Inoculation of Maize Leaves with the Bacterial Foliar Pathogen Clavibacter nebraskensis

Maize significantly contributes to food and fuel production. Yields can be reduced due to foliar diseases, which reduce photosynthetic leaf area. The bacterial foliar disease Goss's wilt (caused by Clavibacter nebraskensis) can cause significant yield losses in susceptible maize varieties. C. nebraskensis can infect leaves through wounds and colonize the vascular tissue of the leaf. We present a protocol that replicates this process with the use of a "clapper" with pins on one end to create wounds and a sponge soaked in inoculum on the other end, which allows for efficient field inoculations of maize leaves. Disease severity is then rated on a percentage scale multiple times over the season to generate an area under disease progress curve (AUDPC). Genetic host resistance is one of the most effective forms of foliar disease control in maize, as there are few effective forms of chemical control for bacterial diseases that affect maize. Screening for resistance in diverse germplasm, or for fine mapping a specific resistance gene, requires inoculating large populations in the field for obtaining phenotypic data. Our high-throughput protocol allows for large-scale disease evaluations and is useful for finding forms of genetic resistance or to understand plant-pathogen interactions of bacterial foliar pathogens.