RESUMO
Durum wheat (T. turgidum L.) is threatened by the appearance of new virulent races of leaf rust, caused by Puccinia triticina, in recent years. This study was conducted to determine the leaf rust resistance in a modern Canadian durum cultivar Strongfield. Six populations derived from crosses of Strongfield with six tetraploid wheat lines, respectively, were tested at seedling plant stage with different P. triticina races. Two of the populations were evaluated for adult plant leaf rust infection in Canada and Mexico. A stepwise regression joint linkage QTL mapping and analysis by MapQTL were performed. Strongfield contributed the majority of QTL detected, contributing seven QTL detected in field tests, and eight QTL conditioning seedling resistance. A 1B QTL, QLr-Spa-1B.1, from Strongfield had a significant effect in both Canadian and Mexican field tests, and corresponded with Lr46/Yr29. The remaining field QTL were found in only the Canadian or the Mexican environment, not both. The QTL from Strongfield on 3A, QLr-Spa-3A, conferred seedling resistance to all races tested and had a significant effect in the field in Canada. This is the first report of the QLr-Spa-3A and Lr46/Yr29 as key components of the genetic resistance in Canadian durum wheat. KASP markers were developed to detect the QLr-Spa-3A for use in marker assisted leaf rust resistance breeding. The susceptible parental lines contributed QTL on 1A, 2B and 5B that were effective in Mexican field tests that may be good targets to integrate into modern durum varieties to improve resistance to new durum virulent races.
RESUMO
KEY MESSAGE: Sr67 is a new stem rust resistance gene that represents a new resource for breeding stem rust resistant wheat cultivars Re-appearance of stem rust disease, caused by the fungal pathogen Puccinia graminis f. sp. tritici (Pgt), in different parts of Europe emphasized the need to develop wheat varieties with effective resistance to local Pgt populations and exotic threats. A Kyoto University wheat (Triticum aestivum L.) accession KU168-2 was reported to carry good resistance to leaf and stem rust. To identify the genomic region associated with the KU168-2 stem rust resistance, a genetic study was conducted using a doubled haploid (DH) population from the cross RL6071 × KU168-2. The DH population was phenotyped with three Pgt races (TTKSK, TPMKC, and QTHSF) and genotyped using the Illumina 90 K wheat SNP array. Linkage mapping showed the resistance to all three Pgt races was conferred by a single stem rust resistance (Sr) gene on chromosome arm 6AL, associated with Sr13. Presently, four Sr13 resistance alleles have been reported. Sr13 allele-specific KASP and STARP markers, and sequencing markers all showed null alleles in KU168-2. KU168-2 showed a unique combination of seedling infection types for five Pgt races (TTKSK, QTHSF, RCRSF, TMRTF, and TPMKC) compared to Sr13 alleles. The phenotypic uniqueness of the stem rust resistance gene in KU168-2 and null alleles for Sr13 allele-specific markers showed the resistance was conferred by a new gene, designated Sr67. Since Sr13 is less effective in hexaploid background, Sr67 will be a good source of stem rust resistance in bread wheat breeding programs.