Development and validation of a breeder-friendly KASPar marker for wheat leaf rust resistance locus Lr21

Development and utilization of genetic markers play a pivotal role in marker-assisted breeding of wheat cultivars with pyramids of disease resistance genes. The objective of this study was to develop a closed-tube, gel-free assay for high-throughput genotyping of leaf rust resistance locus Lr21. Polymorphism identified from re-sequencing of a 2.4-kb fragment covering the functional region of the Lr21 gene from the second to the fourth indels was targeted for assay development. The generated sequence data revealed the 88- or 105-bp indel in the first intron of the Lr21 gene in the selected resistant cultivars compared to susceptible US spring and winter wheat cultivars. Allele-specific primers for a KASPar assay were designed around the junction of the indel at position 1,346 bp. The marker was tested on a panel of 384 US wheat lines and found to be effective in differentiating resistant and susceptible genotypes.