Molecular mapping of resistance to the Pgt race Ug99 group in spring wheat landrace PI 177906
Wheat landrace PI 177906 has seedling and field resistance to Pgt races TTKSK and TTKST. From a cross between PI 177906 and LMPG-6, 138 doubled haploid (DH) lines and 144 recombinant inbred lines (RILs) were developed and tested for seedling resistance to Pgt race TTKSK. Goodness-of-fit tests from both populations indicated that two dominant genes in PI 177906 conditioned resistance to race TTKSK. Parents and the 138 DH lines were evaluated in the field in two experiments in Kenya; one in the main season and one in the off-season. The 90K wheat iSelect SNP genotyping platform was used to genotype the parents and DH lines and data were used to construct a genetic linkage map. Two loci for seedling resistance were mapped to chromosomes 2BL and 4BL. Two major QTL for field resistance mapped to the same regions, a 14.4 cM interval on 2BL and an 8.5 cM interval on 4BL. The QTL on 2BL and 4BL explained, respectively, 31.9-32.3% and 18.2-19.1% of the variation in the off-season and 28.3-30.4% and 5.4-6.5% of the variation in the main-season. Based on the mapping results, race specificity, and the seedling infection types, the resistance gene in 2BL could be Sr28, whereas the gene on chromosome 4BL could be novel. The mapping results will be verified in the RIL population using the flanking SNP markers in KASP assays.