Genetic and environmental contributions to bread-wheat flour quality using the SDS sedimentation test as an index

The contribution of a locus to the genotypic variance depends not only on the effects of its genes but also on their frequency and on the genetic background in which it segregates. In two synthetic populations, involving common cultivars of a collection, estimates were made of the contributions of alleles at the homologous high-molecular-weight glutenin (HMW) loci, Glu-A1, Glu-B1, and Glu-D1, to the variation in flour quality using SDS sedimentation as an index. These estimates were of the magnitude of the contributions relative to each other, relative to the residual genetic variance, and relative to the environmental variance. The first population was a synthetically formed from ten bread-wheat cultivars known for their good quality, and selected under forced random mating for high SDS sedimentation. The second was the selfed progeny of a cross of Ribereno, a very poor quality bread-wheat of genotype (Null. 7-8, 2-12), with line 7681, a very good quality bread-wheat with the genotype (2*, 7-9, 5-10). Slightly over one-half of the phenotypic variance is under genetic control and over one-half of this was accounted for by HMW contributions. The initial response to selection was very rapid, as is expected when genes with large effects are involved. In addition, the frequencies of good HMW alleles increased so quickly that their contribution to the genetic variance was exhausted by the fourth generation of selection. If these estimates are correct, over one-half of the maximum possible advance in quality in heterogeneous populations similar to ours can easily be achieved in 2 years, or less, of marker-assisted selection.