Water: the most important ‘molecular’ component of water stress tolerance research

Abstract

Abstract. Water deficit is the main yield-limiting factor across the Asian and African semiarid tropics and a basic consideration when developing crop cultivars for water-limited conditions is to ensure that crop water demand matches season water supply. Conventional breeding has contributed to the development of varieties that are better adapted to water stress, such as early maturing cultivars that match water supply and demand and then escape terminal water stress. However, an optimisation of this match is possible. Also, further progress in breeding varieties that cope with water stress is hampered by the typically large genotype  environment interactions in most field studies. Therefore, a more comprehensive approach is required to revitalise the development of materials that are adapted to water stress. In the past two decades, transgenic and candidate gene approaches have been proposed for improving crop productivity under water stress, but have had limited real success. The major drawback of these approaches has been their failure to consider realistic water limitations and their link to yield when designing biotechnological experiments. Although the genes are many, the plant traits contributing to crop adaptation to water limitation are few and revolve around the critical need to match water supply and demand. We focus here on the genetic aspects of this, although we acknowledge that crop management options also have a role to play. These traits are related in part to increased, better or more conservative uses of soil water. However, the traits themselves are highly dynamic during crop development: they interact with each other and with the environment. Hence, success in breeding cultivars that are more resilient under water stress requires an understanding of plant traits affecting yield under water deficit as well as an understanding of their mutual and environmental interactions. Given that the phenotypic evaluation of germplasm/breeding material is limited by the number of locations and years of testing, crop simulation modelling then becomes a powerful tool for navigating the complexity of biological systems, for predicting the effects on yield and for determining the probability of success of specific traits or trait combinations across water stress scenarios.

Effects of water deficit on radicle apex elongation and solute accumulation in Zea mays L

“…This growth characteristic is an adaptation to water-limiting conditions, and it is crucial for the formation of the aerial portion of the plant (Hsiao and Xu, 2000;Sharp and Davies, 1979;Westgate and Boyer, 1985;Yamaguchi and Sharp, 2010). Several authors have concluded that, in maize plants, the root architecture, length and water extraction are closely related; however, other studies have shown poor relationships between water uptake and root length and density compared with other crops, such as chickpea and lentil (Valdez et al, 2013). When exposed to water deficit conditions, the elongation zone of the maize radicle has the capacity for osmotic adjustment, and an increase of 45% in the proline concentration has been observed Voetberg and Sharp, 1991).…”

NO to drought-multifunctional role of nitric oxide in plant drought: Do we have all the answers?

“…However, laboratory conditions are substantially different from the actual field and hence, improved plant survival under PEG-induced drought may not always correlate with the gains in the field. Moreover, antioxidative defense have shown to occur at much later stage of stress tolerance in field crops such as Cicer arietinum, Arachis hypogaea and Pennisetum glaucum, bearing no correlation with the actual yield under drought[88]. Nevertheless, the influence of NO on stomatal closure is indeed beneficial for maintaining plant water status, and hence holds relevance.…”

Breeding for enhanced drought resistance in barley and wheat - drought-associated traits, genetic resources and their potential utilization in breeding programmes

“…Water uptake into the cells is regulated by aquaporin protein channels located in the plasma membrane of root hair cells (Agre et al 1993;Tyerman et al 2002) and can be determined by a lysimetric method. The application of lysimetric method in sorghum revealed a large genotypic variation in water extraction capacity from the soil profile and can also be used for a gravimetric screening of transpiration efficiency (TE) (Vadez et al 2008(Vadez et al , 2011(Vadez et al , 2013Vadez 2014). The method can also be applied to other cereals such as wheat and barley.…”

“…the given genetic material cannot adopt all of them. As the most crucial example, the "trade-off " principle between water conservation and biomass accumulation as expressed in terms of WUE and EUW can be given (Tardieu 2012;Vadez et al 2013). Therefore, knowledge of the environment (a season when drought occurs and the severity of the drought stress) appears to be crucial in the selection of the most suitable breeding strategy.…”