First report of Zucchini tigré mosaic virus naturally infecting two different cucurbit species in Argentina

In Argentina, Cucurbita maxima cv. Zapallo Plomo, an indigenous variety, and the hybrid Cucurbita maxima × Cucurbita moschata cv. Tetsukabuto contribute significantly to regional economies, being the fourth most popular vegetable in the domestic market. In March 2022, leaves showing virus-like symptoms, including discolouration, blistering, distortion and mosaics were collected from both cultivars in Balcozna, Catamarca province (Figure 1). The fruits were severely affected, being covered in knobbly warts, blotches and brown bumps (Figure 2). Samples were tested by DAS-ELISA using commercial Papaya ringspot virus (PRSV) antisera (BIOREBA AG, Switzerland), following the manufacturer's instructions. Four ELISA-positive samples were tested by RT-PCR for the PRSV coat protein (CP) gene (Cabrera Mederos et al., 2016) but failed to generate the expected amplicon, suggesting the plants were infected with a different virus in the PRSV cluster. There are seven viruses that are closely related to PRSV which form the PRSV cluster. Cross-reaction with polyclonal antisera between the species of the PRSV cluster has been reported, resulting in misdiagnosis (Desbiez & Lecoq, 2021). While most members of the cluster are geographically restricted, Zucchini tigré mosaic virus (ZTMV) is distributed across Asia, Europe, and the Americas, including the United States, Costa Rica and Venezuela, as well as several islands in the Caribbean Sea and Indian Ocean (Cabrera Mederos et al., 2023). Two-step RT-PCR was done using ZTMV-specific primers which amplify c. 830 bp of the CP region (Romay et al., 2014). The obtained amplicons were sequenced (Macrogen Inc., South Korea). Sequence comparison using BLASTn showed the highest nucleotide identity values (91.37 %, 100% query coverage) with a ZTMV isolate from Martinique (GenBank Accession No. KC345559). The obtained sequences were submitted to GenBank (OR474532-OR474535). Phylogenetic analysis of the CP region of ZTMV were performed using the maximum likelihood method in the IQ-TREE software (Figure 3). All four sequences from Argentina clustered together with those from America. This finding suggests ZTMV might be more widespread than previously thought, potentially explaining recent yield losses in Balcozna due to reduced fruit growth and quality. The virus poses a significant threat to cucurbit crop yields in Argentina, highlighting the importance of characterising viral pathosystems to develop sustainable management practices and anticipate future outbreaks. Here, we report the first detection of ZTMV infecting cucurbits in Argentina, with Cucurbita maxima and Cucurbita maxima × Cucurbita moschata identified as novel hosts.