Understanding the Genetic Basis of Spike Fertility to Improve Grain Number, Harvest Index, and Grain Yield in Wheat Under High Temperature Stress Environments.

Sumit Pradhan,Salvador Gezan,Jia Guo,Paul St Amand,Richard Esten Mason,Madhav Bhatta,Byung-Kee Baik,Muhsin Avci,Guihua Bai,Mohamed Mergoum,Ann Blount,Jahangir Khan,Senthold Asseng,Md Ali Babar,Dipendra Shahi,Mohammad Maksud Hossain,Kelly Robbins,Amy Bernardo

doi:10.3389/fpls.2019.01481

Abstract

Moderate heat stress accompanied by short episodes of extreme heat during the post-anthesis stage is common in most US wheat growing areas and causes substantial yield losses. Sink strength (grain number) is a key yield limiting factor in modern wheat varieties. Increasing spike fertility (SF) and improving the partitioning of assimilates can optimize sink strength which is essential to improve wheat yield potential under a hot and humid environment. A genome-wide association study (GWAS) allows identification of novel quantitative trait loci (QTLs) associated with SF and other partitioning traits that can assist in marker assisted breeding. In this study, GWAS was performed on a soft wheat association mapping panel (SWAMP) comprised of 236 elite lines using 27,466 single nucleotide polymorphisms (SNPs). The panel was phenotyped in two heat stress locations over 3 years. GWAS identified 109 significant marker-trait associations (MTAs) (p ≤ 9.99 x 10−5) related to eight phenotypic traits including SF (a major component of grain number) and spike harvest index (SHI, a major component of grain weight). MTAs detected on chromosomes 1B, 3A, 3B, and 5A were associated with multiple traits and are potentially important targets for selection. More than half of the significant MTAs (60 out of 109) were found in genes encoding different types of proteins related to metabolism, disease, and abiotic stress including heat stress. These MTAs could be potential targets for further validation study and may be used in marker-assisted breeding for improving wheat grain yield under post-anthesis heat stress conditions. This is the first study to identify novel QTLs associated with SF and SHI which represent the major components of grain number and grain weight, respectively, in wheat.

Highlights

Wheat (Triticum aestivum L.) is one of the major food crops worldwide and is grown on more than 218 million hectares of land with an average grain yield (GY) of 3.3 t ha−1 (FAOSTAT, 2016)
Principal components (PC) analysis showed that PC1 and PC2 explained 72.9, 66, and 71.5% of the total variation for phenotypic trait data from Citra, Quincy, and the combined
We identified 109 significant marker-trait associations (MTAs) for 8 phenotypic traits distributed across 18 chromosomes with phenotypic variations explained (PVE) ranging from 7 to 31% (Table S2, Figures 2 and 3)

Summary

Introduction

Wheat (Triticum aestivum L.) is one of the major food crops worldwide and is grown on more than 218 million hectares of land with an average grain yield (GY) of 3.3 t ha−1 (FAOSTAT, 2016). Environmental constraints, especially high temperature and drought stress are serious threats to wheat production (Pradhan et al, 2012). Lobell et al (2011) reported a 5.5% decline in world wheat production since 1980, due to increase in global mean temperature. A trend of global warming is expected to continue in the future, increasing temperature up to 2°C by 2050, which may result in further yield losses (IPCC, 2013; Asseng et al, 2015). To keep pace with increasing global population, genetic progress of wheat yield will have to increase from 0.3 to 1.1% per year by 2050 under a changing climate including heat stress (Bruinsma, 2011; Asseng et al, 2015)

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