Genome-Wide Association Studies to Identify Loci and Candidate Genes Controlling Kernel Weight and Length in a Historical United States Wheat Population.

Sintayehu D Daba,Gina Brown-Guedira,Mohsen Mohammadi,Priyanka Tyagi

doi:10.3389/fpls.2018.01045

Abstract

Although kernel weight (KW) is a major component of grain yield, its contribution to yield genetic gain during breeding history has been minimal. This highlights an untapped potential for further increases in yield via improving KW. We investigated variation and genetics of KW and kernel length (KL) via genome-wide association studies (GWAS) using a historical and contemporary soft red winter wheat population representing 200 years of selection and breeding history in the United States. The observed changes of KW and KL over time did not show any conclusive trend. The population showed a structure, which was mainly explained by the time and location of germplasm development. Cluster sharing by germplasm from more than one breeding population was suggestive of episodes of germplasm exchange. Using 2 years of field-based phenotyping, we detected 26 quantitative trait loci (QTL) for KW and 27 QTL for KL with –log10(p) > 3.5. The search for candidate genes near the QTL on the wheat genome version IWGSCv1.0 has resulted in over 500 genes. The predicted functions of several of these genes are related to kernel development, photosynthesis, sucrose and starch synthesis, and assimilate remobilization and transport. We also evaluated the effect of allelic polymorphism of genes previously reported for KW and KL by using Kompetitive Allele Specific PCR (KASP) markers. Only TaGW2 showed significant association with KW. Two genes, i.e., TaSus2-2B and TaGS-D1 showed significant association with KL. Further physiological studies are needed to decipher the involvement of these genes in KW and KL development.

Highlights

Yield genetic gains in wheat slowed down over the last two decades (Brisson et al, 2010; Lin and Huybers, 2012; Ray et al, 2012), threatening world food security. Simmonds et al (2014) highlighted that grain number (GN) per unit area and kernel weight (KW) are main determinants of grain yield (GY)
We evaluated the variation of KW and kernel length (KL) in a historical and contemporary collection of cultivars and experimental breeding lines, representing 200 years of breeding and selection history
The 20 greatest KW entries showed an average of 44.8 ± 2.5 mg and the 20 smallest KW entries showed an average of 27.7 ± 1.4 mg

Summary

Introduction

Yield genetic gains in wheat slowed down over the last two decades (Brisson et al, 2010; Lin and Huybers, 2012; Ray et al, 2012), threatening world food security. Simmonds et al (2014) highlighted that grain number (GN) per unit area and kernel weight (KW) are main determinants of grain yield (GY). Simmonds et al (2014) highlighted that grain number (GN) per unit area and kernel weight (KW) are main determinants of grain yield (GY). These two traits, i.e., GN and KW together represent total sink-strength in Kernel Traits GWAS in Wheat wheat. Kernel development in wheat involves cell division, water uptake, accumulation of starch and protein, maturation, and desiccation (Altenbach and Kothari, 2004). While grain expansion enforced by endosperm cell division and water uptake are components of sink-strength, assimilate (e.g., starch) supply (Emes et al, 2003) through current photosynthesis or remobilization of reserves from vegetative tissues (Bidinger et al, 1977; Schnyder, 1993; Gebbing and Schnyder, 1999) are components of source-strength

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