Files
Abstract
Genetic resistance is the most efficient and cost-effective way to control leaf rust (LR) disease caused by Puccinia triticina (Pt) in wheat (Triticum aestivum L.). The objectives of this study were to map genomic loci conferring seedling and adult plant LR resistance and develop user-friendly markers for marker-assisted selection (MAS). In our first study, we developed a recombinant inbred line (RIL) population by crossing two soft red winter wheat (SRWW) lines, AGS 2038 (LR resistant) and UGA 111729 (LR susceptible) and phenotyped the parents and RIL population for adult plant LR reaction in four environments. Utilizing high-density linkage map, we detected five QTL for adult plant LR resistance. Of these, a QTL on chromosome 1AL, QLr.ags-1AL, was detected on all environments and explained up to 34.45% of phenotypic variation (PV). Molecular marker analysis using diagnostic marker linked to Lr59 showed that QLr.ags-1AL was different from Lr59, the only known leaf rust resistance gene on 1AL – therefore the QTL was temporarily designated as Lr2K38. In our second study, we utilized a different RIL population derived from SRWW cultivars, AGS 2000 and Pioneer® variety 26R61 (26R61) and mapped a single common QTL, QLr.uga.2BS, for resistance to two Pt races (MFGKG and MBTNB) at seedling stage. QLr.uga.2BS explained up to 75.30% of PV. Based on the physical and genetic positions, this QTL was different from other genes/QTL reported on 2BS, and therefore, we temporarily designated it as LrA2K. In the third study, we evaluated a panel of 331 genetically diverse wheat germplasm for their reaction to four Pt races at the seedling stage. Phenotypic analysis revealed that majority of the genotypes were susceptible and only 22 genotypes (6.6%) were resistant to all four Pt races. Genome-wide association study (GWAS) detected 11 QTL on 9 chromosomes for LR resistance. Of these, six QTL were identified in the vicinity of known genes or QTL, therefore, more studies are warranted to determine their relationships. The other five QTL, QLr.uga-1AL, QLr.uga-4AS, QLu.uga-5AS, QLr.uga-5AL, and QLr.uga-7AS, were identified on genomic regions where no LR resistance genes have been identified in T. aestivum, therefore, represent potential novel loci for LR resistance. The germplasm and genomic regions/QTL identified in this research can be used in wheat breeding program to develop durable LR resistance wheat cultivars.