Detection and Molecular Characterization of Viral Agents Infecting Cucurbits from South Marmara Region in Türkiye

Although cucurbit viruses have been widely investigated throughout different regions of Turkey, studies focusing on the molecular characterization of isolates from the South Marmara Region (SMR) are still scarce. To expand the current understanding of cucurbit viral diseases, a total of 76 leaf samples exhibiting virus-like symptoms were obtained from different cultivated cucurbit species in the provinces of Balıkesir, Bursa, and Çanakkale. These samples were screened for seven cucurbit-infecting viruses previously documented in Türkiye by employing reverse transcription polymerase chain reaction (RT-PCR). Among the tested samples, 52 were determined to be infected with at least one viral agent. The viruses identified included zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), and cucumber mosaic virus (CMV), while cucumber green mottle mosaic virus (CGMMV), cucumber vein yellowing virus (CVYV), cucurbit yellow stunting disorder virus (CYSDV), and cucurbit chlorotic yellows virus (CCYV) were not detected in any tested samples. Among the detected viruses, ZYMV was the most prevalent (34.21%), whereas CMV exhibited the lowest incidence (2.63%). The prevalence of WMV was found to be 14.47%. The most frequent symptom associated with infection was mosaic-type chlorotic mottling on the leaves. For further molecular characterization, nine representative isolates (three from each detected virus) were selected, and their coat protein gene sequences were determined. Comparative sequence analysis demonstrated that Turkish isolates shared 95–97% nucleotide identity with each other but differed by up to 10% when compared with reference isolates from other geographical regions. Phylogenetic reconstruction revealed that ZYMV isolates clustered closely within a single lineage, while WMV and CMV isolates were separated into multiple phylogenetic groups, suggesting distinct evolutionary histories. Overall, this research constitutes the first molecular characterization of ZYMV and WMV isolates from the South Marmara Region, thereby providing new insights into cucurbit virus diversity and epidemiology in Türkiye.