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al., 2019; Khan et al., 2019; Ahmed et al., 2020; Hrmova & Hussain, 2021).

However, these genetic engineering approaches are flexible because they can

aid in conventional breeding efforts (Capell et al., 2004).

In addition, development of novel high throughput techniques in molec­

ular biology in combination with bioinformatic science have contributed

to the emergence of system based high throughput tools such as genome

editing tools, thus ensuring a comprehensive source of biological resources

which transformed conventional plant breeding to precision plant breeding

(Deikman et al., 2011; Weber & Fussenegger, 2011; Tardieu, 2012; Cabello

et al., 2014). Importance of cis-trans engineering using genome editing tools

and manipulation of synthetic/artificial transcription factors (ATFs) would be

highlighted and discussed with emphasis on the role of such TFs as genetic

switches in stress tolerance.

7.1.1 CONTRIBUTION OF CONVENTIONAL BREEDING FOR PLANT

ABIOTIC STRESS TOLERANCE

Development of high yielding and stress-tolerant genotypes is a long-standing

goal of agricultural scientists, but conventional breeding has met with limited

success in realization of this goal due to multigenic nature of tolerance traits

(Richards, 1996; Hussain et al., 2012; Hrmova & Hussain, 2021). Another

reason of this understanding is low heritability of the tolerance genes in crop

plants (Fritsche-Neto & Borem, 2012). Generally, breeding schemes use

different selection procedures which constitutes critical steps in the early

selection of superior materials. For example, quantitative characters like

environmental stress tolerance, selection strategy involve both stress and non-

stress scenarios for selection. Generally breeding methods for quantitative

characters such as abiotic stress tolerance, yield, and other economic traits

are the same. Although conventional breeding has significantly contributed

to tolerant crop lines development, specific phenotype identification with

abiotic stress tolerance traits is still a big challenge for using this approach

in other commercial crop plants. Wild relatives of grasses could be the main

source of stress-related genes because these usually demonstrated high toler­

ance to various stresses. Therefore, there is the possibility that these desired

traits can be transferred from wild relatives to domesticated plants. As a

matter of fact, 10–20% of such variations have already been introgressed

into modern tetraploid/hexaploidy wheat varieties (Langridge et al., 2006).

Despite challenges, conventional breeding efforts have contributed towards

the development of drought and heat tolerant crops. For example, Haley et al.