RHt

Rht is an abbreviation commonly used in cereal genetics to refer to reduced-height dwarfing genes in wheat. These genes encode alleles that shorten the overall plant stature, increase lodging resistance, and improve the harvest index. The most influential alleles are Rht-B1b and Rht-D1b, which were derived from the Japanese variety Norin 10 and were widely deployed during the Green Revolution to boost wheat yields through better responses to fertilizer and improved standing stability.

Genetic and biochemical basis: Rht-B1b and Rht-D1b are semi-dwarf, gibberellin-insensitive mutations that affect the plant’s GA signaling pathway through altered DELLA repressor proteins. This reduced sensitivity to gibberellins limits stem elongation. Other Rht loci, such as Rht8, Rht9, and Rht11, have different allelic forms and mechanisms, with some being GA-sensitive. The effect of Rht alleles varies with genetic background and environment, producing a range of height reductions and associated architectural changes.

Impact, applications, and considerations: The adoption of semi-dwarf Rht alleles contributed to substantial yield gains by enabling higher fertilizer inputs and reducing lodging risk. However, some Rht alleles are linked to shorter coleoptiles, which can hinder seedling establishment in deep or dry sowing conditions. Breeders often combine multiple Rht alleles with other traits to tailor performance to specific environments, balancing height, emergence, and stress responses for improved end-use quality.