Gene differences in heading date, height, seed weight and seed yield between two pure line varieties of Triticum aestivum L.

Reciprocal sets of homozygous inbred backcross lines were developed by crossing two pure line varieties (Baart 46 and Ramona) of Triticum aestivum L., followed by two backcrosses to each of the two parent varieties, and six to eight generations of selfing. Data on each inbred backcross line was obtained from twelve plots (from replications in three years). Five genes were responsible for over 95% of the genetic variation for heading date. These genes had pleiotropic effects on plant height that were proportional to their effects on heading date. Two additional genes had detectable effects on plant height. The genes with a measurable effect on height accounted for 90% of the genetic variation in the Baart 46 genetic background. One gene affected seed weight. In the Ramona background, this gene accounted for 80% of the genetic variation in seed weight and 16% of the genetic variation in seed yield. Two genes, responsible for the earliest and latest heading date classes, had large pleiotropic effects on seed yield. They accounted for 60% of the genetic variation in yield. One gene, with no effect on heading date, caused a detectable reduction in yield of 23% in the Baart 46 inbred backcross lines. This gene had no apparent effect in the Ramona genetic background. Quantitative trait genes are sparsely distributed in the genome: fewer than one in four chromosome arms carries a gene with a detectable effect. Gene effects on quantitative traits are not small and similar. The distribution of 22 gene effects for heading date and height is slightly skewed to the right: as the magnitude of effect increases, the frequency of genes having the effect decreases.