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 ge netic background in which it segregates. In two synthetic populations, involving common cultivars of our collection, estimates were made of the contributions of alleles at the homoeologous 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 wer e of the magnitude of the contributions relative to each other, relati ve to the residual genetic variance, and relative to the environmental variance. The first population was a synthetic formed from ten bread- wheat cultivars known for their good quality, and selected under force d random mating for high SDS sedimentation. The second was the selfed progeny of a cross of Ribereno, a very poor quality bread-wheat of gen otype(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 phen otypic 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 invo lved. In addition, the frequencies of good HMW alleles increased so qu ickly that their contribution to the genetic variance was exhausted by the fourth generation of selection. If our estimates are correct, ove r one-half of the maximum possible advance in quality in heterogeneous populations similar to ours can easily be achieved in 2 years, or les s, of marker-assisted selection.