Identification of New Resistance Loci to African Stem Rust Race TTKSK in Tetraploid Wheats Based on Linkage and Genome-Wide Association Mapping.

Giovanni Laidò,Anna M Mastrangelo,Valentina Giovanniello,Pasquale De Vita,Daniela Marone,Donatella B M Ficco,Maria A Russo,Brian Steffenson,Luigi Cattivelli,Giosuè Panio

doi:10.3389/fpls.2015.01033

Giovanni Laidò, Anna M Mastrangelo + Show 8 more

Open Access

https://doi.org/10.3389/fpls.2015.01033

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Abstract

Stem rust, caused by Puccinia graminis Pers. f. sp. tritici Eriks. and E. Henn. (Pgt), is one of the most destructive diseases of wheat. Races of the pathogen in the “Ug99 lineage” are of international concern due to their virulence for widely used stem rust resistance genes and their spread throughout Africa. Disease resistant cultivars provide one of the best means for controlling stem rust. To identify quantitative trait loci (QTL) conferring resistance to African stem rust race TTKSK at the seedling stage, we evaluated an association mapping (AM) panel consisting of 230 tetraploid wheat accessions under greenhouse conditions. A high level of phenotypic variation was observed in response to race TTKSK in the AM panel, allowing for genome-wide association mapping of resistance QTL in wild, landrace, and cultivated tetraploid wheats. Thirty-five resistance QTL were identified on all chromosomes, and seventeen are of particular interest as identified by multiple associations. Many of the identified resistance loci were coincident with previously identified rust resistance genes; however, nine on chromosomes 1AL, 2AL, 4AL, 5BL, and 7BS may be novel. To validate AM results, a biparental population of 146 recombinant inbred lines was also considered, which derived from a cross between the resistant cultivar “Cirillo” and susceptible “Neodur.” The stem rust resistance of Cirillo was conferred by a single gene on the distal region of chromosome arm 6AL in an interval map coincident with the resistance gene Sr13, and confirmed one of the resistance loci identified by AM. A search for candidate resistance genes was carried out in the regions where QTL were identified, and many of them corresponded to NBS-LRR genes and protein kinases with LRR domains. The results obtained in the present study are of great interest as a high level of genetic variability for resistance to race TTKSK was described in a germplasm panel comprising most of the tetraploid wheat sub-species.

Highlights

Stem rust, caused by Puccinia graminis Pers. f. sp. tritici Eriks. and E
A high level of variability was observed in response to stem rust race TTKSK in the tetraploid wheat collection (Figure S2), thereby allowing for the identification of resistance loci in both the domesticated subgroups and the gene pool of cultivated durum wheat cultivars
Association mapping is a useful approach as indicated by the growing interest in its application to identify disease resistance genes/quantitative trait loci (QTL) in a wide range of crops (Hall et al, 2010; Letta et al, 2013)

Summary

Introduction

Stem rust, caused by Puccinia graminis Pers. f. sp. tritici Eriks. and E. Combinations of different stem rust resistance (Sr) genes were successfully introgressed into wheat cultivars worldwide since the 1950s, and this gene deployment scheme has effectively controlled the disease for many years (Singh et al, 2011). The discovery of a new aggressive race (TTKSK, isolate Ug99) of Pgt in Uganda in 1998 (Pretorius et al, 2000) threatens wheat production due to its wide virulence on over 80% of wheat cultivars worldwide (Singh et al, 2006; Yu et al, 2012; Sharma et al, 2013). At least eight variants with different virulence patterns have been described from the “Ug99 lineage” of African stem rust races, further complicating the resistance breeding process (rusttracker.cimmyt.org)

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