IDENTIFICATION OF MOLECULAR MARKERS LINKED TO THE STEM RUST RESISTANCE GENE RPG4 IN BARLEY

The gene rpg4 in barley confers resistance to pathotype QCC of Puccinia graminis f. sp. tritici. To facilitate the efficient transfer of rpg4 into breeding lines, an investigation was initiated to identify molecular markers linked to the gene. A doubled haploid population (125 individuals) derived from Q21861, the source of rpg4, was subjected to bulked segregant analysis by using random amplified polymorphic DNAs (RAPDs) and restriction fragment length polymorphisms (RFLPs). From 500 10-mer primers evaluated, only three reliably amplified fragments in one of the DNA bulks and not in the other. Linkage of the three RAPD markers, OPP-05 (900), OPH-13 (1600), and OPH-I5 (1000), with rpg4 was confirmed by segregation analysis of the doubled haploid progeny. Primer OPH-15 generated the most closely linked (0.8 centimorgans [cM]) marker to rpg4. RFLP probes were used to map rpg4 and associated RAPD markers to chromosome 7M. The RFLP markers, ABG390 and MWG740, mapped 5.7 and 4.9 cM distal and proximal to the resistance gene, respectively. The RAPD and RFLP markers identified for rpg4 in this study should facilitate the efficient transfer of stem rust resistance in barley germ plasm.