Impact of Inoculum Concentration on Goss's Wilt Development in Corn and Alternative Hosts

Goss's bacterial wilt and blight of corn (Zea mays L.) is caused by Clavibacter nebraskensis (Cn). Research on Cn has confirmed alternative hosts for the disease, yet little is known about disease development in these alternative hosts. A greenhouse study was conducted to determine the inoculum concentration at which disease occurred for annual ryegrass (Lolium multiflorum Lam.), giant foxtail (Setaria faberi Herrm.), and johnsongrass (Sorghum halepense L.), compared with Goss's wilt susceptible and moderately resistant corn hybrids. Inoculum concentrations from 1 × 100 to 1 × 107 CFU/ml were compared for each individual species. Time for initial lesion development to occur was measured and compared among the hosts and inoculum concentrations. At 21 days after inoculation, both corn hybrids had higher disease severity than the alternative hosts, and disease severity increased for both corn hybrids when inoculum concentrations increased. Alternative hosts had no differences in disease severity as inoculum concentrations increased. Days required for initial lesion development to occur were similar for all hosts, and lesion development occurred sooner when inoculum concentration increased. Results demonstrate corn contributes more to the inoculum potential of Cn, but alternative hosts can still be a refuge for Cn.