Dwarfing genes, water-use efficiency and agronomic performance of spring wheat

The Rht1 and Rht2 dwarfing genes have been used extensively to reduce height in wheat (Triticum aestivum L.). The Rht3 gene is also a potent dwarfing gene. Information in the literature is limited or conflicting as to the comparative effects of these genes on water-use efficiency (WUE) and agronomic performance under different environments. Four near-isogenic lines, rhtrht, Rht1Rht1, Rht2Rht2, and Rht3Rht3 in Maringa and three, rhtrht, Rht2Rht2, and Rht3Rht3 in Nainan 60 bread wheat backgrounds were used to determine the effects of dwarfing genes on plant height, total dry matter (TDM) and its components, evapotranspiration efficiency (ETE, TDM/water evapotranspired), WUE (grain yield/water evapotranspired), and carbon isotope discrimination (Δ) in well-watered and droughted pot experiments in the glasshouse. The near-isogenic lines were also grown in well-watered and droughted field experiments. The dwarfing genes consistently reduced plant height and kernel weight in Maringa and Nainari 60 backgrounds under all environmental conditions. The dwarfing genes significantly increased number of spikes per plant in Nainari 60 background in the glasshouse and number of grains per plant in Maringa background under field conditions. In most cases, TDM or shoot dry matter (SDM) in short isogenic lines was significantly reduced. The reduction in grain yield was less than that of TDM or SDM. Therefore, harvest index was greater in short isogenic lines than their respective tall standard counterparts. The effects of the dwarfing genes on root dry matter were relatively small. The dwarfing genes, on average, depressed ETE by 21% and WUE by 15% only in Maringa background. Plant height was positively correlated with TDM and ETE but negatively so with Δ in glasshouse experiments. Grain yield and TDM were positively correlated with ETE. Δ was negatively associated with ETE, TDM, SDM, and grain yield under glasshouse conditions. Key words: Spring wheat, dwarfing genes, near-isogenic lines, water-use efficiency, carbon isotope discrimination