Development of a Marker within the Candidate Un8 True Loose Smut Resistance Gene for Use in Barley Breeding

Breeding for resistance to true loose smut infection caused by the pathogen (Ustilago nuda (Jens.) Rostr.) is an economical and environmentally safe way to limit the effect of this pathogen on barley. However, screening for resistance using natural infection can lead to inconsistent results and artificial inoculation is labour intensive, and unless done in growth chambers or greenhouses, can also be affected by environmental conditions, leading to inconsistent phenotyping. Marker-assisted selection of genes conferring disease resistance can increase the efficiency of breeding programmes. A candidate gene for Un8 resistance was used to develop a genetic marker, which was tested on a recombinant inbred line (RIL) population derived from the resistant 'CDC Freedom' and the susceptible 'Samson' varieties. The RIL population (98 lines) was pheno-typed for resistance to true loose smut by artificial inoculation and genotyped with the newly developed marker. Only one of the 98 RILs tested had a resistant genotype, but was susceptible according to the artificial inoculation results. The marker was also tested in 47 additional barley cultivars and breeding material, and of the five lines with inconsistent results, four were susceptible according to the genotyping results, but were resistant according to the artificial inoculation results, while one line was resistant according to the genotyping results but had a susceptible resistance phenotype.