A major genetic factor for durable leaf rust resistance in durum wheat maps in the distal region of chromosome arm 7BL

The genetic basis of leaf rust (Puccinia triticina Eriks.) resistance was studied using 176 RILs from Colosseo × Lloyd and 62 advanced lines derived from multiple crosses. RILs were tested under field conditions with a mixture of leaf rust isolates and at the seedling stage with single isolates. In the field experiment, the percentage of infected leaf area was evaluated through the disease developmental cycle and the area under disease progress curve (AUDPC) was calculated. A major QTL (QLr.ubo-7B.2) for leaf rust resistance at both adult (field conditions) and seedling stages was identified on the distal region of chr. 7BL. In the field, the QTL showed an R2 of 72.9% and a peak LOD score of 44.5 for AUDPC. The presence of this major QTL was validated by a linkage disequilibrium-based test using field data of advanced lines from multiple crosses. The association results confirmed the QTL location between Xbarc340.2 and Xgwm344.2, with the corresponding AUDPC R2 values ranging from ca. 10 to ca. 35% depending on the year. QLr.ubo-7B.2 maps in a gene-dense region (7BL10-0.78-1.00) known to carry several genes/QTLs in wheat and barley for resistance to rusts and other major cereal fungal diseases, including Lr14a and Lr19, two major candidates for this gene