OPINION

Exploiting plant drought stress biology to increase resourceuse efficiency and yield of crops under water scarcity

William J. Davies

Received: 5 September 2013 / Accepted: 6 September 2013

� The Author(s) 2014

Increasing the availability of food to meet a growing

global demand is one of the greatest challenges facing

humankind in the twenty-first century. Accelerating

trends in urbanization, environmental degradation,

and climate change as well as a host of social issues all

hinder our ability to feed the world’s growing human

population, projected to exceed 9 billion by 2050

(Godfray et al. 2010).

We fully recognize that increased food security is

not just about producing more but it seems perverse to

argue, as has often been the case, that we already

produce enough food (and have the science to

underpin its delivery!) and focus solely on the many

other issues underpinning the food system. Rather, we

argue here that there are many opportunities available

to exploit existing science via both crop improvement

and crop management, to increase potential yield,

reduce the yield gap and increase the efficiency of

resource use in agriculture (e.g. Foulkes et al. 2010). In

addition, addressing some of the grand challenges of

plant science (Reaping the Benefits, The Royal

Society of London 2009) provides substantial oppor-

tunities to move towards these targets.

Many countries in the world have responded to the

challenge of increasing global food insecurity by

focusing efforts on increasing food production. For

example, in China between 1949 and 2011, total grain

output increased by fivefold from 113 to 571 MT (Fan

et al. 2012), while per capita grain production grew

from 209 to 424 kg/year (National Bureau of Statistics

of China 2012). This marked achievement, which is an

inspiration to researchers and producers in many parts

of the world, is attributed to the introduction of new

genetic material and new intensive cropping systems

but largely to massive increases in the use of irrigation,

fertilizer, and other agricultural chemicals (Zhu and

Chen 2002). However, resulting environmental issues

such as reduced ground water levels, water contam-

ination from diffuse pollution (Kang et al. 2008) and

soil acidification are now causing concern in many

parts of the world. Hence, whether or not grain

production can grow in a sustainable way to meet

increasing global demand remains an open question.

For many parts of the world, water availability for

agriculture is recognized as a significant and growing

limitation. For example, on the North China Plain

(NCP) a crucial food producing region for China, a

winter wheat crop will consume around 450 mm of

water while annual precipitation averages only

500 mm. Furthermore, only 20–30 % of the precipi-

tation occurs during the winter wheat growing season

and therefore the crop relies heavily on irrigation. In

this region, around 70 % of water used in agriculture is

derived from groundwater. Excessive mining of

groundwater aquifers in many parts of the world has

caused water tables to recede from a few meters below

the soil surface in 1970s to 30 m or more (e.g. Kang

W. J. Davies (&)

Lancaster Environment Centre, Lancaster University,

Lancaster LA1 4YQ, UK

e-mail: w.davies@lancaster.ac.uk

123

Theor. Exp. Plant Physiol.

DOI 10.1007/s40626-014-0004-4

et al. 2008), an enormous problem for farmers and for

the natural environment. The total groundwater

reserves in the NCP are around 75 billion tons.

Assuming realistic water use efficiencies for wheat

and maize, Li et al. (2013) calculate that to attain the

wheat and maize output required for an appropriate

contribution to national yield targets for 2030, would

require nearly 100 billion tons of water. Climate

change predictions suggest that in future, an even

bigger mismatch between supply and demand is likely.

Calculation like these suggest that in most regions

of the world either there already is, or there will be, a

shortfall in the availability of water for agriculture and

that to sustain yields and minimize environmental

impact, we must seek to exploit plant drought stress

biology to increase resource use efficiency and yield of

crops. This can be done through modified management

practices (e.g. deficit irrigation) (Davies et al. 2011).

Optimisation of these methods (and also the produc-

tion of drought resistant genotypes) requires some

understanding of how droughted plants regulate yield.

In this paper we focus upon the need to understand the

role of phytohormones in both vegetative and repro-

ductive development of crops. We argue that it is

important to discriminate effects of altered chemical

status and water status, as many studies indicate that

cereal crops can maintain turgor in vegetative and

reproductive structures in the field in response to a

range of environmental challenges. Environmental

effects on yield development in cereals can be

extremely subtle. For example, Boyer (1982) has

shown that even well irrigated, well fed crops in the

USA may yield only 20 % of potential yield values.

We believe that hormonal and other chemical signals

have an important role to play in regulating yield, even

in plants that are to all appearances ‘unstressed’.

Deficit irrigation (DI) techniques have generated

substantial increases in water use efficiency and mild

water deficits can, if scheduled appropriately, actually

increase yields as result of modified partitioning to

grains (Yang and Zhang 2010). DI may also enhance

food safety (Price et al. 2013). We suggest that

appropriate operation of these techniques and progress

towards the development of new genotypes with

improved yielding and water productivity under

drought might be made via exploitation of new

understanding of the involvement of ethylene, ABA

and CK in yield regulation. Modified trait screening for

drought productivity might include physiological

variables such as maximal stress ethylene production

(‘‘eth-max’’), ABA-ACC/ethylene concentration

ratios (Yang et al. 2007) and sensitivity of plant

development and physiology to ethylene and

ABA:Eth. Maximal ethylene production can be wheat

genotype-dependent in response to stress (Balota et al.

2004). Exploitation of this kind of information might

be achieved by combining relevant physiological traits

(PTs) deterministically whereby progeny might show,

for example, expression of low Eth-max and/or

appropriate ABA:Eth with additional stress adaptive

traits in elite agronomic backgrounds. This approach

might allow the development of a crop that is resilient

under a combination of stresses. To accelerate genetic

gains in yield in the future, it is now accepted that

complex physiological traits can be incorporated as

additional criteria in more conventional trait selection

programmes (e.g. Lopes and Reynolds 2010) but it will

be necessary to carefully define targets and environ-

ments. Impacts might be assessed across a broad range

of scenarios via modeling of G 9 E 9 M (genet-

ics 9 environment 9 management) (Tardieu (2012).

References

Balota M, Cristescu S, Paynete WA, te Lintel Hekkert S, Laa-

rhoven LJJ, Harren FJM (2004) Ethylene production of two

wheat cultivars exposed to desiccation, heat, and paraquat-

induced oxidation. Crop Sci 44:812–818

Boyer JS (1982) Plant productivity and environment. Science

218:443–448

Davies WJ, Zhang J, Yang J, Dodd IC (2011) Novel crop science

to improve yield and resource use efficiency in water-

limited agriculture. J Agric Sci 149:123–131

Fan MS, Shen JB, Yuan LX, Jiang RF, Chen XP, Davies WJ,

Zhang FS (2012) Improving crop productivity and resource

use efficiency to ensure food security and environmental

quality in China. J Exp Bot 63:13–24

Foulkes MJ, Slafer GA, Davies WJ, Berry PM, Sylvester-

Bradley R, Martre P, Calderini DF, Reynolds MP (2010)

Raising yield potential in wheat: optimizing partitioning to

grain yield while maintaining lodging resistance. J Exp Bot

62:469–486

Godfray HCJ, Beddington JR, Crute IR, Haddad L, Lawrence D,

Muir JF, Pretty J, Robinson S, Thomas SM, Toulmin C

(2010) Food security: the challenge of feeding 9 billion

people. Science 327:812–818

Kang SZ, Su XL, Tong L, Zhang JH, Zhang L, Davies WJ

(2008) A warning from an ancient oasis: intensive human

activities are leading to potential ecological and social

catastrophe. Int J Sustain Dev 15:440–447

Li Y, Zhang W, Ma L, Wu L, Shen J, Davies WJ, Oenema O,

Zhang F, Dou Z (2013) An analysis of China’s grain

Theor. Exp. Plant Physiol.

123

production: looking back and looking forward. Food

Energy Secur. doi:10.1002/fes3.41

Lopes MS, Reynolds MP (2010) Partitioning of assimilates to

deeper roots is associated with cooler canopies and

increased yield under drought in wheat. Funct Plant Biol

37:147–156

National Bureau of Statistics of China (2012) China statistical

yearbook. China Statistics Press, Beijing

Price AH, Norton GJ, Salt DE, Ebenhoeh O, Meharg AA, Me-

harg C, Islam MR, Sarma RN, Dasgupta T, Ismail AM,

McNally KL, Zhang H, Dodd IC, Davies WJ (2013)

Alternate wetting and drying irrigation for rice in Bangla-

desh: is it sustainable and has plant breeding something to

offer? Food Energy Secur 2:120–129

Tardieu F (2012) Any trait or trait-related allele can confer

drought tolerance: just design the right drought scenario.

J Exp Bot 63:25–31

The Royal Society of London (2009) Reaping the benefits:

science for sustainable intensification. The Royal Society

of London, London, pp 1–78

Yang J, Zhang JH (2010) Crop management techniques to

enhance harvest index in rice. J Exp Bot 61:3177–3189

Yang J, Zhang J, Liu K, Wang Z, Liu L (2007) Abscisic acid and

ethylene interact in rice spikelets in response to water stress

during meiosis. J Plant Growth Regul 26:318–328

Zhu ZL, Chen DL (2002) Nitrogen fertilizer use in China—

contributions to food production, impacts on the environ-

ment and best management strategies. Nutr Cycl Agro-

ecosyst 63:117–127

Theor. Exp. Plant Physiol.

123