Quantitative Trait Loci Analysis for the Effect of Rht-B1 Dwarfing Gene on Coleoptile Length and Seedling Root Length and Number of Bread Wheat

It has been documented that the dwarfing genes, Rht-B1b and Rht-D1b, can reduce wheat (Triticum aestivum L.) coleoptile length (CL), but their effects on number of roots (RN) and root length (RL) have not been determined. Our objectives were to identify quantitative trait loci (QTL) controlling CL, RN, and RL and to determine if any of the QTL correspond to wheat dwarfing genes. A population consisting of 159 recombinant inbred lines (RILs) was derived from the cross of Rio Blanco (Rht-B1b, Rht-D1a), a semidwarf cultivar with short CL, and IDO444 (Rht-B1a, Rht-D1a), a tall germplasm with long CL. The CL, RN, longest root length (LRL), and total root length (TRL) were evaluated at two temperature regimes (18 and 22°C). A major QTL mapped to the Rht-B1 locus on chromosome 4B explained 64% of the phenotypic variation for CL, 9% for LRL, 26% for TRL, and 14% for plant height. The CL of the semidwarf RILs was significantly less than that of the tall lines while the reverse results were observed for LRL and TRL. Our results indicated that the Rht-B1 gene had the pleiotropic effect of decreasing CL while increasing LRL and TRL. None of the six QTL for RN were mapped to the regions containing the Rht-B1 locus although semidwarf RILs had more roots than the tall lines. This study suggested that selection of the Rht-B1b allele tended to increase root biomass, perhaps ameliorating its negative effect of reduced CL.