UC Davis

High grain protein content (GPC) is a frequent target of wheat breeding programmes because of its positive effect on bread and pasta quality. A wild wheat allele at the Gpc-B1 locus with a significant impact on this trait was identified previously. The precise mapping of several senescence-related traits in a set of tetraploid recombinant substitution lines (RSLs) segregating for Gpc-B1 is reported here. Flag leaf chlorophyll degradation, change in peduncle colour, and spike water content were completely linked to the Gpc-B1 locus and to the differences in GPC within a 0.3 cM interval corresponding to a physical distance of only 250 kb. The effect of Gpc-B1 was also examined in different environments and genetic backgrounds using a set of tetraploid and hexaploid pairs of isogenic lines. The results were consistent with those observed in the RSLs. The high GPC allele conferred a shorter duration of grain fill due to earlier flag leaf senescence and increased GPC in all four genetic backgrounds. The effect on grain size was more variable, depending on the genotype-environment combinations. These results are consistent with a model in which the wild-type allele of Gpc-B1 accelerates senescence in flag leaves producing pleiotropic effects on nitrogen remobilization, total GPC, and grain size.