Uncovering the Infection Strategy ofPhyllachora maydisduring Maize Colonization: A Comprehensive Analysis

Abstract

ABSTRACTTar spot, a disease caused by the ascomycete fungal pathogenPhyllachora maydis, is considered one of the most significant yield-limiting diseases of maize (Zea maysL.) within the United States.P. maydismay also be found in association with other fungi, forming a disease complex with characteristic fish eye lesions. Understanding howP. maydiscolonizes maize leaf cells is essential for developing effective disease control strategies. Here, we used histological approaches to elucidate howP. maydisinfects and multiplies within susceptible maize leaves. We collected tar spot-infected maize leaf samples from four different fields in northern Indiana at three different time points during the growing season. Samples were chemically fixed and paraffin-embedded for high-resolution light and scanning electron microscopy. We observed a consistent pattern of disease progression in independent leaf samples collected across different geographical regions. Each stromata contained a central pycnidium that produced asexual spores. Perithecia with sexual spores developed in the stomatal chambers adjacent to the pycnidia, and a cap of spores formed over the stromata.P. maydisreproductive structures formed around but not within the vasculature. In our samples containing fish eye lesions,P. maydisis associated with two additional fungi, one of which is likely a member of theParaphaeospheriagenus; the other is an unknown fungi. Our data provide fundamental insights into how this pathogen colonizes and spreads within maize leaves. This knowledge can inform new approaches to managing tar spot, which could help mitigate the significant economic losses caused by this disease.