Effect of a 7EL Translocation Carrying Leaf and Stem Rust Resistance Genes (Lr9 & Sr25) and Yellow Pigment Gene (Y) on Yield and Semolina Color in Durum Wheat

The concentration of yellow pigment in the grain endosperm is an important quality characteristic for durum wheat.  The distal segment of chromosome 7EL from Lophopyrum ponticum, which carries the endosperm yellow pigment gene Y and additional genes for leaf rust (Lr19) and stem rust resistance (Sr25), was translocated into chromosome 7AL (henceforth 7AL/7EL). The translocated chromosome was backcrossed for six generations into different durum lines to generate pairs of near isogenic lines (NILs). The NILs were evaluated for three years (2010-2012) in Davis (Sacramento Valley, CA, USA) and El Centro (Imperial Valley, CA, USA). The presence of the 7AL/7EL introgression was consistently associated with a significant increase in semolina color (Minolta b-values) across NILs both in Davis (+11.4%) and El Centro (+11.4%). Unfortunately, the presence of the 7A/7EL introgression was also consistently associated with a significant negative effect on grain size (thousand-kernel weight, TKW) both in Davis (-9.6%) and El Centro (-11.1%). This reduction in grain size was associated with yield reductions of -4.6% in Davis and -5.9% in El Centro, but the differences were significant only in 2010. To separate the beneficial effects of the 7EL yellow pigment gene and the tightly linked Sr25 stem rust resistance gene (effective against race Ug99) from the negative effect on yield we have initiated the dissection of this 7EL segment in durum wheat using the ph1c mutant to induce homoeologous recombination between the 7EL and 7AL chromosome arms.