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

https://doi.org/10.1016/j.fcr.2007.07.004Get rights and content

Abstract

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 for breeding, 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 superior performance in dry environments.

Introduction

Drought is by far the most important environmental stress in agriculture and many efforts have been made to improve crop productivity under water-limiting conditions. While natural selection has favoured mechanisms for adaptation and survival, breeding activity has directed selection towards increasing the economic yield of cultivated species. More than 80 years of breeding activities have led to some yield increase in drought environments for many crop plants. Meanwhile, fundamental research has provided significant gains in the understanding of the physiological and molecular responses of plants to water deficits, but there is still a large gap between yields in optimal and stress conditions. Minimizing the ‘yield gap’ and increasing yield stability under different stress conditions are of strategic importance in guaranteeing food for the future.

The evolution of crops since their domestication has been driven by the selection of desired traits recognized at the phenotypic level. Nevertheless, direct selection for grain yield under water-stressed conditions has been hampered by low heritability, polygenic control, epistasis, significant genotype-by-environment (G × E) interaction and quantitative trait loci (QTLs)-by-environment (QTL × E) interaction (Piepho, 2000). The complexity of drought tolerance mechanisms explains the slow progress in yield improvement in drought-prone environments. In recent years, crop physiology and genomics have led to new insights in drought tolerance providing breeders with new knowledge and tools for plant improvement (Tuberosa and Salvi, 2006). This article aims to provide an overview of the breeding progress in drought tolerance, and highlight future perspectives in plant breeding that could result from the integration of the recent advances in physiology and genomics.

Section snippets

Breeding progress in favourable versus drought-prone environments

Increases in yield potential achieved by plant breeding during the last Century have been well documented for numerous crops. Frequently, genetic gain has been studied by comparing in the same field trial the yield of cultivars characterized by different years of release. For most crops a linear relation between yield and year of release was found, the slope of which gives an estimate of the genetic improvement. Comparison of the different cultivars then enabled identification of the main

Drought tolerance assessment

A crucial aspect in all studies dedicated to drought tolerance is the assessment of the degree of drought tolerance of different genotypes. In many studies the identification of tolerant and susceptible cultivars is based on few physiological measures related to drought response. The difficulty in identifying a physiological parameter as a reliable indicator of yield in dry conditions has suggested that yield performance over a range of environments should be used as the main indicator for

Physiological bases for yield under drought

The physiologically relevant integrators of drought effects are the water content and the water potential of plant tissues (Jones, 2007). They in turn depend on the relative fluxes of water through the plant within the soil-plant-atmosphere continuum. Thus, apart from the resistances and water storage capacities of the plant, it is the gradient of water vapour pressure from leaf to air, and the soil water content and potential that impose conditions of drought on the plant. Once a drop in water

Molecular markers to dissect drought tolerance-related traits

Molecular markers can be used to explore germplasm through segregation and association mapping to identify useful alleles in both cultivated varieties and wild relatives. Although association mapping is intrinsically more powerful than ‘classical’ genetic linkage mapping because it scrutinizes the results of thousands of generations of recombination and selection (Syvänen, 2005), most of the data available up to date on drought tolerance are based on segregation mapping and QTL analysis. Many

Genes and metabolites conferring drought tolerance

New chances to further improve yield and/or yield stability under limiting conditions come from the last 10 years’ progress in the identification of the genetic determinants of the physiological responses related to stress tolerance. Adaptation of plants to drought and to the consequent cellular dehydration induces an active plant molecular response. This response significantly improves the tolerance to negative constraints and it is to a great extent under transcriptional control. Many

Field phenotyping

A comprehensive and careful field evaluation of mapping populations and transgenic plants is urgently needed in order to provide reliable information on the effectiveness of QTLs, candidate genes and transgenes. Due to the multigenic nature of drought tolerance, the introduction of a single gene or QTL into an elite germplasm may result in a subtle phenotypic effect or yield increase. Capacity for precise phenotyping under reliable conditions probably represents the most limiting factor for the

Future directions

When phenotypic selection was the only tool available to improve yield under drought, the improvements in crop yield observed were likely due to an increase in yield potential through the unconscious pyramiding of yield-related traits or loci. Research in the last three decades has opened up three main approaches: (i) plant physiology provided new tools to understand the complex network of drought-related traits and several drought-related traits useful to improve selection efficiency have been

Acknowledgements

The authors wish to thank an anonymous referee who provided a number of stimulating comments useful for the improvement of this review. This work was supported by grants from the Italian Ministry of Agriculture (Progetto FRUMISIS), the Italian Ministry of Science (Progetto AGROGEN) and by EU INCOA3 Project MABDE No. ICA3-2002-10073.

References (141)

  • I. Rajcan et al.

    Source-sink ratio and leaf senescence in maize. I. Dry matter accumulation and partitioning during the grain-filling period

    Field Crop Res.

    (1999)
  • A.R. Reddy et al.

    Drought-induced responses of photosynthesis and antioxidant metabolism in higher plants

    J. Plant Physiol.

    (2004)
  • R.A. Richards

    Physiological traits used in the breeding of new cultivars for water-scarce environments

    Agric. Water Manage.

    (2006)
  • S. Salvi et al.

    To clone or not to clone plant QTLs: present and future challenges

    Trends Plant Sci.

    (2005)
  • T. Abebe et al.

    Tolerance of mannitol-accumulating transgenic wheat to water stress and salinity

    Plant Physiol.

    (2003)
  • J.L. Araus et al.

    Plant breeding and drought in C3 cereals: what should we breed for?

    Ann. Bot.

    (2002)
  • J.L. Araus et al.

    Environmental factors determining carbon isotope discrimination and yield in durum wheat under Mediterranean conditions

    Crop Sci.

    (2003)
  • C.R. Babu et al.

    Genetic analysis of drought resistance in rice by molecular markers: association between secondary traits and field performance

    Crop Sci.

    (2003)
  • A. Bahieldin et al.

    Field evaluation of transgenic wheat plants stably expressing the HVA1 gene for drought tolerance

    Physiol. Plant

    (2005)
  • M. Bänziger et al.

    Selection for drought tolerance increases maize yield across a range of nitrogen levels

    Crop Sci.

    (1999)
  • T. Barker et al.

    Improving drought tolerance in maize

    Plant Breed. Rev.

    (2005)
  • W.D. Beavis et al.

    Identification of quantitative trait loci that are affected by environment

  • A. Blum

    Improving wheat grain filling under stress by stem reserve mobilisation

    Euphytica

    (1988)
  • J.S. Boyer et al.

    Grain yields with limited water

    J. Exp. Bot.

    (2004)
  • C.D. Buchanan et al.

    Sorghum bicolor's transcriptome response to dehydration, high salinity and ABA

    Plant Mol. Biol.

    (2005)
  • L. Cattivelli et al.

    Chromosome regions and stress-related sequences involved in resistance to abiotic stress in Triticeae

    Plant Mol. Biol.

    (2002)
  • L. Cattivelli et al.

    Progress in barley breeding

  • M. Causse et al.

    A genetic map of candidate genes and QTLs involved in tomato fruit size and composition

    J. Exp. Bot.

    (2004)
  • M.M. Chaves et al.

    Understanding plant responses to drought—from genes to the whole plant

    Funct. Plant Biol.

    (2003)
  • X. Chen et al.

    A potato molecular-function map for carbohydrate metabolism and transport

    Theor. Appl. Genet.

    (2001)
  • B. Courtois et al.

    Locating QTLs controlling constitutive root traits in the rice population IAC 165 × Co39

    Euphytica

    (2003)
  • J.C. Cushman

    Crasulacean acid metabolism. A plastic photosynthetic adaptation to arid environments

    Plant Physiol.

    (2001)
  • M. De Block et al.

    Poly(ADP-ribose) polymerase in plants affects energy homeostasis, cell death and stress tolerance

    Plant J.

    (2005)
  • A.A. Diab et al.

    Identification of drought-inducible genes and differentially expressed sequence tags in barley

    Theor. Appl. Genet.

    (2004)
  • S. Dorion et al.

    Induction of male sterility in wheat by meiotic-stage water deficit is preceded by a decline in invertase activity and changes in carbohydrate metabolism in anthers

    Plant Physiol.

    (1996)
  • J.G. Dubouzet et al.

    OsDREB genes in rice, Oryza sativa L., encode transcription activators that function in drought-, high-salt- and cold-responsive gene expression.

    Plant J.

    (2003)
  • S.A. Eberhart et al.

    Stability parameters for comparing varieties

    Crop Sci.

    (1966)
  • Edmeades, G.O., Bolaños, J., Elings, A., Ribaut, J.-M., Bänziger, M., Westgate, M.E., 2000. The role and regulation of...
  • G.D. Farquhar et al.

    Isotopic composition of plant carbon correlates with water-use efficiency of wheat genotypes

    Aust. J. Plant Physiol.

    (1984)
  • K.W. Finlay et al.

    The analysis of adaptation in a plant breeding programme

    Aust. J. Agric. Res.

    (1963)
  • R.A. Fischer et al.

    Drought resistance in spring wheat cultivars. I. Grain yield response

    Aust. J. Agric. Res.

    (1978)
  • R.A. Fischer et al.

    Wheat yield progress associated with higher stomatal conductance and photosynthetic rate and cooler canopies

    Crop Sci.

    (1998)
  • R.A. Fischer et al.

    Drought resistance in spring wheat cultivars. III. Yield association with morpho-physiological traits

    Aust. J. Agric. Res.

    (1979)
  • B.P. Forster et al.

    Genotype and phenotype associations with drought tolerance in barley tested in North Africa

    Ann. Appl. Biol.

    (2004)
  • E. Francia et al.

    Marker assisted selection in crop plants

    Plant Cell Tissue Organ Cult.

    (2005)
  • J.R. Frederick et al.

    Seed yield and agronomic traits of old and modern soybean cultivars under irrigation and soil water-deficit

    Field Crops Res.

    (1990)
  • J.R. Frederick et al.

    Water deficit development in old and new soybean cultivars

    Agron. J.

    (1991)
  • A. Garg et al.

    Trehalose accumulation in rice plants confers high tolerance levels to different abiotic stresses

    Proc. Natl. Acad. Sci. U.S.A.

    (2002)
  • R.A. Gaxiola et al.

    Drought- and salt-tolerant plants result from overexpression of the AVP1 H+-pump

    Proc. Natl. Acad. Sci. U.S.A.

    (2001)
  • K. Harris et al.

    Sorghum stay-green QTL individually reduce post-flowering drought-induced leaf senescence

    J. Exp. Bot.

    (2007)
  • Cited by (0)

    1

    Present address: University of Modena and Reggio Emilia, Department of Agricultural Sciences, Via J.F. Kennedy 17, I-42100 Reggio Emilia, Italy.

    View full text