Development of RAPD and SCAR markers linked to the Russian wheat aphid resistance gene Dn2 in wheat

RAPD (random amplified polymorphic DNA) analysis was used to identify molecular markers linked to the Dn2 gene conferring resistance to the Russian wheat aphid (Diuraphis noxia Mordvilko).,A set of near-isogenic lines (NILs) was screened with 300 RAPD primers for polymorphisms linked to the Dn2 gene. A total of 2700 RAPD loci were screened for linkage to the resistance locus. Four polymorphic RAPD fragments; two in coupling phase and two in repulsion phase, were identified as putative RAPD markers for the Dn2 gene. Segregation analysis of these markers in an F-2 population segregating for the resistance gene revealed that all four markers were closely linked to the Dn2 locus. Linkage distances ranged from 3.3 cM to 4.4 cM. Southern analysis of the RAPD products using the cloned RAPD markers as probes confirmed the homology of the RAPD amplification products. The coupling-phase marker OPB10(880c) and the repulsion-phase marker OPN1(400r) were converted to sequence characterized amplified region (SCAR) markers. SCAR analysis of the F-2 population and other resistant and susceptible South African wheat cultivars corroborated the observed linkage of the RAPD markers to the Dn2 resistance locus. These markers will be useful for marker-assisted selection of the Dn2 gene for resistance breeding and-gene pyramiding.