Genetic and Molecular Characterization of Leaf Rust Resistance from Uncharacterized Sources of Durum Wheat (Triticum turgidum L. ssp. durum)

The emergence of highly virulent races of Puccinia triticina Eriks. in Mexico and the Great Plains of the United States makes leaf rust a rising threat to durum wheat production in the Canadian prairies. Whereas the genetic variation existing within the cultivated wheat gene pools is limited, introgression of resistance genes from wild relatives offers a valuable alternative to cope with the constantly evolving rust pathogens. This study aimed to map genes for leaf rust resistance from uncharacterized sources of durum wheat, and to evaluate the potential impact of DNA introgressions from wild relatives that carry Lr19 or Lr47, in durum wheat genetic backgrounds. Seven mapping populations derived from the resistant cultivars Geromtel_3 (ICARDA), Tunsyr_2 (ICARDA), Amria (Morocco), Byblos (France), Gaza (Middle East), Saragolla (Italy) and Arnacoris (France), which were crossed to the susceptible line Atil*2/Local_Red, were evaluated for their reaction to the Mexican race BBG/BP of P. triticina. Selective genotyping and bulked segregant analysis, using the wheat 90K iSelect SNP array, identified two genomic regions for leaf rust resistance; 6BS for Geromtel_3 and Tunsyr_2 and 7BL for Amria and Byblos. Quantitative trait loci (QTL) analyses revealed a total of six QTL for leaf rust resistance; two QTL in Gaza on chromosomes 6BS and 6BL, major QTL on chromosome 7BL in Arnacoris and 2BS in Saragolla, and additional minor QTL on chromosome 1BL in the latter two lines. SNP markers linked to the Lr genes and QTL identified in the present study were anchored to the reference sequence of tetraploid wheat accession “Zavitan”, which identified several candidate resistance genes. These molecular markers will be useful for pyramiding the resistance genes into adapted, elite durum wheat cultivars. Series of 89 near-isogenic lines (NILs) carrying the alien genes Lr19 or Lr47 in four genetic backgrounds of durum wheat, were tested in replicated field trials to evaluate their agronomic and quality attributes. The presence of the Lophopyrum ponticum translocation that carries Lr19 and the endosperm yellow pigment gene Psy1, has significantly increased the abundance of yellow pigment, an important target in durum wheat breeding. Lines with the Triticum speltoides segment that carries Lr47 showed higher grain protein concentration. However, grain yield penalties, reduced thousand kernel weights and a lower grain density were associated with both translocations. The 90K iSelect SNP array was used to identify molecular markers associated with the donor DNA for each of the NILs. These markers can be used in future breeding programs to identify resistant lines with small introgressions that may experience reduced effects on agronomic performance