Mapping and Validation of a QTL Conferring Partial Resistance to Stripe Rust in Hexaploid Wheat

A mapping population of 96 recombinant inbred lines (RIL) was developed from a cross of Klein Proteo and Klein Chajá. Using the iSelect Illumina platform for 9,000 wheat SNP, a map was built including 2,698 SNP and 108 SSR markers. The population was evaluated during four seasons for stripe rust response in field experiments at Davis, CA, by measuring infection type (IT) and disease severity (S). Independent QTL analyses were performed on data from each year. A partial resistance QTL (QYr.ucw-1BL) contributed by Klein Chajá was identified on the distal region of chromosome 1BL in all four years (explained variation, 22% IT for and 23% for S). A validation population was generated by crossing one of the original RIL carrying only the QYr.ucw-1BL resistance locus, with a RIL carrying susceptible alleles for all QTL discovered. In 2015, 1,300 segregating F_2:3 plants from the validation population were evaluated for rust resistance in the field to refine the mapping. Fingerprinting of the parental lines with the 90,000 iSelect SNP marker platform was used to develop eight new markers and reduce the QTL region to 2.8 cM. To test if QYr.ucw-1BL was different from Yr29/Lr46, we evaluated 759 F₂ plants segregating for both genes in the field in 2014. We identified 15 fully susceptible plants suggesting that QYr.ucw-1BL is different from Yr29/Lr46 and that the two genes are approximately 5cM apart. Yr29/Lr46 presented lower levels of resistance than QYr.ucw-1BL under field conditions, the combination of both genes resulted in the best resistance.