Genome-Wide Association Study of Septoria tritici Blotch Resistance in Ethiopian Durum Wheat Landraces.

Yosef G Kidane,Carlo Fadda,Dejene K Mengistu,Bogale N Hailemariam,Matteo Dell'Acqua,Mario Enrico Pè

doi:10.3389/fpls.2017.01586

Abstract

Septoria tritici blotch (STB) is a devastating fungal disease affecting durum and bread wheat cultivation worldwide. The identification, development, and employment of resistant wheat genetic material is the key to overcoming costs and limitations of fungicide treatments. The search for resistance sources in untapped genetic material may speed up the deployment of STB genetic resistance in the field. Ethiopian durum wheat landraces represent a valuable source of such diversity. In this study, 318 Ethiopian durum wheat genotypes, for the most part traditional landraces, were phenotyped for resistance to different aspects of STB infection. Phenology, yield and yield component traits were concurrently measured the collection. Here we describe the distribution of STB resistance traits in modern varieties and in landraces, and the relation existing between STB resistance and other agronomic traits. STB resistance sources were found in landraces as well as in modern varieties tested, suggesting the presence of alleles of breeding relevance. The genetic material was genotyped with more than 16 thousand genome-wide polymorphic markers to describe the linkage disequilibrium and genetic structure existing within the panel of genotypes, and a genome-wide association (GWA) study was run to allow the identification of genomic loci involved in STB resistance. High diversity and low genetic structure in the panel allowed high efficiency GWA. The GWA scan detected five major putative QTL for STB resistance, only partially overlapping those already reported in the wheat literature. We report four putative loci for Septoria resistance with no match in previous literature: two highly significant ones on Chr 3A and 5A, and two suggestive ones on Chr 4B and 5B. Markers underlying these QTL explained as much as 10% of the phenotypic variance for disease resistance. We found three cases in which putative QTL for agronomic traits overlapped marker trait association deriving from STB GWA. Our results show that the Ethiopian untapped allelic diversity bears a great value in studying the molecular basis of STB resistance and in breeding for resistance in local and international material.

Highlights

Septoria tritici blotch (STB), caused by the ascomycete fungus Zymoseptoria tritici, is among the most devastating foliar diseases of wheat
The diversity of Ethiopian durum wheat was described in relation to open field STB infection
The experiment, conducted for two consecutive years on the Ethiopian highlands, is the first exploring the genetic bases of STB resistance in Ethiopian material representative of the diversity of durum wheat cultivated in the region

Summary

Introduction

Septoria tritici blotch (STB), caused by the ascomycete fungus Zymoseptoria tritici (anamorph S. tritici and Mycosphaerella graminicola), is among the most devastating foliar diseases of wheat This disease impacts wheat production in Europe, in the Mediterranean area, in Africa, the Americas, and in Australia (Kosina et al, 2007; Dean et al, 2012; Fones and Gurr, 2015) where, under favorable environmental conditions, can cause relevant yield losses (Eyal, 1999; Duveiller et al, 2007). The investment required to control STB by these means is outside the reach of developing countries, where STB severely impacts the economy and food security (Kosina et al, 2007) For all these reasons, breeding for host plant resistance is an appealing perspective to achieve an economical, durable, and environmentally friendly control of STB in wheat fields (Orton et al, 2011; Fones and Gurr, 2015)

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