Annual Ryegrass (Lolium multiflorum), Johnsongrass (Sorghum halepense), and Large Crabgrass (Digitaria sanguinalis) are Alternative Hosts for Clavibacter michiganensis subsp. nebraskensis, Causal Agent of Goss's Wilt of Corn

Goss's bacterial wilt and leaf blight of corn is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis (Cmn). This disease has recently re-emerged as an important disease in the Midwestern United States (US) and continues to spread. Cultural practices are currently the only methods available for controlling the disease. Weedy species in the genera Echinochloa, Setaria, and Sorghum have previously been described as alternative hosts of Cmn. The objective of this research was to use an isolate of Cmn from the eastern Midwest to examine the host status of previously confirmed hosts, as well as test whether additional weedy or cover crop species are alternative hosts of the bacterium. Plants were inoculated with a suspension of 1 × 10⁸ colony-forming units of Cmn per milliliter in a greenhouse experiment. Leaves were observed for typical symptoms of Goss's wilt 7 d after inoculation. Pathogen presence was determined by observing bacterial streaming microscopically, and isolating Cmn from symptomatic plants. Putative colonies of Cmn were confirmed with the use of morphological and molecular methods. Koch's Postulates were completed on populations of new plant species that showed symptoms. Results revealed three new hosts of Cmn: annual ryegrass, johnsongrass, and large crabgrass. In contradiction to previous reports, barnyardgrass was not a host of Cmn in this study. Results also confirm that giant foxtail, green foxtail, shattercane, and yellow foxtail are hosts of Cmn. These results redefine the known host range of Cmn and are important in identifying additional sources of inoculum to improve our understanding of the epidemiology of Goss's wilt.Nomenclature: Annual ryegrass, Lolium multiflorum Lam.; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; giant foxtail, Setaria faberi Herm.; green foxtail, Setaria viridis (L.) Beauv.; johnsongrass, Sorghum halepense (L.) Pers.; large crabgrass, Digitaria sanguinalis (L.) Scop.; shattercane, Sorghum bicolor (L.) Moench ssp. arundinaceum (Desv.) de Wet & Harlan; yellow foxtail, Setaria pumila (Poir.) Roemer & J.A. Schultes; corn, Zea mays L.