3 GENETIC-LOCI CONTROL RESISTANCE TO WHEAT STREAK MOSAIC-VIRUS IN THEMAIZE INBRED PA405

Wheat streak mosaic virus (WSMV), a mite-transmitted potyvirus, infect s certain maize inbreds. To identify genes for resistance to WSMV, (Pa 405 x Oh28)F-2 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) sim ilar to the symptoms observed on the susceptible inbred Oh28, and plan ts with dispersed, chlorotic spots and rings (DSR). DNAs pooled from 2 5 plants with GM symptoms and from 25 plants with DSR symptoms were us ed to detect linkage to RFLP loci by ''bulked segregant'' analysis. Th is analysis identified two previously unreported genes for resistance to WSMV, designated wsm2 (chromosome 3 near umc102) and wsm3 (chromoso me 10 near umc163), and confirmed the presence of wsm2 on chromosome 6 S. RFLP analyses of DNA from individual plants revealed that the plant s that exhibited GRP symptoms were homozygous for Oh28 alleles at wsm1 , wsm2, and wsm3. Plants that exhibited DSR symptoms were homozygous f or Oh28 alleles at wsm1 and wsm2, but were heterozygous or homozygous for the allele from Pa405 at wsm3.