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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

can be done up to RIL population (Korte & Farlow, 2013). To overcome

the drawbacks of QTL mapping, GWAS was introduced. GWAS is basically

free from any hypothesis but can generate hypothesis. Also, GWAS can

be used in the identification of more variants related to any trait. In any

GWAS study, the SNPs present in the sequence data are used to correlate

different genetic variants, phenotypes, etc., in any population of organism.

Other similar approaches investigate a particular portion of the chromosome

while GWAS is able to explore the whole genome. GWAS has been used

in various biotic and abiotic stress responses in the plants discussed later in

the chapter. Different stresses are controlled by various genes like biotic is

mostly controlled by a single gene while abiotic stress is based on multiple

genes (Wan et al., 2017). So far, many studies have been done using GWAS

mentioned in Table 10.1.

10.5.1 ABIOTIC STRESS

Abiotic stress affects the plant development and growth by affecting plant

metabolism and cellular pathways. To understand the effect of genes respon­

sible for the stress response, such putative genes need to be identified from

population of any organism. For this several studies based on GWAS have

been performed recently in response to abiotic stresses. A study has been

reported in which the identification of genes responsible for drought resis­

tance in rice plant was observed with an aim to develop tools that can be used

in future rice breeding. For the analysis of 175 rice accessions have been

done with variable water availability. As a result, 13 SNP markers related to

the yield under drought were identified and the stepwise regression analysis,

8 SNP markers were validated by in silico methods. The PCR validation

revealed that two SNP markers have been found similar to the genotypes

with higher yield under water deficit conditions. This drought experiment

also showed that 30 genes out of 50 were annotated and 10 (e.g., WRKY TFs

and other enzymes) have been reported as linked to drought and other abiotic

stresses (Pantaliao et al., 2016). Arbuscular mycorrhizal symbiosis has a

typical role in the improvement of drought stress resistance in wheat. But the

related QTLs associated in response to drought stress are not well known.

Therefore, a GWAS was conducted to reveal such QTL regions responsible

for controlling the stress response against low water conditions. Such studies

will help in future work related to the gene identification too (Lehnert et al.,

2018).