Responses of maize (Zea mays L.) near isogenic lines carrying Wsm1, Wsm2, and Wsm3 to three viruses in the Potyviridae

Genes on chromosomes six (Wsm1), three (Wsm2) and ten (Wsm3) in the maize (Zea mays L.) inbred line Pa405 control resistance to Wheat streak mosaic virus (WSMV), and the same or closely linked genes control resistance to Maize dwarf mosaic virus (MDMV) and Sugarcane mosaic virus (SCMV). Near isogenic lines (NIL) carrying one or two of the genes were developed by introgressing regions of the respective chromosomes into the susceptible line Oh28 and tested for their responses to WSMV, MDMV, and SCMV in the field and greenhouse. F-1 progeny from NIL x Oh28 were also tested. Wsm1, or closely linked genes, provided resistance to all three viruses, as determined by symptom incidence and severity. Wsm2 and Wsm3 provided resistance to WSMV. Wsm2 and/or Wsm3 provided no resistance to MDMV, but significantly increased resistance in plants with one Wsm1 allele. NIL carrying Wsm1, Wsm2, or Wsm3 had similar SCMV resistance in the field, but NIL with Wsm2 and Wsm3 were not resistant in the greenhouse. Addition of Wsm2 to Wsm1 increased SCMV resistance in the field. For all viruses, symptom incidence was higher in the greenhouse than in the field, and relative disease severity was higher in the greenhouse for WSMV and MDMV. An Italian MDMV isolate and the Ohio SCMV infected the Wsm1 NIL, while the Ohio MDMV and Seehausen SCMV isolates did not. Our results indicate that the three genes, or closely linked loci, provide virus resistance. Resistance conferred by the three genes is influenced by interactions among the genes, the virus species, the virus isolate, and the environment.