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

In dry conditions, tall and fast‐growing wheat plants with good tolerance to drought may offer higher grain yields than ‘Green revolution’ wheat. In the 1960s, a new era termed the ‘Green revolution’, saw wheat yields double in near‐equatorial India and Pakistan, and increase four‐fold in Mexico as a result of advances made by the International Maize and Wheat Improvement Center, CIMMYT (Evenson & Gollin, 2003; Trethowan, Reynolds, Ortiz‐Monasterio, & Ortiz, 2007). The impact of this development on global agriculture and human nutrition was unprecedented and indeed so great that the wheat breeder, Norman Borlaug, the ‘father of the Green Revolution’, was awarded the Nobel Peace Prize in 1970. The introgression of mutant alleles of dwarfing genes Rht (Reduced height) from Japanese wheat cv. Norin 10 into other wheat germplasms via conventional hybridisation resulted in the initial evaluation of semi‐dwarf homologous mutant genes Rht‐1 (synonym = Rht‐B1b), Rht‐2 (synonym = Rht‐D1b) or both. The dramatic effect of thicker and shorter stems in the production of non‐lodging commercial wheat cultivars resulted in a superior grain yield (GY), with semi‐dwarf wheat genotypes carrying large and heavy, fully filled spikes, with improved Harvest index (HI) compared to their non‐dwarf wild‐type counterparts (Allan, 1989; Gent & Kiyomoto, 1998; Hedden, 2003; Peng et al., 1999; Sakamoto & Matsuoka, 2004).