First report of <i>Curvularia lunata</i> causing leaf blight on muskmelon (<i>Cucumis melo</i>)

In November 2023, muskmelon (Cucumis melo) cultivated in the Tamil Nadu Agricultural University orchard in India (latitude 11.01520°, longitude 76.9326°) was affected by a leaf blight disease with a mean severity (percent disease index) reaching 74.8% over an area of two hectares. The symptoms initially appeared as green-yellowish circular spots, which later turned into irregular blackish-brown enlarged spots. Eventually, the spots joined together and covered the leaf causing blight symptoms, and finally, the blighted leaves drooped (Figure 1). A pathogen was isolated from six diseased leaves. A pure culture was obtained through single spore isolation (Choi et al., 1999). The colony on potato dextrose agar medium was brownish to black. Conidia were 22.9-26.1 × 7.12-10.68 µm in size, melanised and curved with three transverse septa (Figure 2). The colony and morphology of conidia were consistent with the description of Curvularia lunata (Garcia-Aroca et al., 2018). DNA from the culture was amplified using ITS1 and ITS4 primers (Khan & Javaid, 2020) The amplicon (555 bp) was sequenced and submitted to GenBank (Accession No. PP535557.1). A BLASTn search confirmed 100% identity to a C. lunata reference sequence (KU221454.1). A phylogenetic tree was constructed using MEGA-11 which revealed that the PP535557.1 sequence is closely related to the reference sequences KU221454.1 and MF611691.1 (Figure 3). To prove pathogenicity, the pathogen was inoculated on six 45-day-old glasshouse-grown muskmelon (cv. Mridula) plants using the pinprick method and spraying a conidial suspension (5×105 conidia/ml) on the leaves. The inoculated plants and six mock-inoculated control plants were maintained in a glasshouse at 25–28°C. Disease symptoms resembling those observed in the field appeared on the inoculated leaves four days after inoculation (Figure 4), and the fungus was re-isolated from the inoculated plants. Curvularia lunata causing leaf blight disease was reported in watermelon in Hongkong (Lu et al., 2000). To our knowledge, this is the first report of C. lunata causing leaf blight on muskmelon in India and worldwide.