Reactions of sweet corn hybrids with resistance to maize dwarf mosaic

Maize dwarf mosaic (MDM), caused by the sugarcane mosaic subgroup of potyviruses, can substantially reduce yield and ear quality of sweet corn (Zea mays). The effects of strain A of maize dwarf mosaic virus (MDMV-A) and strain MDMV-B of sugarcane mosaic virus (SCMV-MB) on resistant sweet corn hybrids were evaluated. Incidence of symptomatic plants, types of symptomatic responses, yield, and ear quality were compared among 20 hybrids in 1993 and 14 hybrids in 1994. Incidence of symptomatic plants measured at the beginning of harvest ranged from 4 to 100% in 1993 and 1 to 100% in 1994 and differed among hybrids inoculated with MDMV-A and/or SCMV-MB. Hybrids BiGuard, Dallas, HMX 9352, and Topacio had low (<20%) incidences of symptomatic plants when inoculated with MDMV-A, SCMV-B, or MDMV-A/SCMV-MB. Some hybrids had moderate responses, with incidence varying around 25%. Some hybrids appeared to have greater resistance to MDMV-A than to SCMV-MB. The incidence of sectoring plants (i.e., distinct bands or sectors of asymptomatic and symptomatic tissue) was higher for hybrids with high levels of resistance and ranged from 0 to 14% in 1993 and 0 to 83% in 1994. Ear weight of inoculated hybrids, expressed as a percentage of the noninoculated control, ranged from 84 to 109% in 1993 and from 84 to 105% in 1994. Slope coefficients from regressions of percent ear weight on incidence ranged from -0.085 to -0.15. Putt blanking was associated with high incidence of MDM-symptomatic plants. None of the commercially available MDM-resistant sweet corn hybrids were 100% asymptomatic, but levels of resistance in most of these hybrids were adequate to minimize the effects of MDM on yield.