Teilprojekt 09

High resolution mapping of a BaYMV/BaYMV-2 resistance gene located on barley chromosome 5H

Frank Ordon (JKI), Andreas Graner (IPK)

Barley  yellow mosaic virus diseases caused by different strains of soil-borne  Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV)  is one of the most important diseases of winter barley in Europe and  Asia. Until now 9 different loci conferring resistance to the different  strains of these viruses are known. Out of these the one located on  chromosome 5H is effective against BaYMV and BaYMV-2. Based on the   availability of about 5000 F2 seeds (0.01 cM resolution) of the cross  ´HHOR4242´ x ´Igri´ and two co-dominant flanking markers spanning an  interval of about 4cM, the project aims at the isolation of this locus  applying a map based cloning approach. This comprises the following  steps (i) construction of a high resolution mapping population, (ii)  marker saturation using all sequence and marker information available  for the target interval in barley and employing synteny to rice,  Brachypodium and sorghum, as well as data available from low coverage  sequencing of chromosome 5H, (iii) establishment of a BAC contig, (iv)  identification of candidate genes. On the one hand the results obtained  within this project  will lead to a deeper understanding of resistance  of barley to BaMMV/BaYMV and on the other hand knowledge on the sequence  of this resistance gene will allow for allele mining in gene bank  accessions in order to identify the most effective alleles and further  deploy these in marker assisted breeding programmes. The availability of  a gene-based marker will allow for the stringent introgression of this  gene from its non adapted donor variety into European breeding material.  Moreover, marker assisted selection will be instrumental to minimize  the linkage drag around the introgressed fragment, and thus minimize the  genetic erosion around the target locus. The introgression of new  resistance genes/alleles is of special importance as the two alleles  rym4 and rym5 which at the moment are exclusively used in European  barley breeding have been overcome by resistance breaking strains of  BaMMV and BaYMV. Moreover, isolation of this gene will be a significant  contribution to further unravel the genetic basis of resistance to  soil-borne bymoviruses. Isolation of the gene and knowledge on its  structure will facilitate subsequent  investigations on host-pathogen  interaction, including the evolution of resistance and virulence as well  as the interplay between allelic variation and gene function.

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