Genome-wide superior alleles, haplotypes and candidate genes associated with tolerance on sodic-dispersive soils in wheat (Triticum aestivum L.)

Genome-wide analysis for root and leaf architecture traits associated with drought tolerance at the seedling stage in a highly ecologically diverse wheat population

Drought stress occurred at early growth stages in wheat affecting the following growth stages. Therefore, selecting promising drought-tolerant genotypes with highly adapted traits at the seedling stage is an important task for wheat breeders and geneticists. Few research efforts were conducted on the genetic control for drought-adaptive traits at the seedling stage in wheat. In this study, a set of 146 highly diverse spring wheat core collections representing 28 different countries was evaluated under drought stress at the seedling stage. All genotypes were exposed to drought stress for 13 days by water withholding. Leaf traits including seedling length, leaf wilting, days to wilting, leaf area, and leaf rolling were scored. Moreover, root traits such as root length, maximum width, emergence angle, tip angle, and number of roots were scored. Considerable significant genetic variation was found among all genotypes tested in these experiments. The heritability estimates ranged from 0.74 (leaf witling) to 0.99 (root tip angle). A set of nine genotypes were selected and considered drought-tolerant genotypes. Among all leaf traits, shoot length had significant correlations with all root traits under drought stress. The 146 genotypes were genotyped using the Infinium Wheat 15 K single nucleotide polymorphism (SNP) array and diversity arrays technology (DArT) marker platform. The result of genotyping revealed 12,999 SNPs and 2150 DArT markers which were used to run a genome-wide association study (GWAS). The results of GWAS revealed 169 markers associated with leaf and root traits under drought stress. Out of the 169 markers, 82 were considered major quantitative trait loci (QTL). The GWAS revealed 95 candidate genes were identified with 53 genes showing evidence for drought tolerance in wheat, while the remaining candidate genes were considered novel. No shared markers were found between leaf and root traits. The results of the study provided mapping novel markers associated with new root traits at the seedling stage. Also, the selected genotypes from different countries could be employed in future wheat breeding programs not only for improving adaptive drought-tolerant traits but also for expanding genetic diversity.

Exome-based new allele-specific PCR markers and transferability for sodicity tolerance in bread wheat (Triticum aestivum L.)

Targeted exome-based genotype by sequencing (t-GBS), a sequencing technology that tags SNPs and haplotypes in gene-rich regions was used in previous genome-wide association studies (GWAS) for sodicity tolerance in bread wheat. Thirty-nine novel SNPs including 18 haplotypes for yield and yield-components were identified. The present study aimed at developing SNP-derived markers by precisely locating new SNPs on ~180 bp allelic sequence of t-GBS, marker validation, and SNP functional characterization based on its exonic location. We identified unknown locations of significant SNPs/haplotypes by aligning allelic sequences on to IWGSC RefSeqv1.0 on respective chromosomes. Eighteen out of the target 39 SNP locations fulfilled the criteria for producing PCR markers, among which only eight produced polymorphic signals. These eight markers associated with yield, plants m-2, heads m-2, and harvest index, including a pleiotropic marker for yield, harvest index, and grains/head were validated for its amplification efficiency and phenotypic effects in focused identification germplasm strategy (FIGS) wheat set and a doubled haploid (DH) population (Scepter/IG107116). The phenotypic variation explained by these markers are in the range of 4.1-37.6 in the FIGS population. High throughput PCR-based genotyping using new markers and association with phenotypes in FIGS wheat set and DH population validated the effect of functional SNP on closely associated genes-calcineurin B-like- and dirigent protein, basic helix-loop-helix (BHLH-), plant homeodomain (PHD-) and helix-turn-helix myeloblastosis (HTH myb) type -transcription factor. Further, genome-wide SNP annotation using SnpEff tool confirmed that these SNPs are in gene regulatory regions (upstream, 3'-UTR, and intron) modifying gene expression and protein-coding. This integrated approach of marker design for t-GBS alleles, SNP functional annotation, and high-throughput genotyping of functional SNP offers translation solutions across crops and complex traits in crop improvement programs.

Identification of QTL for reducing loss of grain yield under salt stress conditions in bi-parental populations derived from wheat landrace Hongmangmai

A novel QTL (QSt.nftec-2BL) was mapped to a 0.7 cM interval on chromosome 2B. Plants carrying QSt.nftec-2BL produced higher grain yields by up to 21.4% than otherwise in salinized fields. Wheat yield has been limited by soil salinity in many wheat-growing areas globally. The wheat landrace Hongmangmai (HMM) possesses salt tolerance as it produced higher grain yields than other tested wheat varieties including Early Premium (EP) under salt stresses. To detect QTL underlying this tolerance, wheat cross EP × HMM was chosen to serve as mapping population that was homozygous at Ppd (photoperiod response gene), Rht (reduced plant height gene) and Vrn (vernalization gene); thus, interference with QTL detection by these loci could be minimized. QTL mapping was conducted firstly using 102 recombinant inbred lines (RILs) that were selected from the EP × HMM population (827 RILs) for similarity in grain yield under non-saline condition. Under salt stresses, however, the 102 RILs varied significantly in grain yield. These RILs were genotyped using a 90 K SNP (single nucleotide polymorphism) array; consequently, a QTL (QSt.nftec-2BL) was detected on chromosome 2B. Then, using 827 RILs and new simple sequence repeat (SSR) markers developed according to the reference sequence IWGSC RefSeq v1.0, location of QSt.nftec-2BL was refined to a 0.7 cM (6.9 Mb) interval flanked by SSR markers 2B-557.23 and 2B-564.09. Selection for QSt.nftec-2BL was performed based on the flanking markers using two bi-parental wheat populations. Trials for validating effectiveness of the selection were conducted in salinized fields in two geographical areas and two crop seasons, demonstrating that wheat plants with the salt-tolerant allele in homozygous status at QSt.nftec-2BL produced higher grain yields by up to 21.4% than otherwise.