Trade-offs between crop yield and water productivity (WP; yield divided by water use) are important in water-limited situations. Genetic improvement for WP generally has yield trade-offs, whereas management measures devised to improve WP tend to enhance yield as well. In contrast to the behaviour of the major herbaceous crops, WP increases in woody crops in response to water stress, facilitating the application of deficit irrigation strategies.

Stay-green crops retain green leaves longer after anthesis which can improve yield, particularly under water-limitation. We describe a new method to monitor and analyse the dynamics of canopy greenness with improved detection and interpretation of genotypic variation in stay-green. It is anticipated that selection for the identified novel stay-green traits will enhance genetic progress toward high-yielding cultivars.

Improving the ratio of biomass produced to water transpired is one way to improve water productivity, which is necessary to increase production to feed 9.6 billion by 2050. The study aimed to understand the genetic basis of the transpiration ratio (A : E), and the genetic and physiological determinants of water use in sorghum. Favourable alleles for A : E traits related to preflowering drought tolerance along with stay-green may help develop more drought-tolerant sorghum cultivars.

The major-effect drought-yield quantitative trait locus qDTY_12.1 in rice was evaluated across 18 upland experiments. The yield advantage from qDTY_12.1 was highest under intermittent drought stress, where yields were greater than 0.5 t ha^–1, whereas the effects of qDTY_12.1 on lateral root and transpiration efficiency were observed under a range of conditions. qDTY_12.1 therefore showed different environmental responses for grain yield and physiological traits.

Accessing sufficient soil moisture is vital to maintaining yield during droughts, but to produce improved varieties for such conditions breeders must be able to identify lines with deep root systems. We found that wheat varieties differed in the ability to mine water from deep soil layers, which was related to drought tolerance and without significant yield penalty. These findings and the methods employed should help validate new candidate lines to realise greater breeding progress for water limited conditions.

High irrigation volumes applied to the wet part of the root system are critical to successfully implement partial root zone drying irrigation (PRI) to improve vine performance compared to regulated deficit irrigation under semiarid conditions. Physiological responses induced by PRI were due to both the placement of irrigation and the volume of water. Thresholds and optima of soil water content in wet and dry root zones were established.

Since potato crops often require supplemental irrigation, selecting drought-tolerant varieties might help save water. We tested the importance of root biomass growth by comparing the physiology of two varieties with contrasting drought tolerance. When root growth was constrained, there were no genotypic differences in shoot physiological responses as the soil dried. Under field conditions, the drought-tolerant variety had greater root growth and maintained yield with less irrigation by better accessing moist soil layers deeper in the profile.

The ecophysiological behaviour of grapevine cultivars in response to drought is influenced by the soil conditions and by the plant genotype. These two components interact through a complex of hydraulic and hormonal signal exchanges occurring between roots and leaves. Our work highlights the differences in these signals observed in a near-isohydric and a near-anisohydric grapevine cultivars on two soil substrates with different textures, causing different dynamics of water deprivation during an imposed increasing water stress.

As roots take up water and the soil dries, water depletion is expected to occur near the root surface, ultimately limiting root water uptake. By exuding mucilage, a gel that can hold much water, roots keep the soil in their vicinity wet and can better extract water from dry soils. Mucilage exudation seems to be an optimal plant trait that favours the capture of water during drought.

Despite the predicted increase in ambient CO₂ concentration ([CO₂]), agricultural production is expected to be impacted by stressful conditions. We aimed to characterise the role of harvest index (HI) in durum wheat under elevated [CO₂] and terminal drought stress. Regardless of water treatment, plants with high HI increased biomass production under elevated [CO₂], but those with low HI showed photosynthetic acclimation symptoms. Leaf N assimilation, carbohydrate build-up and limitations in CO₂ diffusion were the main parameters involved in responsiveness.

Droughts are often accompanied by rising temperatures, severely affecting seed filling. The effects of these stresses, individually or combined, on biochemical processes related to seed filling was investigated in chickpea genotypes having contrasting sensitivity to heat and drought stress. Leaf photosynthetic function and sucrose metabolism in seeds were severely disrupted, especially by combined stress, resulting in reductions in seed weight and yield. A drought-tolerant genotype appeared to have partial cross-tolerance to heat stress.

Salinity is a growing problem worldwide that causes a significant reduction in crop yields. We have addressed this problem by manipulating the programmed cell death pathways in rice, resulting in enhanced salt stress tolerance. The implication is that farmers could grow rice containing such a trait in environments where salinisation of the soil exists, thereby addressing food security needs.

This Perspective paper inquires why, after 20 years of extensive research into the genomics of drought resistance, there are hardly any transgenic genetically modified drought-resistant crop cultivar on the market to date. An important reason is that often, the drought stress simulations and testing methods used in genomics are at fault. Guidelines for relevant drought stress physiological methods in genomics are suggested.

Agronomic and genetic progress to improve the drought tolerance of crops for water-limited environments was showcased at the interdisciplinary InterDrought-IV conference held In Perth Australia in September 2013. The integration of breeding, precision phenotyping, genomics and molecular technologies, field evaluation in target environments, and the use of crop growth models has resulted in cultivars with increased yields in drought-prone environments. The paper recommends that further research is required to ensure that progress continues and even increases to meet the nutritional demands of the world’s increasing population in the face of climate change.