Pyramiding greater early vigour and integrated transpiration efficiency in bread wheat; trade-offs and benefits

•Greater early vigour and improved integrated transpiration efficiency can be combined in wheat by selection in multi-parent populations.•To avoid trade offs, larger leaves and pseudo-stems, and increase photosynthetic capacity, should be selected for.•Use of alternate dwarfing alleles allows full expression of the early vigour trait without affecting integrated transpiration efficiency.

Increases in wheat performance under drought have been demonstrated in selection for factors contributing to greater water-use efficiency. Crop growth models have indicated the potential for significant increases in wheat yields across a wide range of wheat growing environments when both greater early vigour and higher integrated transpiration efficiency (TE) are selected together. However, greater early vigour comes with the possible trade-off of decreasing TE due to the production of larger, thinner leaves. A number of topcross-derived populations were specially developed for greater early vigour across a range of elite commercial backgrounds. These populations were assessed across multiple field environments and shown to vary significantly for early leaf area development (mean plant leaf area of 17-54 cm2 at 3.5 leaf stage) and carbon isotope discrimination (20.8-22.4%), and exceeded the range for both traits across tested commercial varieties and parental genotypes. We demonstrate that it is possible to combine greater early vigour and greater integrated TE (measured as lower carbon isotope discrimination (CID)), and that increased integrated TE is associated, in part, with increases in photosynthetic activity. We also show that alternate GA-sensitive dwarfing alleles allow greater expression of early vigour when compared to traditional GA-insensitive dwarfing alleles. The potential exists for development of high water use efficiency wheat varieties combining alleles for greater early vigour and integrated transpiration efficiency.