Physiological traits used in the breeding of new cultivars for water-scarce environments

A physiological understanding of plants’ responses to drought has often been sought on the pretext that this understanding will assist plant breeders develop higher yielding varieties for water-scarce environments. However, despite an extensive literature on plants’ response to drought there are few documented examples where a physiological understanding of drought has identified traits that limit yield under drought and where these have been used in successful crop improvement programs to enhance crop yields. This paper selects seven examples where a physiological understanding has resulted in more precise targeting of genetic variation and has resulted in higher yielding or more productive germplasm or varieties. The underlying features of these successes are then examined to identify the elements of success that may be used to further enhance yield improvement in dry environments. The conclusions are that all of these traits directly or indirectly transfer their effects to yield over long time scales by increasing either water-use (amount and pattern), water-use efficiency or partitioning of more biomass to grain.