Morpho-Molecular Identification, Virulence and In Vitro Sporulation of Fungi Associated with Maize Foliar Diseases in Egypt

Maize (Zea mays L.) is an important crop in Egypt. Foliar diseases including northern maize leaf blight (NCLB), southern corn leaf blight (SCLB), and Curvularia leaf spot (CLS) pose considerable economic threats to its yield. This study aimed to identify the primary fungal pathogens responsible for foliar blight and spot symptoms on maize in Egypt. Their pathogenic variability on both maize and sorghum was assessed, and optimal media for in vitro sporulation were determined. A survey in high-incidence areas in Egypt led to the collection of 15 symptomatic samples, from which seven single-spore fungal isolates were obtained. Pathogenicity experiments on maize showed varying virulences. Isolates Eg_57 and Eg_60 had the highest disease index, recording 88.75% and 83.75% respectively. Furthermore, only isolates Eg_52 and Eg_60 demonstrated cross-pathogenicity on sorghum. Morphological features of conidia and colony traits, supported by molecular characterization (ITS sequencing), identified the isolates as five isolates of Bipolaris maydis (Eg_57, Eg_59, Eg_60, Eg_73, and Eg_88), one isolate of Exserohilum turcicum (Eg_52), and single isolate of Curvularia lunata (Eg_23). Phylogenetic analysis validated their identities, with strong bootstrap support (100%). A considerable interaction between isolate and media was observed for sporulation. Of the seven media tested, potato dextrose agar with maize leaf pieces (MLP) produced the most count of spores across all tested isolates, averaging 48.3×104 spores/mL. These results suggested B. maydis as the most prevalent pathogen, and MLP was the most effective medium for conidia production. This research provides a basis for future epidemiological investigations and resistance-breeding programs.