Adaptation of Dryland Crops to Water Limitation and Climate Change: From Traits to Yield.

In the last few years we have acquired strong evidence in legume and cereal crops species adapted to the semi-arid tropics that the availability of small amount of water during the reproductive and grain filling period were critical for enhancing their grain yield under water limited conditions. We have then shown that water availability during grain filling was a consequence of a number of plant traits responsible for altering the plant water budget, and operating mostly in the absence of stress. These different traits will be reviewed as an attempt to crack the plant water budget into simpler “building blocks”. One such trait is the capacity to restrict the transpiration under high vapor pressure deficit (VPD) conditions. It has high relevance for both drought adaptation and climate change adaptation where an increase in VPD is expected. Data will be presented on the genetic variation in different species, on the methods to measure them, and on the possible mechanisms underlying this trait. In particular we will show the close relationship between the differences in the capacity to restrict transpiration under high VPD and differences in aquaporin gene expression in leaves and roots. From a breeding application perspective, we will show the close linkages between some of these traits and QTLs related to drought adaptation (staygreen in sorghum, terminal drought tolerance in pearl millet). We will also show the current development of a large scale phenotyping platform to target these “building blocks”. Because drought adaptation is complex, crop simulation modelling comes here as a critical tool to test the values of such traits, or trait-by-management combinations, on yield across locations, and then to guide trait breeding and agronomic management targets. Crop simulations will then be presented on several traits and trait-by-management combinations.