Effects of the Chromosome Region Including the Gpc-B1 Locus on Wheat Grain and Protein

The recent cloning of the Gpc-B1 gene from Triticum turgidum ssp. dicoccoides (Korn. ex Asch. and Graebn.) Thell. (DIC hereafter) chromosome 6BS revealed that modern wheat varieties have a nonfunctional allele. The DIC allele accelerates senescence and increases grain protein concentration (GPC) relative to the nonfunctional allele, but its effect on yield is not known. Here we describe the effect of Gpc-B1 on grain yield, grain weight, protein yield (grain yield by GPC), and N harvest index (NHI) of common (T aestivum L.) and durum [T turgidum ssp. durum (Desf.) Husn.] wheat using BC6F3 near-isogenic lines (NILS, >99% identical) with and without the DIC Gpc-B1 allele. Six hexaploid and three tetraploid pairs of NILS were tested in three California locations (2005-2007) and all showed higher GPC when the functional Gpc-B1 allele was present (P < 0.0001). Hexaploid NILS with the DIC Gpc-B1 allele showed a significant decrease in grain weight (2.8%, P = 0.0004) and a similar trend was observed between tetraploid NILS, although the differences were marginally not significant (P = 0.08). In spite of this reduction, the differences in grain yield between NILS with different Gpc-B1 alleles across genotypes and environments were not significant. Protein yield was increased in the Gpc-B1 NILS of both hexaploid (P < 0.0001) and tetraploid (P = 0.06) wheat. The Gpc-B1 introgression in hexaploid NILS resulted in significantly (P < 0.01) lower straw N concentration at maturity and higher NHI, which suggests that the functional Gpc-B1 allele improves N remobilization.