Molecular mapping of a new gene Rrs4CI11549 for resistance to barley scald (Rhynchosporium secalis)

Doubled haploid (DH) progeny from a cross between the scald susceptible barley (Hordeum vulgare L.) cultivar 'Ingrid' and the resistant accession 'CI 11549' ('Nigrinudum') was evaluated for resistance in the pathogen Rhynchosporium secalis (Oudem) J.J. Davis. Two linked and incompletely dominant loci confer resistance 'CI 11549' against isolate '4004'. One is an allele at the complex Rrs1 locus on chromosome 3H close to the centromere; the other is located 22 cM distally on the long arm. The latter locus is designated Rrs4. In BC3-lines into 'Ingrid' from 'CI 2222' (another 'Nigrinudum') resistance seems governed by one locus close to the telomeric region of chromosome 7H, probably allelic to Rrs2. In neither case did we find any trace of the recessive gene rh8 reported to be present in 'Nigrinudum'. Various resistance donors of Ethiopian origin designated as 'Nigrinudum', 'Jet' or 'Abyssinian' were identical to a great extent with respect to markers, but differed in resistance to different isolates of scald or in barley yellow dwarf virus (BYDV) resistance. The implications for their use as differentials in scald tests and screening of germplasm collections are discussed.