Drought tolerance improvement in crop plants: An integrated view from breeding to genomics.

Drought is the most significant environmental stress in agriculture worldwide and improving yield under drought is a major goal of plant breeding. A review of breeding progress pointed out that selection for high yield in stress-free conditions has, to a certain extent, indirectly improved yield in many water-limiting conditions. Further progress requires the introduction of traits that reduce the gap between yield potential and actual yield in drought-prone environments. To achieve this three main approaches can now be exploited: (i) plant physiology has provided new insights and developed new tools to understand the complex network of drought-related traits, (ii) molecular genetics has discovered many QTLs affecting yield under drought or the expression of drought tolerance-related traits, (iii) molecular biology has provided genes useful either as candidate sequences to dissect QTLs or for a transgenic approach. The extent of information that breeders have now offers them new tools forbreeding, such as markers for QTLs and single genes for plant transformation. Breeders are thus asked to blend together all knowledge on the traits sustaining yield under drought and to accumulate the most effective QTLs and/or transgenes into elite genotypes without detrimental effects on yield potential. This strategy will lead to new cultivars with high yield potential and high yield stability, that in turn will result in superiorperformance in dry environments.