Evidence for polygenic control of fibre differentiation in spring wheat and its relationship with the gibberellin-insensitivity locus Rht1

The relationship between culm anatomy and the rht (reduced height) system of wheat was studied in rht1 (GA-sensitive, tall) and Rht1 (GA-insensitive, semidwarf) spring wheat F₁₁ isolines. The experimental design allowed to distinguish between the effect of the major height-controlling gene (rht1) and that of the genetic (polygenes) background. Counting the number of fibre cell files in the cortex of the first internode at heading time, we found no structural differences between the tall (rht1) and the semidwarf (Rht1) isolines. It appears that stem elongation and the determination of cell fate to fibres are regulated by two different mechanisms. However, a significant polygenic effect on the number of fibre cell files in the culm cortex was found. These data are consistent with the hypothesis that wheat lodging is not affected by the culm structure but mainly by root characteristics such as anchorage.