Three Genetic Loci Control Resistance to Wheat Streak Mosaic Virus in the Maize Inbred Pa405. Michael D. McMullen. (1) Corn & Soybean Res. Unit, USDA-Agricultural Research Service, OARDC, Wooster, OH 44691 U.S.A. (2) Dept. of Agronomy, OARDC, Wooster, OH 44691, U.S.A. Mark W. Jones (1,2), Kevin D. Simcox (1), and Raymond Louie (1,3). (1) Corn & Soybean Res. Unit, USDA-Agricultural Research Service, OARDC, Wooster, OH 44691 U.S.A. (2) Dept. of Agronomy, OARDC, Wooster, OH 44691, U.S.A. (3) Dept. of Plant Pathology, OARDC, Wooster, OH 44691, U.S.A. MPMI 7:708-712. Accepted 9 September 1994. This article is in the public domain and not copyrightable. II may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994.

Wheat streak mosaic virus (WSMV), a mite-transmitted potyvirus, infects certain maize inbreds. To identify genes for resistance to WSMV, (Pa405 x Oh28)F2 plants were inoculated with WSMV and symptom responses observed. In addition to resistant (symptomless) plants, two types of symptomatic plants were noted: plants with generalized mosaic (GM) similar to the symptoms observed on the susceptible inbred Oh28, and plants with dispersed, chlorotic spots and rings (DSR). DNAs pooled from 25 plants with GM symptoms and from 25 plants with DSR symptoms were used to detect linkage to RFLP loci by "bulked segregant" analysis. This analysis identified two previously unreported genes for resistance to WSMV, designated wsm2 (chromosome 3 near umc102) and wsm3 (chromosome 10 near umc163), and confirmed the presence of wsml on chromosome 6S. RFLP analyses of DNA from individual plants revealed that the plants that exhibited GM symptoms were homozygous for Oh28 alleles at wsm1, wsm2, and wsm3. Plants that exhibited DSR symptoms were homozygous for Oh28 alleles at wsml and wsm2, but were heterozygous or homozygous for the allele from Pa405 at wsm3.