Abstract
Aim/Background:
Watermelon mosaic virus (WMV) represents a member of the Potyvirus genus of the Potyviridae family. This study was conducted during the growing seasons of 2022 and 2023 in Qaen County, South Khorasan Province, Iran. The fundamental aim of this investigation was to identify the viral pathogen causing severe mosaic using the dsRNA extraction technique and to assess its potential spread to key crops, specifically saffron, in the vicinity.

Methods:
The 25 pumpkin leaves from different pumpkin plants exhibiting viral symptoms, including mosaic patterns, leaf distortion, color breaking, and warts on fruits, as well as 10 leaves from saffron exhibiting yellow symptoms, were collected. The cellulose column chromatography method was used to examine the presence of double-stranded RNA (dsRNA). Utilizing degenerate primers tailored to target the Helper Component Proteinase (HC-Pro) gene of potyviruses, RT-PCR amplification was carried out. Subsequently, the resulting amplicon underwent sequencing in the reverse direction.

Results:
The BLASTn analysis of the acquired sequence unveiled the highest nucleotide identity (98.28%) with WMV isolates originating from Spain and Italy (accession nos. OQ680560 and FJ823122, respectively) while displaying the lowest identities (94.36%) with those from South Korea (KU240110). The phylogenetic assessment delineated two distinct clusters within all WMV isolates. The WMV isolate from South Khorasan, designated as WMV-SKh, is notably grouped with isolates from India, Spain, Italy, and France within a singular cluster.

Conclusion:
Our results provide strong evidence that the WMV-SKh isolate is the primary cause of the recent outbreak in pumpkin fields. However, no dsRNA was found in the saffron samples.