**5. Molecular and genomic prospects for improvement of drought tolerance**

Traditionally, there have been several efforts to develop drought-tolerant crop genotypes through usual breeding methods [58, 59]. In this method, two groups of plants with desirable traits are selected and crossed to obtain offsprings having new genetic arrangements [60]. Drought resistance is directly or indirectly incorporated in the crop species via genetic variability of traits and thus selection in breeding is ought to be useful. Important traits to target in plant breeding might include waterextraction efficiency, water-use efficiency, conductance of water, osmo-elastic adjustments and leaf area modulation [15]. Genetic data improves the efficiency of the breeding method. Polymorphisms based on molecular markers that occur naturally in the DNA like restriction fragment length polymorphisms (RFLPs), sequence characteristic amplified regions (SCARs), random amplified polymorphic DNA (RAPDs), simple sequence repeats (SSRs), amplified fragment length polymorphism (AFLPs), and others have been effectively utilized. The use of plant breeding methods has an enormous potential to accelerate drought-tolerant plant production and help drought management assist these plants [15].

Marker assisted selection (MAS) and genomic selection (GS) are the two well versed approaches of genomic assisted breeding. For the first approach, foremost step is to identify the molecular markers linked to the trait of interest so that selection can be performed in breeding programs. However, GS depends on progress of selection models based on genetic markers present on the whole genome and selection of genome estimated breeding values (GEBVs) in breeding populations through phenotyping of "training population".

*Drought Stress: Manifestation and Mechanisms of Alleviation in Plants DOI: http://dx.doi.org/10.5772/intechopen.102780*

MAS utilizes molecular markers in identification of quantitative trait loci (QTL) or specific genes that are linked with the target trait and are used to identify the individual with desirable alleles (**Figure 7**) [61]. Through these methods, QTLs for the traits linked with drought resistance are identified in various crops i.e., rice, wheat, maize, sorghum, pearl millet, soybean and many other crops [62–67].

Genomic selection utilizes all the markers available for a population of GEBVs and GS models are used for selection of elite lines without phenotyping [61]. Contrary to MAS, the information about QTLs is not the prerequisite for GS [68]. However, GS requires denser marker data than MAS. GS is being applied for breeding in maize tolerant to drought by the international maize and wheat improvement center (CIMMYT) [69]. Research efforts through this approach are progressing in other crops i.e., sugarcane, legumes and wheat [70–72].

Many studies have elucidated molecular responses in plants related to droughtinduced transcription signaling pathways. In recent times, various stress-responsive genes and transcription factors having potential to mitigate drought-induced oxidative stress have been identified [73]. The TFs operate specific interaction with the cis-elements present in the genes' promoter region and, stimulate the expression of stress-inducible genes of various signaling pathways upon binding [74, 75]. These TFs are categorized into different families based on their conserved motifs that code their DNA binding domain (DBD), viz., APETALA 2 (AP2)/ethylene-responsive element binding factor (ERF); dehydration-responsive element binding protein (DREB); no apical meristem/*Arabidopsis* transcription activation factor, cup-shaped cotyledon

## **Figure 7.**

*Model for the role of signaling factors in stomatal closure and retrograde signaling during water stress. Source: [16].*


## *Drought - Impacts and Management*

