Green revolution "stumbles" in a dry environment: Dwarf wheat with Rht genes fails to produce higher grain yield than taller plants under drought.

Rht genes control reduced height in wheat, and two identified loci, Rht1 (Rht-B1b) and Rht2 (Rht-D1b) and mutants thereof, were central in achieving the much celebrated "Green revolution". Dwarf and semi-dwarf wheat plants have thicker and shorter stems and are less prone to lodging in irrigated fields, resulting in much higher grain yield. Serious limitations, however, have begun to emerge following cultivation of dwarf or semi-dwarf wheat plants in drier environments. A clear grain yield penalty in dwarf and semi-dwarf compared to taller wheats has been reported for young plants, particularly under early and severe drought. Shorter coleoptiles, smaller leaves with altered thickness, and insensitivity to gibberellic acid were identified as the major biological factors responsible for an increased vulnerability to drought in dwarf or semi-dwarf wheat seedlings. This means that, in dry conditions, tall and fast-growing wheat plants with good tolerance to drought may offer higher grain yields than "Green revolution" wheat. In a future climate where drier environments are more likely, tall wheat genotypes, or those only moderately reduced in stature that carry alternative or novel Rht genes and alleles, may be better suited to many wheat-growing regions. Dwarf and semi-dwarf wheat genotypes are likely, however, to remain the best choice for irrigated or well-watered and fertilised fields where their high yield potential can be realised. This article is protected by copyright. All rights reserved.