The Linkage of Molecular Markers to a Gene Controlling the Symptom Response in Maize to Maize Dwarf Mosaic Virus. Michael D. McMullen. United States Department of Agriculture, Agricultural Research Service, and the Department of Agronomy, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691 U.S.A. Raymond Louie(1,3). (1)United States Department of Agriculture, Agricultural Research Service, and the Department of (3)Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691 U.S.A. MPMI 2:309-314. Accepted 26 June 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological society,1989.

Restriction fragment length polymorphism (RFLP) analysis was used to identify a major gene for symptom response (resistance) to MDMV strain A (MDMV-A) on chromosome 6 of the maize inbred Pa405. RFLP analysis of individual backcross plants of the genotypes (Pa405 X yM14) X yM14 and (Pa405 X K55) X K55, inoculated with MDMV-A, mapped this resistance gene to a region near the centromere of chromosome 6. This gene is tightly linked to and located between the RFLP marker loci, UMC85 and BNL6.29. This gene is essential for any resistance response because all plants lacking this gene rapidly developed generalized mosaic symptoms. In yM14 backcross plants, this gene both delayed symptom appearance and reduced symptom severity. In K55 backcross plants, this gene caused a similar delay in symptom appearance; however, the delayed symptoms were more variable and more severe than in the yM14 backcross plants, indicating that the effect of this gene on symptom development can be influenced by the genotype of the susceptible parents. We propose to designate this gene Mdm1 for maize dwarf mosaic virus resistance, gene 1.