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-isogeni c lines (NILs) was screened with 300 RAPD primers for polymorphisms li nked to the Dn2 gene. A total of 2700 RAPD loci were screened for link age to the resistance locus. Four polymorphic RAPD fragments; two in c oupling phase and two in repulsion phase, were identified as putative RAPD markers for the Dn2 gene. Segregation analysis of these markers i n an F-2 population segregating for the resistance gene revealed that all four markers were closely linked to the Dn2 locus. Linkage distanc es ranged from 3.3 cM to 4.4 cM. Southern analysis of the RAPD product s using the cloned RAPD markers as probes confirmed the homology of th e RAPD amplification products. The coupling-phase marker OPB10(880c) a nd the repulsion-phase marker OPN1(400r) were converted to sequence ch aracterized amplified region (SCAR) markers. SCAR analysis of the F-2 population and other resistant and susceptible South African wheat cul tivars corroborated the observed linkage of the RAPD markers to the Dn 2 resistance locus. These markers will be useful for marker-assisted s election of the Dn2 gene for resistance breeding and-gene pyramiding.