Breeding for drought tolerance in Wheat
Authors: Vikas Gupta, Chandra Nath Mishra and Satish Kumar
Indian Institute of Wheat and Barley Research, Karnal-132001 Haryana

Wheat (Triticum aestivum) is a major source for human food consumption. Wheat production is affected by several biotic and abiotic factors. Among the abiotic factors, wheat production is adversely affected by drought in 50% of the area under production in the developing countries. In India, total arable raga is 143.8 mha of which 65.5 and 34.5 mha area is rainfed and dryland, respectively affected by drought. Drought tolerance is a complex trait having low heritability, high genotype x environment interaction which hampers the progress towards drought resistance breeding. Variation and unpredictability of environmental conditions have hindered breeder's efforts to select for drought tolerance. Drought tolerance is defined as the ability of a plant to live, grow and reproduce satisfactorily with limited water supply or under periodic conditions of water deficit (Turner, 1979). Drought stress can influence the performance of plants drastically at cellular level, plant growth, development and yield. Drought resistance referred to as the ways of minimizing the loss of yield in drought environment as compared to the normal environment.

Breeding parameters for drought tolerance
• Osmotic adjustment
• Stomatal conductance
• Cell membrane stability
• Molecular markers and QTLs

Osmotic adjustment

• Assists the plant to get rid of ion toxicity and water uptake under drought stress

• Plant accumulate large amount of osmolytes

• Inorganic ions including sodium potassium, calcium and chloride ions play a vital role in osmotic adjustment

• P5CS gene has been discovered on 7A of wheat involved in osmotic adjustment

• P5CS showed positive correlation with drought tolerance in wheat

Stomatal Conductance

• Plants uptake CO2 from air and transpire water through stomata.

• Plants with lowered stomatal conductance have better adaptability under drought stress

• Genes Rht-B1b and Rht-D1b showed strong association with drought tolerance as well as stomatal conductance

Cell membrane stability

• Plant cell membrane stability is used as an indicator of drought tolerance

• Rate of injury can be assayed through the measurement of electrolytes leaked from the leaves.
• The wheat genotypes with higher cell membrane stability (71-80 %) have been noticed to perform better under drought
Molecular markers and QTLs

• QTLS for drought tolerance discovered on 5B, 4B and 7B

• A QTL on chromosome 5B showed positive correlation with drought tolerance.

• QTLs discovered on chromosome 4B and 7B showed negative effect on drought tolerance

• Chromosome 4A reported to carry important genes for production under drought stress.

• A marker located on chromosome 4A (Xwmc89) was found significantly associated with drought tolerance in tolerant wheat genotypes

Genes involved in drought tolerance in wheat

Gene Reference Gene Reference
Dreb 1 Huseynova and Rustamova, 2010; Sakuma et al., 2006 opato and Langridge; Wei et al., 2009 TaEXPB23 Han et al., 2012
Dreb 2 Liu et al., 1998; Nakashima and Yamaguchi-Shinozaki, 2005 TaSRK2C1 Du et al., 2013b
LEA Lopato and Langridge TaASR1 Hu et al., 2013
Rht 8 Gasperini et al., 2012 TaHPS Xiao et al., 2012
TaAQP7 Zhou et al., 2012 TaSRHP Hou X. et al., 2013
TaSnRK2.8 Zhang et al., 2010 TaSIP Du et al., 2013a
TaMYB33 Qin et al., 2012 TaWRKY2 Niu et al., 2012
TaMYB2 Garg et al., 2012 TaWRKY19 Niu et al., 2012
R2R3-MYB Zhang et al., 2012 R2R3-MYB, TaMYB30-B Zhang et al., 2012
TaNAC2a, TaNAC4a, TaNAC6, TaNAC7, TaNAC13, TaNTL Tang et al., 2012

Interventions for trait accumulation in practical breeding

• Potential parental lines for target environments should be identified.

• Crosses are designed to encompass as many of the target-traits as possible

• Selection in F2 considers simply inherited traits in well-watered conditions

• Early generation bulks are screened for canopy temperature (CT); families with warm canopies compared to checks are mainly discarded
CT is well studied and positively correlated trait for drought tolerance.

About Author / Additional Info:
I am working as a Scientist in Indian Institute of Wheat and Barley Karnal, Haryana under ICAR, New Delhi