Genome-Wide Association Mapping for Resistance to Leaf and Stripe Rust in Winter-Habit Hexaploid Wheat Landraces

<div><p>Leaf rust, caused by <i>Puccinia triticina (Pt</i>), and stripe rust, caused by <i>P</i>. <i>striiformis</i> f. sp. <i>tritici (Pst</i>), are destructive foliar diseases of wheat worldwide. Breeding for disease resistance is the preferred strategy of managing both diseases. The continued emergence of new races of <i>Pt</i> and <i>Pst</i> requires a constant search for new sources of resistance. Here we report a genome-wide association analysis of 567 winter wheat (<i>Triticum aestivum</i>) landrace accessions using the Infinium iSelect 9K wheat SNP array to identify loci associated with seedling resistance to five races of <i>Pt</i> (MDCL, MFPS, THBL, TDBG, and TBDJ) and one race of <i>Pst</i> (PSTv-37) frequently found in the Northern Great Plains of the United States. Mixed linear models identified 65 and eight significant markers associated with leaf rust and stripe rust, respectively. Further, we identified 31 and three QTL associated with resistance to <i>Pt</i> and <i>Pst</i>, respectively. Eleven QTL, identified on chromosomes 3A, 4A, 5A, and 6D, are previously unknown for leaf rust resistance in <i>T</i>. <i>aestivum</i>.</p></div

Infection type of six accessions from Iran that show resistance to all five races of <i>Puccinia triticina</i> (<i>Pt</i>) and a race of <i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>).

<p>(-) indicates slightly smaller uredinia than the standard, (+) indicates slighter larger uredinia, two infection types (IT) (such as 12-) indicates a mixed reaction on the same leaf, two IT separated by slash (such as 2/3) indicates varying reaction among seedling plants of the same accession (some seedlings are 2, other seedlings are 3). The linearized disease rating for leaf rust shown in parentheses was used in association analysis.</p><p>Infection type of six accessions from Iran that show resistance to all five races of <i>Puccinia triticina</i> (<i>Pt</i>) and a race of <i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>).</p

Stepwise regression for each rust race.

<p>Stepwise regression for each rust race.</p

Number of accessions resistant to each race of <i>P</i>. <i>triticina</i> and <i>P</i>. <i>striiformis</i> f. sp. <i>tritici</i> tested.

<p>A total of 567 accessions were screened at the seedling stage with five races of <i>P</i>. <i>triticina</i> and one race of <i>P</i>. <i>striiformis</i> f. sp. <i>tritici</i>.</p

Significant markers associated with resistance to each rust pathogen race.

<p>Markers labelled with ‘x’ were maintained after stepwise regression.</p><p>^aChrom = Chromosome;</p><p>^bcM = Marker position on consensus map;</p><p>^cpFDR = Positive false discovery rate;</p><p>^dMAF = Minor allele frequency;</p><p>^eUnk = Chromosomal location is unknown.</p><p>Significant markers associated with resistance to each rust pathogen race.</p

A graph showing two principal components obtained from 4234 polymorphic SNPs.

<p>PC1 and PC2 explain 19.41% and 5.22% variation, respectively.</p

Mean square difference (MSD) for each disease race and model.

<p>The best model was used to investigate SNP-rust resistance associations.</p><p>Numbers in bold indicate lowest mean square difference (MSD) and best model for each rust race.</p><p>Mean square difference (MSD) for each disease race and model.</p