Key message: A new gene for Ug99 resistance from wheat landrace PI 374670 was detected on the long arm of chromosome 7A.
Abstract: Wheat landrace PI 374670 has seedling and field resistance to stem rust caused by Puccinia graminis f. sp tritici Eriks. & E. Henn (Pgt) race TTKSK. To elucidate the inheritance of resistance, 216 BC1F2 families, 192 double haploid (DH) lines, and 185 recombinant inbred lines (RILs) were developed by crossing PI 374670 and the susceptible line LMPG-6. The parents and progeny were evaluated for seedling resistance to Pgt races TTKSK, MCCFC, and TPMKC. The DH lines were tested in field stem rust nurseries in Kenya and Ethiopia. The DH lines were genotyped with the 90K wheat iSelect SNP genotyping platform. Goodness-of-fit tests indicated that a single dominant gene in PI 374670 conditioned seedling resistance to the three Pgt races. The seedling resistance locus mapped to the long arm of chromosome 7A and this result was verified in the RIL population screened with the flanking SNP markers using KASP assays. In the same region, a major QTL for field resistance was detected in a 7.7 cM interval and explained 34–54 and 29–36 % of the variation in Kenya and Ethiopia, respectively. Results from tests with specific Pgt races and the csIH81 marker showed that the resistance was not due to Sr22. Thus, a new stem rust resistance gene or allele, either closely linked or allelic to Sr15, is responsible for the seedling and field resistance of PI 374670 to Ug99.
Bibliographical noteFunding Information:
We are very grateful to Gebre Hiwot Abraha, Sam Stoxen, and Sam Gale for their technical assistance. This research was supported by the USDA-ARS National Plant Disease Recovery System, the USDA-ARS CRIS project 2050-21000-029-00D, and the Durable Rust Resistance in Wheat (DRRW) project managed by Cornell University and funded by the Bill and Melinda Gates Foundation and the United Kingdom Department for International development. This work was supported in part by National Research Initiative Competitive Grant 2011-68002-30029 (Triticeae-CAP) from the USDA National Institute of Food and Agriculture.
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