Prioritizing quantitative trait loci for root system architecture in tetraploid wheat.

Marco Maccaferri,Walid El-Feki,Maria Chiara Colalongo,Silvio Salvi,Ghasemali Nazemi,Roberto Tuberosa,Sandra Stefanelli,Maria Angela Canè

doi:10.1093/jxb/erw039

Abstract

Optimization of root system architecture (RSA) traits is an important objective for modern wheat breeding. Linkage and association mapping for RSA in two recombinant inbred line populations and one association mapping panel of 183 elite durum wheat (Triticum turgidum L. var. durum Desf.) accessions evaluated as seedlings grown on filter paper/polycarbonate screening plates revealed 20 clusters of quantitative trait loci (QTLs) for root length and number, as well as 30 QTLs for root growth angle (RGA). Divergent RGA phenotypes observed by seminal root screening were validated by root phenotyping of field-grown adult plants. QTLs were mapped on a high-density tetraploid consensus map based on transcript-associated Illumina 90K single nucleotide polymorphisms (SNPs) developed for bread and durum wheat, thus allowing for an accurate cross-referencing of RSA QTLs between durum and bread wheat. Among the main QTL clusters for root length and number highlighted in this study, 15 overlapped with QTLs for multiple RSA traits reported in bread wheat, while out of 30 QTLs for RGA, only six showed co-location with previously reported QTLs in wheat. Based on their relative additive effects/significance, allelic distribution in the association mapping panel, and co-location with QTLs for grain weight and grain yield, the RSA QTLs have been prioritized in terms of breeding value. Three major QTL clusters for root length and number (RSA_QTL_cluster_5#, RSA_QTL_cluster_6#, and RSA_QTL_cluster_12#) and nine RGA QTL clusters (QRGA.ubo-2A.1, QRGA.ubo-2A.3, QRGA.ubo-2B.2/2B.3, QRGA.ubo-4B.4, QRGA.ubo-6A.1, QRGA.ubo-6A.2, QRGA.ubo-7A.1, QRGA.ubo-7A.2, and QRGA.ubo-7B) appear particularly valuable for further characterization towards a possible implementation of breeding applications in marker-assisted selection and/or cloning of the causal genes underlying the QTLs.

Highlights

Root system architecture (RSA) plays a pivotal role in and Muchow, 1990; de Dorlodot et al, 2007; Paez-Garcia crop performance, for cultivation under non- et al, 2015)
Co×Ld and Mr×Cl recombinant inbred line (RIL) populations were assessed for seminal RSA traits at the seedling stage
A two-pronged approach based on biparental linkage and association mapping allowed the most comprehensive dissection of the QTLome for RSA in durum and bread wheat at the seedling stage while providing valuable information on the associated effects of these QTLs on grain yield of durum wheat across a range of environments differing widely in water availability and productivity

Summary

Introduction

Root system architecture (RSA) plays a pivotal role in and Muchow, 1990; de Dorlodot et al, 2007; Paez-Garcia crop performance, for cultivation under non- et al, 2015). Based on the expected climate changes and the optimal water and nutritional supply conditions Genetic capacity of the plant to acquire soil resources is a primary target to increase crop productivity and yield stability (Hawkesford et al, 2014; Mickelbart et al, 2015). A narrow and deep root ideotype for enhancing drought resistance has been successfully pursued based on direct field observation of root distribution (Steele et al, 2013; Uga et al, 2013) or root growth angle (RGA) measurements in rhizotrons (Kitomi et al, 2015). Stay-green genotypes have contributed additional evidence for the positive role on yield of narrow RGA quantitative trait loci (QTLs) under drought conditions (Borrell et al, 2014). RGA is of paramount importance for the acquisition of phosphorus, a low-mobility nutrient usually more abundant in the upper soil layer (Miguel et al, 2015)

Methods

Results

Discussion

Conclusion