Development of Expressed Sequence Tag (EST)-based Markers for Genomic Analysis of a Barley 6H Region Harboring Multiple Net Form Net Blotch Resistance Genes

We previously identified a region near the centromere of barley (Hordeum vulgare L.) chromosome 6H that harbors two closely linked net form net blotch resistance genes (rpt.r and rpt.k). In this study, we mined barley expressed sequence tag (EST) databases and developed EST-derived markers for further mapping of this region in a population derived from 'Rika' and 'Kombar'. Additionally, we did a comparative analysis of this region to other grass species. Fifteen newly developed markers were added to the previous map, and most were distributed within a 27.0-cM interval spanning rpt.r and rpt.k. The two resistance loci were delineated to a 1.6 cM genetic interval. Comparison of mapped ESTs along chromosome 6H to wheat bin-mapped ESTs suggests that rpt.r and rpt.k are most likely located on the long arm of chromosome 6H. Comparative analysis revealed that a 12.6-cM region containing the two resistance loci is colinear with a region of rice chromosome 2 between 23.7 and 29.9 Mb with only a few rearrangements, and nearly the same level of colinearity was observed between barley and Brachypodium in this region. This work refines the genetic and physical location of rpt.r and rpt.k and provides an initial step toward the map-based cloning of these two genes.