Combination of seedling and adult plant resistance to leaf scald for stable resistance in barley

Rhynchosporium secalis can overcome a single resistance gene of barley in a relatively short period of time. Novel genes and quantitative trait locis (QTLs) are therefore vital to control scald in barley. A population of 220 double haploid lines was developed from a cross of Vlamingh and WABAR2147, where Vlamingh showed adult plant resistance (APR) and WABAR2147 showed seedling resistance to a group of isolates. The population was tested for APR to scald under natural infection in two consecutive seasons in addition to a seedling screen with three isolates. One single gene was mapped to chromosome 6H based on the seedling test, and two QTLs (QSc.VlWa.4H and QSc.VlWa.6H) were mapped to chromosomes 4H and 6H based on APR. Epistatic interaction was observed between the two QTLs, and environment/QTL interaction was only observed for QSc.VlWa.6H which co-segregated with the seedling resistance gene and contributed to basal resistance against scald during whole growth stages. QSc.VlWa.4H explained 42.5 and 57.8 % of the phenotypic variation in the two independent trials when the effect of QSc.VlWa.6H was excluded from the analysis. We developed a high-density consensus genetic map with 7,876 molecular makers and anchored 43 QTLs and 7 genes for scald resistance from different mapping populations. No known QTLs or genes were reported in a similar position to QSc.VlWa.4H, and it was the first major QTL for APR of scald on chromosome 4HS in barley. Combination of the two QTLs achieved better and stable scald resistance across four different environments.