Development of PCR-based markers for a gene (Un8) conferring true loose smut resistance in barley

Breeding for true loose smut (Ustilago nuda (Jens.) Rostr.) resistance in barley is expensive because of the great requirements for time, labour, and growth space, and thus is an ideal candidate for screening by indirect methods. One gene (Un8) confers resistance to most known races of the true loose smut pathogen and is the gene present in the majority of western Canadian barley cultivars. Here we report on linkage between this gene and a restriction fragment length polymorphism marker, or various forms of the marker, in a number of segregating barley populations. The different forms of the marker were developed through sequencing and postamplification restriction. The resulting allele-specific amplicon markers can be used in a relatively simple assay, based on the polymerase chain reaction, specific for either the resistant or susceptible allele. The marker was linked to the resistance gene in five crosses involving two sources of resistance and was located on chromosome 5 (1HL). The allele-specific amplicons are being routinely used for marker-assisted selection in conjunction with a rapid DNA template preparation method.