Development of novel EST-derived resistance gene markers in hop (Humulus lupulus L.)

Although sources of resistance to major pathogens exist in cultivated hop germplasm, little effort has been invested to date in developing resistance-linked markers. The aim of this study was to design and evaluate resistance gene analogs (RGAs) potentially useful for marker-assisted selection towards novel resistant hop cultivars. A set of 34 putative hop RGAs was retrieved by screening publicly available hop expressed sequence tags (ESTs) for conserved sequence motifs of common resistance protein domains. Seventeen of these were identified as putative RGAs by BLAST analyses. Exon/intron boundary prediction enabled re-sequencing of 24 EST-RGAs, allowing the acquisition of approximately 5 kbp of novel intronic sequence and 8 kbp of re-sequenced exons. Fifteen EST-RGAs exhibited polymorphisms and were added to a framework linkage map of hop. In addition to providing EST-derived markers potentially useful for resistant hop cultivar development, this study provides valuable insights into the utility of targeting hop introns for marker development.