Mapping Ug99-Effective APR QTLs in a Biparental Spring Wheat Population

The newly emerged stem rust race Ug99 of wheat, and its lineal group of races threaten wheat production globally. Because of their emergence and spread, there is urgency to discover effective resistance sources against this group of races. It has been well documented that adult plant resistance (APR) genes provide resistance to multiple races, and are more durable than race specific genes. With the goal of mapping putatively novel APR genes, a biparental population of 141 recombinant inbred lines (RILs) was generated by crossing RB07, a hard red spring wheat cultivar, with MN06113-8, a hard red spring wheat experimental line from the University of Minnesota wheat breeding program. Both parents are susceptible to Ug99 races at the seedling stage, but provide high levels of field resistance to the Ug99 family of races when grown in inoculated nurseries in Kenya.  Pedigree information and molecular screening confirm the absence of known rust resistance APR genes in both parents. F₆ RILs were evaluated for Ug99 resistance in hotspot regions of Ethiopia and Kenya. Genomes of each line in the population were scanned using two genotyping methods: the 9K Infinium array (developed by Illumina) and de novo SNPs obtained from genotyping-by-sequencing. Using composite interval mapping, we have identified several QTLs in this population. Inconsistency in QTL discovery among different environments can be attributed to difference in disease pressure, and environmental conditions affecting QTL expression. Identified markers and QTLs can be used to enhance resistance breeding via marker assisted and genome-wide selection approaches.