Of growing importance: combining greater early vigour and transpiration efficiency for wheat in variable rainfed environments.

Increasing climate variability, particularly variability in the timing and amount of soil water, means that breeding wheat (Triticum aestivum L.) varieties with stable high grain yields is increasingly more challenging. Changing environmental conditions in water-limited rainfed environments will alter genotype ranking to reduce confidence in the identification of consistently higher yielding performers. Greater early vigour (EV) and transpiration efficiency (TE) are two physiological traits that have demonstrated benefits as breeding targets for efficient water-use in Mediterranean in-season water and monsoonal stored water environments, respectively. This Perspective discusses the hypothesis that combining higher TE and greater EV will broaden the adaptation and increase grain yields for wheats grown across most rainfed environments. We examine the physiology underpinning adaptation with greater EV and higher TE, as well as the challenges and potential benefits of deploying these traits in combination. We then discuss how these two traits interact with different environments and, in particular, the different wheat-growing regions of Australia. We conclude that the combination of these two traits is genetically and physiologically feasible, as well theoretically beneficial to average yield in most rainfed environments. Hence, we suggest a strategy for reliably managing the complex genetics underpinning EV and TE when phenotyping and selecting both traits in commercial wheat breeding programs.