High-density genetic mapping of leaf spot resistance quantitative trait loci in a durum wheat × T. Turgidum ssp. Carthlicum population

Leaf spot (LS) diseases are a hindrance to wheat productivity worldwide. The objective of this study was to identify and map LS resistance quantitative trait loci (QTL) and identify the interactions between the identified QTL. A durum wheat cv. Strongfield by Triticum turgidum ssp. carthlicum cv. Blackbird population high-density genetic map was analyzed with phenotypic data from multiple field nurseries. Haplotypes and recombination within the QTL in a set of 401 breeding lines was also identified. DNA sequence of cv. Strongfield and Blackbird supplied genetic variants within the QTL. QTL with resistance alleles from Blackbird were detected on chromosomes 1B, 3A, 3B, 4B and 7B, and from cv. Strongfield as second loci on chromosomes 1B and 7B, as well as unique loci on chromosomes 5A and 5B. The QTL on chromosome 1B from Blackbird showed stronger and more consistent expression than the other QTL. The two QTL on chromosome 7B expressed additive interaction. Comparative mapping analysis indicated that the strong QTL on chromosome 1B co-located with a number of rust resistance genes and a powdery mildew resistance gene. Linkage disequilibrium analysis in the 401 breeding lines identified three main recombination break points in the 1B interval. In a 4.7 Mb interval within the 1B QTL, sequencing revealed polymorphisms in a cluster of 20 receptor genes, but further work will be required to determine involvement in recognition of multiple pathogens by the host immune system. The discovery of recombination provides the opportunity to assemble favorable alleles at the 1B locus, paving the way for breeding durum wheat varieties with combined LS, rust and powdery mildew resistance.