EVIDENCE FOR POLYGENIC CONTROL OF FIBER DIFFERENTIATION IN SPRING WHEAT AND ITS RELATIONSHIP WITH THE GIBBERELLIN-INSENSITIVITY LOCUS RHT1

The relationship between culm anatomy and the rht (reduced height) sys tem of wheat was studied in rht1 (GA-sensitive, tall) and Rht1 (GA-ins ensitive, semidwarf) spring wheat F-11 isolines. The experimental desi gn allowed to distinguish between the effect of the major height-contr olling gene (rht1) and that of the genetic (polygenes) background. Cou nting the number of fibre cell files in the cortex of the first intern ode at heading time, we found no structural differences between the ta ll (rht1) and the semidwarf (Rht1) isolines. It appears that stem elon gation and the determination of cell fate to fibres are regulated by t wo different mechanisms. However, a significant polygenic effect on th e 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 ancho rage.