Curvularia leaf spot affects maize plants worldwide and is commonly caused by Curvularia lunata, C. geniculata, and C. pallescens (Manzar et al. 2022; Manzar et al. 2021; Choudhary et al. 2011). In February 2017, leaf spot symptoms were observed in a Deogaon, (25.74 N, 82.99 E) in Uttar Pradesh, India, with disease incidence of less than 10% of the plants in maize fields. On the leaves and sheaths, variously shaped yellow spots were developed. The spots were 2.5 mm in diameter and frequently grew larger, reaching a diameter of 1 cm. They were encircled by a chlorotic halo with dark borders. The symptomatic tissue showing leaf spots of 10 plants was taken and cut into pieces (4 mm2) then surface sterilized with 1% sodium hypochlorite for 1 min, and rinsed three times with distilled water. The cut leaf tissue was placed on the Petri plate containing potato dextrose agar medium amended with streptomycin sulfate (125 ppm). Then incubated at 25±2°C with a 12-h light and dark period, after 5 days of incubation, five pure cultures were obtained using the hyphal tip technique. The pure culture was incubated at 26±2°C for 10 days. The upper surface of the colony was dark grayish black with fluffy mycelia, and the reverse colony was dark brown. The conidia have three septa, are light brown to dark brown in color, straight to curved, ellipsoidal to fusiform, and have two bigger, darker central cells than terminal cells. On average, conidia are between 27.22 to 31.21 mm long and 10.61 to 12.62 mm wide (n=30). The morphological description is similar to the Curvularia verruculosa morphological traits described by Tandon & Bilgrami (Ellis 1966). Molecular identification was done in addition to supporting morphological identification. The nucleopore GDNA Fungus Kit (Genetix Brand, India) was used to extract the genomic DNA of the E40 isolate. The ITS rDNA region (White et al. 1990) and the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene (Berbee et al. 1999) were amplified through PCR(Manzar et al., 2022).The amplicons were bidirectional sequenced through the Sanger sequencing method. The similarity percentage of E40 isolate matched 100% with MH859788 (CBS444.70 ) of Curvularia verruculosa strain for ITS, and 100% with LT715824 (CBS150.63) of Curvularia verruculosa strain for gpd after Blastn analysis. The gene sequences were deposited to GenBank and accession no. OR262893 for ITS, and LC773704 for gpd were assigned. As a result, C. verruculosa was determined to be the presumed pathogen by both morphology and molecular characteristics. The pathogenicity of E40 isolate was performed twice by spraying (106 conidia/ml in sterile water) onto the leaves of 25 days old maize plant cv. Kanchan (n = 10). Uninoculated healthy maize plants (n=5) were sprayed only with autoclaved water. All pots are kept in a glass house at 25°C±2°C with 90% relative humidity. After 15 days of pathogen inoculation the foliar spots with chlorotic halo, enlarger upto 1cm, and from these spots the identical fungus was reisolated. The reisolated fungus showed similar morphological characteristics to C. verruculosa. Control plants showed no symptoms. C. verruculosa has been previously reported as a causative agent of leaf spot disease in Common beans (Wei et al., 2022), Cotton (Shirsath et al., 2018). To our knowledge, this is the first report of leaf blight caused by C. verruculosa on maize in India.
Keywords: Curvularia leaf spot; Curvularia verruculosa; E40; Maize.