QTL Mapping of Grain Zn and Fe Concentrations in Two Hexaploid Wheat RIL Populations with Ample Transgressive Segregation

Abstract

More than 50% of undernourished children live in Asia and more than 25% live in Africa. Coupled with an inadequate food supply, mineral deficiencies are widespread in these populations; particularly zinc (Zn) and iron (Fe) deficiencies that lead to retarded growth, adverse effects on both the immune system and an individual's cognitive abilities. Biofortification is one solution aimed at reducing the incidence of these deficiencies. To efficiently breed a biofortified wheat variety, it is important to generate knowledge of the genomic regions associated with grain Zn (GZn) and Fe (GFe) concentration. This allows for the introgression of favorable alleles into elite germplasm. In this study we evaluated two bi-parental populations of 188 recombinant inbred lines (RILs) displaying a significant range of transgressive segregation for GZn and GFe during three crop cycles in CIMMYT, Mexico. Parents of the RILs were derived from Triticum spelta L. and synthetic hexaploid wheat crosses. QTL analysis identified a number of significant QTL with a region denominated as QGZn.cimmyt-7B_1P2 on chromosome 7B explaining the largest (32.7%) proportion of phenotypic variance (PVE) for GZn and leading to an average additive effect of −1.3. The QTL with the largest average additive effect for GFe (−0.161) was found on chromosome 4A (QGFe.cimmyt-4A_P2), with 21.14% of the PVE. The region QGZn.cimmyt-7B_1P2 co-localized closest to the region QGZn.cimmyt-7B_1P1 in a consensus map built from the linkage maps of both populations. Pleiotropic or tightly linked QTL were also found on chromosome 3B, however of minor effects and PVE between 4.3 and 10.9%. Further efforts are required to utilize the QTL information in marker assisted backcrossing schemes for wheat biofortification. A strategy to follow is to intercross the transgressive individuals from both populations and then utilize them as sources in biofortification breeding pipelines.

Identification of Novel Genomic Regions and Superior Alleles Associated with Zn Accumulation in Wheat Using a Genome-Wide Association Analysis Method

“…These loci coincided with the loci identified in our study, on chromosomes 5A (AX-110931014, 650.24Mb), 6B (AX-109538092, 708.67Mb), and 7A (AX-111012263, 261.69Mb). Similarly, in a study conducted on a hexaploid wheat RIL, populations were identified five loci on chromosomes 1B, 2B, 3A, 3B, and 6A associated with Zn grain accumulation and explaining from 9% to 15% of the phenotypic variation [31]. In this study, we also identified 7 unique loci in 1B, 2B (2 loci), 3A, 3B (2 loci), and 6A, which could be associated with the QTL in the hexaploid bread wheat population [31].…”

“…Many QTLs for Zn accumulation in grains have been detected by bi-parental linkage mapping [19,23,31,32,37], which allowed a comparison between known QTLs and loci identified in the present study. In the current study, 29 significant non-redundant loci were scattered across all wheat genome (except on chromosomes 2A, 4D, 5D, 7B, and 7D).…”

QTLs identified for Biofortification Traits in Wheat: A Review

“…QTLs for grain zinc and iron have also been mapped in populations derived from crosses between T. boeoticum and T. monococcum [106], durum wheat and wild emmer [64] synthetic hexaploid wheat and T. spelta [107,108,109]. Tiwari et al [106] mapped 2 QTL for grain Fe on chromosomes 2A and 7A explaining 12.6 and 11.7% of phenotypic variation and 1 QTL for grain Zn on chromosome 7A explaining 18.8% of total phenotypic variation, using a RIL population derived from a cross between T. boeoticum accession 'pau5088' and T. monococcum accession 'pau14087'.…”

“…Tiwari et al [106] mapped 2 QTL for grain Fe on chromosomes 2A and 7A explaining 12.6 and 11.7% of phenotypic variation and 1 QTL for grain Zn on chromosome 7A explaining 18.8% of total phenotypic variation, using a RIL population derived from a cross between T. boeoticum accession 'pau5088' and T. monococcum accession 'pau14087'. Recently in 2017, Crespo-Herrera et al [108] identified several significant QTLs with a region named as nQGZn.cimmyt-7B_1P2 on chromosome 7B explaining the largest proportion (32.7%) of total phenotypic variance for GZn and one QTL on chromosome 4A (QGFe.cimmyt-4A_P2), explaining the largest (21.14%) proportion of phenotypic variance of the GFe in two RIL populations derived from T. spelta L. and synthetic hexaploid wheat crosses. In other study, Krishnappa et al [109] mapped four QTLs, explaining 20 % of total phenotypic variation and five QTLs, explaining 32% of total phenotypic variation for GFe and GZn, respectively using a RIL population derived from a cross between an Indian wheat variety 'WH542' and a synthetic derivative.…”

Foliar applied zinc increases yield, zinc concentration, and germination in wheat genotypes

“…Plants growing in soil with <1 μg g −1 may not provide an adequate amount of Zn for people with plant‐based diets. Since 2000, efforts to biofortify food crops with micronutrients have led to better understanding of the physiological, genetic, and molecular basis of Zn accumulation in grain (Crespo‐Herrera, Velu, Stangoulis, Hao, & Singh, 2017). In addition, the effects of agronomic management and environmental situations on Zn uptake, translocation, and loading into grains have been illuminated (Velu, Ortiz‐Monasterio, Cakmak, Hao, & Singh, 2014).…”