Origin of Scm1 and Scm2 - two loci conferring resistance to sugarcane mosaic virus (SCMV) in maize

Sugarcane mosaic virus (SCMV) causes serious losses of grain and forage yie ld of maize (Zen mays L.) in Europe. Two dominant genes, Scm1 and Scm2, hav e been identified to confer resistance to SCMV. Scm1 is located on the shor t arm of chromosome 6 and Scm2 near the centromere region of chromosome 3. In the present study, resistant, partially resistant, and susceptible maize inbred lines, together with their ancestral lines, were evaluated with mol ecular markers to trace back the origin of Scm1 and Scm2. The banding patte rns indicated that the Scm1 region, originally identified in resistant Euro pean line FAP1360A, was derived from its ancestral line FAP954A. The other two resistant European lines, D21 and D32, most likely carry the same Semi region, which originated from their common ancestral line A632. This Semi r egion was also present in three partially resistant lines, D09, FAP1396A an d FAP693A, but not in the resistant U.S. inbred Pa405. Apart from FAP954A a nd A632, none of the remaining ancestral lines and none of the susceptible lines harbored the Scm1 region. The Scm2 region present in FAP1360A was obv iously transmitted from its ancestral line Co125. However, the presence of the respective Scm2 region was not confirmed in the other three resistant l ines (D21, D32 and Pa405), the remaining ancestral lines, and all partially resistant lines by using closely linked markers.