First Report of Curvularia Leaf Spot of Corn, Caused by Curvularia lunata , in Wisconsin

In August 2025, low levels (10% incidence and 5% severity on lower leaves) of small tan leaf lesions were observed on corn in Columbia County, Wisconsin. Given corn is the number one cash crop in Wisconsin, symptomatic leaves were collected and analyzed at the University of Wisconsin-Madison Field Crops Pathology Lab for pathogen identification. Sections of the symptomatic leaves were surface disinfested in a 0.825% NaOCl solution for 1 min, rinsed in sterile deionized water, disinfested in 95% ethanol for 1 min then rinsed in sterile deionized water. The disinfested leaf pieces were blotted onto sterile filter paper prior to cutting them into smaller pieces and placing them on potato dextrose agar (PDA) amended with 250 µg/ml ampicillin, 10 µg/ml rifampicin and 25 µg/ml streptomycin. After 7 days, dark brown-black to gray colonies were observed. Conidia produced were melanized, curved and 3-septate, measuring 18-27 X 9-13 µm. Pure cultures were obtained from single conidia, and a representative isolate (CV1-A) was sequenced to confirm identity via amplification of the internal transcribed spacer (ITS) region of rDNA using primers ITS4 and ITS5 (White et al. 1990). Primers GPD-1 and GPD-2 (Wang et al. 2024) were used to amplify a portion of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. Primers EF1-983F and EF1-2128R (Wang et al., 2024) were used to amplify a portion of the translation elongation factor 1-a (EF-1α) gene. Amplicons were sequenced and submitted to NCBI and assigned accession numbers PZ453030 (ITS), PZ464379 (GAPDH) and PZ464378 (EF-1α). BLAST searches resulted in 100% identity to C. lunata for ITS (GenBank accession nos. KX442659 and PX925100), GAPDH (GenBank accession nos. LC744294 and OP312087) and EF-1α (GenBank accession nos. PX063961 and PQ407938). To fulfill Koch’s postulates, an actively growing culture of C. lunata isolate CV1-A was flooded with sterile deionized water, scraped to dislodge spores, and the resulting inoculum was transferred to a sterile tube. The spore concentration was adjusted to 1 X 103 spores/ml in a volume of 30 ml and one drop of Tween-20 was added to the inoculum. A control solution was prepared with sterile deionized water and Tween-20. Six pots containing 3 corn plants (Croplan 3899VT2/R1B) each were grown in a controlled environment grow room until the V4 growth stage (four fully emerged leaves). Plants in three pots were sprayed to leaf wetness with the C. lunata inoculum. Plants in the remaining three pots were sprayed to leaf wetness with the water control. All pots were covered with a plastic bag to maintain humidity and incubated in a controlled environment chamber at 25°C under grow lights (14 h light, 10 h dark). The plastic bags were removed after 24 hours. Twelve days post inoculation, isolations were made from corn leaves with lesions indicative of Curvularia leaf spot. The control plants did not develop lesions and remained healthy. Curvularia lunata was re-isolated from symptomatic plants and identified by cultural characteristics, spore morphology and DNA sequencing. The pathogenicity experiment was repeated a second time with the same results. These findings confirm the presence of Curvularia lunata causing Curvularia leaf spot of corn in Columbia County, Wisconsin. Ongoing evaluations of hybrid resistance and fungicide performance will be key to limiting the impact of Curvularia leaf spot in Wisconsin corn production.