High density mapping of the major stem-solidness locus SSt1 in durum and common wheat

Breeding for solid-stemmed durum (Triticum turgidum L. var durum) and common wheat (Triticum
aestivum L.) cultivars is one strategy to minimize yield losses caused by the wheat stem sawfly (Cephus
cinctus) Norton. Major stem-solidness QTL (SSt1) have been localized to the long arm of chromosome 3B
in both wheat species, but it remains unclear whether the two QTL share a common genetic interval. In
order to further the genetic characterization of the SSt1 locus, we have improved the resolution of the 3B
QTL in durum (Kofa/W9262-2690D3) and common wheat (Lillian/Vesper) mapping populations using the
90K SNP array. Coincident QTL (LOD = 77 - 127, R2 = 70 - 92 %) were localized near the telomere of
chromosome 3BL in both mapping populations. According to the current chromosome 3B emmer genome
assembly, the markers mapping within the QTL intervals anchored to an approximate 10 Mb interval in
Lillian x Vesper, and 12 Mb interval in Kofa x W9262-260D3. In addition, minor QTL were identified on
chromosomes 2A, 2D, 4A, and 5A that were found to synergistically enhance expression of SSt1 to
increase stem-solidness. These results also suggest that developing new wheat cultivars with improved
stem-solidness is possible by combining SSt1 with favorable alleles at minor loci within both wheat
species.