to genes for quantitative resistance to scald (Rhynchosporium secalis). The gene Mlg on chromosome 4H was flanked by two AFLP markers at a distance of 2.0 and 2.4 cM, respectively. QTLs for resistance to scald were detected on chromosomes 2H and 3H. This association of molecular markers with qualitative and quantitative disease resistance loci represents a valuable starting-point for marker-assisted selection. [ABSTRACT FROM AUTHOR]

Leaf scald caused by Rhynchosporium commune (formerly R. secalis) is an important fungal disease in barley (Hordeum vulgare) in western Canada. Pyramiding multiple scald resistance qualitative trait loci (QTL) is considered an effective strategy for breeding durable scald resistance into barley. The objective of this study was to map QTLs with restriction site-associated (RAD) markers and identify single nucleotide polymorphism (SNP) markers for scald resistance. Two recombinant inbred line (RIL) populations (crosses Harrington/Seebe and Seebe/Shyri) with good resistance to local scald isolates were genotyped by RAD sequencing (RADseq). A total of 4203 SNPs were obtained from the RADseq analysis of 162 F7 RILs. Inclusive composite interval mapping identified multiple major QTLs for scald resistance on chromosomes 3H, 4H, and 5H in Shyri, and 2H and 6H in Seebe. SNP markers from Shyri were located in the same region as the previously reported 3H QTL Rrs1. Several SNP markers from Seebe clustered on chromosome 6H near a major scald resistance QTL. The 6H QTL appeared effective for both adult plant resistance and seedling resistance, and explained up to 70.9% of the phenotypic variation among the sequenced lines. A tightly linked SNP for the major 6H QTL was converted into an allele specific PCR marker. The QTLs and their genetic markers found in this study will be useful in barley breeding for the selection of resistance to barley leaf scald. [ABSTRACT FROM AUTHOR]