Integrated genomics, physiology and breeding approaches for improving drought tolerance in crops

Abstract

Drought is one of the most serious production constraint for world agriculture and is projected to worsen with anticipated climate change. Inter-disciplinary scientists have been trying to understand and dissect the mechanisms of plant tolerance to drought stress using a variety of approaches; however, success has been limited. Modern genomics and genetic approaches coupled with advances in precise phenotyping and breeding methodologies are expected to more effectively unravel the genes and metabolic pathways that confer drought tolerance in crops. This article discusses the most recent advances in plant physiology for precision phenotyping of drought response, a vital step before implementing the genetic and molecular-physiological strategies to unravel the complex multilayered drought tolerance mechanism and further exploration using molecular breeding approaches for crop improvement. Emphasis has been given to molecular dissection of drought tolerance by QTL or gene discovery through linkage and association mapping, QTL cloning, candidate gene identification, transcriptomics and functional genomics. Molecular breeding approaches such as marker-assisted backcrossing, marker-assisted recurrent selection and genome-wide selection have been suggested to be integrated in crop improvement strategies to develop drought-tolerant cultivars that will enhance food security in the context of a changing and more variable climate.

Fig. 1

A holistic approach for integrating genomics, physiology and breeding approaches for developing the superior varieties with enhanced drought tolerance

Fig. 2

An example of involvement of several physiological traits for conferring terminal drought tolerance in chickpea. A set of eight chickpea genotypes including four tolerant (ICC 14799, ICC 867, ICC14788 and ICC 3325) and four susceptible (ICC 4814, ICC 8058, ICC 3776 and ICC 7184) to drought stress (green filled circle tolerant and orange filled circle sensitive) have been characterized for: canopy temperature (°C) and canopy conductance (mg H₂O m⁻² h⁻¹) measured at 42 DAS under well-watered conditions; fraction of transpirable soil water (FTSW) threshold measured in plants exposed to progressive water stress and leaf expansion rate (LER; cm² day⁻¹), measured between 42 and 56 DAS. Susceptible genotypes tended to have lower canopy temperature and FTSW, but higher canopy conductance and LER as compared to tolerant genotypes (color figure online)

Fig. 3

An overview of three-tier screening of germplasm collection for traits related to drought tolerance. Three screening tiers are shown on the right side and the procedure of selection of germplasm followed in each tier of screening is provided on the left side