Plant Genome III Conference Plant Genome III Conference
The CIMMYT breeding line Q21961 is a valuable source of resistance to wheat stem rust (Puccinia graminis f. sp. tritici), and leaf rust (Puccinia hordei) in barley. It possesses Rpgl, a durable stem rust resistance gene; rpg4, a recently described gene that confers resistance to the stem rust pathotype QCC; and RphQ, a gene for leaf rust resistance. To facilitate the rapid and efficient transfer of these rust resistance genes from Q21861, a study was undertaken to identify molecular markers linked to the resistance genes and test their efficacy in a marker assisted selection program. For this study, doubled haploid lines derived from the cross Q21861/SM89010 were used as the mapping population. Using bulked segregant analysis, several molecular markers were found linked to each of the resistance genes. Three RAPD markers (OPH-15-1000, OPP-05-900 and OPH-13-1600) were found linked to rpg4 at 1.6, 6.5 and 15.1 cM, respectively. RAPD markers OPI-04-2200 and OPP-04-1200 were found to be linked within 3.4 and 10.0 cM, respectively, of RphQ. These markers, plus ABG704, a PCR-based marker closely linked to Rpgl, were used for marker assisted selection of the rust resistance genes in an F2, population derived from Q21861/SM990IO (150 progeny). By using markers in seeing and repulsion, homozygous resistant plants could be differentiated from heterozygous plants. A double blind test indicated that disease assessment data were in very close agreement with the molecular marker data, differing only for recombinant plants. Only one plant among 150 carried together all three rust genes. This plant was selected based on molecular markers, and the presence of the resistance genes were verified by disease tests. These results demonstrate the great potential of molecular markers for selecting and transferring multiple rust resistance genes in barley.