Genetic analysis of grain protein content and deviation in wheat

Grain protein content (GPC) is generally inversely correlated with grain yield (GY) but some genotypes consistently have higher grain protein contents than predicted by simple regression analysis: this is called grain protein deviation (GPD). GPD reflects greater nitrogen use efficiency and is an important target for breeders to develop more sustainable types of wheat. Here, we investigate the genetic architecture of GPC, GY, thousand grain weight (TGW) and GPD using a population of 104 doubled haploid lines derived from a cross between two cultivars with positive (Hereward) and negative (Malacca) GPD and grown in replicated randomised field trials over three years. A total of 9 QTL were detected for all traits, five for GPC, two for GPD and one each for GY and TGW. All of the increasing alleles for GPC and GPD and for the single QTL for TGW were contributed by Hereward while Malacca contributed the single increasing allele for GY. The two QTLs for GPD located on chromosomes 3A and 5B explained 23.3% and 16.6% of the variance in the sample sets, respectively. Three QTL for GPC (on chromosomes 3A, 3B, 5B) each explained more than 14% of the variance, with those on chromosomes 3A and 5B having similar locations to the GPC QTLs on the same chromosomes. A survey of the gene content between the markers bordering the confidence intervals for the two GPD QTLs on chromosomes 3A and 5B identified 136 and 704 protein coding genes, respectively, including possible candidate genes.