Drought tolerance at wheat seedling stage: tolerance and survival traits are controlled by two different genetic mechanisms

Ahmed Sallan1*, Shams Eltaher2, Vikas Belamkar3, Waseem Hussain4, Ahamed. M. Alqudah5 and P. Stephen Baenziger3

1** Department of Genetics, Faculty of Agriculture, Assiut University, Egypt.

2** Genetic Engineering and Biotechnology Research Institute, University of Sadat City, Egypt.

3** Department of Agronomy & Horticulture, University of Nebraska-Lincoln, USA.

4**  International Rice Research Institute, Los Baños, Laguna 403, Philippines.

5**  Resources Genetics and Reproduction, Department Genebank, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK),  Germany.

amsallam@aun.edu.eg

Abstract

Drought stress is one of the most severe abiotic stresses that limit wheat growth and its development. Breeding for drought tolerance at the seedling stage is very important for the wheat plant to continue its growth cycle especially if the drought occurs at this stage. To improve drought tolerance and select the most promising drought-tolerant genotypes, we developed a new protocol for breeding drought tolerance in seedling winter wheat. Two different genetic backgrounds were used in this study; biparental population (BPP, N=147) and diverse population (DP = 160). The genotypes in both populations were evaluated in a greenhouse under controlled conditions. Each population was evaluated in three replications with a randomized complete block design. Two types of traits were scored namely (1) tolerance traits include days to wilting, leaf wilting, and stay green and (2) recovery traits which included days to regrowth, shoot regrowth, drought survival rate, and leaf recovery. Three selection indices were calculated; (1) tolerance index (TI), recovery index (RI), and drought tolerance index (DTI) including TI and RI. A high genetic variation was found among genotypes in both populations for all traits. The heritability estimates were higher in GP (0. 77 – 0.95) than in BPP (0. 53 – 0.90). In both populations, no or very weak correlation was found between tolerance and recovery traits. The TI and RI had the same trend of correlation in BPP (r = 0.03) and GP (r = 0.04). The drought tolerance index had high significant phenotypic and genotypic correlations with all traits in both populations. Both populations were genotyped using genotyping-by-sequencing. Linkage mapping was performed on BPP, while GWAS was performed on GP to detect genomic regions and alleles associated with tolerance and recovery traits. In both populations, no common QTL were shared in both types of traits. In conclusion, recovery and tolerance traits are controlled by different genetic mechanisms. Drought selection index (including RI and TI) facilitated selecting the most promising genotypes in both populations. One genomic region on chromosome 2B was found to control survival traits in both populations. The results of this study helped in understanding some complexity of drought tolerance in wheat.

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Keywords: GWAS, QTL mapping, Drought, Heritability, Recovery index, Tolerance index.