Agronomic performance of Rht alleles in a spring wheat population across a range of moisture levels

Reduced height alleles at the Rht-B1 and Rht-D1 loci have been widely incorporated into wheat (Triticum aestivum L.) cultivars with the intent of improving partitioning of assimilates to grain. Although generally effective at increasing yield in high yield environments, their effects under heat and drought stress have been variable. We undertook this study to evaluate the effects of the Rht-B1b and Rht-D1b dwarfing alleles in a recombinant inbred line (RIL) spring wheat population under a range of soil moisture conditions. Rht-B1 and Rht-D1 genotypes of 140 RILs derived from a cross between 'Kauz' and MTRWA116 were determined by polymerase chain reactions (PCR). The population was evaluated for yield and agronomic traits in four Colorado environments under fully irrigated, partially irrigated, and rainfed conditions in 2001 and 2002. Lines with both dwarfing alleles were significantly (P < 0.01) shorter, lower yielding, and later heading in all environments compared with lines with one or no dwarfing allele. Lines with both tall alleles performed equal to or better (P < 0.05) than all other classes for grain yield, test weight, and kernel weight in all environments. Among lines with a single dwarfing allele, those with Rht-B1b on average outyielded those with Rht-D1b in the fully irrigated environment (5432 versus 4993 kg ha-1, P < 0.05), but elsewhere their yields did not differ (P > 0.05). Desirable values for most traits occurred across a relatively wide range of plant heights, with the best performing lines either shorter lines in the tall class or taller lines in the semidwarf classes.