Browsing by Author "Kleczewski, Nathan M."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    A new and effective method to induce infection of Phyllachora maydis into corn for tar spot studies in controlled environments
    (Plant Methods, 2023) Solórzano, José E.; Issendorf, Shea E.; Drott, Milton T.; Check, Jill C.; Roggenkamp, Emily M.; Cruz, C. D.; Kleczewski, Nathan M.; Gongóra-Canul, Carlos C.; Malvick, Dean K.
    Background Tar spot of corn is a significant and spreading disease in the continental U.S. and Canada caused by the obligate biotrophic fungus Phyllachora maydis. As of 2023, tar spot had been reported in 18 U.S. states and one Canadian Province. The symptoms of tar spot include chlorotic flecking followed by the formation of black stromata where conidia and ascospores are produced. Advancements in research and management for tar spot have been limited by a need for a reliable method to inoculate plants to enable the study of the disease. The goal of this study was to develop a reliable method to induce tar spot in controlled conditions. Results We induced infection of corn by P. maydis in 100% of inoculated plants with a new inoculation method. This method includes the use of vacuum-collection tools to extract ascospores from field-infected corn leaves, application of spores to leaves, and induction of the disease in the dark at high humidity and moderate temperatures. Infection and disease development were consistently achieved in four independent experiments on different corn hybrids and under different environmental conditions in a greenhouse and growth chamber. Disease induction was impacted by the source and storage conditions of spores, as tar spot was not induced with ascospores from leaves stored dry at 25 degrees C for 5 months but was induced using ascospores from infected leaves stored at -20 degrees C for 5 months. The time from inoculation to stromata formation was 10 to 12 days and ascospores were present 19 days after inoculation throughout our experiments. In addition to providing techniques that enable in-vitro experimentation, our research also provides fundamental insights into the conditions that favor tar spot epidemics. Conclusions We developed a method to reliably inoculate corn with P. maydis. The method was validated by multiple independent experiments in which infection was induced in 100% of the plants, demonstrating its consistency in controlled conditions. This new method facilitates research on tar spot and provides opportunities to study the biology of P. maydis, the epidemiology of tar spot, and for identifying host resistance.
  • Thumbnail Image
    Item
    Tar Spot of Corn: A Diagnostic and Methods Guide
    (Plant Health Progress, 2023) Solórzano, José E.; Cruz, C. D.; Arenz, Brett E.; Malvick, Dean K.; Kleczewski, Nathan M.
    Tar spot of corn is an emerging plant disease in the continental United States and Canada caused by the fungal pathogen Phyllachora maydis Maubl. Tar spot has been known to occur in Mexico, the Caribbean, and Central and South America since the early to mid-1900s. In 2015, it was reported for the first time in the continental United States. Since that time, tar spot has spread across corn-producing areas in the United States with epidemics as recent as 2021 resulting in significant yield losses. Although tar spot has been known to affect corn for over a century in the Americas, the biology of the pathogen, etiology, and epidemiology of the disease are not well understood. Additionally, symptoms and signs of tar spot resemble other foliar diseases and abiotic disorders of corn, which may lead to misdiagnosis. In this paper, we provide a brief description of current knowledge about tar spot of corn, including pathogen taxonomy, host range, symptoms and signs, specimen storage, pathogenicity testing, diagnostic protocols, and geographic distribution. This information will be useful to diagnosticians, researchers, and other professionals working with this disease.