The complex quantitative barley-Rhynchosporium secalis interaction: newly identified QTL may represent already known resistance genes

Two barley populations, i.e. 135 doubled haploid (DH) lines of the cross ‘Igri’ (rrs1) £ ‘Triton’ (Rrs1) (I £ T) and 76 DH lines of the cross ‘Post’ £ ‘Vixen’ (both rrs1) (P £ V), were analysed to identify QTL for Rhynchosporium secalis resistance independent of the Rrs1 locus by using the single spore R. secalis isolate 271 (Rrs1- virulent). A major QTL with its positive allele derived from cv. ‘Triton’ was detected in the I £ T population on chromosome 2HS explaining almost 80% of the phenotypic variance. Thus, it can be considered as an R-gene corresponding to the already described Rrs15CI8288 on chromosome 2HS. In addition, two minor QTL were identi- Wed, one in the centromeric region of 6H in a highly polymorphic region with already several mapped R-genes and a second one at the end of the short arm of chromosome 7H which may be an allele of Rrs2 because of its chromosomal position. Regarding the DH population P £ V diVerent minor QTL were identiWed on chromosomes 6H and 7H. The Wrst one is corresponding to the genomic region of the Rrs13 gene whereas the QTL on chromosome 7H maps in a genomic region where several R-genes against diVerent pathogens have been localized. A comparison of both QTL analyses reveals no R. secalis isolate 271-speciWc resistance locus but leads to the hypothesis that two of the identiWed QTL may be alleles of the R-genes Rrs15CI8288 and Rrs2.