Response of Tibetan Wild Barley Genotypes to Drought Stress and Identification of Quantitative Trait Loci by Genome-Wide Association Analysis

Abstract

Tibetan wild barley has been identified to show large genetic variation and stress tolerance. A genome-wide association (GWA) analysis was performed to detect quantitative trait loci (QTLs) for drought tolerance using 777 Diversity Array Technology (DArT) markers and morphological and physiological traits of 166 Tibetan wild barley accessions in both hydroponic and pot experiments. Large genotypic variation for these traits was found; and population structure and kinship analysis identified three subpopulations among these barley genotypes. The average LD (linkage disequilibrium) decay distance was 5.16 cM, with the minimum on 6H (0.03 cM) and the maximum on 4H (23.48 cM). A total of 91 DArT markers were identified to be associated with drought tolerance-related traits, with 33, 26, 16, 1, 3, and 12 associations for morphological traits, H⁺K⁺-ATPase activity, antioxidant enzyme activities, malondialdehyde (MDA) content, soluble protein content, and potassium concentration, respectively. Furthermore, 7 and 24 putative candidate genes were identified based on the reference Meta-QTL map and by searching the Barleymap. The present study implicated that Tibetan annual wild barley from Qinghai⁻Tibet Plateau is rich in genetic variation for drought stress. The QTLs detected by genome-wide association analysis could be used in marker-assisting breeding for drought-tolerant barley genotypes and provide useful information for discovery and functional analysis of key genes in the future.

Keywords: Diversity Array Technology (DArT) markers; Hordeum vulgare L. ssp. vulgare; drought stress; genome-wide association (GWA); quantitative trait loci (QTL) mapping.

Figure 1

Frequency distribution of the relative value of different growth and physiological parameters of Tibetan wild barley plants under drought treatment in hydroponic experiment. Relative value of a given parameter was calculated as parameters under drought stress relative to control conditions (i.e., relative value = (parameter under drought stress)/(parameter under control)). (a) RSDW, relative shoot dry weight; (b) RRDW, relative root dry weight; (c) RSFW, relative shoot fresh weight; (d) RRFW, relative root fresh weight; (e) RSH, relative shoot height; (f) RRL, relative root length; (g) RLATPase, relative activity of leaf ATPase; (h) RRATPase, relative activity of root ATPase; (i) RSK, relative K concentration in shoots; (j) RRK, relative K concentration in roots.

Figure 2

Frequency distribution of the relative value of different traits of Tibetan wild barley plants under drought treatment in pot experiment. Relative value of a given parameter was calculated as parameters under drought stress relative to control conditions (i.e., relative value = (parameter under drought stress)/(parameter under control)). (a) RSDW, relative shoot dry weight; (b) RCAT, relative catalase (CAT) activity in leaf; (c) RPro, relative soluble protein content in leaf; (d) RMDA: relative malondialdehyde (MDA) content in leaf; (e) RPOD, relative peroxidase (POD) activity in leaf; (f) REL: relative ear length; (g) RAL: relative awn length; (h) RINL: relative internode length below spike; (i) RSK, relative K concentration in shoots;(j) RGW: relative grain weight per spike.

Figure 3

(a) The distribution of Δk, indicating the most appropriate cluster number (k) is three; (b) Population structure of 166 Tibetan wild barley genotypes at k = 3 based on genetic diversity detected by 777 DArT markers.

Figure 3

(a) The distribution of Δk, indicating the most appropriate cluster number (k) is three; (b) Population structure of 166 Tibetan wild barley genotypes at k = 3 based on genetic diversity detected by 777 DArT markers.