Viral diseases in cucurbit crops related to mixed infection of two whitefly-transmitted viruses in Sonora, Mexico

Climate change and globalization are facilitating the introduction of whitefly-vectored viral species into new ecological niches, threatening cucurbit cultivation. Cucurbit yellow stunting disorder virus (CYSDV, Crinivirus cucurbitae) and and four species have been (WmCSV, Begomovirus citrulli) are two of the most aggressive cucurbit-affecting viruses among whitefly-transmitted species. CYSDV was introduced to North America in 1999, and WmCSV was recently reported and is a concern in the agronomic sector. In 2021, an outbreak of melon and watermelon crops showing symptoms resembling those caused by viruses was observed in Sonora, Mexico. PCR-based detection of cucurbit-infecting viruses in leaf and fruit revealed that the mixed infection of CYSDV and WmCSV is predominant in both crops. It is noteworthy that WmCSV was not detected in melon fruits. Molecular and phylogenetic analyses were conducted on the Hsp70h/CP genes for CYSDV and the full-length genome for WmCSV. The isolates of CYSDV showed low variability and are closely related ( >99%) to isolates previously introduced in the Americas. WmCSV (DNA-A and DNA-B) isolates showed sequence and phylogenetic topology similarity to isolates from Sonora and Arizona (99.4–99.6% and 96.5–96.9%, respectively). Interestingly, WmCSV DNA-B segments showed putative recombination-driven evolution. To our knowledge, this is the first report of WmCSV occurring in mixed infection with CYSDV in Northern Mexico.