The present invention provides a wheat plant comprising an Rht-B1 allele which encodes an Rht-B1 (DELLA) poly-peptide. Grain from a near-isogenic wheat line comprising the dwarfing Rht-B1c allele was subjected to sodium azide mutagenesis. Plants exhibiting early leaf elongation rates or mature plant height greater than the dwarf parent were selected and the Rht-B1 gene sequenced. This identified 35 mutated alleles of Rht-B1c. Similar methods were also used to identify mutant alleles of the dwarfing s1n1d allele in barley, where DELLA is encoded by the s1n1 gene.