Incidence and genetic diversity of cucurbit viruses in the Spanish Mediterranean area

Viral infections on cucurbit fields can cause major economic losses. Monitoring of the main producing areas is essential to identify both prevalent and emerging viruses. For two consecutive years (2019-2020), the presence and molecular diversity of nine aphid- and whitefly-transmitted viruses in the main cucurbit-producing areas of the Spanish Mediterranean basin and other important regions were studied. In analyses of symptomatic plants, watermelon mosaic virus (WMV), cucurbit aphid-borne yellows virus (CABYV) and cucumber mosaic virus (CMV) were found to be prevalent in all the monitored areas, regardless of the crop and the farming conditions. Moroccan watermelon mosaic virus (MWMV) and tomato leaf curl New Delhi virus (ToLCNDV) were also found at lower rates, mainly in mixed infections with WMV. Phylogenetic analyses were conducted to determine the molecular variability of the different isolates. Whereas the sequences of CABYV, MWMV and ToLCNDV isolates all clustered within their corresponding Mediterranean clade, new viral variants of WMV and CMV were found. Seven new WMV profiles and a reassorting CMV isolate (IB-IB-IA) were observed. Moreover, the complete genome of the newly described WMV isolates was sequenced. Further studies should be done to determine if these new variants spread to new areas and if they can overcome the previously described resistances. WMV, CABYV and CMV were the main viruses infecting cucurbits fields in the Spanish Mediterranean area. Phylogenetic analysis revealed frequent recombination/reassortment events in WMV and CMV isolates.image