RhtD1b

RhtD1b is a semi-dwarfing allele of the Rht-D1 locus on chromosome 4D in hexaploid bread wheat (Triticum aestivum). The Rht-D1 gene encodes a DELLA family growth repressor involved in gibberellin signaling. The D1b mutation yields a GA-insensitive allele, leading to reduced degradation of DELLA proteins and suppression of gibberellin–mediated stem elongation. As a result, plants carrying RhtD1b are shorter than GA-responsive lines, with improved lodging resistance and often earlier maturity.

The allele influences several agronomic traits beyond height. Height reduction is the primary effect, but RhtD1b can affect coleoptile length, grain number per spike, and kernel size, with outcomes that depend on genetic background and environmental conditions. It is commonly combined with other semi-dwarfing alleles, such as Rht-B1b, in modern cultivars to optimize plant architecture and yield potential.

History and use: RhtD1b is one of the major semi-dwarfing alleles adopted globally during and after the Green Revolution, contributing to higher harvest index and yield stability in many environments. However, its performance can be sensitive to sowing depth and nitrogen management, and breeders consider these interactions when deploying the allele.

See also: Rht-B1b, Rht-D1a, DELLA proteins, gibberellin signaling.