The eyespot resistance genes Pch1 and Pch2 of wheat are not homoeoloci

M Pasquariello,S Paillard,C Burt,P Nicholson,C Uauy,J Jahier,J Ham

doi:10.1007/s00122-016-2796-x

Abstract

Key messagePhenotyping and mapping data reveal that chromosome intervals containing eyespot resistance genesPch1 andPch2 on 7D and 7A, respectively, do not overlap, and thus, these genes are not homoeloci.Eyespot is a stem-base fungal disease of cereals growing in temperate regions. Two main resistances are currently available for use in wheat. Pch1 is a potent single major gene transferred to wheat from Aegilops ventricosa and located on the distal end of chromosome 7D. Pch2, a moderate resistance deriving from Cappelle Desprez, is located at the end of 7AL. The relative positions of Pch1 and Pch2 on 7D and 7A, respectively, suggest that they are homoeoloci. A single seed decent recombinant F7 population was used to refine the position of Pch2 on 7A. New markers designed to 7D also allowed the position of Pch1 to be further defined. We exploited the syntenic relationship between Brachypodium distachyon and wheat to develop 7A and 7D specific KASP markers tagging inter-varietal and interspecific SNPs and allow the comparison of the relative positions of Pch1 and Pch2 on 7D and 7A. Together, phenotyping and mapping data reveal that the intervals containing Pch1 and Pch2 do not overlap, and thus, they cannot be considered homoeloci. Using this information, we analysed two durum wheat lines carrying Pch1 on 7A to determine whether the Ae.ventricosa introgression extended into the region associated with Pch2. This identified that the introgression is distal to Pch2 on 7A, providing further evidence that the genes are not homoeoloci. However, it is feasible to use this material to pyramid Pch1 and Pch2 on 7A in a tetraploid background and also to increase the copy number of Pch1 in combination with Pch2 in a hexaploid background.

Highlights

Eyespot is an important fungal disease of the stem base of cereals growing in temperate regions, such as North West Europe, North West USA, and New Zealand
Two main reasons account for this low successful ratio (48 %): (1) PCR primers designed at locations with high levels of sequence conservation between Brachypodium distachyon (Bd) and wheat failed to amplify a specific PCR product on the Ae. ventricosa introgressed DNA and (2) after sequencing of PCR products, no useful single nucleotide polymorphism (SNP) between Ae. ventricosa and wheat 7D genes were identified
The main objective of this work was to refine the position of Pch1 and Pch2 on wheat chromosome 7D and 7A, respectively, to determine whether they are homoeoloci

Summary

Introduction

Eyespot is an important fungal disease of the stem base of cereals growing in temperate regions, such as North West Europe, North West USA, and New Zealand. It is caused by two species of fungi, Oculimacula acuformis and O. yallundae (Crous et al 2003), and affects a wide range of hosts, including wheat, barley, rye, and oats. Pch has been mapped to a 0.26 cM region between five co-segregating proximal markers (Xcos, X4CD7A8, Xorw, Xtr383, and Xwg7S) and the distal COS (Conserved Orthologous Sequence) marker Xcos (Burt and Nicholson 2011). Marker-assisted selection for Pch commonly relied upon the presence of allele Ep-D1b of a co-segregating

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