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In recent years, yield losses due to chickpea chlorotic dwarf virus (CpCDV, Mastrevirus, Geminiviridae) infection have been intensified in a large number of plants such as watermelon, okra and cotton and the virus has been reported around the world (Kanakala and Kuria 2018). In the current study, natural infection of watermelon with CpCDV was investigated. Watermelon samples showing leaf chlorosis, hardness and discoloration of the flesh with whitish stripes, deformation and increasing seed abortion of fruits (Fig. 1) were collected from watermelon-growing farms in Behbahan (Khuzestan Province) in 2018. Total DNA of the samples was extracted from leaf tissue using the cetyltrimethylammonium bromide (CTAB) method followed by the enrichment of the extracted circular DNA molecules by rolling circle amplification (RCA) method using phi 29 DNA polymerase (TempliPhi kit, GE Healthcare, USA). Polymerase chain reaction (PCR) tests using RCA product as DNA template and the primer pair CpCDV-752-F/CpCDV-1326-R (Askari et al. 2021) resulted in the amplification of an expected 575 bp DNA fragment (Fig. 2) indicating the infection of the all tested samples with CpCDV. The definitive infection of a PCR positive sample (W1) with CpCDV was confirmed by sequencing of PCR product. CpCDV has a broad host range and infects members of 11 plant families including several cucurbitaceous plants, such as cucumber, squash and watermelon (Kanakala and Kuria 2018; Zaagueri et al. 2017). The observed symptoms of the infected watermelon plants in this study were very similar to the symptoms of infected samples of the same plant, which was previously reported as “hard fruit syndrome” of watermelon in Tunisia, and the pathogenesis of the causal virus (CpCDV) was demonstrated (Zaagueri et al. 2017). The surveys of this study showed that the disease severity is remarkable in watermelon-growing farms in Behbahan and similar symptoms were also observed in some watermelon farms in Kerman and Hormozgan Provinces. Considering the wide host range of the virus, for example, several grain legumes, okra, tomato, spinach, pepper and cotton in neighboring countries of Iran and recent findings, it seems that CpCDV may has more natural hosts and a wide spread in Iran. However, further studied are required to confirm this hypothesis. This is the first report of the CpCDV infection of watermelon in Iran. [ABSTRACT FROM AUTHOR]