Molecular and Cytogenetic Characterization of Six Wheat-Aegilops markgrafii Disomic Addition Lines and Their Resistance to Rusts and Powdery Mildew.

Zhixia Niu,Rebecca B Whetten,Christina Cowger,Daryl L Klindworth,Shiaoman Chao,Xiwen Cai,Bernd Friebe,Steven S Xu,Bikram S Gill,Jack B Rasmussen,Xianming Chen,Matthew Breiland

doi:10.3389/fpls.2018.01616

Abstract

Aegilops markgrafii (Greuter) Hammer is an important source of genes for resistance to abiotic stresses and diseases in wheat (Triticum aestivum L.). A series of six wheat ‘Alcedo’-Ae. markgrafii chromosome disomic addition lines, designated as AI(B), AII(C), AIII(D), AV(E), AIV(F), and AVIII(G) carrying the Ae. markgrafii chromosomes B, C, D, E, F, and G, respectively, were tested with SSR markers to establish homoeologous relationships to wheat and identify markers useful in chromosome engineering. The addition lines were evaluated for resistance to rust and powdery mildew diseases. The parents Alcedo and Ae. markgrafii accession ‘S740-69’ were tested with 1500 SSR primer pairs and 935 polymorphic markers were identified. After selecting for robust markers and confirming the polymorphisms on the addition lines, 132 markers were considered useful for engineering and establishing homoeologous relationships. Based on the marker analysis, we concluded that the chromosomes B, C, D, E, F, and G belong to wheat homoeologous groups 2, 5, 6, 7, 3, and 4, respectively. Also, we observed chromosomal rearrangements in several addition lines. When tested with 20 isolates of powdery mildew pathogen (Blumeria graminis f. sp. tritici) from five geographic regions of the United States, four addition lines [AIII(D), AV(E), AIV(F), and AVIII(G)] showed resistance to some isolates, with addition line AV(E) being resistant to 19 of 20 isolates. The addition lines were tested with two races (TDBJ and TNBJ) of the leaf rust pathogen (Puccinia triticina), and only addition line AI(B) exhibited resistance at a level comparable to the Ae. markgrafii parent. Addition lines AII(C) and AIII(D) had been previously identified as resistant to the Ug99 race group of the stem rust pathogen (Puccinia graminis f. sp. tritici). The addition lines were also tested for resistance to six United States races (PSTv-4, PSTv-14, PSTv-37, PSTv-40, PSTv-51, and PSTv-198) of the stripe rust pathogen (Puccinia striiformis f. sp. tritici); we found no resistance either in Alcedo or any of the addition lines. The homoeologous relationships of the chromosomes in the addition lines, molecular markers located on each chromosome, and disease resistance associated with each chromosome will allow for chromosome engineering of the resistance genes.

Highlights

IntroductionTritici Eriks.) (Valkoun et al, 1985; Dyck et al, 1990; Schubert and Blüthner, 1995; Xu et al, 2009; Weidner et al, 2012)
Aegilops markgrafii (Greuter) Hammer, is one of the most important diploid wild relatives of wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD genomes) because it carries resistance to powdery mildew [caused by Blumeria graminis f. sp. tritici (DC.) Speer], leaf rust (Puccinia triticina Erikss.), stem rust
We observed that AI(B) is unique in its non-free threshing spikes, AII(C) has large glumes, AIII(D) and AV(E) have awns, and AIV(F) has club spikes with brittle rachis

Summary

Introduction

Tritici Eriks.) (Valkoun et al, 1985; Dyck et al, 1990; Schubert and Blüthner, 1995; Xu et al, 2009; Weidner et al, 2012). A set of chromosome disomic addition lines carrying Ae. markgrafii accession ‘S 74069’ chromosomes B, C, D, E, F, and G in wheat variety ‘Alcedo’ were developed by Schubert and Blüthner (1992, 1995). This set of disomic addition lines can serve as an alternate and direct genetic source for wheat germplasm enhancement. An addition line for chromosome A is absent from this set, and Niu et al (2011) found that none of the six addition lines carried high-molecular-weight glutenins from Ae. markgrafii, suggesting that chromosome A may be homoeologous to group 1. Friebe et al (1992) noted results from unpublished studies which support the conclusion that chromosome A belongs to group 1. Danilova et al (2014, 2017) determined that chromosome A of Ae. markgrafii is homoeologous to the group 1 chromosomes of wheat by using fluorescence in situ hybridization (FISH) with cDNA probes

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