Molecular mapping and gene action of Scm1 and Scm2, two major QTL contributing to SCMV resistance in maize

Sugarcane mosaic virus (SCMV) is one of the most important virus diseases of maize in Europe. In this study, the gene action at two major quantitative trait loci (QTL) affecting resistance to SCMV in maize was mapped and characterized. A total of 121 F-3 lines from cross F7 (susceptible) x FAP1360A (resistant) were evaluated for SCMV resistance in replicated field trials across two environments under artificial inoculation at seven scoring dates. The genotypic variance was always highly significant and heritability increased up to 0.92 for later scoring dates. The method of composite interval mapping was employed for QTL mapping using four simple sequence repeat (SSR) markers flanking two regions identified in a previous study with cross D145 x D32. The presence of two QTL for SCMV resistance, one on chromosome 6 (Scm1 region) and one on chromosome 3 (Scm2 region). was confirmed. These two QTL together explained between 15% (first score) and 62% (final score) of the phenotypic variance at various stages of plant development. Gene action was additive for the Scm2 region but completely dominant for the Scm1 region. Comparison of results of this study with those obtained for cross D145 x D32 suggested that the resistance alleles in the two populations are identical for the Semi region but different for the Srm2 region.