Foliar inoculation ofPhyllachora maydisinto corn induces infection and local spread in field environments

Abstract

Tar spot of corn (Zea maysL.) is a significant disease in the United States and Canada caused byPhyllachora maydis, an obligate biotroph fungus. However, field research critical for understanding, managing, and mitigating the disease has been hindered by a need for methods to inoculate corn withP. maydisin field environments. In this study, we developed a method to initiate tar spot in field settings using inoculations of corn leaves withP. maydisinoculum that had been stored at -20 °C for 10 months. Stromata ofP. maydiswere observed 19 days after inoculation (dai), and the spread of tar spot was initially detected locally from the infection area 39 to 41 dai. Tar spot was not present in the fields beyond the inoculated area or localized spread area, signifying that the establishment of the disease resulted solely from inoculations. This study enhances our understanding of inoculation and infection of corn withP. maydisand tar spot development in field environments. The results will aid new research into understanding the corn tar spot pathosystem and improving management strategies.