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

Abstract Tar spot of corn ( Zea mays L.) is a significant disease in the United States and Canada caused by Phyllachora 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 with P. maydis in field environments. In this study, we developed a method to initiate tar spot in field settings using inoculations of corn leaves with P. maydis inoculum that had been stored at -20 °C for 10 months. Stromata of P. maydis were 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 with P. maydis and tar spot development in field environments. The results will aid new research into understanding the corn tar spot pathosystem and improving management strategies.